FreeBSD/Linux Kernel Cross Reference
sys/kern/subr_bus.c

     /*-
      * Copyright (c) 1997,1998,2003 Doug Rabson
      * All rights reserved.
      *
      * Redistribution and use in source and binary forms, with or without
      * modification, are permitted provided that the following conditions
      * are met:
      * 1. Redistributions of source code must retain the above copyright
      *    notice, this list of conditions and the following disclaimer.
     * 2. Redistributions in binary form must reproduce the above copyright
     *    notice, this list of conditions and the following disclaimer in the
     *    documentation and/or other materials provided with the distribution.
     *
     * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
     * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
     * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
     * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
     * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
     * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
     * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
     * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
     * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
     * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
     * SUCH DAMAGE.
     */
    
    #include <sys/cdefs.h>
    __FBSDID("$FreeBSD: releng/8.3/sys/kern/subr_bus.c 230741 2012-01-29 12:58:07Z marius $");
    
    #include "opt_bus.h"
    
    #include <sys/param.h>
    #include <sys/conf.h>
    #include <sys/filio.h>
    #include <sys/lock.h>
    #include <sys/kernel.h>
    #include <sys/kobj.h>
    #include <sys/limits.h>
    #include <sys/malloc.h>
    #include <sys/module.h>
    #include <sys/mutex.h>
    #include <sys/poll.h>
    #include <sys/proc.h>
    #include <sys/condvar.h>
    #include <sys/queue.h>
    #include <machine/bus.h>
    #include <sys/rman.h>
    #include <sys/selinfo.h>
    #include <sys/signalvar.h>
    #include <sys/sysctl.h>
    #include <sys/systm.h>
    #include <sys/uio.h>
    #include <sys/bus.h>
    #include <sys/interrupt.h>
    
    #include <machine/stdarg.h>
    
    #include <vm/uma.h>
    
    SYSCTL_NODE(_hw, OID_AUTO, bus, CTLFLAG_RW, NULL, NULL);
    SYSCTL_NODE(, OID_AUTO, dev, CTLFLAG_RW, NULL, NULL);
    
    /*
     * Used to attach drivers to devclasses.
     */
    typedef struct driverlink *driverlink_t;
    struct driverlink {
            kobj_class_t    driver;
            TAILQ_ENTRY(driverlink) link;   /* list of drivers in devclass */
            int             pass;
            TAILQ_ENTRY(driverlink) passlink;
    };
    
    /*
     * Forward declarations
     */
    typedef TAILQ_HEAD(devclass_list, devclass) devclass_list_t;
    typedef TAILQ_HEAD(driver_list, driverlink) driver_list_t;
    typedef TAILQ_HEAD(device_list, device) device_list_t;
    
    struct devclass {
            TAILQ_ENTRY(devclass) link;
            devclass_t      parent;         /* parent in devclass hierarchy */
            driver_list_t   drivers;     /* bus devclasses store drivers for bus */
            char            *name;
            device_t        *devices;       /* array of devices indexed by unit */
            int             maxunit;        /* size of devices array */
            int             flags;
    #define DC_HAS_CHILDREN         1
    
            struct sysctl_ctx_list sysctl_ctx;
            struct sysctl_oid *sysctl_tree;
    };
    
    /**
     * @brief Implementation of device.
     */
    struct device {
            /*
            * A device is a kernel object. The first field must be the
            * current ops table for the object.
            */
           KOBJ_FIELDS;
   
           /*
            * Device hierarchy.
            */
           TAILQ_ENTRY(device)     link;   /**< list of devices in parent */
           TAILQ_ENTRY(device)     devlink; /**< global device list membership */
           device_t        parent;         /**< parent of this device  */
           device_list_t   children;       /**< list of child devices */
   
           /*
            * Details of this device.
            */
           driver_t        *driver;        /**< current driver */
           devclass_t      devclass;       /**< current device class */
           int             unit;           /**< current unit number */
           char*           nameunit;       /**< name+unit e.g. foodev0 */
           char*           desc;           /**< driver specific description */
           int             busy;           /**< count of calls to device_busy() */
           device_state_t  state;          /**< current device state  */
           u_int32_t       devflags;       /**< api level flags for device_get_flags() */
           u_int           flags;          /**< internal device flags  */
   #define DF_ENABLED      0x01            /* device should be probed/attached */
   #define DF_FIXEDCLASS   0x02            /* devclass specified at create time */
   #define DF_WILDCARD     0x04            /* unit was originally wildcard */
   #define DF_DESCMALLOCED 0x08            /* description was malloced */
   #define DF_QUIET        0x10            /* don't print verbose attach message */
   #define DF_DONENOMATCH  0x20            /* don't execute DEVICE_NOMATCH again */
   #define DF_EXTERNALSOFTC 0x40           /* softc not allocated by us */
   #define DF_REBID        0x80            /* Can rebid after attach */
           u_int   order;                  /**< order from device_add_child_ordered() */
           void    *ivars;                 /**< instance variables  */
           void    *softc;                 /**< current driver's variables  */
   
           struct sysctl_ctx_list sysctl_ctx; /**< state for sysctl variables  */
           struct sysctl_oid *sysctl_tree; /**< state for sysctl variables */
   };
   
   static MALLOC_DEFINE(M_BUS, "bus", "Bus data structures");
   static MALLOC_DEFINE(M_BUS_SC, "bus-sc", "Bus data structures, softc");
   
   #ifdef BUS_DEBUG
   
   static int bus_debug = 1;
   TUNABLE_INT("bus.debug", &bus_debug);
   SYSCTL_INT(_debug, OID_AUTO, bus_debug, CTLFLAG_RW, &bus_debug, 0,
       "Debug bus code");
   
   #define PDEBUG(a)       if (bus_debug) {printf("%s:%d: ", __func__, __LINE__), printf a; printf("\n");}
   #define DEVICENAME(d)   ((d)? device_get_name(d): "no device")
   #define DRIVERNAME(d)   ((d)? d->name : "no driver")
   #define DEVCLANAME(d)   ((d)? d->name : "no devclass")
   
   /**
    * Produce the indenting, indent*2 spaces plus a '.' ahead of that to
    * prevent syslog from deleting initial spaces
    */
   #define indentprintf(p) do { int iJ; printf("."); for (iJ=0; iJ<indent; iJ++) printf("  "); printf p ; } while (0)
   
   static void print_device_short(device_t dev, int indent);
   static void print_device(device_t dev, int indent);
   void print_device_tree_short(device_t dev, int indent);
   void print_device_tree(device_t dev, int indent);
   static void print_driver_short(driver_t *driver, int indent);
   static void print_driver(driver_t *driver, int indent);
   static void print_driver_list(driver_list_t drivers, int indent);
   static void print_devclass_short(devclass_t dc, int indent);
   static void print_devclass(devclass_t dc, int indent);
   void print_devclass_list_short(void);
   void print_devclass_list(void);
   
   #else
   /* Make the compiler ignore the function calls */
   #define PDEBUG(a)                       /* nop */
   #define DEVICENAME(d)                   /* nop */
   #define DRIVERNAME(d)                   /* nop */
   #define DEVCLANAME(d)                   /* nop */
   
   #define print_device_short(d,i)         /* nop */
   #define print_device(d,i)               /* nop */
   #define print_device_tree_short(d,i)    /* nop */
   #define print_device_tree(d,i)          /* nop */
   #define print_driver_short(d,i)         /* nop */
   #define print_driver(d,i)               /* nop */
   #define print_driver_list(d,i)          /* nop */
   #define print_devclass_short(d,i)       /* nop */
   #define print_devclass(d,i)             /* nop */
   #define print_devclass_list_short()     /* nop */
   #define print_devclass_list()           /* nop */
   #endif
   
   /*
    * dev sysctl tree
    */
   
   enum {
           DEVCLASS_SYSCTL_PARENT,
   };
   
   static int
   devclass_sysctl_handler(SYSCTL_HANDLER_ARGS)
   {
           devclass_t dc = (devclass_t)arg1;
           const char *value;
   
           switch (arg2) {
           case DEVCLASS_SYSCTL_PARENT:
                   value = dc->parent ? dc->parent->name : "";
                   break;
           default:
                   return (EINVAL);
           }
           return (SYSCTL_OUT(req, value, strlen(value)));
   }
   
   static void
   devclass_sysctl_init(devclass_t dc)
   {
   
           if (dc->sysctl_tree != NULL)
                   return;
           sysctl_ctx_init(&dc->sysctl_ctx);
           dc->sysctl_tree = SYSCTL_ADD_NODE(&dc->sysctl_ctx,
               SYSCTL_STATIC_CHILDREN(_dev), OID_AUTO, dc->name,
               CTLFLAG_RD, NULL, "");
           SYSCTL_ADD_PROC(&dc->sysctl_ctx, SYSCTL_CHILDREN(dc->sysctl_tree),
               OID_AUTO, "%parent", CTLFLAG_RD,
               dc, DEVCLASS_SYSCTL_PARENT, devclass_sysctl_handler, "A",
               "parent class");
   }
   
   enum {
           DEVICE_SYSCTL_DESC,
           DEVICE_SYSCTL_DRIVER,
           DEVICE_SYSCTL_LOCATION,
           DEVICE_SYSCTL_PNPINFO,
           DEVICE_SYSCTL_PARENT,
   };
   
   static int
   device_sysctl_handler(SYSCTL_HANDLER_ARGS)
   {
           device_t dev = (device_t)arg1;
           const char *value;
           char *buf;
           int error;
   
           buf = NULL;
           switch (arg2) {
           case DEVICE_SYSCTL_DESC:
                   value = dev->desc ? dev->desc : "";
                   break;
           case DEVICE_SYSCTL_DRIVER:
                   value = dev->driver ? dev->driver->name : "";
                   break;
           case DEVICE_SYSCTL_LOCATION:
                   value = buf = malloc(1024, M_BUS, M_WAITOK | M_ZERO);
                   bus_child_location_str(dev, buf, 1024);
                   break;
           case DEVICE_SYSCTL_PNPINFO:
                   value = buf = malloc(1024, M_BUS, M_WAITOK | M_ZERO);
                   bus_child_pnpinfo_str(dev, buf, 1024);
                   break;
           case DEVICE_SYSCTL_PARENT:
                   value = dev->parent ? dev->parent->nameunit : "";
                   break;
           default:
                   return (EINVAL);
           }
           error = SYSCTL_OUT(req, value, strlen(value));
           if (buf != NULL)
                   free(buf, M_BUS);
           return (error);
   }
   
   static void
   device_sysctl_init(device_t dev)
   {
           devclass_t dc = dev->devclass;
   
           if (dev->sysctl_tree != NULL)
                   return;
           devclass_sysctl_init(dc);
           sysctl_ctx_init(&dev->sysctl_ctx);
           dev->sysctl_tree = SYSCTL_ADD_NODE(&dev->sysctl_ctx,
               SYSCTL_CHILDREN(dc->sysctl_tree), OID_AUTO,
               dev->nameunit + strlen(dc->name),
               CTLFLAG_RD, NULL, "");
           SYSCTL_ADD_PROC(&dev->sysctl_ctx, SYSCTL_CHILDREN(dev->sysctl_tree),
               OID_AUTO, "%desc", CTLFLAG_RD,
               dev, DEVICE_SYSCTL_DESC, device_sysctl_handler, "A",
               "device description");
           SYSCTL_ADD_PROC(&dev->sysctl_ctx, SYSCTL_CHILDREN(dev->sysctl_tree),
               OID_AUTO, "%driver", CTLFLAG_RD,
               dev, DEVICE_SYSCTL_DRIVER, device_sysctl_handler, "A",
               "device driver name");
           SYSCTL_ADD_PROC(&dev->sysctl_ctx, SYSCTL_CHILDREN(dev->sysctl_tree),
               OID_AUTO, "%location", CTLFLAG_RD,
               dev, DEVICE_SYSCTL_LOCATION, device_sysctl_handler, "A",
               "device location relative to parent");
           SYSCTL_ADD_PROC(&dev->sysctl_ctx, SYSCTL_CHILDREN(dev->sysctl_tree),
               OID_AUTO, "%pnpinfo", CTLFLAG_RD,
               dev, DEVICE_SYSCTL_PNPINFO, device_sysctl_handler, "A",
               "device identification");
           SYSCTL_ADD_PROC(&dev->sysctl_ctx, SYSCTL_CHILDREN(dev->sysctl_tree),
               OID_AUTO, "%parent", CTLFLAG_RD,
               dev, DEVICE_SYSCTL_PARENT, device_sysctl_handler, "A",
               "parent device");
   }
   
   static void
   device_sysctl_update(device_t dev)
   {
           devclass_t dc = dev->devclass;
   
           if (dev->sysctl_tree == NULL)
                   return;
           sysctl_rename_oid(dev->sysctl_tree, dev->nameunit + strlen(dc->name));
   }
   
   static void
   device_sysctl_fini(device_t dev)
   {
           if (dev->sysctl_tree == NULL)
                   return;
           sysctl_ctx_free(&dev->sysctl_ctx);
           dev->sysctl_tree = NULL;
   }
   
   /*
    * /dev/devctl implementation
    */
   
   /*
    * This design allows only one reader for /dev/devctl.  This is not desirable
    * in the long run, but will get a lot of hair out of this implementation.
    * Maybe we should make this device a clonable device.
    *
    * Also note: we specifically do not attach a device to the device_t tree
    * to avoid potential chicken and egg problems.  One could argue that all
    * of this belongs to the root node.  One could also further argue that the
    * sysctl interface that we have not might more properly be an ioctl
    * interface, but at this stage of the game, I'm not inclined to rock that
    * boat.
    *
    * I'm also not sure that the SIGIO support is done correctly or not, as
    * I copied it from a driver that had SIGIO support that likely hasn't been
    * tested since 3.4 or 2.2.8!
    */
   
   /* Deprecated way to adjust queue length */
   static int sysctl_devctl_disable(SYSCTL_HANDLER_ARGS);
   /* XXX Need to support old-style tunable hw.bus.devctl_disable" */
   SYSCTL_PROC(_hw_bus, OID_AUTO, devctl_disable, CTLTYPE_INT | CTLFLAG_RW, NULL,
       0, sysctl_devctl_disable, "I", "devctl disable -- deprecated");
   
   #define DEVCTL_DEFAULT_QUEUE_LEN 1000
   static int sysctl_devctl_queue(SYSCTL_HANDLER_ARGS);
   static int devctl_queue_length = DEVCTL_DEFAULT_QUEUE_LEN;
   TUNABLE_INT("hw.bus.devctl_queue", &devctl_queue_length);
   SYSCTL_PROC(_hw_bus, OID_AUTO, devctl_queue, CTLTYPE_INT | CTLFLAG_RW, NULL,
       0, sysctl_devctl_queue, "I", "devctl queue length");
   
   static d_open_t         devopen;
   static d_close_t        devclose;
   static d_read_t         devread;
   static d_ioctl_t        devioctl;
   static d_poll_t         devpoll;
   
   static struct cdevsw dev_cdevsw = {
           .d_version =    D_VERSION,
           .d_flags =      D_NEEDGIANT,
           .d_open =       devopen,
           .d_close =      devclose,
           .d_read =       devread,
           .d_ioctl =      devioctl,
           .d_poll =       devpoll,
           .d_name =       "devctl",
   };
   
   struct dev_event_info
   {
           char *dei_data;
           TAILQ_ENTRY(dev_event_info) dei_link;
   };
   
   TAILQ_HEAD(devq, dev_event_info);
   
   static struct dev_softc
   {
           int     inuse;
           int     nonblock;
           int     queued;
           struct mtx mtx;
           struct cv cv;
           struct selinfo sel;
           struct devq devq;
           struct proc *async_proc;
   } devsoftc;
   
   static struct cdev *devctl_dev;
   
   static void
   devinit(void)
   {
           devctl_dev = make_dev_credf(MAKEDEV_ETERNAL, &dev_cdevsw, 0, NULL,
               UID_ROOT, GID_WHEEL, 0600, "devctl");
           mtx_init(&devsoftc.mtx, "dev mtx", "devd", MTX_DEF);
           cv_init(&devsoftc.cv, "dev cv");
           TAILQ_INIT(&devsoftc.devq);
   }
   
   static int
   devopen(struct cdev *dev, int oflags, int devtype, struct thread *td)
   {
           if (devsoftc.inuse)
                   return (EBUSY);
           /* move to init */
           devsoftc.inuse = 1;
           devsoftc.nonblock = 0;
           devsoftc.async_proc = NULL;
           return (0);
   }
   
   static int
   devclose(struct cdev *dev, int fflag, int devtype, struct thread *td)
   {
           devsoftc.inuse = 0;
           mtx_lock(&devsoftc.mtx);
           cv_broadcast(&devsoftc.cv);
           mtx_unlock(&devsoftc.mtx);
           devsoftc.async_proc = NULL;
           return (0);
   }
   
   /*
    * The read channel for this device is used to report changes to
    * userland in realtime.  We are required to free the data as well as
    * the n1 object because we allocate them separately.  Also note that
    * we return one record at a time.  If you try to read this device a
    * character at a time, you will lose the rest of the data.  Listening
    * programs are expected to cope.
    */
   static int
   devread(struct cdev *dev, struct uio *uio, int ioflag)
   {
           struct dev_event_info *n1;
           int rv;
   
           mtx_lock(&devsoftc.mtx);
           while (TAILQ_EMPTY(&devsoftc.devq)) {
                   if (devsoftc.nonblock) {
                           mtx_unlock(&devsoftc.mtx);
                           return (EAGAIN);
                   }
                   rv = cv_wait_sig(&devsoftc.cv, &devsoftc.mtx);
                   if (rv) {
                           /*
                            * Need to translate ERESTART to EINTR here? -- jake
                            */
                           mtx_unlock(&devsoftc.mtx);
                           return (rv);
                   }
           }
           n1 = TAILQ_FIRST(&devsoftc.devq);
           TAILQ_REMOVE(&devsoftc.devq, n1, dei_link);
           devsoftc.queued--;
           mtx_unlock(&devsoftc.mtx);
           rv = uiomove(n1->dei_data, strlen(n1->dei_data), uio);
           free(n1->dei_data, M_BUS);
           free(n1, M_BUS);
           return (rv);
   }
   
   static  int
   devioctl(struct cdev *dev, u_long cmd, caddr_t data, int fflag, struct thread *td)
   {
           switch (cmd) {
   
           case FIONBIO:
                   if (*(int*)data)
                           devsoftc.nonblock = 1;
                   else
                           devsoftc.nonblock = 0;
                   return (0);
           case FIOASYNC:
                   if (*(int*)data)
                           devsoftc.async_proc = td->td_proc;
                   else
                           devsoftc.async_proc = NULL;
                   return (0);
   
                   /* (un)Support for other fcntl() calls. */
           case FIOCLEX:
           case FIONCLEX:
           case FIONREAD:
           case FIOSETOWN:
           case FIOGETOWN:
           default:
                   break;
           }
           return (ENOTTY);
   }
   
   static  int
   devpoll(struct cdev *dev, int events, struct thread *td)
   {
           int     revents = 0;
   
           mtx_lock(&devsoftc.mtx);
           if (events & (POLLIN | POLLRDNORM)) {
                   if (!TAILQ_EMPTY(&devsoftc.devq))
                           revents = events & (POLLIN | POLLRDNORM);
                   else
                           selrecord(td, &devsoftc.sel);
           }
           mtx_unlock(&devsoftc.mtx);
   
           return (revents);
   }
   
   /**
    * @brief Return whether the userland process is running
    */
   boolean_t
   devctl_process_running(void)
   {
           return (devsoftc.inuse == 1);
   }
   
   /**
    * @brief Queue data to be read from the devctl device
    *
    * Generic interface to queue data to the devctl device.  It is
    * assumed that @p data is properly formatted.  It is further assumed
    * that @p data is allocated using the M_BUS malloc type.
    */
   void
   devctl_queue_data_f(char *data, int flags)
   {
           struct dev_event_info *n1 = NULL, *n2 = NULL;
           struct proc *p;
   
           if (strlen(data) == 0)
                   goto out;
           if (devctl_queue_length == 0)
                   goto out;
           n1 = malloc(sizeof(*n1), M_BUS, flags);
           if (n1 == NULL)
                   goto out;
           n1->dei_data = data;
           mtx_lock(&devsoftc.mtx);
           if (devctl_queue_length == 0) {
                   mtx_unlock(&devsoftc.mtx);
                   free(n1->dei_data, M_BUS);
                   free(n1, M_BUS);
                   return;
           }
           /* Leave at least one spot in the queue... */
           while (devsoftc.queued > devctl_queue_length - 1) {
                   n2 = TAILQ_FIRST(&devsoftc.devq);
                   TAILQ_REMOVE(&devsoftc.devq, n2, dei_link);
                   free(n2->dei_data, M_BUS);
                   free(n2, M_BUS);
                   devsoftc.queued--;
           }
           TAILQ_INSERT_TAIL(&devsoftc.devq, n1, dei_link);
           devsoftc.queued++;
           cv_broadcast(&devsoftc.cv);
           mtx_unlock(&devsoftc.mtx);
           selwakeup(&devsoftc.sel);
           p = devsoftc.async_proc;
           if (p != NULL) {
                   PROC_LOCK(p);
                   psignal(p, SIGIO);
                   PROC_UNLOCK(p);
           }
           return;
   out:
           /*
            * We have to free data on all error paths since the caller
            * assumes it will be free'd when this item is dequeued.
            */
           free(data, M_BUS);
           return;
   }
   
   void
   devctl_queue_data(char *data)
   {
   
           devctl_queue_data_f(data, M_NOWAIT);
   }
   
   /**
    * @brief Send a 'notification' to userland, using standard ways
    */
   void
   devctl_notify_f(const char *system, const char *subsystem, const char *type,
       const char *data, int flags)
   {
           int len = 0;
           char *msg;
   
           if (system == NULL)
                   return;         /* BOGUS!  Must specify system. */
           if (subsystem == NULL)
                   return;         /* BOGUS!  Must specify subsystem. */
           if (type == NULL)
                   return;         /* BOGUS!  Must specify type. */
           len += strlen(" system=") + strlen(system);
           len += strlen(" subsystem=") + strlen(subsystem);
           len += strlen(" type=") + strlen(type);
           /* add in the data message plus newline. */
           if (data != NULL)
                   len += strlen(data);
           len += 3;       /* '!', '\n', and NUL */
           msg = malloc(len, M_BUS, flags);
           if (msg == NULL)
                   return;         /* Drop it on the floor */
           if (data != NULL)
                   snprintf(msg, len, "!system=%s subsystem=%s type=%s %s\n",
                       system, subsystem, type, data);
           else
                   snprintf(msg, len, "!system=%s subsystem=%s type=%s\n",
                       system, subsystem, type);
           devctl_queue_data_f(msg, flags);
   }
   
   void
   devctl_notify(const char *system, const char *subsystem, const char *type,
       const char *data)
   {
   
           devctl_notify_f(system, subsystem, type, data, M_NOWAIT);
   }
   
   /*
    * Common routine that tries to make sending messages as easy as possible.
    * We allocate memory for the data, copy strings into that, but do not
    * free it unless there's an error.  The dequeue part of the driver should
    * free the data.  We don't send data when the device is disabled.  We do
    * send data, even when we have no listeners, because we wish to avoid
    * races relating to startup and restart of listening applications.
    *
    * devaddq is designed to string together the type of event, with the
    * object of that event, plus the plug and play info and location info
    * for that event.  This is likely most useful for devices, but less
    * useful for other consumers of this interface.  Those should use
    * the devctl_queue_data() interface instead.
    */
   static void
   devaddq(const char *type, const char *what, device_t dev)
   {
           char *data = NULL;
           char *loc = NULL;
           char *pnp = NULL;
           const char *parstr;
   
           if (!devctl_queue_length)/* Rare race, but lost races safely discard */
                   return;
           data = malloc(1024, M_BUS, M_NOWAIT);
           if (data == NULL)
                   goto bad;
   
           /* get the bus specific location of this device */
           loc = malloc(1024, M_BUS, M_NOWAIT);
           if (loc == NULL)
                   goto bad;
           *loc = '\0';
           bus_child_location_str(dev, loc, 1024);
   
           /* Get the bus specific pnp info of this device */
           pnp = malloc(1024, M_BUS, M_NOWAIT);
           if (pnp == NULL)
                   goto bad;
           *pnp = '\0';
           bus_child_pnpinfo_str(dev, pnp, 1024);
   
           /* Get the parent of this device, or / if high enough in the tree. */
           if (device_get_parent(dev) == NULL)
                   parstr = ".";   /* Or '/' ? */
           else
                   parstr = device_get_nameunit(device_get_parent(dev));
           /* String it all together. */
           snprintf(data, 1024, "%s%s at %s %s on %s\n", type, what, loc, pnp,
             parstr);
           free(loc, M_BUS);
           free(pnp, M_BUS);
           devctl_queue_data(data);
           return;
   bad:
           free(pnp, M_BUS);
           free(loc, M_BUS);
           free(data, M_BUS);
           return;
   }
   
   /*
    * A device was added to the tree.  We are called just after it successfully
    * attaches (that is, probe and attach success for this device).  No call
    * is made if a device is merely parented into the tree.  See devnomatch
    * if probe fails.  If attach fails, no notification is sent (but maybe
    * we should have a different message for this).
    */
   static void
   devadded(device_t dev)
   {
           char *pnp = NULL;
           char *tmp = NULL;
   
           pnp = malloc(1024, M_BUS, M_NOWAIT);
           if (pnp == NULL)
                   goto fail;
           tmp = malloc(1024, M_BUS, M_NOWAIT);
           if (tmp == NULL)
                   goto fail;
           *pnp = '\0';
           bus_child_pnpinfo_str(dev, pnp, 1024);
           snprintf(tmp, 1024, "%s %s", device_get_nameunit(dev), pnp);
           devaddq("+", tmp, dev);
   fail:
           if (pnp != NULL)
                   free(pnp, M_BUS);
           if (tmp != NULL)
                   free(tmp, M_BUS);
           return;
   }
   
   /*
    * A device was removed from the tree.  We are called just before this
    * happens.
    */
   static void
   devremoved(device_t dev)
   {
           char *pnp = NULL;
           char *tmp = NULL;
   
           pnp = malloc(1024, M_BUS, M_NOWAIT);
           if (pnp == NULL)
                   goto fail;
           tmp = malloc(1024, M_BUS, M_NOWAIT);
           if (tmp == NULL)
                   goto fail;
           *pnp = '\0';
           bus_child_pnpinfo_str(dev, pnp, 1024);
           snprintf(tmp, 1024, "%s %s", device_get_nameunit(dev), pnp);
           devaddq("-", tmp, dev);
   fail:
           if (pnp != NULL)
                   free(pnp, M_BUS);
           if (tmp != NULL)
                   free(tmp, M_BUS);
           return;
   }
   
   /*
    * Called when there's no match for this device.  This is only called
    * the first time that no match happens, so we don't keep getting this
    * message.  Should that prove to be undesirable, we can change it.
    * This is called when all drivers that can attach to a given bus
    * decline to accept this device.  Other errrors may not be detected.
    */
   static void
   devnomatch(device_t dev)
   {
           devaddq("?", "", dev);
   }
   
   static int
   sysctl_devctl_disable(SYSCTL_HANDLER_ARGS)
   {
           struct dev_event_info *n1;
           int dis, error;
   
           dis = devctl_queue_length == 0;
           error = sysctl_handle_int(oidp, &dis, 0, req);
           if (error || !req->newptr)
                   return (error);
           mtx_lock(&devsoftc.mtx);
           if (dis) {
                   while (!TAILQ_EMPTY(&devsoftc.devq)) {
                           n1 = TAILQ_FIRST(&devsoftc.devq);
                           TAILQ_REMOVE(&devsoftc.devq, n1, dei_link);
                           free(n1->dei_data, M_BUS);
                           free(n1, M_BUS);
                   }
                   devsoftc.queued = 0;
                   devctl_queue_length = 0;
           } else {
                   devctl_queue_length = DEVCTL_DEFAULT_QUEUE_LEN;
           }
           mtx_unlock(&devsoftc.mtx);
           return (0);
   }
   
   static int
   sysctl_devctl_queue(SYSCTL_HANDLER_ARGS)
   {
           struct dev_event_info *n1;
           int q, error;
   
           q = devctl_queue_length;
           error = sysctl_handle_int(oidp, &q, 0, req);
           if (error || !req->newptr)
                   return (error);
           if (q < 0)
                   return (EINVAL);
           mtx_lock(&devsoftc.mtx);
           devctl_queue_length = q;
           while (devsoftc.queued > devctl_queue_length) {
                   n1 = TAILQ_FIRST(&devsoftc.devq);
                   TAILQ_REMOVE(&devsoftc.devq, n1, dei_link);
                   free(n1->dei_data, M_BUS);
                   free(n1, M_BUS);
                   devsoftc.queued--;
           }
           mtx_unlock(&devsoftc.mtx);
           return (0);
   }
   
   /* End of /dev/devctl code */
   
   static TAILQ_HEAD(,device)      bus_data_devices;
   static int bus_data_generation = 1;
   
   static kobj_method_t null_methods[] = {
           KOBJMETHOD_END
   };
   
   DEFINE_CLASS(null, null_methods, 0);
   
   /*
    * Bus pass implementation
    */
   
   static driver_list_t passes = TAILQ_HEAD_INITIALIZER(passes);
   int bus_current_pass = BUS_PASS_ROOT;
   
   /**
    * @internal
    * @brief Register the pass level of a new driver attachment
    *
    * Register a new driver attachment's pass level.  If no driver
    * attachment with the same pass level has been added, then @p new
    * will be added to the global passes list.
    *
    * @param new           the new driver attachment
    */
   static void
   driver_register_pass(struct driverlink *new)
   {
           struct driverlink *dl;
   
           /* We only consider pass numbers during boot. */
           if (bus_current_pass == BUS_PASS_DEFAULT)
                   return;
   
           /*
            * Walk the passes list.  If we already know about this pass
            * then there is nothing to do.  If we don't, then insert this
            * driver link into the list.
            */
           TAILQ_FOREACH(dl, &passes, passlink) {
                   if (dl->pass < new->pass)
                           continue;
                   if (dl->pass == new->pass)
                           return;
                   TAILQ_INSERT_BEFORE(dl, new, passlink);
                   return;
           }
           TAILQ_INSERT_TAIL(&passes, new, passlink);
   }
   
   /**
    * @brief Raise the current bus pass
    *
    * Raise the current bus pass level to @p pass.  Call the BUS_NEW_PASS()
    * method on the root bus to kick off a new device tree scan for each
    * new pass level that has at least one driver.
    */
   void
   bus_set_pass(int pass)
   {
           struct driverlink *dl;
   
           if (bus_current_pass > pass)
                   panic("Attempt to lower bus pass level");
   
           TAILQ_FOREACH(dl, &passes, passlink) {
                   /* Skip pass values below the current pass level. */
                   if (dl->pass <= bus_current_pass)
                           continue;
   
                   /*
                    * Bail once we hit a driver with a pass level that is
                    * too high.
                    */
                   if (dl->pass > pass)
                           break;
   
                   /*
                    * Raise the pass level to the next level and rescan
                    * the tree.
                    */
                   bus_current_pass = dl->pass;
                   BUS_NEW_PASS(root_bus);
           }
   
           /*
            * If there isn't a driver registered for the requested pass,
            * then bus_current_pass might still be less than 'pass'.  Set
            * it to 'pass' in that case.
            */
           if (bus_current_pass < pass)
                   bus_current_pass = pass;
           KASSERT(bus_current_pass == pass, ("Failed to update bus pass level"));
   }
   
   /*
    * Devclass implementation
    */
   
   static devclass_list_t devclasses = TAILQ_HEAD_INITIALIZER(devclasses);
   
   /**
    * @internal
    * @brief Find or create a device class
    *
    * If a device class with the name @p classname exists, return it,
    * otherwise if @p create is non-zero create and return a new device
    * class.
    *
    * If @p parentname is non-NULL, the parent of the devclass is set to
    * the devclass of that name.
    *
    * @param classname     the devclass name to find or create
    * @param parentname    the parent devclass name or @c NULL
    * @param create        non-zero to create a devclass
    */
   static devclass_t
   devclass_find_internal(const char *classname, const char *parentname,
                          int create)
   {
           devclass_t dc;
   
           PDEBUG(("looking for %s", classname));
           if (!classname)
                   return (NULL);
   
           TAILQ_FOREACH(dc, &devclasses, link) {
                   if (!strcmp(dc->name, classname))
                           break;
           }
   
           if (create && !dc) {
                   PDEBUG(("creating %s", classname));
                   dc = malloc(sizeof(struct devclass) + strlen(classname) + 1,
                       M_BUS, M_NOWAIT | M_ZERO);
                   if (!dc)
                           return (NULL);
                   dc->parent = NULL;
                   dc->name = (char*) (dc + 1);
                   strcpy(dc->name, classname);
                   TAILQ_INIT(&dc->drivers);
                   TAILQ_INSERT_TAIL(&devclasses, dc, link);
   
                   bus_data_generation_update();
           }
   
           /*
            * If a parent class is specified, then set that as our parent so
            * that this devclass will support drivers for the parent class as
            * well.  If the parent class has the same name don't do this though
            * as it creates a cycle that can trigger an infinite loop in
            * device_probe_child() if a device exists for which there is no
            * suitable driver.
            */
           if (parentname && dc && !dc->parent &&
               strcmp(classname, parentname) != 0) {
                   dc->parent = devclass_find_internal(parentname, NULL, TRUE);
                   dc->parent->flags |= DC_HAS_CHILDREN;
           }
   
           return (dc);
   }
   
   /**
    * @brief Create a device class
    *
    * If a device class with the name @p classname exists, return it,
    * otherwise create and return a new device class.
    *
    * @param classname     the devclass name to find or create
    */
   devclass_t
  devclass_create(const char *classname)
  {
          return (devclass_find_internal(classname, NULL, TRUE));
  }
  
  /**
   * @brief Find a device class
   *
   * If a device class with the name @p classname exists, return it,
   * otherwise return @c NULL.
   *
   * @param classname     the devclass name to find
   */
  devclass_t
  devclass_find(const char *classname)
  {
          return (devclass_find_internal(classname, NULL, FALSE));
  }
  
  /**
   * @brief Register that a device driver has been added to a devclass
   *
   * Register that a device driver has been added to a devclass.  This
   * is called by devclass_add_driver to accomplish the recursive
   * notification of all the children classes of dc, as well as dc.
   * Each layer will have BUS_DRIVER_ADDED() called for all instances of
   * the devclass.
   *
   * We do a full search here of the devclass list at each iteration
   * level to save storing children-lists in the devclass structure.  If
   * we ever move beyond a few dozen devices doing this, we may need to
   * reevaluate...
   *
   * @param dc            the devclass to edit
   * @param driver        the driver that was just added
   */
  static void
  devclass_driver_added(devclass_t dc, driver_t *driver)
  {
          devclass_t parent;
          int i;
  
          /*
           * Call BUS_DRIVER_ADDED for any existing busses in this class.
           */
          for (i = 0; i < dc->maxunit; i++)
                  if (dc->devices[i] && device_is_attached(dc->devices[i]))
                          BUS_DRIVER_ADDED(dc->devices[i], driver);
  
          /*
           * Walk through the children classes.  Since we only keep a
           * single parent pointer around, we walk the entire list of
           * devclasses looking for children.  We set the
           * DC_HAS_CHILDREN flag when a child devclass is created on
           * the parent, so we only walk the list for those devclasses
           * that have children.
           */
          if (!(dc->flags & DC_HAS_CHILDREN))
                  return;
          parent = dc;
          TAILQ_FOREACH(dc, &devclasses, link) {
                  if (dc->parent == parent)
                          devclass_driver_added(dc, driver);
          }
  }
  
  /**
   * @brief Add a device driver to a device class
   *
   * Add a device driver to a devclass. This is normally called
   * automatically by DRIVER_MODULE(). The BUS_DRIVER_ADDED() method of
   * all devices in the devclass will be called to allow them to attempt
   * to re-probe any unmatched children.
   *
   * @param dc            the devclass to edit
   * @param driver        the driver to register
   */
  static int
  devclass_add_driver(devclass_t dc, driver_t *driver, int pass, devclass_t *dcp)
  {
          driverlink_t dl;
          const char *parentname;
  
          PDEBUG(("%s", DRIVERNAME(driver)));
  
          /* Don't allow invalid pass values. */
          if (pass <= BUS_PASS_ROOT)
                  return (EINVAL);
  
          dl = malloc(sizeof *dl, M_BUS, M_NOWAIT|M_ZERO);
          if (!dl)
                  return (ENOMEM);
  
          /*
           * Compile the driver's methods. Also increase the reference count
           * so that the class doesn't get freed when the last instance
           * goes. This means we can safely use static methods and avoids a
           * double-free in devclass_delete_driver.
           */
          kobj_class_compile((kobj_class_t) driver);
  
          /*
           * If the driver has any base classes, make the
           * devclass inherit from the devclass of the driver's
           * first base class. This will allow the system to
           * search for drivers in both devclasses for children
           * of a device using this driver.
           */
          if (driver->baseclasses)
                  parentname = driver->baseclasses[0]->name;
          else
                  parentname = NULL;
          *dcp = devclass_find_internal(driver->name, parentname, TRUE);
  
          dl->driver = driver;
          TAILQ_INSERT_TAIL(&dc->drivers, dl, link);
          driver->refs++;         /* XXX: kobj_mtx */
          dl->pass = pass;
          driver_register_pass(dl);
  
          devclass_driver_added(dc, driver);
          bus_data_generation_update();
          return (0);
  }
  
  /**
   * @brief Register that a device driver has been deleted from a devclass
   *
   * Register that a device driver has been removed from a devclass.
   * This is called by devclass_delete_driver to accomplish the
   * recursive notification of all the children classes of busclass, as
   * well as busclass.  Each layer will attempt to detach the driver
   * from any devices that are children of the bus's devclass.  The function
   * will return an error if a device fails to detach.
   * 
   * We do a full search here of the devclass list at each iteration
   * level to save storing children-lists in the devclass structure.  If
   * we ever move beyond a few dozen devices doing this, we may need to
   * reevaluate...
   *
   * @param busclass      the devclass of the parent bus
   * @param dc            the devclass of the driver being deleted
   * @param driver        the driver being deleted
   */
  static int
  devclass_driver_deleted(devclass_t busclass, devclass_t dc, driver_t *driver)
  {
          devclass_t parent;
          device_t dev;
          int error, i;
  
          /*
           * Disassociate from any devices.  We iterate through all the
           * devices in the devclass of the driver and detach any which are
           * using the driver and which have a parent in the devclass which
           * we are deleting from.
           *
           * Note that since a driver can be in multiple devclasses, we
           * should not detach devices which are not children of devices in
           * the affected devclass.
           */
          for (i = 0; i < dc->maxunit; i++) {
                  if (dc->devices[i]) {
                          dev = dc->devices[i];
                          if (dev->driver == driver && dev->parent &&
                              dev->parent->devclass == busclass) {
                                  if ((error = device_detach(dev)) != 0)
                                          return (error);
                                  (void)device_set_driver(dev, NULL);
                                  BUS_PROBE_NOMATCH(dev->parent, dev);
                                  devnomatch(dev);
                                  dev->flags |= DF_DONENOMATCH;
                          }
                  }
          }
  
          /*
           * Walk through the children classes.  Since we only keep a
           * single parent pointer around, we walk the entire list of
           * devclasses looking for children.  We set the
           * DC_HAS_CHILDREN flag when a child devclass is created on
           * the parent, so we only walk the list for those devclasses
           * that have children.
           */
          if (!(busclass->flags & DC_HAS_CHILDREN))
                  return (0);
          parent = busclass;
          TAILQ_FOREACH(busclass, &devclasses, link) {
                  if (busclass->parent == parent) {
                          error = devclass_driver_deleted(busclass, dc, driver);
                          if (error)
                                  return (error);
                  }
          }
          return (0);
  }
  
  /**
   * @brief Delete a device driver from a device class
   *
   * Delete a device driver from a devclass. This is normally called
   * automatically by DRIVER_MODULE().
   *
   * If the driver is currently attached to any devices,
   * devclass_delete_driver() will first attempt to detach from each
   * device. If one of the detach calls fails, the driver will not be
   * deleted.
   *
   * @param dc            the devclass to edit
   * @param driver        the driver to unregister
   */
  static int
  devclass_delete_driver(devclass_t busclass, driver_t *driver)
  {
          devclass_t dc = devclass_find(driver->name);
          driverlink_t dl;
          int error;
  
          PDEBUG(("%s from devclass %s", driver->name, DEVCLANAME(busclass)));
  
          if (!dc)
                  return (0);
  
          /*
           * Find the link structure in the bus' list of drivers.
           */
          TAILQ_FOREACH(dl, &busclass->drivers, link) {
                  if (dl->driver == driver)
                          break;
          }
  
          if (!dl) {
                  PDEBUG(("%s not found in %s list", driver->name,
                      busclass->name));
                  return (ENOENT);
          }
  
          error = devclass_driver_deleted(busclass, dc, driver);
          if (error != 0)
                  return (error);
  
          TAILQ_REMOVE(&busclass->drivers, dl, link);
          free(dl, M_BUS);
  
          /* XXX: kobj_mtx */
          driver->refs--;
          if (driver->refs == 0)
                  kobj_class_free((kobj_class_t) driver);
  
          bus_data_generation_update();
          return (0);
  }
  
  /**
   * @brief Quiesces a set of device drivers from a device class
   *
   * Quiesce a device driver from a devclass. This is normally called
   * automatically by DRIVER_MODULE().
   *
   * If the driver is currently attached to any devices,
   * devclass_quiesece_driver() will first attempt to quiesce each
   * device.
   *
   * @param dc            the devclass to edit
   * @param driver        the driver to unregister
   */
  static int
  devclass_quiesce_driver(devclass_t busclass, driver_t *driver)
  {
          devclass_t dc = devclass_find(driver->name);
          driverlink_t dl;
          device_t dev;
          int i;
          int error;
  
          PDEBUG(("%s from devclass %s", driver->name, DEVCLANAME(busclass)));
  
          if (!dc)
                  return (0);
  
          /*
           * Find the link structure in the bus' list of drivers.
           */
          TAILQ_FOREACH(dl, &busclass->drivers, link) {
                  if (dl->driver == driver)
                          break;
          }
  
          if (!dl) {
                  PDEBUG(("%s not found in %s list", driver->name,
                      busclass->name));
                  return (ENOENT);
          }
  
          /*
           * Quiesce all devices.  We iterate through all the devices in
           * the devclass of the driver and quiesce any which are using
           * the driver and which have a parent in the devclass which we
           * are quiescing.
           *
           * Note that since a driver can be in multiple devclasses, we
           * should not quiesce devices which are not children of
           * devices in the affected devclass.
           */
          for (i = 0; i < dc->maxunit; i++) {
                  if (dc->devices[i]) {
                          dev = dc->devices[i];
                          if (dev->driver == driver && dev->parent &&
                              dev->parent->devclass == busclass) {
                                  if ((error = device_quiesce(dev)) != 0)
                                          return (error);
                          }
                  }
          }
  
          return (0);
  }
  
  /**
   * @internal
   */
  static driverlink_t
  devclass_find_driver_internal(devclass_t dc, const char *classname)
  {
          driverlink_t dl;
  
          PDEBUG(("%s in devclass %s", classname, DEVCLANAME(dc)));
  
          TAILQ_FOREACH(dl, &dc->drivers, link) {
                  if (!strcmp(dl->driver->name, classname))
                          return (dl);
          }
  
          PDEBUG(("not found"));
          return (NULL);
  }
  
  /**
   * @brief Return the name of the devclass
   */
  const char *
  devclass_get_name(devclass_t dc)
  {
          return (dc->name);
  }
  
  /**
   * @brief Find a device given a unit number
   *
   * @param dc            the devclass to search
   * @param unit          the unit number to search for
   * 
   * @returns             the device with the given unit number or @c
   *                      NULL if there is no such device
   */
  device_t
  devclass_get_device(devclass_t dc, int unit)
  {
          if (dc == NULL || unit < 0 || unit >= dc->maxunit)
                  return (NULL);
          return (dc->devices[unit]);
  }
  
  /**
   * @brief Find the softc field of a device given a unit number
   *
   * @param dc            the devclass to search
   * @param unit          the unit number to search for
   * 
   * @returns             the softc field of the device with the given
   *                      unit number or @c NULL if there is no such
   *                      device
   */
  void *
  devclass_get_softc(devclass_t dc, int unit)
  {
          device_t dev;
  
          dev = devclass_get_device(dc, unit);
          if (!dev)
                  return (NULL);
  
          return (device_get_softc(dev));
  }
  
  /**
   * @brief Get a list of devices in the devclass
   *
   * An array containing a list of all the devices in the given devclass
   * is allocated and returned in @p *devlistp. The number of devices
   * in the array is returned in @p *devcountp. The caller should free
   * the array using @c free(p, M_TEMP), even if @p *devcountp is 0.
   *
   * @param dc            the devclass to examine
   * @param devlistp      points at location for array pointer return
   *                      value
   * @param devcountp     points at location for array size return value
   *
   * @retval 0            success
   * @retval ENOMEM       the array allocation failed
   */
  int
  devclass_get_devices(devclass_t dc, device_t **devlistp, int *devcountp)
  {
          int count, i;
          device_t *list;
  
          count = devclass_get_count(dc);
          list = malloc(count * sizeof(device_t), M_TEMP, M_NOWAIT|M_ZERO);
          if (!list)
                  return (ENOMEM);
  
          count = 0;
          for (i = 0; i < dc->maxunit; i++) {
                  if (dc->devices[i]) {
                          list[count] = dc->devices[i];
                          count++;
                  }
          }
  
          *devlistp = list;
          *devcountp = count;
  
          return (0);
  }
  
  /**
   * @brief Get a list of drivers in the devclass
   *
   * An array containing a list of pointers to all the drivers in the
   * given devclass is allocated and returned in @p *listp.  The number
   * of drivers in the array is returned in @p *countp. The caller should
   * free the array using @c free(p, M_TEMP).
   *
   * @param dc            the devclass to examine
   * @param listp         gives location for array pointer return value
   * @param countp        gives location for number of array elements
   *                      return value
   *
   * @retval 0            success
   * @retval ENOMEM       the array allocation failed
   */
  int
  devclass_get_drivers(devclass_t dc, driver_t ***listp, int *countp)
  {
          driverlink_t dl;
          driver_t **list;
          int count;
  
          count = 0;
          TAILQ_FOREACH(dl, &dc->drivers, link)
                  count++;
          list = malloc(count * sizeof(driver_t *), M_TEMP, M_NOWAIT);
          if (list == NULL)
                  return (ENOMEM);
  
          count = 0;
          TAILQ_FOREACH(dl, &dc->drivers, link) {
                  list[count] = dl->driver;
                  count++;
          }
          *listp = list;
          *countp = count;
  
          return (0);
  }
  
  /**
   * @brief Get the number of devices in a devclass
   *
   * @param dc            the devclass to examine
   */
  int
  devclass_get_count(devclass_t dc)
  {
          int count, i;
  
          count = 0;
          for (i = 0; i < dc->maxunit; i++)
                  if (dc->devices[i])
                          count++;
          return (count);
  }
  
  /**
   * @brief Get the maximum unit number used in a devclass
   *
   * Note that this is one greater than the highest currently-allocated
   * unit.  If a null devclass_t is passed in, -1 is returned to indicate
   * that not even the devclass has been allocated yet.
   *
   * @param dc            the devclass to examine
   */
  int
  devclass_get_maxunit(devclass_t dc)
  {
          if (dc == NULL)
                  return (-1);
          return (dc->maxunit);
  }
  
  /**
   * @brief Find a free unit number in a devclass
   *
   * This function searches for the first unused unit number greater
   * that or equal to @p unit.
   *
   * @param dc            the devclass to examine
   * @param unit          the first unit number to check
   */
  int
  devclass_find_free_unit(devclass_t dc, int unit)
  {
          if (dc == NULL)
                  return (unit);
          while (unit < dc->maxunit && dc->devices[unit] != NULL)
                  unit++;
          return (unit);
  }
  
  /**
   * @brief Set the parent of a devclass
   *
   * The parent class is normally initialised automatically by
   * DRIVER_MODULE().
   *
   * @param dc            the devclass to edit
   * @param pdc           the new parent devclass
   */
  void
  devclass_set_parent(devclass_t dc, devclass_t pdc)
  {
          dc->parent = pdc;
  }
  
  /**
   * @brief Get the parent of a devclass
   *
   * @param dc            the devclass to examine
   */
  devclass_t
  devclass_get_parent(devclass_t dc)
  {
          return (dc->parent);
  }
  
  struct sysctl_ctx_list *
  devclass_get_sysctl_ctx(devclass_t dc)
  {
          return (&dc->sysctl_ctx);
  }
  
  struct sysctl_oid *
  devclass_get_sysctl_tree(devclass_t dc)
  {
          return (dc->sysctl_tree);
  }
  
  /**
   * @internal
   * @brief Allocate a unit number
   *
   * On entry, @p *unitp is the desired unit number (or @c -1 if any
   * will do). The allocated unit number is returned in @p *unitp.
  
   * @param dc            the devclass to allocate from
   * @param unitp         points at the location for the allocated unit
   *                      number
   *
   * @retval 0            success
   * @retval EEXIST       the requested unit number is already allocated
   * @retval ENOMEM       memory allocation failure
   */
  static int
  devclass_alloc_unit(devclass_t dc, device_t dev, int *unitp)
  {
          const char *s;
          int unit = *unitp;
  
          PDEBUG(("unit %d in devclass %s", unit, DEVCLANAME(dc)));
  
          /* Ask the parent bus if it wants to wire this device. */
          if (unit == -1)
                  BUS_HINT_DEVICE_UNIT(device_get_parent(dev), dev, dc->name,
                      &unit);
  
          /* If we were given a wired unit number, check for existing device */
          /* XXX imp XXX */
          if (unit != -1) {
                  if (unit >= 0 && unit < dc->maxunit &&
                      dc->devices[unit] != NULL) {
                          if (bootverbose)
                                  printf("%s: %s%d already exists; skipping it\n",
                                      dc->name, dc->name, *unitp);
                          return (EEXIST);
                  }
          } else {
                  /* Unwired device, find the next available slot for it */
                  unit = 0;
                  for (unit = 0;; unit++) {
                          /* If there is an "at" hint for a unit then skip it. */
                          if (resource_string_value(dc->name, unit, "at", &s) ==
                              0)
                                  continue;
  
                          /* If this device slot is already in use, skip it. */
                          if (unit < dc->maxunit && dc->devices[unit] != NULL)
                                  continue;
  
                          break;
                  }
          }
  
          /*
           * We've selected a unit beyond the length of the table, so let's
           * extend the table to make room for all units up to and including
           * this one.
           */
          if (unit >= dc->maxunit) {
                  device_t *newlist, *oldlist;
                  int newsize;
  
                  oldlist = dc->devices;
                  newsize = roundup((unit + 1), MINALLOCSIZE / sizeof(device_t));
                  newlist = malloc(sizeof(device_t) * newsize, M_BUS, M_NOWAIT);
                  if (!newlist)
                          return (ENOMEM);
                  if (oldlist != NULL)
                          bcopy(oldlist, newlist, sizeof(device_t) * dc->maxunit);
                  bzero(newlist + dc->maxunit,
                      sizeof(device_t) * (newsize - dc->maxunit));
                  dc->devices = newlist;
                  dc->maxunit = newsize;
                  if (oldlist != NULL)
                          free(oldlist, M_BUS);
          }
          PDEBUG(("now: unit %d in devclass %s", unit, DEVCLANAME(dc)));
  
          *unitp = unit;
          return (0);
  }
  
  /**
   * @internal
   * @brief Add a device to a devclass
   *
   * A unit number is allocated for the device (using the device's
   * preferred unit number if any) and the device is registered in the
   * devclass. This allows the device to be looked up by its unit
   * number, e.g. by decoding a dev_t minor number.
   *
   * @param dc            the devclass to add to
   * @param dev           the device to add
   *
   * @retval 0            success
   * @retval EEXIST       the requested unit number is already allocated
   * @retval ENOMEM       memory allocation failure
   */
  static int
  devclass_add_device(devclass_t dc, device_t dev)
  {
          int buflen, error;
  
          PDEBUG(("%s in devclass %s", DEVICENAME(dev), DEVCLANAME(dc)));
  
          buflen = snprintf(NULL, 0, "%s%d$", dc->name, INT_MAX);
          if (buflen < 0)
                  return (ENOMEM);
          dev->nameunit = malloc(buflen, M_BUS, M_NOWAIT|M_ZERO);
          if (!dev->nameunit)
                  return (ENOMEM);
  
          if ((error = devclass_alloc_unit(dc, dev, &dev->unit)) != 0) {
                  free(dev->nameunit, M_BUS);
                  dev->nameunit = NULL;
                  return (error);
          }
          dc->devices[dev->unit] = dev;
          dev->devclass = dc;
          snprintf(dev->nameunit, buflen, "%s%d", dc->name, dev->unit);
  
          return (0);
  }
  
  /**
   * @internal
   * @brief Delete a device from a devclass
   *
   * The device is removed from the devclass's device list and its unit
   * number is freed.
  
   * @param dc            the devclass to delete from
   * @param dev           the device to delete
   *
   * @retval 0            success
   */
  static int
  devclass_delete_device(devclass_t dc, device_t dev)
  {
          if (!dc || !dev)
                  return (0);
  
          PDEBUG(("%s in devclass %s", DEVICENAME(dev), DEVCLANAME(dc)));
  
          if (dev->devclass != dc || dc->devices[dev->unit] != dev)
                  panic("devclass_delete_device: inconsistent device class");
          dc->devices[dev->unit] = NULL;
          if (dev->flags & DF_WILDCARD)
                  dev->unit = -1;
          dev->devclass = NULL;
          free(dev->nameunit, M_BUS);
          dev->nameunit = NULL;
  
          return (0);
  }
  
  /**
   * @internal
   * @brief Make a new device and add it as a child of @p parent
   *
   * @param parent        the parent of the new device
   * @param name          the devclass name of the new device or @c NULL
   *                      to leave the devclass unspecified
   * @parem unit          the unit number of the new device of @c -1 to
   *                      leave the unit number unspecified
   *
   * @returns the new device
   */
  static device_t
  make_device(device_t parent, const char *name, int unit)
  {
          device_t dev;
          devclass_t dc;
  
          PDEBUG(("%s at %s as unit %d", name, DEVICENAME(parent), unit));
  
          if (name) {
                  dc = devclass_find_internal(name, NULL, TRUE);
                  if (!dc) {
                          printf("make_device: can't find device class %s\n",
                              name);
                          return (NULL);
                  }
          } else {
                  dc = NULL;
          }
  
          dev = malloc(sizeof(struct device), M_BUS, M_NOWAIT|M_ZERO);
          if (!dev)
                  return (NULL);
  
          dev->parent = parent;
          TAILQ_INIT(&dev->children);
          kobj_init((kobj_t) dev, &null_class);
          dev->driver = NULL;
          dev->devclass = NULL;
          dev->unit = unit;
          dev->nameunit = NULL;
          dev->desc = NULL;
          dev->busy = 0;
          dev->devflags = 0;
          dev->flags = DF_ENABLED;
          dev->order = 0;
          if (unit == -1)
                  dev->flags |= DF_WILDCARD;
          if (name) {
                  dev->flags |= DF_FIXEDCLASS;
                  if (devclass_add_device(dc, dev)) {
                          kobj_delete((kobj_t) dev, M_BUS);
                          return (NULL);
                  }
          }
          dev->ivars = NULL;
          dev->softc = NULL;
  
          dev->state = DS_NOTPRESENT;
  
          TAILQ_INSERT_TAIL(&bus_data_devices, dev, devlink);
          bus_data_generation_update();
  
          return (dev);
  }
  
  /**
   * @internal
   * @brief Print a description of a device.
   */
  static int
  device_print_child(device_t dev, device_t child)
  {
          int retval = 0;
  
          if (device_is_alive(child))
                  retval += BUS_PRINT_CHILD(dev, child);
          else
                  retval += device_printf(child, " not found\n");
  
          return (retval);
  }
  
  /**
   * @brief Create a new device
   *
   * This creates a new device and adds it as a child of an existing
   * parent device. The new device will be added after the last existing
   * child with order zero.
   * 
   * @param dev           the device which will be the parent of the
   *                      new child device
   * @param name          devclass name for new device or @c NULL if not
   *                      specified
   * @param unit          unit number for new device or @c -1 if not
   *                      specified
   * 
   * @returns             the new device
   */
  device_t
  device_add_child(device_t dev, const char *name, int unit)
  {
          return (device_add_child_ordered(dev, 0, name, unit));
  }
  
  /**
   * @brief Create a new device
   *
   * This creates a new device and adds it as a child of an existing
   * parent device. The new device will be added after the last existing
   * child with the same order.
   * 
   * @param dev           the device which will be the parent of the
   *                      new child device
   * @param order         a value which is used to partially sort the
   *                      children of @p dev - devices created using
   *                      lower values of @p order appear first in @p
   *                      dev's list of children
   * @param name          devclass name for new device or @c NULL if not
   *                      specified
   * @param unit          unit number for new device or @c -1 if not
   *                      specified
   * 
   * @returns             the new device
   */
  device_t
  device_add_child_ordered(device_t dev, u_int order, const char *name, int unit)
  {
          device_t child;
          device_t place;
  
          PDEBUG(("%s at %s with order %u as unit %d",
              name, DEVICENAME(dev), order, unit));
  
          child = make_device(dev, name, unit);
          if (child == NULL)
                  return (child);
          child->order = order;
  
          TAILQ_FOREACH(place, &dev->children, link) {
                  if (place->order > order)
                          break;
          }
  
          if (place) {
                  /*
                   * The device 'place' is the first device whose order is
                   * greater than the new child.
                   */
                  TAILQ_INSERT_BEFORE(place, child, link);
          } else {
                  /*
                   * The new child's order is greater or equal to the order of
                   * any existing device. Add the child to the tail of the list.
                   */
                  TAILQ_INSERT_TAIL(&dev->children, child, link);
          }
  
          bus_data_generation_update();
          return (child);
  }
  
  /**
   * @brief Delete a device
   *
   * This function deletes a device along with all of its children. If
   * the device currently has a driver attached to it, the device is
   * detached first using device_detach().
   * 
   * @param dev           the parent device
   * @param child         the device to delete
   *
   * @retval 0            success
   * @retval non-zero     a unit error code describing the error
   */
  int
  device_delete_child(device_t dev, device_t child)
  {
          int error;
          device_t grandchild;
  
          PDEBUG(("%s from %s", DEVICENAME(child), DEVICENAME(dev)));
  
          /* remove children first */
          while ( (grandchild = TAILQ_FIRST(&child->children)) ) {
                  error = device_delete_child(child, grandchild);
                  if (error)
                          return (error);
          }
  
          if ((error = device_detach(child)) != 0)
                  return (error);
          if (child->devclass)
                  devclass_delete_device(child->devclass, child);
          TAILQ_REMOVE(&dev->children, child, link);
          TAILQ_REMOVE(&bus_data_devices, child, devlink);
          kobj_delete((kobj_t) child, M_BUS);
  
          bus_data_generation_update();
          return (0);
  }
  
  /**
   * @brief Find a device given a unit number
   *
   * This is similar to devclass_get_devices() but only searches for
   * devices which have @p dev as a parent.
   *
   * @param dev           the parent device to search
   * @param unit          the unit number to search for.  If the unit is -1,
   *                      return the first child of @p dev which has name
   *                      @p classname (that is, the one with the lowest unit.)
   *
   * @returns             the device with the given unit number or @c
   *                      NULL if there is no such device
   */
  device_t
  device_find_child(device_t dev, const char *classname, int unit)
  {
          devclass_t dc;
          device_t child;
  
          dc = devclass_find(classname);
          if (!dc)
                  return (NULL);
  
          if (unit != -1) {
                  child = devclass_get_device(dc, unit);
                  if (child && child->parent == dev)
                          return (child);
          } else {
                  for (unit = 0; unit < devclass_get_maxunit(dc); unit++) {
                          child = devclass_get_device(dc, unit);
                          if (child && child->parent == dev)
                                  return (child);
                  }
          }
          return (NULL);
  }
  
  /**
   * @internal
   */
  static driverlink_t
  first_matching_driver(devclass_t dc, device_t dev)
  {
          if (dev->devclass)
                  return (devclass_find_driver_internal(dc, dev->devclass->name));
          return (TAILQ_FIRST(&dc->drivers));
  }
  
  /**
   * @internal
   */
  static driverlink_t
  next_matching_driver(devclass_t dc, device_t dev, driverlink_t last)
  {
          if (dev->devclass) {
                  driverlink_t dl;
                  for (dl = TAILQ_NEXT(last, link); dl; dl = TAILQ_NEXT(dl, link))
                          if (!strcmp(dev->devclass->name, dl->driver->name))
                                  return (dl);
                  return (NULL);
          }
          return (TAILQ_NEXT(last, link));
  }
  
  /**
   * @internal
   */
  int
  device_probe_child(device_t dev, device_t child)
  {
          devclass_t dc;
          driverlink_t best = NULL;
          driverlink_t dl;
          int result, pri = 0;
          int hasclass = (child->devclass != NULL);
  
          GIANT_REQUIRED;
  
          dc = dev->devclass;
          if (!dc)
                  panic("device_probe_child: parent device has no devclass");
  
          /*
           * If the state is already probed, then return.  However, don't
           * return if we can rebid this object.
           */
          if (child->state == DS_ALIVE && (child->flags & DF_REBID) == 0)
                  return (0);
  
          for (; dc; dc = dc->parent) {
                  for (dl = first_matching_driver(dc, child);
                       dl;
                       dl = next_matching_driver(dc, child, dl)) {
                          /* If this driver's pass is too high, then ignore it. */
                          if (dl->pass > bus_current_pass)
                                  continue;
  
                          PDEBUG(("Trying %s", DRIVERNAME(dl->driver)));
                          result = device_set_driver(child, dl->driver);
                          if (result == ENOMEM)
                                  return (result);
                          else if (result != 0)
                                  continue;
                          if (!hasclass) {
                                  if (device_set_devclass(child,
                                      dl->driver->name) != 0) {
                                          printf("driver bug: Unable to set "
                                              "devclass (devname: %s)\n",
                                              device_get_name(child));
                                          (void)device_set_driver(child, NULL);
                                          continue;
                                  }
                          }
  
                          /* Fetch any flags for the device before probing. */
                          resource_int_value(dl->driver->name, child->unit,
                              "flags", &child->devflags);
  
                          result = DEVICE_PROBE(child);
  
                          /* Reset flags and devclass before the next probe. */
                          child->devflags = 0;
                          if (!hasclass)
                                  (void)device_set_devclass(child, NULL);
  
                          /*
                           * If the driver returns SUCCESS, there can be
                           * no higher match for this device.
                           */
                          if (result == 0) {
                                  best = dl;
                                  pri = 0;
                                  break;
                          }
  
                          /*
                           * The driver returned an error so it
                           * certainly doesn't match.
                           */
                          if (result > 0) {
                                  (void)device_set_driver(child, NULL);
                                  continue;
                          }
  
                          /*
                           * A priority lower than SUCCESS, remember the
                           * best matching driver. Initialise the value
                           * of pri for the first match.
                           */
                          if (best == NULL || result > pri) {
                                  /*
                                   * Probes that return BUS_PROBE_NOWILDCARD
                                   * or lower only match when they are set
                                   * in stone by the parent bus.
                                   */
                                  if (result <= BUS_PROBE_NOWILDCARD &&
                                      child->flags & DF_WILDCARD)
                                          continue;
                                  best = dl;
                                  pri = result;
                                  continue;
                          }
                  }
                  /*
                   * If we have an unambiguous match in this devclass,
                   * don't look in the parent.
                   */
                  if (best && pri == 0)
                          break;
          }
  
          /*
           * If we found a driver, change state and initialise the devclass.
           */
          /* XXX What happens if we rebid and got no best? */
          if (best) {
                  /*
                   * If this device was atached, and we were asked to
                   * rescan, and it is a different driver, then we have
                   * to detach the old driver and reattach this new one.
                   * Note, we don't have to check for DF_REBID here
                   * because if the state is > DS_ALIVE, we know it must
                   * be.
                   *
                   * This assumes that all DF_REBID drivers can have
                   * their probe routine called at any time and that
                   * they are idempotent as well as completely benign in
                   * normal operations.
                   *
                   * We also have to make sure that the detach
                   * succeeded, otherwise we fail the operation (or
                   * maybe it should just fail silently?  I'm torn).
                   */
                  if (child->state > DS_ALIVE && best->driver != child->driver)
                          if ((result = device_detach(dev)) != 0)
                                  return (result);
  
                  /* Set the winning driver, devclass, and flags. */
                  if (!child->devclass) {
                          result = device_set_devclass(child, best->driver->name);
                          if (result != 0)
                                  return (result);
                  }
                  result = device_set_driver(child, best->driver);
                  if (result != 0)
                          return (result);
                  resource_int_value(best->driver->name, child->unit,
                      "flags", &child->devflags);
  
                  if (pri < 0) {
                          /*
                           * A bit bogus. Call the probe method again to make
                           * sure that we have the right description.
                           */
                          DEVICE_PROBE(child);
  #if 0
                          child->flags |= DF_REBID;
  #endif
                  } else
                          child->flags &= ~DF_REBID;
                  child->state = DS_ALIVE;
  
                  bus_data_generation_update();
                  return (0);
          }
  
          return (ENXIO);
  }
  
  /**
   * @brief Return the parent of a device
   */
  device_t
  device_get_parent(device_t dev)
  {
          return (dev->parent);
  }
  
  /**
   * @brief Get a list of children of a device
   *
   * An array containing a list of all the children of the given device
   * is allocated and returned in @p *devlistp. The number of devices
   * in the array is returned in @p *devcountp. The caller should free
   * the array using @c free(p, M_TEMP).
   *
   * @param dev           the device to examine
   * @param devlistp      points at location for array pointer return
   *                      value
   * @param devcountp     points at location for array size return value
   *
   * @retval 0            success
   * @retval ENOMEM       the array allocation failed
   */
  int
  device_get_children(device_t dev, device_t **devlistp, int *devcountp)
  {
          int count;
          device_t child;
          device_t *list;
  
          count = 0;
          TAILQ_FOREACH(child, &dev->children, link) {
                  count++;
          }
          if (count == 0) {
                  *devlistp = NULL;
                  *devcountp = 0;
                  return (0);
          }
  
          list = malloc(count * sizeof(device_t), M_TEMP, M_NOWAIT|M_ZERO);
          if (!list)
                  return (ENOMEM);
  
          count = 0;
          TAILQ_FOREACH(child, &dev->children, link) {
                  list[count] = child;
                  count++;
          }
  
          *devlistp = list;
          *devcountp = count;
  
          return (0);
  }
  
  /**
   * @brief Return the current driver for the device or @c NULL if there
   * is no driver currently attached
   */
  driver_t *
  device_get_driver(device_t dev)
  {
          return (dev->driver);
  }
  
  /**
   * @brief Return the current devclass for the device or @c NULL if
   * there is none.
   */
  devclass_t
  device_get_devclass(device_t dev)
  {
          return (dev->devclass);
  }
  
  /**
   * @brief Return the name of the device's devclass or @c NULL if there
   * is none.
   */
  const char *
  device_get_name(device_t dev)
  {
          if (dev != NULL && dev->devclass)
                  return (devclass_get_name(dev->devclass));
          return (NULL);
  }
  
  /**
   * @brief Return a string containing the device's devclass name
   * followed by an ascii representation of the device's unit number
   * (e.g. @c "foo2").
   */
  const char *
  device_get_nameunit(device_t dev)
  {
          return (dev->nameunit);
  }
  
  /**
   * @brief Return the device's unit number.
   */
  int
  device_get_unit(device_t dev)
  {
          return (dev->unit);
  }
  
  /**
   * @brief Return the device's description string
   */
  const char *
  device_get_desc(device_t dev)
  {
          return (dev->desc);
  }
  
  /**
   * @brief Return the device's flags
   */
  u_int32_t
  device_get_flags(device_t dev)
  {
          return (dev->devflags);
  }
  
  struct sysctl_ctx_list *
  device_get_sysctl_ctx(device_t dev)
  {
          return (&dev->sysctl_ctx);
  }
  
  struct sysctl_oid *
  device_get_sysctl_tree(device_t dev)
  {
          return (dev->sysctl_tree);
  }
  
  /**
   * @brief Print the name of the device followed by a colon and a space
   *
   * @returns the number of characters printed
   */
  int
  device_print_prettyname(device_t dev)
  {
          const char *name = device_get_name(dev);
  
          if (name == NULL)
                  return (printf("unknown: "));
          return (printf("%s%d: ", name, device_get_unit(dev)));
  }
  
  /**
   * @brief Print the name of the device followed by a colon, a space
   * and the result of calling vprintf() with the value of @p fmt and
   * the following arguments.
   *
   * @returns the number of characters printed
   */
  int
  device_printf(device_t dev, const char * fmt, ...)
  {
          va_list ap;
          int retval;
  
          retval = device_print_prettyname(dev);
          va_start(ap, fmt);
          retval += vprintf(fmt, ap);
          va_end(ap);
          return (retval);
  }
  
  /**
   * @internal
   */
  static void
  device_set_desc_internal(device_t dev, const char* desc, int copy)
  {
          if (dev->desc && (dev->flags & DF_DESCMALLOCED)) {
                  free(dev->desc, M_BUS);
                  dev->flags &= ~DF_DESCMALLOCED;
                  dev->desc = NULL;
          }
  
          if (copy && desc) {
                  dev->desc = malloc(strlen(desc) + 1, M_BUS, M_NOWAIT);
                  if (dev->desc) {
                          strcpy(dev->desc, desc);
                          dev->flags |= DF_DESCMALLOCED;
                  }
          } else {
                  /* Avoid a -Wcast-qual warning */
                  dev->desc = (char *)(uintptr_t) desc;
          }
  
          bus_data_generation_update();
  }
  
  /**
   * @brief Set the device's description
   *
   * The value of @c desc should be a string constant that will not
   * change (at least until the description is changed in a subsequent
   * call to device_set_desc() or device_set_desc_copy()).
   */
  void
  device_set_desc(device_t dev, const char* desc)
  {
          device_set_desc_internal(dev, desc, FALSE);
  }
  
  /**
   * @brief Set the device's description
   *
   * The string pointed to by @c desc is copied. Use this function if
   * the device description is generated, (e.g. with sprintf()).
   */
  void
  device_set_desc_copy(device_t dev, const char* desc)
  {
          device_set_desc_internal(dev, desc, TRUE);
  }
  
  /**
   * @brief Set the device's flags
   */
  void
  device_set_flags(device_t dev, u_int32_t flags)
  {
          dev->devflags = flags;
  }
  
  /**
   * @brief Return the device's softc field
   *
   * The softc is allocated and zeroed when a driver is attached, based
   * on the size field of the driver.
   */
  void *
  device_get_softc(device_t dev)
  {
          return (dev->softc);
  }
  
  /**
   * @brief Set the device's softc field
   *
   * Most drivers do not need to use this since the softc is allocated
   * automatically when the driver is attached.
   */
  void
  device_set_softc(device_t dev, void *softc)
  {
          if (dev->softc && !(dev->flags & DF_EXTERNALSOFTC))
                  free(dev->softc, M_BUS_SC);
          dev->softc = softc;
          if (dev->softc)
                  dev->flags |= DF_EXTERNALSOFTC;
          else
                  dev->flags &= ~DF_EXTERNALSOFTC;
  }
  
  /**
   * @brief Get the device's ivars field
   *
   * The ivars field is used by the parent device to store per-device
   * state (e.g. the physical location of the device or a list of
   * resources).
   */
  void *
  device_get_ivars(device_t dev)
  {
  
          KASSERT(dev != NULL, ("device_get_ivars(NULL, ...)"));
          return (dev->ivars);
  }
  
  /**
   * @brief Set the device's ivars field
   */
  void
  device_set_ivars(device_t dev, void * ivars)
  {
  
          KASSERT(dev != NULL, ("device_set_ivars(NULL, ...)"));
          dev->ivars = ivars;
  }
  
  /**
   * @brief Return the device's state
   */
  device_state_t
  device_get_state(device_t dev)
  {
          return (dev->state);
  }
  
  /**
   * @brief Set the DF_ENABLED flag for the device
   */
  void
  device_enable(device_t dev)
  {
          dev->flags |= DF_ENABLED;
  }
  
  /**
   * @brief Clear the DF_ENABLED flag for the device
   */
  void
  device_disable(device_t dev)
  {
          dev->flags &= ~DF_ENABLED;
  }
  
  /**
   * @brief Increment the busy counter for the device
   */
  void
  device_busy(device_t dev)
  {
          if (dev->state < DS_ATTACHED)
                  panic("device_busy: called for unattached device");
          if (dev->busy == 0 && dev->parent)
                  device_busy(dev->parent);
          dev->busy++;
          dev->state = DS_BUSY;
  }
  
  /**
   * @brief Decrement the busy counter for the device
   */
  void
  device_unbusy(device_t dev)
  {
          if (dev->state != DS_BUSY)
                  panic("device_unbusy: called for non-busy device %s",
                      device_get_nameunit(dev));
          dev->busy--;
          if (dev->busy == 0) {
                  if (dev->parent)
                          device_unbusy(dev->parent);
                  dev->state = DS_ATTACHED;
          }
  }
  
  /**
   * @brief Set the DF_QUIET flag for the device
   */
  void
  device_quiet(device_t dev)
  {
          dev->flags |= DF_QUIET;
  }
  
  /**
   * @brief Clear the DF_QUIET flag for the device
   */
  void
  device_verbose(device_t dev)
  {
          dev->flags &= ~DF_QUIET;
  }
  
  /**
   * @brief Return non-zero if the DF_QUIET flag is set on the device
   */
  int
  device_is_quiet(device_t dev)
  {
          return ((dev->flags & DF_QUIET) != 0);
  }
  
  /**
   * @brief Return non-zero if the DF_ENABLED flag is set on the device
   */
  int
  device_is_enabled(device_t dev)
  {
          return ((dev->flags & DF_ENABLED) != 0);
  }
  
  /**
   * @brief Return non-zero if the device was successfully probed
   */
  int
  device_is_alive(device_t dev)
  {
          return (dev->state >= DS_ALIVE);
  }
  
  /**
   * @brief Return non-zero if the device currently has a driver
   * attached to it
   */
  int
  device_is_attached(device_t dev)
  {
          return (dev->state >= DS_ATTACHED);
  }
  
  /**
   * @brief Set the devclass of a device
   * @see devclass_add_device().
   */
  int
  device_set_devclass(device_t dev, const char *classname)
  {
          devclass_t dc;
          int error;
  
          if (!classname) {
                  if (dev->devclass)
                          devclass_delete_device(dev->devclass, dev);
                  return (0);
          }
  
          if (dev->devclass) {
                  printf("device_set_devclass: device class already set\n");
                  return (EINVAL);
          }
  
          dc = devclass_find_internal(classname, NULL, TRUE);
          if (!dc)
                  return (ENOMEM);
  
          error = devclass_add_device(dc, dev);
  
          bus_data_generation_update();
          return (error);
  }
  
  /**
   * @brief Set the driver of a device
   *
   * @retval 0            success
   * @retval EBUSY        the device already has a driver attached
   * @retval ENOMEM       a memory allocation failure occurred
   */
  int
  device_set_driver(device_t dev, driver_t *driver)
  {
          if (dev->state >= DS_ATTACHED)
                  return (EBUSY);
  
          if (dev->driver == driver)
                  return (0);
  
          if (dev->softc && !(dev->flags & DF_EXTERNALSOFTC)) {
                  free(dev->softc, M_BUS_SC);
                  dev->softc = NULL;
          }
          kobj_delete((kobj_t) dev, NULL);
          dev->driver = driver;
          if (driver) {
                  kobj_init((kobj_t) dev, (kobj_class_t) driver);
                  if (!(dev->flags & DF_EXTERNALSOFTC) && driver->size > 0) {
                          dev->softc = malloc(driver->size, M_BUS_SC,
                              M_NOWAIT | M_ZERO);
                          if (!dev->softc) {
                                  kobj_delete((kobj_t) dev, NULL);
                                  kobj_init((kobj_t) dev, &null_class);
                                  dev->driver = NULL;
                                  return (ENOMEM);
                          }
                  }
          } else {
                  kobj_init((kobj_t) dev, &null_class);
          }
  
          bus_data_generation_update();
          return (0);
  }
  
  /**
   * @brief Probe a device, and return this status.
   *
   * This function is the core of the device autoconfiguration
   * system. Its purpose is to select a suitable driver for a device and
   * then call that driver to initialise the hardware appropriately. The
   * driver is selected by calling the DEVICE_PROBE() method of a set of
   * candidate drivers and then choosing the driver which returned the
   * best value. This driver is then attached to the device using
   * device_attach().
   *
   * The set of suitable drivers is taken from the list of drivers in
   * the parent device's devclass. If the device was originally created
   * with a specific class name (see device_add_child()), only drivers
   * with that name are probed, otherwise all drivers in the devclass
   * are probed. If no drivers return successful probe values in the
   * parent devclass, the search continues in the parent of that
   * devclass (see devclass_get_parent()) if any.
   *
   * @param dev           the device to initialise
   *
   * @retval 0            success
   * @retval ENXIO        no driver was found
   * @retval ENOMEM       memory allocation failure
   * @retval non-zero     some other unix error code
   * @retval -1           Device already attached
   */
  int
  device_probe(device_t dev)
  {
          int error;
  
          GIANT_REQUIRED;
  
          if (dev->state >= DS_ALIVE && (dev->flags & DF_REBID) == 0)
                  return (-1);
  
          if (!(dev->flags & DF_ENABLED)) {
                  if (bootverbose && device_get_name(dev) != NULL) {
                          device_print_prettyname(dev);
                          printf("not probed (disabled)\n");
                  }
                  return (-1);
          }
          if ((error = device_probe_child(dev->parent, dev)) != 0) {              
                  if (bus_current_pass == BUS_PASS_DEFAULT &&
                      !(dev->flags & DF_DONENOMATCH)) {
                          BUS_PROBE_NOMATCH(dev->parent, dev);
                          devnomatch(dev);
                          dev->flags |= DF_DONENOMATCH;
                  }
                  return (error);
          }
          return (0);
  }
  
  /**
   * @brief Probe a device and attach a driver if possible
   *
   * calls device_probe() and attaches if that was successful.
   */
  int
  device_probe_and_attach(device_t dev)
  {
          int error;
  
          GIANT_REQUIRED;
  
          error = device_probe(dev);
          if (error == -1)
                  return (0);
          else if (error != 0)
                  return (error);
          return (device_attach(dev));
  }
  
  /**
   * @brief Attach a device driver to a device
   *
   * This function is a wrapper around the DEVICE_ATTACH() driver
   * method. In addition to calling DEVICE_ATTACH(), it initialises the
   * device's sysctl tree, optionally prints a description of the device
   * and queues a notification event for user-based device management
   * services.
   *
   * Normally this function is only called internally from
   * device_probe_and_attach().
   *
   * @param dev           the device to initialise
   *
   * @retval 0            success
   * @retval ENXIO        no driver was found
   * @retval ENOMEM       memory allocation failure
   * @retval non-zero     some other unix error code
   */
  int
  device_attach(device_t dev)
  {
          int error;
  
          device_sysctl_init(dev);
          if (!device_is_quiet(dev))
                  device_print_child(dev->parent, dev);
          if ((error = DEVICE_ATTACH(dev)) != 0) {
                  printf("device_attach: %s%d attach returned %d\n",
                      dev->driver->name, dev->unit, error);
                  /* Unset the class; set in device_probe_child */
                  if (dev->devclass == NULL)
                          (void)device_set_devclass(dev, NULL);
                  (void)device_set_driver(dev, NULL);
                  device_sysctl_fini(dev);
                  dev->state = DS_NOTPRESENT;
                  return (error);
          }
          device_sysctl_update(dev);
          dev->state = DS_ATTACHED;
          dev->flags &= ~DF_DONENOMATCH;
          devadded(dev);
          return (0);
  }
  
  /**
   * @brief Detach a driver from a device
   *
   * This function is a wrapper around the DEVICE_DETACH() driver
   * method. If the call to DEVICE_DETACH() succeeds, it calls
   * BUS_CHILD_DETACHED() for the parent of @p dev, queues a
   * notification event for user-based device management services and
   * cleans up the device's sysctl tree.
   *
   * @param dev           the device to un-initialise
   *
   * @retval 0            success
   * @retval ENXIO        no driver was found
   * @retval ENOMEM       memory allocation failure
   * @retval non-zero     some other unix error code
   */
  int
  device_detach(device_t dev)
  {
          int error;
  
          GIANT_REQUIRED;
  
          PDEBUG(("%s", DEVICENAME(dev)));
          if (dev->state == DS_BUSY)
                  return (EBUSY);
          if (dev->state != DS_ATTACHED)
                  return (0);
  
          if ((error = DEVICE_DETACH(dev)) != 0)
                  return (error);
          devremoved(dev);
          if (!device_is_quiet(dev))
                  device_printf(dev, "detached\n");
          if (dev->parent)
                  BUS_CHILD_DETACHED(dev->parent, dev);
  
          if (!(dev->flags & DF_FIXEDCLASS))
                  devclass_delete_device(dev->devclass, dev);
  
          dev->state = DS_NOTPRESENT;
          (void)device_set_driver(dev, NULL);
          device_set_desc(dev, NULL);
          device_sysctl_fini(dev);
  
          return (0);
  }
  
  /**
   * @brief Tells a driver to quiesce itself.
   *
   * This function is a wrapper around the DEVICE_QUIESCE() driver
   * method. If the call to DEVICE_QUIESCE() succeeds.
   *
   * @param dev           the device to quiesce
   *
   * @retval 0            success
   * @retval ENXIO        no driver was found
   * @retval ENOMEM       memory allocation failure
   * @retval non-zero     some other unix error code
   */
  int
  device_quiesce(device_t dev)
  {
  
          PDEBUG(("%s", DEVICENAME(dev)));
          if (dev->state == DS_BUSY)
                  return (EBUSY);
          if (dev->state != DS_ATTACHED)
                  return (0);
  
          return (DEVICE_QUIESCE(dev));
  }
  
  /**
   * @brief Notify a device of system shutdown
   *
   * This function calls the DEVICE_SHUTDOWN() driver method if the
   * device currently has an attached driver.
   *
   * @returns the value returned by DEVICE_SHUTDOWN()
   */
  int
  device_shutdown(device_t dev)
  {
          if (dev->state < DS_ATTACHED)
                  return (0);
          return (DEVICE_SHUTDOWN(dev));
  }
  
  /**
   * @brief Set the unit number of a device
   *
   * This function can be used to override the unit number used for a
   * device (e.g. to wire a device to a pre-configured unit number).
   */
  int
  device_set_unit(device_t dev, int unit)
  {
          devclass_t dc;
          int err;
  
          dc = device_get_devclass(dev);
          if (unit < dc->maxunit && dc->devices[unit])
                  return (EBUSY);
          err = devclass_delete_device(dc, dev);
          if (err)
                  return (err);
          dev->unit = unit;
          err = devclass_add_device(dc, dev);
          if (err)
                  return (err);
  
          bus_data_generation_update();
          return (0);
  }
  
  /*======================================*/
  /*
   * Some useful method implementations to make life easier for bus drivers.
   */
  
  /**
   * @brief Initialise a resource list.
   *
   * @param rl            the resource list to initialise
   */
  void
  resource_list_init(struct resource_list *rl)
  {
          STAILQ_INIT(rl);
  }
  
  /**
   * @brief Reclaim memory used by a resource list.
   *
   * This function frees the memory for all resource entries on the list
   * (if any).
   *
   * @param rl            the resource list to free               
   */
  void
  resource_list_free(struct resource_list *rl)
  {
          struct resource_list_entry *rle;
  
          while ((rle = STAILQ_FIRST(rl)) != NULL) {
                  if (rle->res)
                          panic("resource_list_free: resource entry is busy");
                  STAILQ_REMOVE_HEAD(rl, link);
                  free(rle, M_BUS);
          }
  }
  
  /**
   * @brief Add a resource entry.
   *
   * This function adds a resource entry using the given @p type, @p
   * start, @p end and @p count values. A rid value is chosen by
   * searching sequentially for the first unused rid starting at zero.
   *
   * @param rl            the resource list to edit
   * @param type          the resource entry type (e.g. SYS_RES_MEMORY)
   * @param start         the start address of the resource
   * @param end           the end address of the resource
   * @param count         XXX end-start+1
   */
  int
  resource_list_add_next(struct resource_list *rl, int type, u_long start,
      u_long end, u_long count)
  {
          int rid;
  
          rid = 0;
          while (resource_list_find(rl, type, rid) != NULL)
                  rid++;
          resource_list_add(rl, type, rid, start, end, count);
          return (rid);
  }
  
  /**
   * @brief Add or modify a resource entry.
   *
   * If an existing entry exists with the same type and rid, it will be
   * modified using the given values of @p start, @p end and @p
   * count. If no entry exists, a new one will be created using the
   * given values.  The resource list entry that matches is then returned.
   *
   * @param rl            the resource list to edit
   * @param type          the resource entry type (e.g. SYS_RES_MEMORY)
   * @param rid           the resource identifier
   * @param start         the start address of the resource
   * @param end           the end address of the resource
   * @param count         XXX end-start+1
   */
  struct resource_list_entry *
  resource_list_add(struct resource_list *rl, int type, int rid,
      u_long start, u_long end, u_long count)
  {
          struct resource_list_entry *rle;
  
          rle = resource_list_find(rl, type, rid);
          if (!rle) {
                  rle = malloc(sizeof(struct resource_list_entry), M_BUS,
                      M_NOWAIT);
                  if (!rle)
                          panic("resource_list_add: can't record entry");
                  STAILQ_INSERT_TAIL(rl, rle, link);
                  rle->type = type;
                  rle->rid = rid;
                  rle->res = NULL;
          }
  
          if (rle->res)
                  panic("resource_list_add: resource entry is busy");
  
          rle->start = start;
          rle->end = end;
          rle->count = count;
          return (rle);
  }
  
  /**
   * @brief Find a resource entry by type and rid.
   *
   * @param rl            the resource list to search
   * @param type          the resource entry type (e.g. SYS_RES_MEMORY)
   * @param rid           the resource identifier
   *
   * @returns the resource entry pointer or NULL if there is no such
   * entry.
   */
  struct resource_list_entry *
  resource_list_find(struct resource_list *rl, int type, int rid)
  {
          struct resource_list_entry *rle;
  
          STAILQ_FOREACH(rle, rl, link) {
                  if (rle->type == type && rle->rid == rid)
                          return (rle);
          }
          return (NULL);
  }
  
  /**
   * @brief Delete a resource entry.
   *
   * @param rl            the resource list to edit
   * @param type          the resource entry type (e.g. SYS_RES_MEMORY)
   * @param rid           the resource identifier
   */
  void
  resource_list_delete(struct resource_list *rl, int type, int rid)
  {
          struct resource_list_entry *rle = resource_list_find(rl, type, rid);
  
          if (rle) {
                  if (rle->res != NULL)
                          panic("resource_list_delete: resource has not been released");
                  STAILQ_REMOVE(rl, rle, resource_list_entry, link);
                  free(rle, M_BUS);
          }
  }
  
  /**
   * @brief Helper function for implementing BUS_ALLOC_RESOURCE()
   *
   * Implement BUS_ALLOC_RESOURCE() by looking up a resource from the list
   * and passing the allocation up to the parent of @p bus. This assumes
   * that the first entry of @c device_get_ivars(child) is a struct
   * resource_list. This also handles 'passthrough' allocations where a
   * child is a remote descendant of bus by passing the allocation up to
   * the parent of bus.
   *
   * Typically, a bus driver would store a list of child resources
   * somewhere in the child device's ivars (see device_get_ivars()) and
   * its implementation of BUS_ALLOC_RESOURCE() would find that list and
   * then call resource_list_alloc() to perform the allocation.
   *
   * @param rl            the resource list to allocate from
   * @param bus           the parent device of @p child
   * @param child         the device which is requesting an allocation
   * @param type          the type of resource to allocate
   * @param rid           a pointer to the resource identifier
   * @param start         hint at the start of the resource range - pass
   *                      @c 0UL for any start address
   * @param end           hint at the end of the resource range - pass
   *                      @c ~0UL for any end address
   * @param count         hint at the size of range required - pass @c 1
   *                      for any size
   * @param flags         any extra flags to control the resource
   *                      allocation - see @c RF_XXX flags in
   *                      <sys/rman.h> for details
   * 
   * @returns             the resource which was allocated or @c NULL if no
   *                      resource could be allocated
   */
  struct resource *
  resource_list_alloc(struct resource_list *rl, device_t bus, device_t child,
      int type, int *rid, u_long start, u_long end, u_long count, u_int flags)
  {
          struct resource_list_entry *rle = NULL;
          int passthrough = (device_get_parent(child) != bus);
          int isdefault = (start == 0UL && end == ~0UL);
  
          if (passthrough) {
                  return (BUS_ALLOC_RESOURCE(device_get_parent(bus), child,
                      type, rid, start, end, count, flags));
          }
  
          rle = resource_list_find(rl, type, *rid);
  
          if (!rle)
                  return (NULL);          /* no resource of that type/rid */
  
          if (rle->res)
                  panic("resource_list_alloc: resource entry is busy");
  
          if (isdefault) {
                  start = rle->start;
                  count = ulmax(count, rle->count);
                  end = ulmax(rle->end, start + count - 1);
          }
  
          rle->res = BUS_ALLOC_RESOURCE(device_get_parent(bus), child,
              type, rid, start, end, count, flags);
  
          /*
           * Record the new range.
           */
          if (rle->res) {
                  rle->start = rman_get_start(rle->res);
                  rle->end = rman_get_end(rle->res);
                  rle->count = count;
          }
  
          return (rle->res);
  }
  
  /**
   * @brief Helper function for implementing BUS_RELEASE_RESOURCE()
   * 
   * Implement BUS_RELEASE_RESOURCE() using a resource list. Normally
   * used with resource_list_alloc().
   * 
   * @param rl            the resource list which was allocated from
   * @param bus           the parent device of @p child
   * @param child         the device which is requesting a release
   * @param type          the type of resource to allocate
   * @param rid           the resource identifier
   * @param res           the resource to release
   * 
   * @retval 0            success
   * @retval non-zero     a standard unix error code indicating what
   *                      error condition prevented the operation
   */
  int
  resource_list_release(struct resource_list *rl, device_t bus, device_t child,
      int type, int rid, struct resource *res)
  {
          struct resource_list_entry *rle = NULL;
          int passthrough = (device_get_parent(child) != bus);
          int error;
  
          if (passthrough) {
                  return (BUS_RELEASE_RESOURCE(device_get_parent(bus), child,
                      type, rid, res));
          }
  
          rle = resource_list_find(rl, type, rid);
  
          if (!rle)
                  panic("resource_list_release: can't find resource");
          if (!rle->res)
                  panic("resource_list_release: resource entry is not busy");
  
          error = BUS_RELEASE_RESOURCE(device_get_parent(bus), child,
              type, rid, res);
          if (error)
                  return (error);
  
          rle->res = NULL;
          return (0);
  }
  
  /**
   * @brief Print a description of resources in a resource list
   *
   * Print all resources of a specified type, for use in BUS_PRINT_CHILD().
   * The name is printed if at least one resource of the given type is available.
   * The format is used to print resource start and end.
   *
   * @param rl            the resource list to print
   * @param name          the name of @p type, e.g. @c "memory"
   * @param type          type type of resource entry to print
   * @param format        printf(9) format string to print resource
   *                      start and end values
   * 
   * @returns             the number of characters printed
   */
  int
  resource_list_print_type(struct resource_list *rl, const char *name, int type,
      const char *format)
  {
          struct resource_list_entry *rle;
          int printed, retval;
  
          printed = 0;
          retval = 0;
          /* Yes, this is kinda cheating */
          STAILQ_FOREACH(rle, rl, link) {
                  if (rle->type == type) {
                          if (printed == 0)
                                  retval += printf(" %s ", name);
                          else
                                  retval += printf(",");
                          printed++;
                          retval += printf(format, rle->start);
                          if (rle->count > 1) {
                                  retval += printf("-");
                                  retval += printf(format, rle->start +
                                                   rle->count - 1);
                          }
                  }
          }
          return (retval);
  }
  
  /**
   * @brief Releases all the resources in a list.
   *
   * @param rl            The resource list to purge.
   * 
   * @returns             nothing
   */
  void
  resource_list_purge(struct resource_list *rl)
  {
          struct resource_list_entry *rle;
  
          while ((rle = STAILQ_FIRST(rl)) != NULL) {
                  if (rle->res)
                          bus_release_resource(rman_get_device(rle->res),
                              rle->type, rle->rid, rle->res);
                  STAILQ_REMOVE_HEAD(rl, link);
                  free(rle, M_BUS);
          }
  }
  
  device_t
  bus_generic_add_child(device_t dev, u_int order, const char *name, int unit)
  {
  
          return (device_add_child_ordered(dev, order, name, unit));
  }
  
  /**
   * @brief Helper function for implementing DEVICE_PROBE()
   *
   * This function can be used to help implement the DEVICE_PROBE() for
   * a bus (i.e. a device which has other devices attached to it). It
   * calls the DEVICE_IDENTIFY() method of each driver in the device's
   * devclass.
   */
  int
  bus_generic_probe(device_t dev)
  {
          devclass_t dc = dev->devclass;
          driverlink_t dl;
  
          TAILQ_FOREACH(dl, &dc->drivers, link) {
                  /*
                   * If this driver's pass is too high, then ignore it.
                   * For most drivers in the default pass, this will
                   * never be true.  For early-pass drivers they will
                   * only call the identify routines of eligible drivers
                   * when this routine is called.  Drivers for later
                   * passes should have their identify routines called
                   * on early-pass busses during BUS_NEW_PASS().
                   */
                  if (dl->pass > bus_current_pass)
                                  continue;
                  DEVICE_IDENTIFY(dl->driver, dev);
          }
  
          return (0);
  }
  
  /**
   * @brief Helper function for implementing DEVICE_ATTACH()
   *
   * This function can be used to help implement the DEVICE_ATTACH() for
   * a bus. It calls device_probe_and_attach() for each of the device's
   * children.
   */
  int
  bus_generic_attach(device_t dev)
  {
          device_t child;
  
          TAILQ_FOREACH(child, &dev->children, link) {
                  device_probe_and_attach(child);
          }
  
          return (0);
  }
  
  /**
   * @brief Helper function for implementing DEVICE_DETACH()
   *
   * This function can be used to help implement the DEVICE_DETACH() for
   * a bus. It calls device_detach() for each of the device's
   * children.
   */
  int
  bus_generic_detach(device_t dev)
  {
          device_t child;
          int error;
  
          if (dev->state != DS_ATTACHED)
                  return (EBUSY);
  
          TAILQ_FOREACH(child, &dev->children, link) {
                  if ((error = device_detach(child)) != 0)
                          return (error);
          }
  
          return (0);
  }
  
  /**
   * @brief Helper function for implementing DEVICE_SHUTDOWN()
   *
   * This function can be used to help implement the DEVICE_SHUTDOWN()
   * for a bus. It calls device_shutdown() for each of the device's
   * children.
   */
  int
  bus_generic_shutdown(device_t dev)
  {
          device_t child;
  
          TAILQ_FOREACH(child, &dev->children, link) {
                  device_shutdown(child);
          }
  
          return (0);
  }
  
  /**
   * @brief Helper function for implementing DEVICE_SUSPEND()
   *
   * This function can be used to help implement the DEVICE_SUSPEND()
   * for a bus. It calls DEVICE_SUSPEND() for each of the device's
   * children. If any call to DEVICE_SUSPEND() fails, the suspend
   * operation is aborted and any devices which were suspended are
   * resumed immediately by calling their DEVICE_RESUME() methods.
   */
  int
  bus_generic_suspend(device_t dev)
  {
          int             error;
          device_t        child, child2;
  
          TAILQ_FOREACH(child, &dev->children, link) {
                  error = DEVICE_SUSPEND(child);
                  if (error) {
                          for (child2 = TAILQ_FIRST(&dev->children);
                               child2 && child2 != child;
                               child2 = TAILQ_NEXT(child2, link))
                                  DEVICE_RESUME(child2);
                          return (error);
                  }
          }
          return (0);
  }
  
  /**
   * @brief Helper function for implementing DEVICE_RESUME()
   *
   * This function can be used to help implement the DEVICE_RESUME() for
   * a bus. It calls DEVICE_RESUME() on each of the device's children.
   */
  int
  bus_generic_resume(device_t dev)
  {
          device_t        child;
  
          TAILQ_FOREACH(child, &dev->children, link) {
                  DEVICE_RESUME(child);
                  /* if resume fails, there's nothing we can usefully do... */
          }
          return (0);
  }
  
  /**
   * @brief Helper function for implementing BUS_PRINT_CHILD().
   *
   * This function prints the first part of the ascii representation of
   * @p child, including its name, unit and description (if any - see
   * device_set_desc()).
   *
   * @returns the number of characters printed
   */
  int
  bus_print_child_header(device_t dev, device_t child)
  {
          int     retval = 0;
  
          if (device_get_desc(child)) {
                  retval += device_printf(child, "<%s>", device_get_desc(child));
          } else {
                  retval += printf("%s", device_get_nameunit(child));
          }
  
          return (retval);
  }
  
  /**
   * @brief Helper function for implementing BUS_PRINT_CHILD().
   *
   * This function prints the last part of the ascii representation of
   * @p child, which consists of the string @c " on " followed by the
   * name and unit of the @p dev.
   *
   * @returns the number of characters printed
   */
  int
  bus_print_child_footer(device_t dev, device_t child)
  {
          return (printf(" on %s\n", device_get_nameunit(dev)));
  }
  
  /**
   * @brief Helper function for implementing BUS_PRINT_CHILD().
   *
   * This function simply calls bus_print_child_header() followed by
   * bus_print_child_footer().
   *
   * @returns the number of characters printed
   */
  int
  bus_generic_print_child(device_t dev, device_t child)
  {
          int     retval = 0;
  
          retval += bus_print_child_header(dev, child);
          retval += bus_print_child_footer(dev, child);
  
          return (retval);
  }
  
  /**
   * @brief Stub function for implementing BUS_READ_IVAR().
   * 
   * @returns ENOENT
   */
  int
  bus_generic_read_ivar(device_t dev, device_t child, int index,
      uintptr_t * result)
  {
          return (ENOENT);
  }
  
  /**
   * @brief Stub function for implementing BUS_WRITE_IVAR().
   * 
   * @returns ENOENT
   */
  int
  bus_generic_write_ivar(device_t dev, device_t child, int index,
      uintptr_t value)
  {
          return (ENOENT);
  }
  
  /**
   * @brief Stub function for implementing BUS_GET_RESOURCE_LIST().
   * 
   * @returns NULL
   */
  struct resource_list *
  bus_generic_get_resource_list(device_t dev, device_t child)
  {
          return (NULL);
  }
  
  /**
   * @brief Helper function for implementing BUS_DRIVER_ADDED().
   *
   * This implementation of BUS_DRIVER_ADDED() simply calls the driver's
   * DEVICE_IDENTIFY() method to allow it to add new children to the bus
   * and then calls device_probe_and_attach() for each unattached child.
   */
  void
  bus_generic_driver_added(device_t dev, driver_t *driver)
  {
          device_t child;
  
          DEVICE_IDENTIFY(driver, dev);
          TAILQ_FOREACH(child, &dev->children, link) {
                  if (child->state == DS_NOTPRESENT ||
                      (child->flags & DF_REBID))
                          device_probe_and_attach(child);
          }
  }
  
  /**
   * @brief Helper function for implementing BUS_NEW_PASS().
   *
   * This implementing of BUS_NEW_PASS() first calls the identify
   * routines for any drivers that probe at the current pass.  Then it
   * walks the list of devices for this bus.  If a device is already
   * attached, then it calls BUS_NEW_PASS() on that device.  If the
   * device is not already attached, it attempts to attach a driver to
   * it.
   */
  void
  bus_generic_new_pass(device_t dev)
  {
          driverlink_t dl;
          devclass_t dc;
          device_t child;
  
          dc = dev->devclass;
          TAILQ_FOREACH(dl, &dc->drivers, link) {
                  if (dl->pass == bus_current_pass)
                          DEVICE_IDENTIFY(dl->driver, dev);
          }
          TAILQ_FOREACH(child, &dev->children, link) {
                  if (child->state >= DS_ATTACHED)
                          BUS_NEW_PASS(child);
                  else if (child->state == DS_NOTPRESENT)
                          device_probe_and_attach(child);
          }
  }
  
  /**
   * @brief Helper function for implementing BUS_SETUP_INTR().
   *
   * This simple implementation of BUS_SETUP_INTR() simply calls the
   * BUS_SETUP_INTR() method of the parent of @p dev.
   */
  int
  bus_generic_setup_intr(device_t dev, device_t child, struct resource *irq,
      int flags, driver_filter_t *filter, driver_intr_t *intr, void *arg, 
      void **cookiep)
  {
          /* Propagate up the bus hierarchy until someone handles it. */
          if (dev->parent)
                  return (BUS_SETUP_INTR(dev->parent, child, irq, flags,
                      filter, intr, arg, cookiep));
          return (EINVAL);
  }
  
  /**
   * @brief Helper function for implementing BUS_TEARDOWN_INTR().
   *
   * This simple implementation of BUS_TEARDOWN_INTR() simply calls the
   * BUS_TEARDOWN_INTR() method of the parent of @p dev.
   */
  int
  bus_generic_teardown_intr(device_t dev, device_t child, struct resource *irq,
      void *cookie)
  {
          /* Propagate up the bus hierarchy until someone handles it. */
          if (dev->parent)
                  return (BUS_TEARDOWN_INTR(dev->parent, child, irq, cookie));
          return (EINVAL);
  }
  
  /**
   * @brief Helper function for implementing BUS_ADJUST_RESOURCE().
   *
   * This simple implementation of BUS_ADJUST_RESOURCE() simply calls the
   * BUS_ADJUST_RESOURCE() method of the parent of @p dev.
   */
  int
  bus_generic_adjust_resource(device_t dev, device_t child, int type,
      struct resource *r, u_long start, u_long end)
  {
          /* Propagate up the bus hierarchy until someone handles it. */
          if (dev->parent)
                  return (BUS_ADJUST_RESOURCE(dev->parent, child, type, r, start,
                      end));
          return (EINVAL);
  }
  
  /**
   * @brief Helper function for implementing BUS_ALLOC_RESOURCE().
   *
   * This simple implementation of BUS_ALLOC_RESOURCE() simply calls the
   * BUS_ALLOC_RESOURCE() method of the parent of @p dev.
   */
  struct resource *
  bus_generic_alloc_resource(device_t dev, device_t child, int type, int *rid,
      u_long start, u_long end, u_long count, u_int flags)
  {
          /* Propagate up the bus hierarchy until someone handles it. */
          if (dev->parent)
                  return (BUS_ALLOC_RESOURCE(dev->parent, child, type, rid,
                      start, end, count, flags));
          return (NULL);
  }
  
  /**
   * @brief Helper function for implementing BUS_RELEASE_RESOURCE().
   *
   * This simple implementation of BUS_RELEASE_RESOURCE() simply calls the
   * BUS_RELEASE_RESOURCE() method of the parent of @p dev.
   */
  int
  bus_generic_release_resource(device_t dev, device_t child, int type, int rid,
      struct resource *r)
  {
          /* Propagate up the bus hierarchy until someone handles it. */
          if (dev->parent)
                  return (BUS_RELEASE_RESOURCE(dev->parent, child, type, rid,
                      r));
          return (EINVAL);
  }
  
  /**
   * @brief Helper function for implementing BUS_ACTIVATE_RESOURCE().
   *
   * This simple implementation of BUS_ACTIVATE_RESOURCE() simply calls the
   * BUS_ACTIVATE_RESOURCE() method of the parent of @p dev.
   */
  int
  bus_generic_activate_resource(device_t dev, device_t child, int type, int rid,
      struct resource *r)
  {
          /* Propagate up the bus hierarchy until someone handles it. */
          if (dev->parent)
                  return (BUS_ACTIVATE_RESOURCE(dev->parent, child, type, rid,
                      r));
          return (EINVAL);
  }
  
  /**
   * @brief Helper function for implementing BUS_DEACTIVATE_RESOURCE().
   *
   * This simple implementation of BUS_DEACTIVATE_RESOURCE() simply calls the
   * BUS_DEACTIVATE_RESOURCE() method of the parent of @p dev.
   */
  int
  bus_generic_deactivate_resource(device_t dev, device_t child, int type,
      int rid, struct resource *r)
  {
          /* Propagate up the bus hierarchy until someone handles it. */
          if (dev->parent)
                  return (BUS_DEACTIVATE_RESOURCE(dev->parent, child, type, rid,
                      r));
          return (EINVAL);
  }
  
  /**
   * @brief Helper function for implementing BUS_BIND_INTR().
   *
   * This simple implementation of BUS_BIND_INTR() simply calls the
   * BUS_BIND_INTR() method of the parent of @p dev.
   */
  int
  bus_generic_bind_intr(device_t dev, device_t child, struct resource *irq,
      int cpu)
  {
  
          /* Propagate up the bus hierarchy until someone handles it. */
          if (dev->parent)
                  return (BUS_BIND_INTR(dev->parent, child, irq, cpu));
          return (EINVAL);
  }
  
  /**
   * @brief Helper function for implementing BUS_CONFIG_INTR().
   *
   * This simple implementation of BUS_CONFIG_INTR() simply calls the
   * BUS_CONFIG_INTR() method of the parent of @p dev.
   */
  int
  bus_generic_config_intr(device_t dev, int irq, enum intr_trigger trig,
      enum intr_polarity pol)
  {
  
          /* Propagate up the bus hierarchy until someone handles it. */
          if (dev->parent)
                  return (BUS_CONFIG_INTR(dev->parent, irq, trig, pol));
          return (EINVAL);
  }
  
  /**
   * @brief Helper function for implementing BUS_DESCRIBE_INTR().
   *
   * This simple implementation of BUS_DESCRIBE_INTR() simply calls the
   * BUS_DESCRIBE_INTR() method of the parent of @p dev.
   */
  int
  bus_generic_describe_intr(device_t dev, device_t child, struct resource *irq,
      void *cookie, const char *descr)
  {
  
          /* Propagate up the bus hierarchy until someone handles it. */
          if (dev->parent)
                  return (BUS_DESCRIBE_INTR(dev->parent, child, irq, cookie,
                      descr));
          return (EINVAL);
  }
  
  /**
   * @brief Helper function for implementing BUS_GET_DMA_TAG().
   *
   * This simple implementation of BUS_GET_DMA_TAG() simply calls the
   * BUS_GET_DMA_TAG() method of the parent of @p dev.
   */
  bus_dma_tag_t
  bus_generic_get_dma_tag(device_t dev, device_t child)
  {
  
          /* Propagate up the bus hierarchy until someone handles it. */
          if (dev->parent != NULL)
                  return (BUS_GET_DMA_TAG(dev->parent, child));
          return (NULL);
  }
  
  /**
   * @brief Helper function for implementing BUS_GET_RESOURCE().
   *
   * This implementation of BUS_GET_RESOURCE() uses the
   * resource_list_find() function to do most of the work. It calls
   * BUS_GET_RESOURCE_LIST() to find a suitable resource list to
   * search.
   */
  int
  bus_generic_rl_get_resource(device_t dev, device_t child, int type, int rid,
      u_long *startp, u_long *countp)
  {
          struct resource_list *          rl = NULL;
          struct resource_list_entry *    rle = NULL;
  
          rl = BUS_GET_RESOURCE_LIST(dev, child);
          if (!rl)
                  return (EINVAL);
  
          rle = resource_list_find(rl, type, rid);
          if (!rle)
                  return (ENOENT);
  
          if (startp)
                  *startp = rle->start;
          if (countp)
                  *countp = rle->count;
  
          return (0);
  }
  
  /**
   * @brief Helper function for implementing BUS_SET_RESOURCE().
   *
   * This implementation of BUS_SET_RESOURCE() uses the
   * resource_list_add() function to do most of the work. It calls
   * BUS_GET_RESOURCE_LIST() to find a suitable resource list to
   * edit.
   */
  int
  bus_generic_rl_set_resource(device_t dev, device_t child, int type, int rid,
      u_long start, u_long count)
  {
          struct resource_list *          rl = NULL;
  
          rl = BUS_GET_RESOURCE_LIST(dev, child);
          if (!rl)
                  return (EINVAL);
  
          resource_list_add(rl, type, rid, start, (start + count - 1), count);
  
          return (0);
  }
  
  /**
   * @brief Helper function for implementing BUS_DELETE_RESOURCE().
   *
   * This implementation of BUS_DELETE_RESOURCE() uses the
   * resource_list_delete() function to do most of the work. It calls
   * BUS_GET_RESOURCE_LIST() to find a suitable resource list to
   * edit.
   */
  void
  bus_generic_rl_delete_resource(device_t dev, device_t child, int type, int rid)
  {
          struct resource_list *          rl = NULL;
  
          rl = BUS_GET_RESOURCE_LIST(dev, child);
          if (!rl)
                  return;
  
          resource_list_delete(rl, type, rid);
  
          return;
  }
  
  /**
   * @brief Helper function for implementing BUS_RELEASE_RESOURCE().
   *
   * This implementation of BUS_RELEASE_RESOURCE() uses the
   * resource_list_release() function to do most of the work. It calls
   * BUS_GET_RESOURCE_LIST() to find a suitable resource list.
   */
  int
  bus_generic_rl_release_resource(device_t dev, device_t child, int type,
      int rid, struct resource *r)
  {
          struct resource_list *          rl = NULL;
  
          rl = BUS_GET_RESOURCE_LIST(dev, child);
          if (!rl)
                  return (EINVAL);
  
          return (resource_list_release(rl, dev, child, type, rid, r));
  }
  
  /**
   * @brief Helper function for implementing BUS_ALLOC_RESOURCE().
   *
   * This implementation of BUS_ALLOC_RESOURCE() uses the
   * resource_list_alloc() function to do most of the work. It calls
   * BUS_GET_RESOURCE_LIST() to find a suitable resource list.
   */
  struct resource *
  bus_generic_rl_alloc_resource(device_t dev, device_t child, int type,
      int *rid, u_long start, u_long end, u_long count, u_int flags)
  {
          struct resource_list *          rl = NULL;
  
          rl = BUS_GET_RESOURCE_LIST(dev, child);
          if (!rl)
                  return (NULL);
  
          return (resource_list_alloc(rl, dev, child, type, rid,
              start, end, count, flags));
  }
  
  /**
   * @brief Helper function for implementing BUS_CHILD_PRESENT().
   *
   * This simple implementation of BUS_CHILD_PRESENT() simply calls the
   * BUS_CHILD_PRESENT() method of the parent of @p dev.
   */
  int
  bus_generic_child_present(device_t dev, device_t child)
  {
          return (BUS_CHILD_PRESENT(device_get_parent(dev), dev));
  }
  
  /*
   * Some convenience functions to make it easier for drivers to use the
   * resource-management functions.  All these really do is hide the
   * indirection through the parent's method table, making for slightly
   * less-wordy code.  In the future, it might make sense for this code
   * to maintain some sort of a list of resources allocated by each device.
   */
  
  int
  bus_alloc_resources(device_t dev, struct resource_spec *rs,
      struct resource **res)
  {
          int i;
  
          for (i = 0; rs[i].type != -1; i++)
                  res[i] = NULL;
          for (i = 0; rs[i].type != -1; i++) {
                  res[i] = bus_alloc_resource_any(dev,
                      rs[i].type, &rs[i].rid, rs[i].flags);
                  if (res[i] == NULL && !(rs[i].flags & RF_OPTIONAL)) {
                          bus_release_resources(dev, rs, res);
                          return (ENXIO);
                  }
          }
          return (0);
  }
  
  void
  bus_release_resources(device_t dev, const struct resource_spec *rs,
      struct resource **res)
  {
          int i;
  
          for (i = 0; rs[i].type != -1; i++)
                  if (res[i] != NULL) {
                          bus_release_resource(
                              dev, rs[i].type, rs[i].rid, res[i]);
                          res[i] = NULL;
                  }
  }
  
  /**
   * @brief Wrapper function for BUS_ALLOC_RESOURCE().
   *
   * This function simply calls the BUS_ALLOC_RESOURCE() method of the
   * parent of @p dev.
   */
  struct resource *
  bus_alloc_resource(device_t dev, int type, int *rid, u_long start, u_long end,
      u_long count, u_int flags)
  {
          if (dev->parent == NULL)
                  return (NULL);
          return (BUS_ALLOC_RESOURCE(dev->parent, dev, type, rid, start, end,
              count, flags));
  }
  
  /**
   * @brief Wrapper function for BUS_ADJUST_RESOURCE().
   *
   * This function simply calls the BUS_ADJUST_RESOURCE() method of the
   * parent of @p dev.
   */
  int
  bus_adjust_resource(device_t dev, int type, struct resource *r, u_long start,
      u_long end)
  {
          if (dev->parent == NULL)
                  return (EINVAL);
          return (BUS_ADJUST_RESOURCE(dev->parent, dev, type, r, start, end));
  }
  
  /**
   * @brief Wrapper function for BUS_ACTIVATE_RESOURCE().
   *
   * This function simply calls the BUS_ACTIVATE_RESOURCE() method of the
   * parent of @p dev.
   */
  int
  bus_activate_resource(device_t dev, int type, int rid, struct resource *r)
  {
          if (dev->parent == NULL)
                  return (EINVAL);
          return (BUS_ACTIVATE_RESOURCE(dev->parent, dev, type, rid, r));
  }
  
  /**
   * @brief Wrapper function for BUS_DEACTIVATE_RESOURCE().
   *
   * This function simply calls the BUS_DEACTIVATE_RESOURCE() method of the
   * parent of @p dev.
   */
  int
  bus_deactivate_resource(device_t dev, int type, int rid, struct resource *r)
  {
          if (dev->parent == NULL)
                  return (EINVAL);
          return (BUS_DEACTIVATE_RESOURCE(dev->parent, dev, type, rid, r));
  }
  
  /**
   * @brief Wrapper function for BUS_RELEASE_RESOURCE().
   *
   * This function simply calls the BUS_RELEASE_RESOURCE() method of the
   * parent of @p dev.
   */
  int
  bus_release_resource(device_t dev, int type, int rid, struct resource *r)
  {
          if (dev->parent == NULL)
                  return (EINVAL);
          return (BUS_RELEASE_RESOURCE(dev->parent, dev, type, rid, r));
  }
  
  /**
   * @brief Wrapper function for BUS_SETUP_INTR().
   *
   * This function simply calls the BUS_SETUP_INTR() method of the
   * parent of @p dev.
   */
  int
  bus_setup_intr(device_t dev, struct resource *r, int flags,
      driver_filter_t filter, driver_intr_t handler, void *arg, void **cookiep)
  {
          int error;
  
          if (dev->parent == NULL)
                  return (EINVAL);
          error = BUS_SETUP_INTR(dev->parent, dev, r, flags, filter, handler,
              arg, cookiep);
          if (error != 0)
                  return (error);
          if (handler != NULL && !(flags & INTR_MPSAFE))
                  device_printf(dev, "[GIANT-LOCKED]\n");
          if (bootverbose && (flags & INTR_MPSAFE))
                  device_printf(dev, "[MPSAFE]\n");
          if (filter != NULL) {
                  if (handler == NULL)
                          device_printf(dev, "[FILTER]\n");
                  else 
                          device_printf(dev, "[FILTER+ITHREAD]\n");
          } else 
                  device_printf(dev, "[ITHREAD]\n");
          return (0);
  }
  
  /**
   * @brief Wrapper function for BUS_TEARDOWN_INTR().
   *
   * This function simply calls the BUS_TEARDOWN_INTR() method of the
   * parent of @p dev.
   */
  int
  bus_teardown_intr(device_t dev, struct resource *r, void *cookie)
  {
          if (dev->parent == NULL)
                  return (EINVAL);
          return (BUS_TEARDOWN_INTR(dev->parent, dev, r, cookie));
  }
  
  /**
   * @brief Wrapper function for BUS_BIND_INTR().
   *
   * This function simply calls the BUS_BIND_INTR() method of the
   * parent of @p dev.
   */
  int
  bus_bind_intr(device_t dev, struct resource *r, int cpu)
  {
          if (dev->parent == NULL)
                  return (EINVAL);
          return (BUS_BIND_INTR(dev->parent, dev, r, cpu));
  }
  
  /**
   * @brief Wrapper function for BUS_DESCRIBE_INTR().
   *
   * This function first formats the requested description into a
   * temporary buffer and then calls the BUS_DESCRIBE_INTR() method of
   * the parent of @p dev.
   */
  int
  bus_describe_intr(device_t dev, struct resource *irq, void *cookie,
      const char *fmt, ...)
  {
          va_list ap;
          char descr[MAXCOMLEN + 1];
  
          if (dev->parent == NULL)
                  return (EINVAL);
          va_start(ap, fmt);
          vsnprintf(descr, sizeof(descr), fmt, ap);
          va_end(ap);
          return (BUS_DESCRIBE_INTR(dev->parent, dev, irq, cookie, descr));
  }
  
  /**
   * @brief Wrapper function for BUS_SET_RESOURCE().
   *
   * This function simply calls the BUS_SET_RESOURCE() method of the
   * parent of @p dev.
   */
  int
  bus_set_resource(device_t dev, int type, int rid,
      u_long start, u_long count)
  {
          return (BUS_SET_RESOURCE(device_get_parent(dev), dev, type, rid,
              start, count));
  }
  
  /**
   * @brief Wrapper function for BUS_GET_RESOURCE().
   *
   * This function simply calls the BUS_GET_RESOURCE() method of the
   * parent of @p dev.
   */
  int
  bus_get_resource(device_t dev, int type, int rid,
      u_long *startp, u_long *countp)
  {
          return (BUS_GET_RESOURCE(device_get_parent(dev), dev, type, rid,
              startp, countp));
  }
  
  /**
   * @brief Wrapper function for BUS_GET_RESOURCE().
   *
   * This function simply calls the BUS_GET_RESOURCE() method of the
   * parent of @p dev and returns the start value.
   */
  u_long
  bus_get_resource_start(device_t dev, int type, int rid)
  {
          u_long start, count;
          int error;
  
          error = BUS_GET_RESOURCE(device_get_parent(dev), dev, type, rid,
              &start, &count);
          if (error)
                  return (0);
          return (start);
  }
  
  /**
   * @brief Wrapper function for BUS_GET_RESOURCE().
   *
   * This function simply calls the BUS_GET_RESOURCE() method of the
   * parent of @p dev and returns the count value.
   */
  u_long
  bus_get_resource_count(device_t dev, int type, int rid)
  {
          u_long start, count;
          int error;
  
          error = BUS_GET_RESOURCE(device_get_parent(dev), dev, type, rid,
              &start, &count);
          if (error)
                  return (0);
          return (count);
  }
  
  /**
   * @brief Wrapper function for BUS_DELETE_RESOURCE().
   *
   * This function simply calls the BUS_DELETE_RESOURCE() method of the
   * parent of @p dev.
   */
  void
  bus_delete_resource(device_t dev, int type, int rid)
  {
          BUS_DELETE_RESOURCE(device_get_parent(dev), dev, type, rid);
  }
  
  /**
   * @brief Wrapper function for BUS_CHILD_PRESENT().
   *
   * This function simply calls the BUS_CHILD_PRESENT() method of the
   * parent of @p dev.
   */
  int
  bus_child_present(device_t child)
  {
          return (BUS_CHILD_PRESENT(device_get_parent(child), child));
  }
  
  /**
   * @brief Wrapper function for BUS_CHILD_PNPINFO_STR().
   *
   * This function simply calls the BUS_CHILD_PNPINFO_STR() method of the
   * parent of @p dev.
   */
  int
  bus_child_pnpinfo_str(device_t child, char *buf, size_t buflen)
  {
          device_t parent;
  
          parent = device_get_parent(child);
          if (parent == NULL) {
                  *buf = '\0';
                  return (0);
          }
          return (BUS_CHILD_PNPINFO_STR(parent, child, buf, buflen));
  }
  
  /**
   * @brief Wrapper function for BUS_CHILD_LOCATION_STR().
   *
   * This function simply calls the BUS_CHILD_LOCATION_STR() method of the
   * parent of @p dev.
   */
  int
  bus_child_location_str(device_t child, char *buf, size_t buflen)
  {
          device_t parent;
  
          parent = device_get_parent(child);
          if (parent == NULL) {
                  *buf = '\0';
                  return (0);
          }
          return (BUS_CHILD_LOCATION_STR(parent, child, buf, buflen));
  }
  
  /**
   * @brief Wrapper function for BUS_GET_DMA_TAG().
   *
   * This function simply calls the BUS_GET_DMA_TAG() method of the
   * parent of @p dev.
   */
  bus_dma_tag_t
  bus_get_dma_tag(device_t dev)
  {
          device_t parent;
  
          parent = device_get_parent(dev);
          if (parent == NULL)
                  return (NULL);
          return (BUS_GET_DMA_TAG(parent, dev));
  }
  
  /* Resume all devices and then notify userland that we're up again. */
  static int
  root_resume(device_t dev)
  {
          int error;
  
          error = bus_generic_resume(dev);
          if (error == 0)
                  devctl_notify("kern", "power", "resume", NULL);
          return (error);
  }
  
  static int
  root_print_child(device_t dev, device_t child)
  {
          int     retval = 0;
  
          retval += bus_print_child_header(dev, child);
          retval += printf("\n");
  
          return (retval);
  }
  
  static int
  root_setup_intr(device_t dev, device_t child, struct resource *irq, int flags,
      driver_filter_t *filter, driver_intr_t *intr, void *arg, void **cookiep)
  {
          /*
           * If an interrupt mapping gets to here something bad has happened.
           */
          panic("root_setup_intr");
  }
  
  /*
   * If we get here, assume that the device is permanant and really is
   * present in the system.  Removable bus drivers are expected to intercept
   * this call long before it gets here.  We return -1 so that drivers that
   * really care can check vs -1 or some ERRNO returned higher in the food
   * chain.
   */
  static int
  root_child_present(device_t dev, device_t child)
  {
          return (-1);
  }
  
  static kobj_method_t root_methods[] = {
          /* Device interface */
          KOBJMETHOD(device_shutdown,     bus_generic_shutdown),
          KOBJMETHOD(device_suspend,      bus_generic_suspend),
          KOBJMETHOD(device_resume,       root_resume),
  
          /* Bus interface */
          KOBJMETHOD(bus_print_child,     root_print_child),
          KOBJMETHOD(bus_read_ivar,       bus_generic_read_ivar),
          KOBJMETHOD(bus_write_ivar,      bus_generic_write_ivar),
          KOBJMETHOD(bus_setup_intr,      root_setup_intr),
          KOBJMETHOD(bus_child_present,   root_child_present),
  
          KOBJMETHOD_END
  };
  
  static driver_t root_driver = {
          "root",
          root_methods,
          1,                      /* no softc */
  };
  
  device_t        root_bus;
  devclass_t      root_devclass;
  
  static int
  root_bus_module_handler(module_t mod, int what, void* arg)
  {
          switch (what) {
          case MOD_LOAD:
                  TAILQ_INIT(&bus_data_devices);
                  kobj_class_compile((kobj_class_t) &root_driver);
                  root_bus = make_device(NULL, "root", 0);
                  root_bus->desc = "System root bus";
                  kobj_init((kobj_t) root_bus, (kobj_class_t) &root_driver);
                  root_bus->driver = &root_driver;
                  root_bus->state = DS_ATTACHED;
                  root_devclass = devclass_find_internal("root", NULL, FALSE);
                  devinit();
                  return (0);
  
          case MOD_SHUTDOWN:
                  device_shutdown(root_bus);
                  return (0);
          default:
                  return (EOPNOTSUPP);
          }
  
          return (0);
  }
  
  static moduledata_t root_bus_mod = {
          "rootbus",
          root_bus_module_handler,
          NULL
  };
  DECLARE_MODULE(rootbus, root_bus_mod, SI_SUB_DRIVERS, SI_ORDER_FIRST);
  
  /**
   * @brief Automatically configure devices
   *
   * This function begins the autoconfiguration process by calling
   * device_probe_and_attach() for each child of the @c root0 device.
   */ 
  void
  root_bus_configure(void)
  {
  
          PDEBUG(("."));
  
          /* Eventually this will be split up, but this is sufficient for now. */
          bus_set_pass(BUS_PASS_DEFAULT);
  }
  
  /**
   * @brief Module handler for registering device drivers
   *
   * This module handler is used to automatically register device
   * drivers when modules are loaded. If @p what is MOD_LOAD, it calls
   * devclass_add_driver() for the driver described by the
   * driver_module_data structure pointed to by @p arg
   */
  int
  driver_module_handler(module_t mod, int what, void *arg)
  {
          struct driver_module_data *dmd;
          devclass_t bus_devclass;
          kobj_class_t driver;
          int error, pass;
  
          dmd = (struct driver_module_data *)arg;
          bus_devclass = devclass_find_internal(dmd->dmd_busname, NULL, TRUE);
          error = 0;
  
          switch (what) {
          case MOD_LOAD:
                  if (dmd->dmd_chainevh)
                          error = dmd->dmd_chainevh(mod,what,dmd->dmd_chainarg);
  
                  pass = dmd->dmd_pass;
                  driver = dmd->dmd_driver;
                  PDEBUG(("Loading module: driver %s on bus %s (pass %d)",
                      DRIVERNAME(driver), dmd->dmd_busname, pass));
                  error = devclass_add_driver(bus_devclass, driver, pass,
                      dmd->dmd_devclass);
                  break;
  
          case MOD_UNLOAD:
                  PDEBUG(("Unloading module: driver %s from bus %s",
                      DRIVERNAME(dmd->dmd_driver),
                      dmd->dmd_busname));
                  error = devclass_delete_driver(bus_devclass,
                      dmd->dmd_driver);
  
                  if (!error && dmd->dmd_chainevh)
                          error = dmd->dmd_chainevh(mod,what,dmd->dmd_chainarg);
                  break;
          case MOD_QUIESCE:
                  PDEBUG(("Quiesce module: driver %s from bus %s",
                      DRIVERNAME(dmd->dmd_driver),
                      dmd->dmd_busname));
                  error = devclass_quiesce_driver(bus_devclass,
                      dmd->dmd_driver);
  
                  if (!error && dmd->dmd_chainevh)
                          error = dmd->dmd_chainevh(mod,what,dmd->dmd_chainarg);
                  break;
          default:
                  error = EOPNOTSUPP;
                  break;
          }
  
          return (error);
  }
  
  /**
   * @brief Enumerate all hinted devices for this bus.
   *
   * Walks through the hints for this bus and calls the bus_hinted_child
   * routine for each one it fines.  It searches first for the specific
   * bus that's being probed for hinted children (eg isa0), and then for
   * generic children (eg isa).
   *
   * @param       dev     bus device to enumerate
   */
  void
  bus_enumerate_hinted_children(device_t bus)
  {
          int i;
          const char *dname, *busname;
          int dunit;
  
          /*
           * enumerate all devices on the specific bus
           */
          busname = device_get_nameunit(bus);
          i = 0;
          while (resource_find_match(&i, &dname, &dunit, "at", busname) == 0)
                  BUS_HINTED_CHILD(bus, dname, dunit);
  
          /*
           * and all the generic ones.
           */
          busname = device_get_name(bus);
          i = 0;
          while (resource_find_match(&i, &dname, &dunit, "at", busname) == 0)
                  BUS_HINTED_CHILD(bus, dname, dunit);
  }
  
  #ifdef BUS_DEBUG
  
  /* the _short versions avoid iteration by not calling anything that prints
   * more than oneliners. I love oneliners.
   */
  
  static void
  print_device_short(device_t dev, int indent)
  {
          if (!dev)
                  return;
  
          indentprintf(("device %d: <%s> %sparent,%schildren,%s%s%s%s%s,%sivars,%ssoftc,busy=%d\n",
              dev->unit, dev->desc,
              (dev->parent? "":"no "),
              (TAILQ_EMPTY(&dev->children)? "no ":""),
              (dev->flags&DF_ENABLED? "enabled,":"disabled,"),
              (dev->flags&DF_FIXEDCLASS? "fixed,":""),
              (dev->flags&DF_WILDCARD? "wildcard,":""),
              (dev->flags&DF_DESCMALLOCED? "descmalloced,":""),
              (dev->flags&DF_REBID? "rebiddable,":""),
              (dev->ivars? "":"no "),
              (dev->softc? "":"no "),
              dev->busy));
  }
  
  static void
  print_device(device_t dev, int indent)
  {
          if (!dev)
                  return;
  
          print_device_short(dev, indent);
  
          indentprintf(("Parent:\n"));
          print_device_short(dev->parent, indent+1);
          indentprintf(("Driver:\n"));
          print_driver_short(dev->driver, indent+1);
          indentprintf(("Devclass:\n"));
          print_devclass_short(dev->devclass, indent+1);
  }
  
  void
  print_device_tree_short(device_t dev, int indent)
  /* print the device and all its children (indented) */
  {
          device_t child;
  
          if (!dev)
                  return;
  
          print_device_short(dev, indent);
  
          TAILQ_FOREACH(child, &dev->children, link) {
                  print_device_tree_short(child, indent+1);
          }
  }
  
  void
  print_device_tree(device_t dev, int indent)
  /* print the device and all its children (indented) */
  {
          device_t child;
  
          if (!dev)
                  return;
  
          print_device(dev, indent);
  
          TAILQ_FOREACH(child, &dev->children, link) {
                  print_device_tree(child, indent+1);
          }
  }
  
  static void
  print_driver_short(driver_t *driver, int indent)
  {
          if (!driver)
                  return;
  
          indentprintf(("driver %s: softc size = %zd\n",
              driver->name, driver->size));
  }
  
  static void
  print_driver(driver_t *driver, int indent)
  {
          if (!driver)
                  return;
  
          print_driver_short(driver, indent);
  }
  
  static void
  print_driver_list(driver_list_t drivers, int indent)
  {
          driverlink_t driver;
  
          TAILQ_FOREACH(driver, &drivers, link) {
                  print_driver(driver->driver, indent);
          }
  }
  
  static void
  print_devclass_short(devclass_t dc, int indent)
  {
          if ( !dc )
                  return;
  
          indentprintf(("devclass %s: max units = %d\n", dc->name, dc->maxunit));
  }
  
  static void
  print_devclass(devclass_t dc, int indent)
  {
          int i;
  
          if ( !dc )
                  return;
  
          print_devclass_short(dc, indent);
          indentprintf(("Drivers:\n"));
          print_driver_list(dc->drivers, indent+1);
  
          indentprintf(("Devices:\n"));
          for (i = 0; i < dc->maxunit; i++)
                  if (dc->devices[i])
                          print_device(dc->devices[i], indent+1);
  }
  
  void
  print_devclass_list_short(void)
  {
          devclass_t dc;
  
          printf("Short listing of devclasses, drivers & devices:\n");
          TAILQ_FOREACH(dc, &devclasses, link) {
                  print_devclass_short(dc, 0);
          }
  }
  
  void
  print_devclass_list(void)
  {
          devclass_t dc;
  
          printf("Full listing of devclasses, drivers & devices:\n");
          TAILQ_FOREACH(dc, &devclasses, link) {
                  print_devclass(dc, 0);
          }
  }
  
  #endif
  
  /*
   * User-space access to the device tree.
   *
   * We implement a small set of nodes:
   *
   * hw.bus                       Single integer read method to obtain the
   *                              current generation count.
   * hw.bus.devices               Reads the entire device tree in flat space.
   * hw.bus.rman                  Resource manager interface
   *
   * We might like to add the ability to scan devclasses and/or drivers to
   * determine what else is currently loaded/available.
   */
  
  static int
  sysctl_bus(SYSCTL_HANDLER_ARGS)
  {
          struct u_businfo        ubus;
  
          ubus.ub_version = BUS_USER_VERSION;
          ubus.ub_generation = bus_data_generation;
  
          return (SYSCTL_OUT(req, &ubus, sizeof(ubus)));
  }
  SYSCTL_NODE(_hw_bus, OID_AUTO, info, CTLFLAG_RW, sysctl_bus,
      "bus-related data");
  
  static int
  sysctl_devices(SYSCTL_HANDLER_ARGS)
  {
          int                     *name = (int *)arg1;
          u_int                   namelen = arg2;
          int                     index;
          struct device           *dev;
          struct u_device         udev;   /* XXX this is a bit big */
          int                     error;
  
          if (namelen != 2)
                  return (EINVAL);
  
          if (bus_data_generation_check(name[0]))
                  return (EINVAL);
  
          index = name[1];
  
          /*
           * Scan the list of devices, looking for the requested index.
           */
          TAILQ_FOREACH(dev, &bus_data_devices, devlink) {
                  if (index-- == 0)
                          break;
          }
          if (dev == NULL)
                  return (ENOENT);
  
          /*
           * Populate the return array.
           */
          bzero(&udev, sizeof(udev));
          udev.dv_handle = (uintptr_t)dev;
          udev.dv_parent = (uintptr_t)dev->parent;
          if (dev->nameunit != NULL)
                  strlcpy(udev.dv_name, dev->nameunit, sizeof(udev.dv_name));
          if (dev->desc != NULL)
                  strlcpy(udev.dv_desc, dev->desc, sizeof(udev.dv_desc));
          if (dev->driver != NULL && dev->driver->name != NULL)
                  strlcpy(udev.dv_drivername, dev->driver->name,
                      sizeof(udev.dv_drivername));
          bus_child_pnpinfo_str(dev, udev.dv_pnpinfo, sizeof(udev.dv_pnpinfo));
          bus_child_location_str(dev, udev.dv_location, sizeof(udev.dv_location));
          udev.dv_devflags = dev->devflags;
          udev.dv_flags = dev->flags;
          udev.dv_state = dev->state;
          error = SYSCTL_OUT(req, &udev, sizeof(udev));
          return (error);
  }
  
  SYSCTL_NODE(_hw_bus, OID_AUTO, devices, CTLFLAG_RD, sysctl_devices,
      "system device tree");
  
  int
  bus_data_generation_check(int generation)
  {
          if (generation != bus_data_generation)
                  return (1);
  
          /* XXX generate optimised lists here? */
          return (0);
  }
  
  void
  bus_data_generation_update(void)
  {
          bus_data_generation++;
  }
  
  int
  bus_free_resource(device_t dev, int type, struct resource *r)
  {
          if (r == NULL)
                  return (0);
          return (bus_release_resource(dev, type, rman_get_rid(r), r));
  }