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

     /*
      * Copyright (c) 1997, 1998, 1999 Kenneth D. Merry.
      * 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.
     * 3. The name of the author may not be used to endorse or promote products
     *    derived from this software without specific prior written permission.
     *
     * 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.
     *
     * $FreeBSD: releng/5.1/sys/kern/subr_devstat.c 113599 2003-04-17 15:06:28Z harti $
     */
    
    #include <sys/param.h>
    #include <sys/kernel.h>
    #include <sys/systm.h>
    #include <sys/bio.h>
    #include <sys/devicestat.h>
    #include <sys/sysctl.h>
    #include <sys/malloc.h>
    #include <sys/lock.h>
    #include <sys/mutex.h>
    #include <sys/conf.h>
    #include <vm/vm.h>
    #include <vm/pmap.h>
    
    #include <machine/atomic.h>
    
    static int devstat_num_devs;
    static long devstat_generation;
    static int devstat_version = DEVSTAT_VERSION;
    static int devstat_current_devnumber;
    static struct mtx devstat_mutex;
    
    static struct devstatlist device_statq;
    static struct devstat *devstat_alloc(void);
    static void devstat_free(struct devstat *);
    static void devstat_add_entry(struct devstat *ds, const void *dev_name, 
                           int unit_number, u_int32_t block_size,
                           devstat_support_flags flags,
                           devstat_type_flags device_type,
                           devstat_priority priority);
    
    /*
     * Allocate a devstat and initialize it
     */
    struct devstat *
    devstat_new_entry(const void *dev_name,
                      int unit_number, u_int32_t block_size,
                      devstat_support_flags flags,
                      devstat_type_flags device_type,
                      devstat_priority priority)
    {
            struct devstat *ds;
            static int once;
    
            if (!once) {
                    STAILQ_INIT(&device_statq);
                    mtx_init(&devstat_mutex, "devstat", NULL, MTX_DEF);
                    once = 1;
            }
            mtx_assert(&devstat_mutex, MA_NOTOWNED);
    
            ds = devstat_alloc();
            mtx_lock(&devstat_mutex);
            if (unit_number == -1) {
                    ds->id = dev_name;
                    binuptime(&ds->creation_time);
                    devstat_generation++;
            } else {
                    devstat_add_entry(ds, dev_name, unit_number, block_size,
                                      flags, device_type, priority);
            }
            mtx_unlock(&devstat_mutex);
            return (ds);
    }
    
    /*
     * Take a malloced and zeroed devstat structure given to us, fill it in 
     * and add it to the queue of devices.  
     */
    static void
   devstat_add_entry(struct devstat *ds, const void *dev_name, 
                     int unit_number, u_int32_t block_size,
                     devstat_support_flags flags,
                     devstat_type_flags device_type,
                     devstat_priority priority)
   {
           struct devstatlist *devstat_head;
           struct devstat *ds_tmp;
   
           mtx_assert(&devstat_mutex, MA_OWNED);
           devstat_num_devs++;
   
           devstat_head = &device_statq;
   
           /*
            * Priority sort.  Each driver passes in its priority when it adds
            * its devstat entry.  Drivers are sorted first by priority, and
            * then by probe order.
            * 
            * For the first device, we just insert it, since the priority
            * doesn't really matter yet.  Subsequent devices are inserted into
            * the list using the order outlined above.
            */
           if (devstat_num_devs == 1)
                   STAILQ_INSERT_TAIL(devstat_head, ds, dev_links);
           else {
                   STAILQ_FOREACH(ds_tmp, devstat_head, dev_links) {
                           struct devstat *ds_next;
   
                           ds_next = STAILQ_NEXT(ds_tmp, dev_links);
   
                           /*
                            * If we find a break between higher and lower
                            * priority items, and if this item fits in the
                            * break, insert it.  This also applies if the
                            * "lower priority item" is the end of the list.
                            */
                           if ((priority <= ds_tmp->priority)
                            && ((ds_next == NULL)
                              || (priority > ds_next->priority))) {
                                   STAILQ_INSERT_AFTER(devstat_head, ds_tmp, ds,
                                                       dev_links);
                                   break;
                           } else if (priority > ds_tmp->priority) {
                                   /*
                                    * If this is the case, we should be able
                                    * to insert ourselves at the head of the
                                    * list.  If we can't, something is wrong.
                                    */
                                   if (ds_tmp == STAILQ_FIRST(devstat_head)) {
                                           STAILQ_INSERT_HEAD(devstat_head,
                                                              ds, dev_links);
                                           break;
                                   } else {
                                           STAILQ_INSERT_TAIL(devstat_head,
                                                              ds, dev_links);
                                           printf("devstat_add_entry: HELP! "
                                                  "sorting problem detected "
                                                  "for name %p unit %d\n",
                                                  dev_name, unit_number);
                                           break;
                                   }
                           }
                   }
           }
   
           ds->device_number = devstat_current_devnumber++;
           ds->unit_number = unit_number;
           strlcpy(ds->device_name, dev_name, DEVSTAT_NAME_LEN);
           ds->block_size = block_size;
           ds->flags = flags;
           ds->device_type = device_type;
           ds->priority = priority;
           binuptime(&ds->creation_time);
           devstat_generation++;
   }
   
   /*
    * Remove a devstat structure from the list of devices.
    */
   void
   devstat_remove_entry(struct devstat *ds)
   {
           struct devstatlist *devstat_head;
   
           mtx_assert(&devstat_mutex, MA_NOTOWNED);
           if (ds == NULL)
                   return;
   
           mtx_lock(&devstat_mutex);
   
           devstat_head = &device_statq;
   
           /* Remove this entry from the devstat queue */
           atomic_add_acq_int(&ds->sequence1, 1);
           if (ds->id == NULL) {
                   devstat_num_devs--;
                   STAILQ_REMOVE(devstat_head, ds, devstat, dev_links);
           }
           devstat_free(ds);
           devstat_generation++;
           mtx_unlock(&devstat_mutex);
   }
   
   /*
    * Record a transaction start.
    *
    * See comments for devstat_end_transaction().  Ordering is very important
    * here.
    */
   void
   devstat_start_transaction(struct devstat *ds, struct bintime *now)
   {
   
           mtx_assert(&devstat_mutex, MA_NOTOWNED);
   
           /* sanity check */
           if (ds == NULL)
                   return;
   
           atomic_add_acq_int(&ds->sequence1, 1);
           /*
            * We only want to set the start time when we are going from idle
            * to busy.  The start time is really the start of the latest busy
            * period.
            */
           if (ds->start_count == ds->end_count) {
                   if (now != NULL)
                           ds->busy_from = *now;
                   else
                           binuptime(&ds->busy_from);
           }
           ds->start_count++;
           atomic_add_rel_int(&ds->sequence0, 1);
   }
   
   void
   devstat_start_transaction_bio(struct devstat *ds, struct bio *bp)
   {
   
           mtx_assert(&devstat_mutex, MA_NOTOWNED);
   
           /* sanity check */
           if (ds == NULL)
                   return;
   
           binuptime(&bp->bio_t0);
           devstat_start_transaction(ds, &bp->bio_t0);
   }
   
   /*
    * Record the ending of a transaction, and incrment the various counters.
    *
    * Ordering in this function, and in devstat_start_transaction() is VERY
    * important.  The idea here is to run without locks, so we are very
    * careful to only modify some fields on the way "down" (i.e. at
    * transaction start) and some fields on the way "up" (i.e. at transaction
    * completion).  One exception is busy_from, which we only modify in
    * devstat_start_transaction() when there are no outstanding transactions,
    * and thus it can't be modified in devstat_end_transaction()
    * simultaneously.
    *
    * The sequence0 and sequence1 fields are provided to enable an application
    * spying on the structures with mmap(2) to tell when a structure is in a
    * consistent state or not.
    *
    * For this to work 100% reliably, it is important that the two fields
    * are at opposite ends of the structure and that they are incremented
    * in the opposite order of how a memcpy(3) in userland would copy them.
    * We assume that the copying happens front to back, but there is actually
    * no way short of writing your own memcpy(3) replacement to guarantee
    * this will be the case.
    *
    * In addition to this, being a kind of locks, they must be updated with
    * atomic instructions using appropriate memory barriers.
    */
   void
   devstat_end_transaction(struct devstat *ds, u_int32_t bytes, 
                           devstat_tag_type tag_type, devstat_trans_flags flags,
                           struct bintime *now, struct bintime *then)
   {
           struct bintime dt, lnow;
   
           mtx_assert(&devstat_mutex, MA_NOTOWNED);
   
           /* sanity check */
           if (ds == NULL)
                   return;
   
           if (now == NULL) {
                   now = &lnow;
                   binuptime(now);
           }
   
           atomic_add_acq_int(&ds->sequence1, 1);
           /* Update byte and operations counts */
           ds->bytes[flags] += bytes;
           ds->operations[flags]++;
   
           /*
            * Keep a count of the various tag types sent.
            */
           if ((ds->flags & DEVSTAT_NO_ORDERED_TAGS) == 0 &&
               tag_type != DEVSTAT_TAG_NONE)
                   ds->tag_types[tag_type]++;
   
           if (then != NULL) {
                   /* Update duration of operations */
                   dt = *now;
                   bintime_sub(&dt, then);
                   bintime_add(&ds->duration[flags], &dt);
           }
   
           /* Accumulate busy time */
           dt = *now;
           bintime_sub(&dt, &ds->busy_from);
           bintime_add(&ds->busy_time, &dt);
           ds->busy_from = *now;
   
           ds->end_count++;
           atomic_add_rel_int(&ds->sequence0, 1);
   }
   
   void
   devstat_end_transaction_bio(struct devstat *ds, struct bio *bp)
   {
           devstat_trans_flags flg;
   
           mtx_assert(&devstat_mutex, MA_NOTOWNED);
   
           /* sanity check */
           if (ds == NULL)
                   return;
   
           if (bp->bio_cmd == BIO_DELETE)
                   flg = DEVSTAT_FREE;
           else if (bp->bio_cmd == BIO_READ)
                   flg = DEVSTAT_READ;
           else if (bp->bio_cmd == BIO_WRITE)
                   flg = DEVSTAT_WRITE;
           else 
                   flg = DEVSTAT_NO_DATA;
   
           devstat_end_transaction(ds, bp->bio_bcount - bp->bio_resid,
                                   DEVSTAT_TAG_SIMPLE, flg, NULL, &bp->bio_t0);
   }
   
   /*
    * This is the sysctl handler for the devstat package.  The data pushed out
    * on the kern.devstat.all sysctl variable consists of the current devstat
    * generation number, and then an array of devstat structures, one for each
    * device in the system.
    *
    * This is more cryptic that obvious, but basically we neither can nor
    * want to hold the devstat_mutex for any amount of time, so we grab it
    * only when we need to and keep an eye on devstat_generation all the time.
    */
   static int
   sysctl_devstat(SYSCTL_HANDLER_ARGS)
   {
           int error;
           long mygen;
           struct devstat *nds;
   
           mtx_assert(&devstat_mutex, MA_NOTOWNED);
   
           if (devstat_num_devs == 0)
                   return(EINVAL);
   
           /*
            * XXX devstat_generation should really be "volatile" but that
            * XXX freaks out the sysctl macro below.  The places where we
            * XXX change it and inspect it are bracketed in the mutex which
            * XXX guarantees us proper write barriers.  I don't belive the
            * XXX compiler is allowed to optimize mygen away across calls
            * XXX to other functions, so the following is belived to be safe.
            */
           mygen = devstat_generation;
   
           error = SYSCTL_OUT(req, &mygen, sizeof(mygen));
   
           if (error != 0)
                   return (error);
   
           mtx_lock(&devstat_mutex);
           nds = STAILQ_FIRST(&device_statq); 
           if (mygen != devstat_generation)
                   error = EBUSY;
           mtx_unlock(&devstat_mutex);
   
           if (error != 0)
                   return (error);
   
           for (;nds != NULL;) {
                   error = SYSCTL_OUT(req, nds, sizeof(struct devstat));
                   if (error != 0)
                           return (error);
                   mtx_lock(&devstat_mutex);
                   if (mygen != devstat_generation)
                           error = EBUSY;
                   else
                           nds = STAILQ_NEXT(nds, dev_links);
                   mtx_unlock(&devstat_mutex);
                   if (error != 0)
                           return (error);
           }
           return(error);
   }
   
   /*
    * Sysctl entries for devstat.  The first one is a node that all the rest
    * hang off of. 
    */
   SYSCTL_NODE(_kern, OID_AUTO, devstat, CTLFLAG_RD, 0, "Device Statistics");
   
   SYSCTL_PROC(_kern_devstat, OID_AUTO, all, CTLFLAG_RD|CTLTYPE_OPAQUE,
       0, 0, sysctl_devstat, "S,devstat", "All devices in the devstat list");
   /*
    * Export the number of devices in the system so that userland utilities
    * can determine how much memory to allocate to hold all the devices.
    */
   SYSCTL_INT(_kern_devstat, OID_AUTO, numdevs, CTLFLAG_RD, 
       &devstat_num_devs, 0, "Number of devices in the devstat list");
   SYSCTL_LONG(_kern_devstat, OID_AUTO, generation, CTLFLAG_RD,
       &devstat_generation, 0, "Devstat list generation");
   SYSCTL_INT(_kern_devstat, OID_AUTO, version, CTLFLAG_RD, 
       &devstat_version, 0, "Devstat list version number");
   
   /*
    * Allocator for struct devstat structures.  We sub-allocate these from pages
    * which we get from malloc.  These pages are exported for mmap(2)'ing through
    * a miniature device driver
    */
   
   #define statsperpage (PAGE_SIZE / sizeof(struct devstat))
   
   static d_mmap_t devstat_mmap;
   
   static struct cdevsw devstat_cdevsw = {
           .d_open =       nullopen,
           .d_close =      nullclose,
           .d_mmap =       devstat_mmap,
           .d_name =       "devstat",
   };
   
   struct statspage {
           TAILQ_ENTRY(statspage)  list;
           struct devstat          *stat;
           u_int                   nfree;
   };
   
   static TAILQ_HEAD(, statspage)  pagelist = TAILQ_HEAD_INITIALIZER(pagelist);
   static MALLOC_DEFINE(M_DEVSTAT, "devstat", "Device statistics");
   
   static int
   devstat_mmap(dev_t dev, vm_offset_t offset, vm_paddr_t *paddr, int nprot)
   {
           struct statspage *spp;
   
           if (nprot != VM_PROT_READ)
                   return (-1);
           TAILQ_FOREACH(spp, &pagelist, list) {
                   if (offset == 0) {
                           *paddr = vtophys(spp->stat);
                           return (0);
                   }
                   offset -= PAGE_SIZE;
           }
           return (-1);
   }
   
   static struct devstat *
   devstat_alloc(void)
   {
           struct devstat *dsp;
           struct statspage *spp;
           u_int u;
           static int once;
   
           mtx_assert(&devstat_mutex, MA_NOTOWNED);
           if (!once) {
                   make_dev(&devstat_cdevsw, 0,
                       UID_ROOT, GID_WHEEL, 0400, DEVSTAT_DEVICE_NAME);
                   once = 1;
           }
           mtx_lock(&devstat_mutex);
           for (;;) {
                   TAILQ_FOREACH(spp, &pagelist, list) {
                           if (spp->nfree > 0)
                                   break;
                   }
                   if (spp != NULL)
                           break;
                   /*
                    * We had no free slot in any of our pages, drop the mutex
                    * and get another page.  In theory we could have more than
                    * one process doing this at the same time and consequently
                    * we may allocate more pages than we will need.  That is
                    * Just Too Bad[tm], we can live with that.
                    */
                   mtx_unlock(&devstat_mutex);
                   spp = malloc(sizeof *spp, M_DEVSTAT, M_ZERO | M_WAITOK);
                   spp->stat = malloc(PAGE_SIZE, M_DEVSTAT, M_ZERO | M_WAITOK);
                   spp->nfree = statsperpage;
                   mtx_lock(&devstat_mutex);
                   /*
                    * It would make more sense to add the new page at the head
                    * but the order on the list determine the sequence of the
                    * mapping so we can't do that.
                    */
                   TAILQ_INSERT_TAIL(&pagelist, spp, list);
           }
           dsp = spp->stat;
           for (u = 0; u < statsperpage; u++) {
                   if (dsp->allocated == 0)
                           break;
                   dsp++;
           }
           spp->nfree--;
           dsp->allocated = 1;
           mtx_unlock(&devstat_mutex);
           return (dsp);
   }
   
   static void
   devstat_free(struct devstat *dsp)
   {
           struct statspage *spp;
   
           mtx_assert(&devstat_mutex, MA_OWNED);
           bzero(dsp, sizeof *dsp);
           TAILQ_FOREACH(spp, &pagelist, list) {
                   if (dsp >= spp->stat && dsp < (spp->stat + statsperpage)) {
                           spp->nfree++;
                           return;
                   }
           }
   }
   
   SYSCTL_INT(_debug_sizeof, OID_AUTO, devstat, CTLFLAG_RD,
       0, sizeof(struct devstat), "sizeof(struct devstat)");

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