FreeBSD/Linux Kernel Cross Reference
sys/netgraph/ng_base.c

     /*
      * ng_base.c
      *
      * Copyright (c) 1996-1999 Whistle Communications, Inc.
      * All rights reserved.
      *
      * Subject to the following obligations and disclaimer of warranty, use and
      * redistribution of this software, in source or object code forms, with or
      * without modifications are expressly permitted by Whistle Communications;
     * provided, however, that:
     * 1. Any and all reproductions of the source or object code must include the
     *    copyright notice above and the following disclaimer of warranties; and
     * 2. No rights are granted, in any manner or form, to use Whistle
     *    Communications, Inc. trademarks, including the mark "WHISTLE
     *    COMMUNICATIONS" on advertising, endorsements, or otherwise except as
     *    such appears in the above copyright notice or in the software.
     *
     * THIS SOFTWARE IS BEING PROVIDED BY WHISTLE COMMUNICATIONS "AS IS", AND
     * TO THE MAXIMUM EXTENT PERMITTED BY LAW, WHISTLE COMMUNICATIONS MAKES NO
     * REPRESENTATIONS OR WARRANTIES, EXPRESS OR IMPLIED, REGARDING THIS SOFTWARE,
     * INCLUDING WITHOUT LIMITATION, ANY AND ALL IMPLIED WARRANTIES OF
     * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE, OR NON-INFRINGEMENT.
     * WHISTLE COMMUNICATIONS DOES NOT WARRANT, GUARANTEE, OR MAKE ANY
     * REPRESENTATIONS REGARDING THE USE OF, OR THE RESULTS OF THE USE OF THIS
     * SOFTWARE IN TERMS OF ITS CORRECTNESS, ACCURACY, RELIABILITY OR OTHERWISE.
     * IN NO EVENT SHALL WHISTLE COMMUNICATIONS BE LIABLE FOR ANY DAMAGES
     * RESULTING FROM OR ARISING OUT OF ANY USE OF THIS SOFTWARE, INCLUDING
     * WITHOUT LIMITATION, ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY,
     * PUNITIVE, OR CONSEQUENTIAL DAMAGES, PROCUREMENT OF SUBSTITUTE GOODS OR
     * SERVICES, LOSS OF USE, DATA OR PROFITS, HOWEVER CAUSED AND UNDER 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 WHISTLE COMMUNICATIONS IS ADVISED OF THE POSSIBILITY
     * OF SUCH DAMAGE.
     *
     * Authors: Julian Elischer <julian@freebsd.org>
     *          Archie Cobbs <archie@freebsd.org>
     *
     * $FreeBSD: releng/5.3/sys/netgraph/ng_base.c 136588 2004-10-16 08:43:07Z cvs2svn $
     * $Whistle: ng_base.c,v 1.39 1999/01/28 23:54:53 julian Exp $
     */
    
    /*
     * This file implements the base netgraph code.
     */
    
    #include <sys/param.h>
    #include <sys/systm.h>
    #include <sys/errno.h>
    #include <sys/kdb.h>
    #include <sys/kernel.h>
    #include <sys/limits.h>
    #include <sys/malloc.h>
    #include <sys/syslog.h>
    #include <sys/sysctl.h>
    #include <sys/queue.h>
    #include <sys/mbuf.h>
    #include <sys/ctype.h>
    #include <sys/sysctl.h>
    
    #include <net/netisr.h>
    
    #include <netgraph/ng_message.h>
    #include <netgraph/netgraph.h>
    #include <netgraph/ng_parse.h>
    
    MODULE_VERSION(netgraph, NG_ABI_VERSION);
    
    /* List of all active nodes */
    static LIST_HEAD(, ng_node) ng_nodelist;
    static struct mtx       ng_nodelist_mtx;
    
    /* Mutex that protects the free queue item list */
    static struct mtx       ngq_mtx;
    
    #ifdef  NETGRAPH_DEBUG
    
    static SLIST_HEAD(, ng_node) ng_allnodes;
    static LIST_HEAD(, ng_node) ng_freenodes; /* in debug, we never free() them */
    static SLIST_HEAD(, ng_hook) ng_allhooks;
    static LIST_HEAD(, ng_hook) ng_freehooks; /* in debug, we never free() them */
    
    static void ng_dumpitems(void);
    static void ng_dumpnodes(void);
    static void ng_dumphooks(void);
    
    #endif  /* NETGRAPH_DEBUG */
    /*
     * DEAD versions of the structures. 
     * In order to avoid races, it is sometimes neccesary to point
     * at SOMETHING even though theoretically, the current entity is 
     * INVALID. Use these to avoid these races.
     */
    struct ng_type ng_deadtype = {
            NG_ABI_VERSION,
            "dead",
            NULL,   /* modevent */
            NULL,   /* constructor */
            NULL,   /* rcvmsg */
           NULL,   /* shutdown */
           NULL,   /* newhook */
           NULL,   /* findhook */
           NULL,   /* connect */
           NULL,   /* rcvdata */
           NULL,   /* disconnect */
           NULL,   /* cmdlist */
   };
   
   struct ng_node ng_deadnode = {
           "dead",
           &ng_deadtype,   
           NGF_INVALID,
           1,      /* refs */
           0,      /* numhooks */
           NULL,   /* private */
           0,      /* ID */
           LIST_HEAD_INITIALIZER(ng_deadnode.hooks),
           {},     /* all_nodes list entry */
           {},     /* id hashtable list entry */
           {},     /* workqueue entry */
           {       0,
                   {}, /* should never use! (should hang) */
                   NULL,
                   &ng_deadnode.nd_input_queue.queue,
                   &ng_deadnode
           },
   #ifdef  NETGRAPH_DEBUG
           ND_MAGIC,
           __FILE__,
           __LINE__,
           {NULL}
   #endif  /* NETGRAPH_DEBUG */
   };
   
   struct ng_hook ng_deadhook = {
           "dead",
           NULL,           /* private */
           HK_INVALID | HK_DEAD,
           1,              /* refs always >= 1 */
           &ng_deadhook,   /* Peer is self */
           &ng_deadnode,   /* attached to deadnode */
           {},             /* hooks list */
           NULL,           /* override rcvmsg() */
           NULL,           /* override rcvdata() */
   #ifdef  NETGRAPH_DEBUG
           HK_MAGIC,
           __FILE__,
           __LINE__,
           {NULL}
   #endif  /* NETGRAPH_DEBUG */
   };
   
   /*
    * END DEAD STRUCTURES
    */
   /* List nodes with unallocated work */
   static TAILQ_HEAD(, ng_node) ng_worklist = TAILQ_HEAD_INITIALIZER(ng_worklist);
   static struct mtx       ng_worklist_mtx;   /* MUST LOCK NODE FIRST */
   
   /* List of installed types */
   static LIST_HEAD(, ng_type) ng_typelist;
   static struct mtx       ng_typelist_mtx;
   
   /* Hash related definitions */
   /* XXX Don't need to initialise them because it's a LIST */
   #define NG_ID_HASH_SIZE 32 /* most systems wont need even this many */
   static LIST_HEAD(, ng_node) ng_ID_hash[NG_ID_HASH_SIZE];
   static struct mtx       ng_idhash_mtx;
   /* Method to find a node.. used twice so do it here */
   #define NG_IDHASH_FN(ID) ((ID) % (NG_ID_HASH_SIZE))
   #define NG_IDHASH_FIND(ID, node)                                        \
           do {                                                            \
                   mtx_assert(&ng_idhash_mtx, MA_OWNED);                   \
                   LIST_FOREACH(node, &ng_ID_hash[NG_IDHASH_FN(ID)],       \
                                                   nd_idnodes) {           \
                           if (NG_NODE_IS_VALID(node)                      \
                           && (NG_NODE_ID(node) == ID)) {                  \
                                   break;                                  \
                           }                                               \
                   }                                                       \
           } while (0)
   
   
   /* Internal functions */
   static int      ng_add_hook(node_p node, const char *name, hook_p * hookp);
   static int      ng_generic_msg(node_p here, item_p item, hook_p lasthook);
   static ng_ID_t  ng_decodeidname(const char *name);
   static int      ngb_mod_event(module_t mod, int event, void *data);
   static void     ng_worklist_remove(node_p node);
   static void     ngintr(void);
   static int      ng_apply_item(node_p node, item_p item);
   static void     ng_flush_input_queue(struct ng_queue * ngq);
   static void     ng_setisr(node_p node);
   static node_p   ng_ID2noderef(ng_ID_t ID);
   static int      ng_con_nodes(node_p node, const char *name, node_p node2,
                                                           const char *name2);
   static void     ng_con_part2(node_p node, hook_p hook, void *arg1, int arg2);
   static void     ng_con_part3(node_p node, hook_p hook, void *arg1, int arg2);
   static int      ng_mkpeer(node_p node, const char *name,
                                                   const char *name2, char *type);
   
   /* imported , these used to be externally visible, some may go back */
   void    ng_destroy_hook(hook_p hook);
   node_p  ng_name2noderef(node_p node, const char *name);
   int     ng_path2noderef(node_p here, const char *path,
           node_p *dest, hook_p *lasthook);
   int     ng_make_node(const char *type, node_p *nodepp);
   int     ng_path_parse(char *addr, char **node, char **path, char **hook);
   void    ng_rmnode(node_p node, hook_p dummy1, void *dummy2, int dummy3);
   void    ng_unname(node_p node);
   
   
   /* Our own netgraph malloc type */
   MALLOC_DEFINE(M_NETGRAPH, "netgraph", "netgraph structures and ctrl messages");
   MALLOC_DEFINE(M_NETGRAPH_HOOK, "netgraph_hook", "netgraph hook structures");
   MALLOC_DEFINE(M_NETGRAPH_NODE, "netgraph_node", "netgraph node structures");
   MALLOC_DEFINE(M_NETGRAPH_ITEM, "netgraph_item", "netgraph item structures");
   MALLOC_DEFINE(M_NETGRAPH_MSG, "netgraph_msg", "netgraph name storage");
   
   /* Should not be visible outside this file */
   
   #define _NG_ALLOC_HOOK(hook) \
           MALLOC(hook, hook_p, sizeof(*hook), M_NETGRAPH_HOOK, M_NOWAIT | M_ZERO)
   #define _NG_ALLOC_NODE(node) \
           MALLOC(node, node_p, sizeof(*node), M_NETGRAPH_NODE, M_NOWAIT | M_ZERO)
   
   #ifdef NETGRAPH_DEBUG /*----------------------------------------------*/
   /*
    * In debug mode:
    * In an attempt to help track reference count screwups
    * we do not free objects back to the malloc system, but keep them
    * in a local cache where we can examine them and keep information safely
    * after they have been freed.
    * We use this scheme for nodes and hooks, and to some extent for items.
    */
   static __inline hook_p
   ng_alloc_hook(void)
   {
           hook_p hook;
           SLIST_ENTRY(ng_hook) temp;
           mtx_lock(&ng_nodelist_mtx);
           hook = LIST_FIRST(&ng_freehooks);
           if (hook) {
                   LIST_REMOVE(hook, hk_hooks);
                   bcopy(&hook->hk_all, &temp, sizeof(temp));
                   bzero(hook, sizeof(struct ng_hook));
                   bcopy(&temp, &hook->hk_all, sizeof(temp));
                   mtx_unlock(&ng_nodelist_mtx);
                   hook->hk_magic = HK_MAGIC;
           } else {
                   mtx_unlock(&ng_nodelist_mtx);
                   _NG_ALLOC_HOOK(hook);
                   if (hook) {
                           hook->hk_magic = HK_MAGIC;
                           mtx_lock(&ng_nodelist_mtx);
                           SLIST_INSERT_HEAD(&ng_allhooks, hook, hk_all);
                           mtx_unlock(&ng_nodelist_mtx);
                   }
           }
           return (hook);
   }
   
   static __inline node_p
   ng_alloc_node(void)
   {
           node_p node;
           SLIST_ENTRY(ng_node) temp;
           mtx_lock(&ng_nodelist_mtx);
           node = LIST_FIRST(&ng_freenodes);
           if (node) {
                   LIST_REMOVE(node, nd_nodes);
                   bcopy(&node->nd_all, &temp, sizeof(temp));
                   bzero(node, sizeof(struct ng_node));
                   bcopy(&temp, &node->nd_all, sizeof(temp));
                   mtx_unlock(&ng_nodelist_mtx);
                   node->nd_magic = ND_MAGIC;
           } else {
                   mtx_unlock(&ng_nodelist_mtx);
                   _NG_ALLOC_NODE(node);
                   if (node) {
                           node->nd_magic = ND_MAGIC;
                           mtx_lock(&ng_nodelist_mtx);
                           SLIST_INSERT_HEAD(&ng_allnodes, node, nd_all);
                           mtx_unlock(&ng_nodelist_mtx);
                   }
           }
           return (node);
   }
   
   #define NG_ALLOC_HOOK(hook) do { (hook) = ng_alloc_hook(); } while (0)
   #define NG_ALLOC_NODE(node) do { (node) = ng_alloc_node(); } while (0)
   
   
   #define NG_FREE_HOOK(hook)                                              \
           do {                                                            \
                   mtx_lock(&ng_nodelist_mtx);                     \
                   LIST_INSERT_HEAD(&ng_freehooks, hook, hk_hooks);        \
                   hook->hk_magic = 0;                                     \
                   mtx_unlock(&ng_nodelist_mtx);                   \
           } while (0)
   
   #define NG_FREE_NODE(node)                                              \
           do {                                                            \
                   mtx_lock(&ng_nodelist_mtx);                     \
                   LIST_INSERT_HEAD(&ng_freenodes, node, nd_nodes);        \
                   node->nd_magic = 0;                                     \
                   mtx_unlock(&ng_nodelist_mtx);                   \
           } while (0)
   
   #else /* NETGRAPH_DEBUG */ /*----------------------------------------------*/
   
   #define NG_ALLOC_HOOK(hook) _NG_ALLOC_HOOK(hook)
   #define NG_ALLOC_NODE(node) _NG_ALLOC_NODE(node)
   
   #define NG_FREE_HOOK(hook) do { FREE((hook), M_NETGRAPH_HOOK); } while (0)
   #define NG_FREE_NODE(node) do { FREE((node), M_NETGRAPH_NODE); } while (0)
   
   #endif /* NETGRAPH_DEBUG */ /*----------------------------------------------*/
   
   /* Warning: Generally use NG_FREE_ITEM() instead */
   #define NG_FREE_ITEM_REAL(item) do { FREE((item), M_NETGRAPH_ITEM); } while (0)
   
   
   /* Set this to kdb_enter("X") to catch all errors as they occur */
   #ifndef TRAP_ERROR
   #define TRAP_ERROR()
   #endif
   
   static  ng_ID_t nextID = 1;
   
   #ifdef INVARIANTS
   #define CHECK_DATA_MBUF(m)      do {                                    \
                   struct mbuf *n;                                         \
                   int total;                                              \
                                                                           \
                   M_ASSERTPKTHDR(m);                                      \
                   for (total = 0, n = (m); n != NULL; n = n->m_next)      \
                           total += n->m_len;                              \
                   if ((m)->m_pkthdr.len != total) {                       \
                           panic("%s: %d != %d",                           \
                               __func__, (m)->m_pkthdr.len, total);        \
                   }                                                       \
           } while (0)
   #else
   #define CHECK_DATA_MBUF(m)
   #endif
   
   
   /************************************************************************
           Parse type definitions for generic messages
   ************************************************************************/
   
   /* Handy structure parse type defining macro */
   #define DEFINE_PARSE_STRUCT_TYPE(lo, up, args)                          \
   static const struct ng_parse_struct_field                               \
           ng_ ## lo ## _type_fields[] = NG_GENERIC_ ## up ## _INFO args;  \
   static const struct ng_parse_type ng_generic_ ## lo ## _type = {        \
           &ng_parse_struct_type,                                          \
           &ng_ ## lo ## _type_fields                                      \
   }
   
   DEFINE_PARSE_STRUCT_TYPE(mkpeer, MKPEER, ());
   DEFINE_PARSE_STRUCT_TYPE(connect, CONNECT, ());
   DEFINE_PARSE_STRUCT_TYPE(name, NAME, ());
   DEFINE_PARSE_STRUCT_TYPE(rmhook, RMHOOK, ());
   DEFINE_PARSE_STRUCT_TYPE(nodeinfo, NODEINFO, ());
   DEFINE_PARSE_STRUCT_TYPE(typeinfo, TYPEINFO, ());
   DEFINE_PARSE_STRUCT_TYPE(linkinfo, LINKINFO, (&ng_generic_nodeinfo_type));
   
   /* Get length of an array when the length is stored as a 32 bit
      value immediately preceding the array -- as with struct namelist
      and struct typelist. */
   static int
   ng_generic_list_getLength(const struct ng_parse_type *type,
           const u_char *start, const u_char *buf)
   {
           return *((const u_int32_t *)(buf - 4));
   }
   
   /* Get length of the array of struct linkinfo inside a struct hooklist */
   static int
   ng_generic_linkinfo_getLength(const struct ng_parse_type *type,
           const u_char *start, const u_char *buf)
   {
           const struct hooklist *hl = (const struct hooklist *)start;
   
           return hl->nodeinfo.hooks;
   }
   
   /* Array type for a variable length array of struct namelist */
   static const struct ng_parse_array_info ng_nodeinfoarray_type_info = {
           &ng_generic_nodeinfo_type,
           &ng_generic_list_getLength
   };
   static const struct ng_parse_type ng_generic_nodeinfoarray_type = {
           &ng_parse_array_type,
           &ng_nodeinfoarray_type_info
   };
   
   /* Array type for a variable length array of struct typelist */
   static const struct ng_parse_array_info ng_typeinfoarray_type_info = {
           &ng_generic_typeinfo_type,
           &ng_generic_list_getLength
   };
   static const struct ng_parse_type ng_generic_typeinfoarray_type = {
           &ng_parse_array_type,
           &ng_typeinfoarray_type_info
   };
   
   /* Array type for array of struct linkinfo in struct hooklist */
   static const struct ng_parse_array_info ng_generic_linkinfo_array_type_info = {
           &ng_generic_linkinfo_type,
           &ng_generic_linkinfo_getLength
   };
   static const struct ng_parse_type ng_generic_linkinfo_array_type = {
           &ng_parse_array_type,
           &ng_generic_linkinfo_array_type_info
   };
   
   DEFINE_PARSE_STRUCT_TYPE(typelist, TYPELIST, (&ng_generic_nodeinfoarray_type));
   DEFINE_PARSE_STRUCT_TYPE(hooklist, HOOKLIST,
           (&ng_generic_nodeinfo_type, &ng_generic_linkinfo_array_type));
   DEFINE_PARSE_STRUCT_TYPE(listnodes, LISTNODES,
           (&ng_generic_nodeinfoarray_type));
   
   /* List of commands and how to convert arguments to/from ASCII */
   static const struct ng_cmdlist ng_generic_cmds[] = {
           {
             NGM_GENERIC_COOKIE,
             NGM_SHUTDOWN,
             "shutdown",
             NULL,
             NULL
           },
           {
             NGM_GENERIC_COOKIE,
             NGM_MKPEER,
             "mkpeer",
             &ng_generic_mkpeer_type,
             NULL
           },
           {
             NGM_GENERIC_COOKIE,
             NGM_CONNECT,
             "connect",
             &ng_generic_connect_type,
             NULL
           },
           {
             NGM_GENERIC_COOKIE,
             NGM_NAME,
             "name",
             &ng_generic_name_type,
             NULL
           },
           {
             NGM_GENERIC_COOKIE,
             NGM_RMHOOK,
             "rmhook",
             &ng_generic_rmhook_type,
             NULL
           },
           {
             NGM_GENERIC_COOKIE,
             NGM_NODEINFO,
             "nodeinfo",
             NULL,
             &ng_generic_nodeinfo_type
           },
           {
             NGM_GENERIC_COOKIE,
             NGM_LISTHOOKS,
             "listhooks",
             NULL,
             &ng_generic_hooklist_type
           },
           {
             NGM_GENERIC_COOKIE,
             NGM_LISTNAMES,
             "listnames",
             NULL,
             &ng_generic_listnodes_type    /* same as NGM_LISTNODES */
           },
           {
             NGM_GENERIC_COOKIE,
             NGM_LISTNODES,
             "listnodes",
             NULL,
             &ng_generic_listnodes_type
           },
           {
             NGM_GENERIC_COOKIE,
             NGM_LISTTYPES,
             "listtypes",
             NULL,
             &ng_generic_typeinfo_type
           },
           {
             NGM_GENERIC_COOKIE,
             NGM_TEXT_CONFIG,
             "textconfig",
             NULL,
             &ng_parse_string_type
           },
           {
             NGM_GENERIC_COOKIE,
             NGM_TEXT_STATUS,
             "textstatus",
             NULL,
             &ng_parse_string_type
           },
           {
             NGM_GENERIC_COOKIE,
             NGM_ASCII2BINARY,
             "ascii2binary",
             &ng_parse_ng_mesg_type,
             &ng_parse_ng_mesg_type
           },
           {
             NGM_GENERIC_COOKIE,
             NGM_BINARY2ASCII,
             "binary2ascii",
             &ng_parse_ng_mesg_type,
             &ng_parse_ng_mesg_type
           },
           { 0 }
   };
   
   /************************************************************************
                           Node routines
   ************************************************************************/
   
   /*
    * Instantiate a node of the requested type
    */
   int
   ng_make_node(const char *typename, node_p *nodepp)
   {
           struct ng_type *type;
           int     error;
   
           /* Check that the type makes sense */
           if (typename == NULL) {
                   TRAP_ERROR();
                   return (EINVAL);
           }
   
           /* Locate the node type. If we fail we return. Do not try to load
            * module.
            */
           if ((type = ng_findtype(typename)) == NULL)
                   return (ENXIO);
   
           /*
            * If we have a constructor, then make the node and
            * call the constructor to do type specific initialisation.
            */
           if (type->constructor != NULL) {
                   if ((error = ng_make_node_common(type, nodepp)) == 0) {
                           if ((error = ((*type->constructor)(*nodepp)) != 0)) {
                                   NG_NODE_UNREF(*nodepp);
                           }
                   }
           } else {
                   /*
                    * Node has no constructor. We cannot ask for one
                    * to be made. It must be brought into existance by
                    * some external agency. The external agency should
                    * call ng_make_node_common() directly to get the
                    * netgraph part initialised.
                    */
                   TRAP_ERROR();
                   error = EINVAL;
           }
           return (error);
   }
   
   /*
    * Generic node creation. Called by node initialisation for externally
    * instantiated nodes (e.g. hardware, sockets, etc ).
    * The returned node has a reference count of 1.
    */
   int
   ng_make_node_common(struct ng_type *type, node_p *nodepp)
   {
           node_p node;
   
           /* Require the node type to have been already installed */
           if (ng_findtype(type->name) == NULL) {
                   TRAP_ERROR();
                   return (EINVAL);
           }
   
           /* Make a node and try attach it to the type */
           NG_ALLOC_NODE(node);
           if (node == NULL) {
                   TRAP_ERROR();
                   return (ENOMEM);
           }
           node->nd_type = type;
           NG_NODE_REF(node);                              /* note reference */
           type->refs++;
   
           mtx_init(&node->nd_input_queue.q_mtx, "ng_node", NULL, MTX_SPIN);
           node->nd_input_queue.queue = NULL;
           node->nd_input_queue.last = &node->nd_input_queue.queue;
           node->nd_input_queue.q_flags = 0;
           node->nd_input_queue.q_node = node;
   
           /* Initialize hook list for new node */
           LIST_INIT(&node->nd_hooks);
   
           /* Link us into the node linked list */
           mtx_lock(&ng_nodelist_mtx);
           LIST_INSERT_HEAD(&ng_nodelist, node, nd_nodes);
           mtx_unlock(&ng_nodelist_mtx);
   
   
           /* get an ID and put us in the hash chain */
           mtx_lock(&ng_idhash_mtx);
           for (;;) { /* wrap protection, even if silly */
                   node_p node2 = NULL;
                   node->nd_ID = nextID++; /* 137/second for 1 year before wrap */
   
                   /* Is there a problem with the new number? */
                   NG_IDHASH_FIND(node->nd_ID, node2); /* already taken? */
                   if ((node->nd_ID != 0) && (node2 == NULL)) {
                           break;
                   }
           }
           LIST_INSERT_HEAD(&ng_ID_hash[NG_IDHASH_FN(node->nd_ID)],
                                                           node, nd_idnodes);
           mtx_unlock(&ng_idhash_mtx);
   
           /* Done */
           *nodepp = node;
           return (0);
   }
   
   /*
    * Forceably start the shutdown process on a node. Either call
    * it's shutdown method, or do the default shutdown if there is
    * no type-specific method.
    *
    * We can only be called form a shutdown message, so we know we have
    * a writer lock, and therefore exclusive access. It also means
    * that we should not be on the work queue, but we check anyhow.
    *
    * Persistent node types must have a type-specific method which
    * Allocates a new node in which case, this one is irretrievably going away,
    * or cleans up anything it needs, and just makes the node valid again,
    * in which case we allow the node to survive. 
    *
    * XXX We need to think of how to tell a persistant node that we
    * REALLY need to go away because the hardware has gone or we
    * are rebooting.... etc.
    */
   void
   ng_rmnode(node_p node, hook_p dummy1, void *dummy2, int dummy3)
   {
           hook_p hook;
   
           /* Check if it's already shutting down */
           if ((node->nd_flags & NGF_CLOSING) != 0)
                   return;
   
           if (node == &ng_deadnode) {
                   printf ("shutdown called on deadnode\n");
                   return;
           }
   
           /* Add an extra reference so it doesn't go away during this */
           NG_NODE_REF(node);
   
           /*
            * Mark it invalid so any newcomers know not to try use it
            * Also add our own mark so we can't recurse
            * note that NGF_INVALID does not do this as it's also set during
            * creation
            */
           node->nd_flags |= NGF_INVALID|NGF_CLOSING;
   
           /* If node has its pre-shutdown method, then call it first*/
           if (node->nd_type && node->nd_type->close)
                   (*node->nd_type->close)(node);
   
           /* Notify all remaining connected nodes to disconnect */
           while ((hook = LIST_FIRST(&node->nd_hooks)) != NULL)
                   ng_destroy_hook(hook);
   
           /*
            * Drain the input queue forceably.
            * it has no hooks so what's it going to do, bleed on someone?
            * Theoretically we came here from a queue entry that was added
            * Just before the queue was closed, so it should be empty anyway.
            * Also removes us from worklist if needed.
            */
           ng_flush_input_queue(&node->nd_input_queue);
   
           /* Ask the type if it has anything to do in this case */
           if (node->nd_type && node->nd_type->shutdown) {
                   (*node->nd_type->shutdown)(node);
                   if (NG_NODE_IS_VALID(node)) {
                           /*
                            * Well, blow me down if the node code hasn't declared
                            * that it doesn't want to die.
                            * Presumably it is a persistant node.
                            * If we REALLY want it to go away,
                            *  e.g. hardware going away,
                            * Our caller should set NGF_REALLY_DIE in nd_flags.
                            */ 
                           node->nd_flags &= ~(NGF_INVALID|NGF_CLOSING);
                           NG_NODE_UNREF(node); /* Assume they still have theirs */
                           return;
                   }
           } else {                                /* do the default thing */
                   NG_NODE_UNREF(node);
           }
   
           ng_unname(node); /* basically a NOP these days */
   
           /*
            * Remove extra reference, possibly the last
            * Possible other holders of references may include
            * timeout callouts, but theoretically the node's supposed to
            * have cancelled them. Possibly hardware dependencies may
            * force a driver to 'linger' with a reference.
            */
           NG_NODE_UNREF(node);
   }
   
   #ifdef  NETGRAPH_DEBUG
   void
   ng_ref_node(node_p node)
   {
           _NG_NODE_REF(node);
   }
   #endif
   
   /*
    * Remove a reference to the node, possibly the last.
    * deadnode always acts as it it were the last.
    */
   int
   ng_unref_node(node_p node)
   {
           int     v;
   
           if (node == &ng_deadnode) {
                   return (0);
           }
   
           do {
                   v = node->nd_refs - 1;
           } while (! atomic_cmpset_int(&node->nd_refs, v + 1, v));
   
           if (v == 0) { /* we were the last */
   
                   mtx_lock(&ng_nodelist_mtx);
                   node->nd_type->refs--; /* XXX maybe should get types lock? */
                   LIST_REMOVE(node, nd_nodes);
                   mtx_unlock(&ng_nodelist_mtx);
   
                   mtx_lock(&ng_idhash_mtx);
                   LIST_REMOVE(node, nd_idnodes);
                   mtx_unlock(&ng_idhash_mtx);
   
                   mtx_destroy(&node->nd_input_queue.q_mtx);
                   NG_FREE_NODE(node);
           }
           return (v);
   }
   
   /************************************************************************
                           Node ID handling
   ************************************************************************/
   static node_p
   ng_ID2noderef(ng_ID_t ID)
   {
           node_p node;
           mtx_lock(&ng_idhash_mtx);
           NG_IDHASH_FIND(ID, node);
           if(node)
                   NG_NODE_REF(node);
           mtx_unlock(&ng_idhash_mtx);
           return(node);
   }
   
   ng_ID_t
   ng_node2ID(node_p node)
   {
           return (node ? NG_NODE_ID(node) : 0);
   }
   
   /************************************************************************
                           Node name handling
   ************************************************************************/
   
   /*
    * Assign a node a name. Once assigned, the name cannot be changed.
    */
   int
   ng_name_node(node_p node, const char *name)
   {
           int i;
           node_p node2;
   
           /* Check the name is valid */
           for (i = 0; i < NG_NODESIZ; i++) {
                   if (name[i] == '\0' || name[i] == '.' || name[i] == ':')
                           break;
           }
           if (i == 0 || name[i] != '\0') {
                   TRAP_ERROR();
                   return (EINVAL);
           }
           if (ng_decodeidname(name) != 0) { /* valid IDs not allowed here */
                   TRAP_ERROR();
                   return (EINVAL);
           }
   
           /* Check the name isn't already being used */
           if ((node2 = ng_name2noderef(node, name)) != NULL) {
                   NG_NODE_UNREF(node2);
                   TRAP_ERROR();
                   return (EADDRINUSE);
           }
   
           /* copy it */
           strlcpy(NG_NODE_NAME(node), name, NG_NODESIZ);
   
           return (0);
   }
   
   /*
    * Find a node by absolute name. The name should NOT end with ':'
    * The name "." means "this node" and "[xxx]" means "the node
    * with ID (ie, at address) xxx".
    *
    * Returns the node if found, else NULL.
    * Eventually should add something faster than a sequential search.
    * Note it aquires a reference on the node so you can be sure it's still there.
    */
   node_p
   ng_name2noderef(node_p here, const char *name)
   {
           node_p node;
           ng_ID_t temp;
   
           /* "." means "this node" */
           if (strcmp(name, ".") == 0) {
                   NG_NODE_REF(here);
                   return(here);
           }
   
           /* Check for name-by-ID */
           if ((temp = ng_decodeidname(name)) != 0) {
                   return (ng_ID2noderef(temp));
           }
   
           /* Find node by name */
           mtx_lock(&ng_nodelist_mtx);
           LIST_FOREACH(node, &ng_nodelist, nd_nodes) {
                   if (NG_NODE_IS_VALID(node)
                   && NG_NODE_HAS_NAME(node)
                   && (strcmp(NG_NODE_NAME(node), name) == 0)) {
                           break;
                   }
           }
           if (node)
                   NG_NODE_REF(node);
           mtx_unlock(&ng_nodelist_mtx);
           return (node);
   }
   
   /*
    * Decode an ID name, eg. "[f03034de]". Returns 0 if the
    * string is not valid, otherwise returns the value.
    */
   static ng_ID_t
   ng_decodeidname(const char *name)
   {
           const int len = strlen(name);
           char *eptr;
           u_long val;
   
           /* Check for proper length, brackets, no leading junk */
           if ((len < 3)
           || (name[0] != '[')
           || (name[len - 1] != ']')
           || (!isxdigit(name[1]))) {
                   return ((ng_ID_t)0);
           }
   
           /* Decode number */
           val = strtoul(name + 1, &eptr, 16);
           if ((eptr - name != len - 1)
           || (val == ULONG_MAX)
           || (val == 0)) {
                   return ((ng_ID_t)0);
           }
           return (ng_ID_t)val;
   }
   
   /*
    * Remove a name from a node. This should only be called
    * when shutting down and removing the node.
    * IF we allow name changing this may be more resurected.
    */
   void
   ng_unname(node_p node)
   {
   }
   
   /************************************************************************
                           Hook routines
    Names are not optional. Hooks are always connected, except for a
    brief moment within these routines. On invalidation or during creation
    they are connected to the 'dead' hook.
   ************************************************************************/
   
   /*
    * Remove a hook reference
    */
   void
   ng_unref_hook(hook_p hook)
   {
           int     v;
   
           if (hook == &ng_deadhook) {
                   return;
           }
           do {
                   v = hook->hk_refs;
           } while (! atomic_cmpset_int(&hook->hk_refs, v, v - 1));
   
           if (v == 1) { /* we were the last */
                   if (_NG_HOOK_NODE(hook)) { /* it'll probably be ng_deadnode */
                           _NG_NODE_UNREF((_NG_HOOK_NODE(hook)));
                           hook->hk_node = NULL;
                   }
                   NG_FREE_HOOK(hook);
           }
   }
   
   /*
    * Add an unconnected hook to a node. Only used internally.
    * Assumes node is locked. (XXX not yet true )
    */
   static int
   ng_add_hook(node_p node, const char *name, hook_p *hookp)
   {
           hook_p hook;
           int error = 0;
   
           /* Check that the given name is good */
           if (name == NULL) {
                   TRAP_ERROR();
                   return (EINVAL);
           }
           if (ng_findhook(node, name) != NULL) {
                   TRAP_ERROR();
                   return (EEXIST);
           }
   
           /* Allocate the hook and link it up */
           NG_ALLOC_HOOK(hook);
           if (hook == NULL) {
                   TRAP_ERROR();
                   return (ENOMEM);
           }
           hook->hk_refs = 1;              /* add a reference for us to return */
           hook->hk_flags = HK_INVALID;
           hook->hk_peer = &ng_deadhook;   /* start off this way */
           hook->hk_node = node;
           NG_NODE_REF(node);              /* each hook counts as a reference */
   
           /* Set hook name */
           strlcpy(NG_HOOK_NAME(hook), name, NG_HOOKSIZ);
   
           /*
            * Check if the node type code has something to say about it
            * If it fails, the unref of the hook will also unref the node.
            */
           if (node->nd_type->newhook != NULL) {
                   if ((error = (*node->nd_type->newhook)(node, hook, name))) {
                           NG_HOOK_UNREF(hook);    /* this frees the hook */
                           return (error);
                   }
           }
           /*
            * The 'type' agrees so far, so go ahead and link it in.
            * We'll ask again later when we actually connect the hooks.
            */
           LIST_INSERT_HEAD(&node->nd_hooks, hook, hk_hooks);
           node->nd_numhooks++;
           NG_HOOK_REF(hook);      /* one for the node */
   
           if (hookp)
                  *hookp = hook;
          return (0);
  }
  
  /*
   * Find a hook
   *
   * Node types may supply their own optimized routines for finding
   * hooks.  If none is supplied, we just do a linear search.
   * XXX Possibly we should add a reference to the hook?
   */
  hook_p
  ng_findhook(node_p node, const char *name)
  {
          hook_p hook;
  
          if (node->nd_type->findhook != NULL)
                  return (*node->nd_type->findhook)(node, name);
          LIST_FOREACH(hook, &node->nd_hooks, hk_hooks) {
                  if (NG_HOOK_IS_VALID(hook)
                  && (strcmp(NG_HOOK_NAME(hook), name) == 0))
                          return (hook);
          }
          return (NULL);
  }
  
  /*
   * Destroy a hook
   *
   * As hooks are always attached, this really destroys two hooks.
   * The one given, and the one attached to it. Disconnect the hooks
   * from each other first. We reconnect the peer hook to the 'dead'
   * hook so that it can still exist after we depart. We then
   * send the peer its own destroy message. This ensures that we only
   * interact with the peer's structures when it is locked processing that 
   * message. We hold a reference to the peer hook so we are guaranteed that
   * the peer hook and node are still going to exist until
   * we are finished there as the hook holds a ref on the node.
   * We run this same code again on the peer hook, but that time it is already 
   * attached to the 'dead' hook. 
   *
   * This routine is called at all stages of hook creation 
   * on error detection and must be able to handle any such stage.
   */
  void
  ng_destroy_hook(hook_p hook)
  {
          hook_p peer = NG_HOOK_PEER(hook);
          node_p node = NG_HOOK_NODE(hook);
  
          if (hook == &ng_deadhook) {     /* better safe than sorry */
                  printf("ng_destroy_hook called on deadhook\n");
                  return;
          }
          hook->hk_flags |= HK_INVALID;           /* as soon as possible */
          if (peer && (peer != &ng_deadhook)) {
                  /*
                   * Set the peer to point to ng_deadhook
                   * from this moment on we are effectively independent it.
                   * send it an rmhook message of it's own.
                   */
                  peer->hk_peer = &ng_deadhook;   /* They no longer know us */
                  hook->hk_peer = &ng_deadhook;   /* Nor us, them */
                  if (NG_HOOK_NODE(peer) == &ng_deadnode) {
                          /* 
                           * If it's already divorced from a node,
                           * just free it.
                           */
                          /* nothing */
                  } else {
                          ng_rmhook_self(peer);   /* Send it a surprise */
                  }
                  NG_HOOK_UNREF(peer);            /* account for peer link */
                  NG_HOOK_UNREF(hook);            /* account for peer link */
          }
  
          /*
           * Remove the hook from the node's list to avoid possible recursion
           * in case the disconnection results in node shutdown.
           */
          if (node == &ng_deadnode) { /* happens if called from ng_con_nodes() */
                  return;
          }
          LIST_REMOVE(hook, hk_hooks);
          node->nd_numhooks--;
          if (node->nd_type->disconnect) {
                  /*
                   * The type handler may elect to destroy the node so don't
                   * trust its existance after this point. (except 
                   * that we still hold a reference on it. (which we
                   * inherrited from the hook we are destroying)
                   */
                  (*node->nd_type->disconnect) (hook);
          }
  
          /*
           * Note that because we will point to ng_deadnode, the original node
           * is not decremented automatically so we do that manually.
           */
          _NG_HOOK_NODE(hook) = &ng_deadnode;
          NG_NODE_UNREF(node);    /* We no longer point to it so adjust count */
          NG_HOOK_UNREF(hook);    /* Account for linkage (in list) to node */
  }
  
  /*
   * Take two hooks on a node and merge the connection so that the given node
   * is effectively bypassed.
   */
  int
  ng_bypass(hook_p hook1, hook_p hook2)
  {
          if (hook1->hk_node != hook2->hk_node) {
                  TRAP_ERROR();
                  return (EINVAL);
          }
          hook1->hk_peer->hk_peer = hook2->hk_peer;
          hook2->hk_peer->hk_peer = hook1->hk_peer;
  
          hook1->hk_peer = &ng_deadhook;
          hook2->hk_peer = &ng_deadhook;
  
          /* XXX If we ever cache methods on hooks update them as well */
          ng_destroy_hook(hook1);
          ng_destroy_hook(hook2);
          return (0);
  }
  
  /*
   * Install a new netgraph type
   */
  int
  ng_newtype(struct ng_type *tp)
  {
          const size_t namelen = strlen(tp->name);
  
          /* Check version and type name fields */
          if ((tp->version != NG_ABI_VERSION)
          || (namelen == 0)
          || (namelen >= NG_TYPESIZ)) {
                  TRAP_ERROR();
                  if (tp->version != NG_ABI_VERSION) {
                          printf("Netgraph: Node type rejected. ABI mismatch. Suggest recompile\n");
                  }
                  return (EINVAL);
          }
  
          /* Check for name collision */
          if (ng_findtype(tp->name) != NULL) {
                  TRAP_ERROR();
                  return (EEXIST);
          }
  
  
          /* Link in new type */
          mtx_lock(&ng_typelist_mtx);
          LIST_INSERT_HEAD(&ng_typelist, tp, types);
          tp->refs = 1;   /* first ref is linked list */
          mtx_unlock(&ng_typelist_mtx);
          return (0);
  }
  
  /*
   * unlink a netgraph type
   * If no examples exist
   */
  int
  ng_rmtype(struct ng_type *tp)
  {
          /* Check for name collision */
          if (tp->refs != 1) {
                  TRAP_ERROR();
                  return (EBUSY);
          }
  
          /* Unlink type */
          mtx_lock(&ng_typelist_mtx);
          LIST_REMOVE(tp, types);
          mtx_unlock(&ng_typelist_mtx);
          return (0);
  }
  
  /*
   * Look for a type of the name given
   */
  struct ng_type *
  ng_findtype(const char *typename)
  {
          struct ng_type *type;
  
          mtx_lock(&ng_typelist_mtx);
          LIST_FOREACH(type, &ng_typelist, types) {
                  if (strcmp(type->name, typename) == 0)
                          break;
          }
          mtx_unlock(&ng_typelist_mtx);
          return (type);
  }
  
  /************************************************************************
                          Composite routines
  ************************************************************************/
  /*
   * Connect two nodes using the specified hooks, using queued functions.
   */
  static void
  ng_con_part3(node_p node, hook_p hook, void *arg1, int arg2)
  {
  
          /*
           * When we run, we know that the node 'node' is locked for us.
           * Our caller has a reference on the hook.
           * Our caller has a reference on the node.
           * (In this case our caller is ng_apply_item() ).
           * The peer hook has a reference on the hook.
           * We are all set up except for the final call to the node, and
           * the clearing of the INVALID flag.
           */
          if (NG_HOOK_NODE(hook) == &ng_deadnode) {
                  /*
                   * The node must have been freed again since we last visited
                   * here. ng_destry_hook() has this effect but nothing else does.
                   * We should just release our references and
                   * free anything we can think of.
                   * Since we know it's been destroyed, and it's our caller
                   * that holds the references, just return.
                   */
                  return ;
          }
          if (hook->hk_node->nd_type->connect) {
                  if ((*hook->hk_node->nd_type->connect) (hook)) {
                          ng_destroy_hook(hook);  /* also zaps peer */
                          printf("failed in ng_con_part3()\n");
                          return ;
                  }
          }
          /*
           *  XXX this is wrong for SMP. Possibly we need
           * to separate out 'create' and 'invalid' flags.
           * should only set flags on hooks we have locked under our node.
           */
          hook->hk_flags &= ~HK_INVALID;
          return ;
  }
  
  static void
  ng_con_part2(node_p node, hook_p hook, void *arg1, int arg2)
  {
  
          /*
           * When we run, we know that the node 'node' is locked for us.
           * Our caller has a reference on the hook.
           * Our caller has a reference on the node.
           * (In this case our caller is ng_apply_item() ).
           * The peer hook has a reference on the hook.
           * our node pointer points to the 'dead' node.
           * First check the hook name is unique.
           * Should not happen because we checked before queueing this.
           */
          if (ng_findhook(node, NG_HOOK_NAME(hook)) != NULL) {
                  TRAP_ERROR();
                  ng_destroy_hook(hook); /* should destroy peer too */
                  printf("failed in ng_con_part2()\n");
                  return ;
          }
          /*
           * Check if the node type code has something to say about it
           * If it fails, the unref of the hook will also unref the attached node,
           * however since that node is 'ng_deadnode' this will do nothing.
           * The peer hook will also be destroyed.
           */
          if (node->nd_type->newhook != NULL) {
                  if ((*node->nd_type->newhook)(node, hook, hook->hk_name)) {
                          ng_destroy_hook(hook); /* should destroy peer too */
                          printf("failed in ng_con_part2()\n");
                          return ;
                  }
          }
  
          /*
           * The 'type' agrees so far, so go ahead and link it in.
           * We'll ask again later when we actually connect the hooks.
           */
          hook->hk_node = node;           /* just overwrite ng_deadnode */
          NG_NODE_REF(node);              /* each hook counts as a reference */
          LIST_INSERT_HEAD(&node->nd_hooks, hook, hk_hooks);
          node->nd_numhooks++;
          NG_HOOK_REF(hook);      /* one for the node */
          
          /*
           * We now have a symetrical situation, where both hooks have been
           * linked to their nodes, the newhook methods have been called
           * And the references are all correct. The hooks are still marked
           * as invalid, as we have not called the 'connect' methods
           * yet.
           * We can call the local one immediatly as we have the 
           * node locked, but we need to queue the remote one.
           */
          if (hook->hk_node->nd_type->connect) {
                  if ((*hook->hk_node->nd_type->connect) (hook)) {
                          ng_destroy_hook(hook);  /* also zaps peer */
                          printf("failed in ng_con_part2(A)\n");
                          return ;
                  }
          }
          if (ng_send_fn(hook->hk_peer->hk_node, hook->hk_peer,
                          &ng_con_part3, arg1, arg2)) {
                  printf("failed in ng_con_part2(B)");
                  ng_destroy_hook(hook);  /* also zaps peer */
                  return ;
          }
          hook->hk_flags &= ~HK_INVALID; /* need both to be able to work */
          return ;
  }
  
  /*
   * Connect this node with another node. We assume that this node is 
   * currently locked, as we are only called from an NGM_CONNECT message.
   */
  static int
  ng_con_nodes(node_p node, const char *name, node_p node2, const char *name2)
  {
          int     error;
          hook_p  hook;
          hook_p  hook2;
  
          if (ng_findhook(node2, name2) != NULL) {
                  return(EEXIST);
          }
          if ((error = ng_add_hook(node, name, &hook)))  /* gives us a ref */
                  return (error);
          /* Allocate the other hook and link it up */
          NG_ALLOC_HOOK(hook2);
          if (hook == NULL) {
                  TRAP_ERROR();
                  ng_destroy_hook(hook);  /* XXX check ref counts so far */
                  NG_HOOK_UNREF(hook);    /* including our ref */
                  return (ENOMEM);
          }
          hook2->hk_refs = 1;             /* start with a reference for us. */
          hook2->hk_flags = HK_INVALID;
          hook2->hk_peer = hook;          /* Link the two together */
          hook->hk_peer = hook2;  
          NG_HOOK_REF(hook);              /* Add a ref for the peer to each*/
          NG_HOOK_REF(hook2);
          hook2->hk_node = &ng_deadnode;  
          strlcpy(NG_HOOK_NAME(hook2), name2, NG_HOOKSIZ);
  
          /*
           * Queue the function above.
           * Procesing continues in that function in the lock context of
           * the other node.
           */
          ng_send_fn(node2, hook2, &ng_con_part2, NULL, 0);
  
          NG_HOOK_UNREF(hook);            /* Let each hook go if it wants to */
          NG_HOOK_UNREF(hook2);
          return (0);
  }
  
  /*
   * Make a peer and connect.
   * We assume that the local node is locked.
   * The new node probably doesn't need a lock until
   * it has a hook, because it cannot really have any work until then,
   * but we should think about it a bit more.
   *
   * The problem may come if the other node also fires up
   * some hardware or a timer or some other source of activation,
   * also it may already get a command msg via it's ID.
   *
   * We could use the same method as ng_con_nodes() but we'd have
   * to add ability to remove the node when failing. (Not hard, just 
   * make arg1 point to the node to remove).
   * Unless of course we just ignore failure to connect and leave
   * an unconnected node?
   */
  static int
  ng_mkpeer(node_p node, const char *name, const char *name2, char *type)
  {
          node_p  node2;
          hook_p  hook1;
          hook_p  hook2;
          int     error;
  
          if ((error = ng_make_node(type, &node2))) {
                  return (error);
          }
  
          if ((error = ng_add_hook(node, name, &hook1))) { /* gives us a ref */
                  ng_rmnode(node2, NULL, NULL, 0);
                  return (error);
          }
  
          if ((error = ng_add_hook(node2, name2, &hook2))) {
                  ng_rmnode(node2, NULL, NULL, 0);
                  ng_destroy_hook(hook1);
                  NG_HOOK_UNREF(hook1);
                  return (error);
          }
  
          /*
           * Actually link the two hooks together.
           */
          hook1->hk_peer = hook2;
          hook2->hk_peer = hook1;
  
          /* Each hook is referenced by the other */
          NG_HOOK_REF(hook1);
          NG_HOOK_REF(hook2);
  
          /* Give each node the opportunity to veto the pending connection */
          if (hook1->hk_node->nd_type->connect) {
                  error = (*hook1->hk_node->nd_type->connect) (hook1);
          }
  
          if ((error == 0) && hook2->hk_node->nd_type->connect) {
                  error = (*hook2->hk_node->nd_type->connect) (hook2);
  
          }
  
          /*
           * drop the references we were holding on the two hooks.
           */
          if (error) {
                  ng_destroy_hook(hook2); /* also zaps hook1 */
                  ng_rmnode(node2, NULL, NULL, 0);
          } else {
                  /* As a last act, allow the hooks to be used */
                  hook1->hk_flags &= ~HK_INVALID;
                  hook2->hk_flags &= ~HK_INVALID;
          }
          NG_HOOK_UNREF(hook1);
          NG_HOOK_UNREF(hook2);
          return (error);
  }
  
  /************************************************************************
                  Utility routines to send self messages
  ************************************************************************/
          
  /* Shut this node down as soon as everyone is clear of it */
  /* Should add arg "immediatly" to jump the queue */
  int
  ng_rmnode_self(node_p node)
  {
          int             error;
  
          if (node == &ng_deadnode)
                  return (0);
          node->nd_flags |= NGF_INVALID;
          if (node->nd_flags & NGF_CLOSING)
                  return (0);
  
          error = ng_send_fn(node, NULL, &ng_rmnode, NULL, 0);
          return (error);
  }
  
  static void
  ng_rmhook_part2(node_p node, hook_p hook, void *arg1, int arg2)
  {
          ng_destroy_hook(hook);
          return ;
  }
  
  int
  ng_rmhook_self(hook_p hook)
  {
          int             error;
          node_p node = NG_HOOK_NODE(hook);
  
          if (node == &ng_deadnode)
                  return (0);
  
          error = ng_send_fn(node, hook, &ng_rmhook_part2, NULL, 0);
          return (error);
  }
  
  /***********************************************************************
   * Parse and verify a string of the form:  <NODE:><PATH>
   *
   * Such a string can refer to a specific node or a specific hook
   * on a specific node, depending on how you look at it. In the
   * latter case, the PATH component must not end in a dot.
   *
   * Both <NODE:> and <PATH> are optional. The <PATH> is a string
   * of hook names separated by dots. This breaks out the original
   * string, setting *nodep to "NODE" (or NULL if none) and *pathp
   * to "PATH" (or NULL if degenerate). Also, *hookp will point to
   * the final hook component of <PATH>, if any, otherwise NULL.
   *
   * This returns -1 if the path is malformed. The char ** are optional.
   ***********************************************************************/
  int
  ng_path_parse(char *addr, char **nodep, char **pathp, char **hookp)
  {
          char   *node, *path, *hook;
          int     k;
  
          /*
           * Extract absolute NODE, if any
           */
          for (path = addr; *path && *path != ':'; path++);
          if (*path) {
                  node = addr;    /* Here's the NODE */
                  *path++ = '\0'; /* Here's the PATH */
  
                  /* Node name must not be empty */
                  if (!*node)
                          return -1;
  
                  /* A name of "." is OK; otherwise '.' not allowed */
                  if (strcmp(node, ".") != 0) {
                          for (k = 0; node[k]; k++)
                                  if (node[k] == '.')
                                          return -1;
                  }
          } else {
                  node = NULL;    /* No absolute NODE */
                  path = addr;    /* Here's the PATH */
          }
  
          /* Snoop for illegal characters in PATH */
          for (k = 0; path[k]; k++)
                  if (path[k] == ':')
                          return -1;
  
          /* Check for no repeated dots in PATH */
          for (k = 0; path[k]; k++)
                  if (path[k] == '.' && path[k + 1] == '.')
                          return -1;
  
          /* Remove extra (degenerate) dots from beginning or end of PATH */
          if (path[0] == '.')
                  path++;
          if (*path && path[strlen(path) - 1] == '.')
                  path[strlen(path) - 1] = 0;
  
          /* If PATH has a dot, then we're not talking about a hook */
          if (*path) {
                  for (hook = path, k = 0; path[k]; k++)
                          if (path[k] == '.') {
                                  hook = NULL;
                                  break;
                          }
          } else
                  path = hook = NULL;
  
          /* Done */
          if (nodep)
                  *nodep = node;
          if (pathp)
                  *pathp = path;
          if (hookp)
                  *hookp = hook;
          return (0);
  }
  
  /*
   * Given a path, which may be absolute or relative, and a starting node,
   * return the destination node.
   */
  int
  ng_path2noderef(node_p here, const char *address,
                                  node_p *destp, hook_p *lasthook)
  {
          char    fullpath[NG_PATHSIZ];
          char   *nodename, *path, pbuf[2];
          node_p  node, oldnode;
          char   *cp;
          hook_p hook = NULL;
  
          /* Initialize */
          if (destp == NULL) {
                  TRAP_ERROR();
                  return EINVAL;
          }
          *destp = NULL;
  
          /* Make a writable copy of address for ng_path_parse() */
          strncpy(fullpath, address, sizeof(fullpath) - 1);
          fullpath[sizeof(fullpath) - 1] = '\0';
  
          /* Parse out node and sequence of hooks */
          if (ng_path_parse(fullpath, &nodename, &path, NULL) < 0) {
                  TRAP_ERROR();
                  return EINVAL;
          }
          if (path == NULL) {
                  pbuf[0] = '.';  /* Needs to be writable */
                  pbuf[1] = '\0';
                  path = pbuf;
          }
  
          /*
           * For an absolute address, jump to the starting node.
           * Note that this holds a reference on the node for us.
           * Don't forget to drop the reference if we don't need it.
           */
          if (nodename) {
                  node = ng_name2noderef(here, nodename);
                  if (node == NULL) {
                          TRAP_ERROR();
                          return (ENOENT);
                  }
          } else {
                  if (here == NULL) {
                          TRAP_ERROR();
                          return (EINVAL);
                  }
                  node = here;
                  NG_NODE_REF(node);
          }
  
          /*
           * Now follow the sequence of hooks 
           * XXX
           * We actually cannot guarantee that the sequence
           * is not being demolished as we crawl along it
           * without extra-ordinary locking etc.
           * So this is a bit dodgy to say the least.
           * We can probably hold up some things by holding
           * the nodelist mutex for the time of this
           * crawl if we wanted.. At least that way we wouldn't have to
           * worry about the nodes dissappearing, but the hooks would still
           * be a problem.
           */
          for (cp = path; node != NULL && *cp != '\0'; ) {
                  char *segment;
  
                  /*
                   * Break out the next path segment. Replace the dot we just
                   * found with a NUL; "cp" points to the next segment (or the
                   * NUL at the end).
                   */
                  for (segment = cp; *cp != '\0'; cp++) {
                          if (*cp == '.') {
                                  *cp++ = '\0';
                                  break;
                          }
                  }
  
                  /* Empty segment */
                  if (*segment == '\0')
                          continue;
  
                  /* We have a segment, so look for a hook by that name */
                  hook = ng_findhook(node, segment);
  
                  /* Can't get there from here... */
                  if (hook == NULL
                      || NG_HOOK_PEER(hook) == NULL
                      || NG_HOOK_NOT_VALID(hook)
                      || NG_HOOK_NOT_VALID(NG_HOOK_PEER(hook))) {
                          TRAP_ERROR();
                          NG_NODE_UNREF(node);
  #if 0 
                          printf("hooknotvalid %s %s %d %d %d %d ",
                                          path,
                                          segment,
                                          hook == NULL,
                                          NG_HOOK_PEER(hook) == NULL,
                                          NG_HOOK_NOT_VALID(hook),
                                          NG_HOOK_NOT_VALID(NG_HOOK_PEER(hook)));
  #endif
                          return (ENOENT);
                  }
  
                  /*
                   * Hop on over to the next node 
                   * XXX
                   * Big race conditions here as hooks and nodes go away 
                   * *** Idea.. store an ng_ID_t in each hook and use that
                   * instead of the direct hook in this crawl?
                   */
                  oldnode = node;
                  if ((node = NG_PEER_NODE(hook)))
                          NG_NODE_REF(node);      /* XXX RACE */
                  NG_NODE_UNREF(oldnode); /* XXX another race */
                  if (NG_NODE_NOT_VALID(node)) {
                          NG_NODE_UNREF(node);    /* XXX more races */
                          node = NULL;
                  }
          }
  
          /* If node somehow missing, fail here (probably this is not needed) */
          if (node == NULL) {
                  TRAP_ERROR();
                  return (ENXIO);
          }
  
          /* Done */
          *destp = node;
          if (lasthook != NULL)
                  *lasthook = (hook ? NG_HOOK_PEER(hook) : NULL);
          return (0);
  }
  
  /***************************************************************\
  * Input queue handling.
  * All activities are submitted to the node via the input queue
  * which implements a multiple-reader/single-writer gate.
  * Items which cannot be handled immeditly are queued.
  *
  * read-write queue locking inline functions                     *
  \***************************************************************/
  
  static __inline item_p ng_dequeue(struct ng_queue * ngq);
  static __inline item_p ng_acquire_read(struct ng_queue * ngq,
                                          item_p  item);
  static __inline item_p ng_acquire_write(struct ng_queue * ngq,
                                          item_p  item);
  static __inline void    ng_leave_read(struct ng_queue * ngq);
  static __inline void    ng_leave_write(struct ng_queue * ngq);
  static __inline void    ng_queue_rw(struct ng_queue * ngq,
                                          item_p  item, int rw);
  
  /*
   * Definition of the bits fields in the ng_queue flag word.
   * Defined here rather than in netgraph.h because no-one should fiddle
   * with them.
   *
   * The ordering here may be important! don't shuffle these.
   */
  /*-
   Safety Barrier--------+ (adjustable to suit taste) (not used yet)
                         |
                         V
  +-------+-------+-------+-------+-------+-------+-------+-------+
  | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | |
  | |A|c|t|i|v|e| |R|e|a|d|e|r| |C|o|u|n|t| | | | | | | | | |R|A|W|
  | | | | | | | | | | | | | | | | | | | | | | | | | | | | | |P|W|P|
  +-------+-------+-------+-------+-------+-------+-------+-------+
  \___________________________ ____________________________/ | | |
                              V                              | | |
                    [active reader count]                    | | |
                                                             | | |
            Read Pending ------------------------------------+ | |
                                                               | |
            Active Writer -------------------------------------+ |
                                                                 |
            Write Pending ---------------------------------------+
  
  
  */
  #define WRITE_PENDING   0x00000001
  #define WRITER_ACTIVE   0x00000002
  #define READ_PENDING    0x00000004
  #define READER_INCREMENT 0x00000008
  #define READER_MASK     0xfffffff0      /* Not valid if WRITER_ACTIVE is set */
  #define SAFETY_BARRIER  0x00100000      /* 64K items queued should be enough */
  
  /* Defines of more elaborate states on the queue */
  /* Mask of bits a read cares about */
  #define NGQ_RMASK       (WRITE_PENDING|WRITER_ACTIVE|READ_PENDING)
  
  /* Mask of bits a write cares about */
  #define NGQ_WMASK       (NGQ_RMASK|READER_MASK)
  
  /* tests to decide if we could get a read or write off the queue */
  #define CAN_GET_READ(flag)      ((flag & NGQ_RMASK) == READ_PENDING)
  #define CAN_GET_WRITE(flag)     ((flag & NGQ_WMASK) == WRITE_PENDING)
  
  /* Is there a chance of getting ANY work off the queue? */
  #define CAN_GET_WORK(flag)      (CAN_GET_READ(flag) || CAN_GET_WRITE(flag))
  
  /*
   * Taking into account the current state of the queue and node, possibly take
   * the next entry off the queue and return it. Return NULL if there was
   * nothing we could return, either because there really was nothing there, or
   * because the node was in a state where it cannot yet process the next item
   * on the queue.
   *
   * This MUST MUST MUST be called with the mutex held.
   */
  static __inline item_p
  ng_dequeue(struct ng_queue *ngq)
  {
          item_p item;
          u_int           add_arg;
  
          if (CAN_GET_READ(ngq->q_flags)) {
                  /*
                   * Head of queue is a reader and we have no write active.
                   * We don't care how many readers are already active. 
                   * Adjust the flags for the item we are about to dequeue.
                   * Add the correct increment for the reader count as well.
                   */
                  add_arg = (READER_INCREMENT - READ_PENDING);
          } else if (CAN_GET_WRITE(ngq->q_flags)) {
                  /*
                   * There is a pending write, no readers and no active writer.
                   * This means we can go ahead with the pending writer. Note
                   * the fact that we now have a writer, ready for when we take
                   * it off the queue.
                   *
                   * We don't need to worry about a possible collision with the
                   * fasttrack reader.
                   *
                   * The fasttrack thread may take a long time to discover that we
                   * are running so we would have an inconsistent state in the
                   * flags for a while. Since we ignore the reader count
                   * entirely when the WRITER_ACTIVE flag is set, this should
                   * not matter (in fact it is defined that way). If it tests
                   * the flag before this operation, the WRITE_PENDING flag
                   * will make it fail, and if it tests it later, the
                   * WRITER_ACTIVE flag will do the same. If it is SO slow that
                   * we have actually completed the operation, and neither flag
                   * is set (nor the READ_PENDING) by the time that it tests
                   * the flags, then it is actually ok for it to continue. If
                   * it completes and we've finished and the read pending is
                   * set it still fails.
                   *
                   * So we can just ignore it,  as long as we can ensure that the
                   * transition from WRITE_PENDING state to the WRITER_ACTIVE
                   * state is atomic.
                   *
                   * After failing, first it will be held back by the mutex, then
                   * when it can proceed, it will queue its request, then it
                   * would arrive at this function. Usually it will have to
                   * leave empty handed because the ACTIVE WRITER bit will be
                   * set.
                   *
                   * Adjust the flags for the item we are about to dequeue
                   * and for the new active writer.
                   */
                  add_arg = (WRITER_ACTIVE - WRITE_PENDING);
                  /*
                   * We want to write "active writer, no readers " Now go make
                   * it true. In fact there may be a number in the readers
                   * count but we know it is not true and will be fixed soon.
                   * We will fix the flags for the next pending entry in a
                   * moment.
                   */
          } else {
                  /*
                   * We can't dequeue anything.. return and say so. Probably we
                   * have a write pending and the readers count is non zero. If
                   * we got here because a reader hit us just at the wrong
                   * moment with the fasttrack code, and put us in a strange
                   * state, then it will be through in just a moment, (as soon
                   * as we release the mutex) and keep things moving.
                   * Make sure we remove ourselves from the work queue.
                   */
                  ng_worklist_remove(ngq->q_node);
                  return (0);
          }
  
          /*
           * Now we dequeue the request (whatever it may be) and correct the
           * pending flags and the next and last pointers.
           */
          item = ngq->queue;
          ngq->queue = item->el_next;
          if (ngq->last == &(item->el_next)) {
                  /*
                   * that was the last entry in the queue so set the 'last
                   * pointer up correctly and make sure the pending flags are
                   * clear.
                   */
                  ngq->last = &(ngq->queue);
                  /*
                   * Whatever flag was set will be cleared and
                   * the new acive field will be set by the add as well,
                   * so we don't need to change add_arg.
                   * But we know we don't need to be on the work list.
                   */
                  atomic_add_long(&ngq->q_flags, add_arg);
                  ng_worklist_remove(ngq->q_node);
          } else {
                  /* 
                   * Since there is something on the queue, note what it is
                   * in the flags word.
                   */
                  if ((ngq->queue->el_flags & NGQF_RW) == NGQF_READER) {
                          add_arg += READ_PENDING;
                  } else {
                          add_arg += WRITE_PENDING;
                  }
                  atomic_add_long(&ngq->q_flags, add_arg);
                  /*
                   * If we see more doable work, make sure we are
                   * on the work queue.
                   */
                  if (CAN_GET_WORK(ngq->q_flags)) {
                          ng_setisr(ngq->q_node);
                  }
          }
          /*
           * We have successfully cleared the old pending flag, set the new one
           * if it is needed, and incremented the appropriate active field.
           * (all in one atomic addition.. )
           */
          return (item);
  }
  
  /*
   * Queue a packet to be picked up by someone else.
   * We really don't care who, but we can't or don't want to hang around
   * to process it ourselves. We are probably an interrupt routine..
   * 1 = writer, 0 = reader
   */
  #define NGQRW_R 0
  #define NGQRW_W 1
  static __inline void
  ng_queue_rw(struct ng_queue * ngq, item_p  item, int rw)
  {
          item->el_next = NULL;   /* maybe not needed */
          *ngq->last = item;
          /*
           * If it was the first item in the queue then we need to
           * set the last pointer and the type flags.
           */
          if (ngq->last == &(ngq->queue)) {
                  /*
                   * When called with constants for rw, the optimiser will
                   * remove the unneeded branch below.
                   */
                  if (rw == NGQRW_W) {
                          atomic_add_long(&ngq->q_flags, WRITE_PENDING);
                  } else {
                          atomic_add_long(&ngq->q_flags, READ_PENDING);
                  }
          }
          ngq->last = &(item->el_next);
  }
  
  
  /*
   * This function 'cheats' in that it first tries to 'grab' the use of the
   * node, without going through the mutex. We can do this becasue of the
   * semantics of the lock. The semantics include a clause that says that the
   * value of the readers count is invalid if the WRITER_ACTIVE flag is set. It
   * also says that the WRITER_ACTIVE flag cannot be set if the readers count
   * is not zero. Note that this talks about what is valid to SET the
   * WRITER_ACTIVE flag, because from the moment it is set, the value if the
   * reader count is immaterial, and not valid. The two 'pending' flags have a
   * similar effect, in that If they are orthogonal to the two active fields in
   * how they are set, but if either is set, the attempted 'grab' need to be
   * backed out because there is earlier work, and we maintain ordering in the
   * queue. The result of this is that the reader request can try obtain use of
   * the node with only a single atomic addition, and without any of the mutex
   * overhead. If this fails the operation degenerates to the same as for other
   * cases.
   *
   */
  static __inline item_p
  ng_acquire_read(struct ng_queue *ngq, item_p item)
  {
  
          /* ######### Hack alert ######### */
          atomic_add_long(&ngq->q_flags, READER_INCREMENT);
          if ((ngq->q_flags & NGQ_RMASK) == 0) {
                  /* Successfully grabbed node */
                  return (item);
          }
          /* undo the damage if we didn't succeed */
          atomic_subtract_long(&ngq->q_flags, READER_INCREMENT);
  
          /* ######### End Hack alert ######### */
          mtx_lock_spin((&ngq->q_mtx));
          /*
           * Try again. Another processor (or interrupt for that matter) may
           * have removed the last queued item that was stopping us from
           * running, between the previous test, and the moment that we took
           * the mutex. (Or maybe a writer completed.)
           */
          if ((ngq->q_flags & NGQ_RMASK) == 0) {
                  atomic_add_long(&ngq->q_flags, READER_INCREMENT);
                  mtx_unlock_spin((&ngq->q_mtx));
                  return (item);
          }
  
          /*
           * and queue the request for later.
           */
          item->el_flags |= NGQF_READER;
          ng_queue_rw(ngq, item, NGQRW_R);
  
          /*
           * Ok, so that's the item successfully queued for later. So now we
           * see if we can dequeue something to run instead.
           */
          item = ng_dequeue(ngq);
          mtx_unlock_spin(&(ngq->q_mtx));
          return (item);
  }
  
  static __inline item_p
  ng_acquire_write(struct ng_queue *ngq, item_p item)
  {
  restart:
          mtx_lock_spin(&(ngq->q_mtx));
          /*
           * If there are no readers, no writer, and no pending packets, then
           * we can just go ahead. In all other situations we need to queue the
           * request
           */
          if ((ngq->q_flags & NGQ_WMASK) == 0) {
                  atomic_add_long(&ngq->q_flags, WRITER_ACTIVE);
                  mtx_unlock_spin((&ngq->q_mtx));
                  if (ngq->q_flags & READER_MASK) {
                          /* Collision with fast-track reader */
                          atomic_subtract_long(&ngq->q_flags, WRITER_ACTIVE);
                          goto restart;
                  }
                  return (item);
          }
  
          /*
           * and queue the request for later.
           */
          item->el_flags &= ~NGQF_RW;
          ng_queue_rw(ngq, item, NGQRW_W);
  
          /*
           * Ok, so that's the item successfully queued for later. So now we
           * see if we can dequeue something to run instead.
           */
          item = ng_dequeue(ngq);
          mtx_unlock_spin(&(ngq->q_mtx));
          return (item);
  }
  
  static __inline void
  ng_leave_read(struct ng_queue *ngq)
  {
          atomic_subtract_long(&ngq->q_flags, READER_INCREMENT);
  }
  
  static __inline void
  ng_leave_write(struct ng_queue *ngq)
  {
          atomic_subtract_long(&ngq->q_flags, WRITER_ACTIVE);
  }
  
  static void
  ng_flush_input_queue(struct ng_queue * ngq)
  {
          item_p item;
          u_int           add_arg;
          mtx_lock_spin(&ngq->q_mtx);
          for (;;) {
                  /* Now take a look at what's on the queue */
                  if (ngq->q_flags & READ_PENDING) {
                          add_arg = -READ_PENDING;
                  } else if (ngq->q_flags & WRITE_PENDING) {
                          add_arg = -WRITE_PENDING;
                  } else {
                          break;
                  }
  
                  item = ngq->queue;
                  ngq->queue = item->el_next;
                  if (ngq->last == &(item->el_next)) {
                          ngq->last = &(ngq->queue);
                  } else {
                          if ((ngq->queue->el_flags & NGQF_RW) == NGQF_READER) {
                                  add_arg += READ_PENDING;
                          } else {
                                  add_arg += WRITE_PENDING;
                          }
                  }
                  atomic_add_long(&ngq->q_flags, add_arg);
  
                  mtx_unlock_spin(&ngq->q_mtx);
                  NG_FREE_ITEM(item);
                  mtx_lock_spin(&ngq->q_mtx);
          }
          /*
           * Take us off the work queue if we are there.
           * We definatly have no work to be done.
           */
          ng_worklist_remove(ngq->q_node);
          mtx_unlock_spin(&ngq->q_mtx);
  }
  
  /***********************************************************************
  * Externally visible method for sending or queueing messages or data.
  ***********************************************************************/
  
  /*
   * The module code should have filled out the item correctly by this stage:
   * Common:
   *    reference to destination node.
   *    Reference to destination rcv hook if relevant.
   * Data:
   *    pointer to mbuf
   * Control_Message:
   *    pointer to msg.
   *    ID of original sender node. (return address)
   * Function:
   *    Function pointer
   *    void * argument
   *    integer argument
   *
   * The nodes have several routines and macros to help with this task:
   */
  
  int
  ng_snd_item(item_p item, int queue)
  {
          hook_p hook = NGI_HOOK(item);
          node_p node = NGI_NODE(item);
          int rw;
          int error = 0, ierror;
          item_p  oitem;
          struct ng_queue * ngq = &node->nd_input_queue;
  
  #ifdef  NETGRAPH_DEBUG
          _ngi_check(item, __FILE__, __LINE__);
  #endif
  
          if (item == NULL) {
                  TRAP_ERROR();
                  return (EINVAL);        /* failed to get queue element */
          }
          if (node == NULL) {
                  NG_FREE_ITEM(item);
                  TRAP_ERROR();
                  return (EINVAL);        /* No address */
          }
          switch(item->el_flags & NGQF_TYPE) {
          case NGQF_DATA:
                  /*
                   * DATA MESSAGE
                   * Delivered to a node via a non-optional hook.
                   * Both should be present in the item even though
                   * the node is derivable from the hook.
                   * References are held on both by the item.
                   */
  
                  /* Protect nodes from sending NULL pointers
                   * to each other
                   */
                  if (NGI_M(item) == NULL)
                          return (EINVAL);
  
                  CHECK_DATA_MBUF(NGI_M(item));
                  if (hook == NULL) {
                          NG_FREE_ITEM(item);
                          TRAP_ERROR();
                          return(EINVAL);
                  }
                  if ((NG_HOOK_NOT_VALID(hook))
                  || (NG_NODE_NOT_VALID(NG_HOOK_NODE(hook)))) {
                          NG_FREE_ITEM(item);
                          return (ENOTCONN);
                  }
                  if ((hook->hk_flags & HK_QUEUE)) {
                          queue = 1;
                  }
                  /* By default data is a reader in the locking scheme */
                  item->el_flags |= NGQF_READER;
                  rw = NGQRW_R;
                  break;
          case NGQF_MESG:
                  /*
                   * CONTROL MESSAGE
                   * Delivered to a node.
                   * Hook is optional.
                   * References are held by the item on the node and
                   * the hook if it is present.
                   */
                  if (hook && (hook->hk_flags & HK_QUEUE)) {
                          queue = 1;
                  }
                  /* Data messages count as writers unles explicitly exempted */
                  if (NGI_MSG(item)->header.cmd & NGM_READONLY) {
                          item->el_flags |= NGQF_READER;
                          rw = NGQRW_R;
                  } else {
                          item->el_flags &= ~NGQF_RW;
                          rw = NGQRW_W;
                  }
                  break;
          case NGQF_FN:
                  item->el_flags &= ~NGQF_RW;
                  rw = NGQRW_W;
                  break;
          default:
                  NG_FREE_ITEM(item);
                  TRAP_ERROR();
                  return (EINVAL);
          }
          /*
           * If the node specifies single threading, force writer semantics
           * Similarly the node may say one hook always produces writers.
           * These are over-rides.
           */
          if ((node->nd_flags & NGF_FORCE_WRITER)
          || (hook && (hook->hk_flags & HK_FORCE_WRITER))) {
                          rw = NGQRW_W;
                          item->el_flags &= ~NGQF_READER;
          }
          if (queue) {
                  /* Put it on the queue for that node*/
  #ifdef  NETGRAPH_DEBUG
          _ngi_check(item, __FILE__, __LINE__);
  #endif
                  mtx_lock_spin(&(ngq->q_mtx));
                  ng_queue_rw(ngq, item, rw);
                  /*
                   * If there are active elements then we can rely on
                   * them. if not we should not rely on another packet
                   * coming here by another path,
                   * so it is best to put us in the netisr list.
                   * We can take the worklist lock with the node locked
                   * BUT NOT THE REVERSE!
                   */
                  if (CAN_GET_WORK(ngq->q_flags)) {
                          ng_setisr(node);
                  }
                  mtx_unlock_spin(&(ngq->q_mtx));
                  return (0);
          }
          /*
           * Take a queue item and a node and see if we can apply the item to
           * the node. We may end up getting a different item to apply instead.
           * Will allow for a piggyback reply only in the case where
           * there is no queueing.
           */
  
          oitem = item;
          /*
           * We already decided how we will be queueud or treated.
           * Try get the appropriate operating permission.
           */
          if (rw == NGQRW_R) {
                  item = ng_acquire_read(ngq, item);
          } else {
                  item = ng_acquire_write(ngq, item);
          }
  
          /*
           * May have come back with a different item.
           * or maybe none at all. The one we started with will
           * have been queued in thises cases.
           */
          if (item == NULL) {
                  return (0);
          }
  
  #ifdef  NETGRAPH_DEBUG
          _ngi_check(item, __FILE__, __LINE__);
  #endif
          /*
           * Take over the reference frm the item.
           * Hold it until the called function returns.
           */
          NGI_GET_NODE(item, node); /* zaps stored node */
  
          ierror = ng_apply_item(node, item); /* drops r/w lock when done */
  
          /* only return an error if it was our initial item.. (compat hack) */
          if (oitem == item) {
                  error = ierror;
          }
  
          /*
           * If the node goes away when we remove the reference, 
           * whatever we just did caused it.. whatever we do, DO NOT
           * access the node again!
           */
          if (NG_NODE_UNREF(node) == 0) {
                  return (error);
          }
  
          /*
           * Now we've handled the packet we brought, (or a friend of it) let's
           * look for any other packets that may have been queued up. We hold
           * no locks, so if someone puts something in the queue after
           * we check that it is empty, it is their problem
           * to ensure it is processed. If we have the netisr thread cme in here
           * while we still say we have stuff to do, we may get a boost
           * in SMP systems. :-)
           */
          for (;;) {
                  /*
                   * dequeue acquires and adjusts the input_queue as it dequeues
                   * packets. It acquires the rw lock as needed.
                   */
                  mtx_lock_spin(&ngq->q_mtx);
                  item = ng_dequeue(ngq); /* fixes worklist too*/
                  if (!item) {
                          mtx_unlock_spin(&ngq->q_mtx);
                          return (error);
                  }
                  mtx_unlock_spin(&ngq->q_mtx);
  
                  /*
                   * Take over the reference frm the item.
                   * Hold it until the called function returns.
                   */
  
                  NGI_GET_NODE(item, node); /* zaps stored node */
  
                  /*
                   * We have the appropriate lock, so run the item.
                   * When finished it will drop the lock accordingly
                   */
                  ierror = ng_apply_item(node, item);
  
                  /*
                   * only return an error if it was our initial
                   * item.. (compat hack)
                   */
                  if (oitem == item) {
                          error = ierror;
                  }
  
                  /*
                   * If the node goes away when we remove the reference, 
                   * whatever we just did caused it.. whatever we do, DO NOT
                   * access the node again!
                   */
                  if (NG_NODE_UNREF(node) == 0) {
                          break;
                  }
          }
          return (error);
  }
  
  /*
   * We have an item that was possibly queued somewhere.
   * It should contain all the information needed
   * to run it on the appropriate node/hook.
   */
  static int
  ng_apply_item(node_p node, item_p item)
  {
          hook_p  hook;
          int     was_reader = ((item->el_flags & NGQF_RW));
          int     error = 0;
          ng_rcvdata_t *rcvdata;
          ng_rcvmsg_t *rcvmsg;
  
          NGI_GET_HOOK(item, hook); /* clears stored hook */
  #ifdef  NETGRAPH_DEBUG
          _ngi_check(item, __FILE__, __LINE__);
  #endif
          switch (item->el_flags & NGQF_TYPE) {
          case NGQF_DATA:
                  /*
                   * Check things are still ok as when we were queued.
                   */
                  if ((hook == NULL)
                  || NG_HOOK_NOT_VALID(hook)
                  || NG_NODE_NOT_VALID(node) ) {
                          error = EIO;
                          NG_FREE_ITEM(item);
                          break;
                  }
                  /*
                   * If no receive method, just silently drop it.
                   * Give preference to the hook over-ride method
                   */
                  if ((!(rcvdata = hook->hk_rcvdata)) 
                  && (!(rcvdata = NG_HOOK_NODE(hook)->nd_type->rcvdata))) {
                          error = 0;
                          NG_FREE_ITEM(item);
                          break;
                  }
                  error = (*rcvdata)(hook, item);
                  break;
          case NGQF_MESG:
                  if (hook) {
                          if (NG_HOOK_NOT_VALID(hook)) {
                                  /*
                                   * The hook has been zapped then we can't
                                   * use it. Immediatly drop its reference.
                                   * The message may not need it.
                                   */
                                  NG_HOOK_UNREF(hook);
                                  hook = NULL;
                          }
                  }
                  /*
                   * Similarly, if the node is a zombie there is
                   * nothing we can do with it, drop everything.
                   */
                  if (NG_NODE_NOT_VALID(node)) {
                          TRAP_ERROR();
                          error = EINVAL;
                          NG_FREE_ITEM(item);
                  } else {
                          /*
                           * Call the appropriate message handler for the object.
                           * It is up to the message handler to free the message.
                           * If it's a generic message, handle it generically,
                           * otherwise call the type's message handler
                           * (if it exists)
                           * XXX (race). Remember that a queued message may
                           * reference a node or hook that has just been
                           * invalidated. It will exist as the queue code
                           * is holding a reference, but..
                           */
  
                          struct ng_mesg *msg = NGI_MSG(item);
  
                          /* 
                           * check if the generic handler owns it.
                           */
                          if ((msg->header.typecookie == NGM_GENERIC_COOKIE)
                          && ((msg->header.flags & NGF_RESP) == 0)) {
                                  error = ng_generic_msg(node, item, hook);
                                  break;
                          }
                          /*
                           * Now see if there is a handler (hook or node specific)
                           * in the target node. If none, silently discard.
                           */
                          if (((!hook) || (!(rcvmsg = hook->hk_rcvmsg)))
                          && (!(rcvmsg = node->nd_type->rcvmsg))) {
                                  TRAP_ERROR();
                                  error = 0; 
                                  NG_FREE_ITEM(item);
                                  break;
                          }
                          error = (*rcvmsg)(node, item, hook);
                  }
                  break;
          case NGQF_FN:
                  /*
                   *  We have to implicitly trust the hook,
                   * as some of these are used for system purposes
                   * where the hook is invalid. In the case of
                   * the shutdown message we allow it to hit
                   * even if the node is invalid.
                   */
                  if ((NG_NODE_NOT_VALID(node)) 
                  && (NGI_FN(item) != &ng_rmnode)) {
                          TRAP_ERROR();
                          error = EINVAL;
                          break;
                  }
                  (*NGI_FN(item))(node, hook, NGI_ARG1(item), NGI_ARG2(item));
                  NG_FREE_ITEM(item);
                  break;
                  
          }
          /*
           * We held references on some of the resources
           * that we took from the item. Now that we have
           * finished doing everything, drop those references.
           */
          if (hook) {
                  NG_HOOK_UNREF(hook);
          }
  
          if (was_reader) {
                  ng_leave_read(&node->nd_input_queue);
          } else {
                  ng_leave_write(&node->nd_input_queue);
          }
          return (error);
  }
  
  /***********************************************************************
   * Implement the 'generic' control messages
   ***********************************************************************/
  static int
  ng_generic_msg(node_p here, item_p item, hook_p lasthook)
  {
          int error = 0;
          struct ng_mesg *msg;
          struct ng_mesg *resp = NULL;
  
          NGI_GET_MSG(item, msg);
          if (msg->header.typecookie != NGM_GENERIC_COOKIE) {
                  TRAP_ERROR();
                  error = EINVAL;
                  goto out;
          }
          switch (msg->header.cmd) {
          case NGM_SHUTDOWN:
                  ng_rmnode(here, NULL, NULL, 0);
                  break;
          case NGM_MKPEER:
              {
                  struct ngm_mkpeer *const mkp = (struct ngm_mkpeer *) msg->data;
  
                  if (msg->header.arglen != sizeof(*mkp)) {
                          TRAP_ERROR();
                          error = EINVAL;
                          break;
                  }
                  mkp->type[sizeof(mkp->type) - 1] = '\0';
                  mkp->ourhook[sizeof(mkp->ourhook) - 1] = '\0';
                  mkp->peerhook[sizeof(mkp->peerhook) - 1] = '\0';
                  error = ng_mkpeer(here, mkp->ourhook, mkp->peerhook, mkp->type);
                  break;
              }
          case NGM_CONNECT:
              {
                  struct ngm_connect *const con =
                          (struct ngm_connect *) msg->data;
                  node_p node2;
  
                  if (msg->header.arglen != sizeof(*con)) {
                          TRAP_ERROR();
                          error = EINVAL;
                          break;
                  }
                  con->path[sizeof(con->path) - 1] = '\0';
                  con->ourhook[sizeof(con->ourhook) - 1] = '\0';
                  con->peerhook[sizeof(con->peerhook) - 1] = '\0';
                  /* Don't forget we get a reference.. */
                  error = ng_path2noderef(here, con->path, &node2, NULL);
                  if (error)
                          break;
                  error = ng_con_nodes(here, con->ourhook, node2, con->peerhook);
                  NG_NODE_UNREF(node2);
                  break;
              }
          case NGM_NAME:
              {
                  struct ngm_name *const nam = (struct ngm_name *) msg->data;
  
                  if (msg->header.arglen != sizeof(*nam)) {
                          TRAP_ERROR();
                          error = EINVAL;
                          break;
                  }
                  nam->name[sizeof(nam->name) - 1] = '\0';
                  error = ng_name_node(here, nam->name);
                  break;
              }
          case NGM_RMHOOK:
              {
                  struct ngm_rmhook *const rmh = (struct ngm_rmhook *) msg->data;
                  hook_p hook;
  
                  if (msg->header.arglen != sizeof(*rmh)) {
                          TRAP_ERROR();
                          error = EINVAL;
                          break;
                  }
                  rmh->ourhook[sizeof(rmh->ourhook) - 1] = '\0';
                  if ((hook = ng_findhook(here, rmh->ourhook)) != NULL)
                          ng_destroy_hook(hook);
                  break;
              }
          case NGM_NODEINFO:
              {
                  struct nodeinfo *ni;
  
                  NG_MKRESPONSE(resp, msg, sizeof(*ni), M_NOWAIT);
                  if (resp == NULL) {
                          error = ENOMEM;
                          break;
                  }
  
                  /* Fill in node info */
                  ni = (struct nodeinfo *) resp->data;
                  if (NG_NODE_HAS_NAME(here))
                          strcpy(ni->name, NG_NODE_NAME(here));
                  strcpy(ni->type, here->nd_type->name);
                  ni->id = ng_node2ID(here);
                  ni->hooks = here->nd_numhooks;
                  break;
              }
          case NGM_LISTHOOKS:
              {
                  const int nhooks = here->nd_numhooks;
                  struct hooklist *hl;
                  struct nodeinfo *ni;
                  hook_p hook;
  
                  /* Get response struct */
                  NG_MKRESPONSE(resp, msg, sizeof(*hl)
                      + (nhooks * sizeof(struct linkinfo)), M_NOWAIT);
                  if (resp == NULL) {
                          error = ENOMEM;
                          break;
                  }
                  hl = (struct hooklist *) resp->data;
                  ni = &hl->nodeinfo;
  
                  /* Fill in node info */
                  if (NG_NODE_HAS_NAME(here))
                          strcpy(ni->name, NG_NODE_NAME(here));
                  strcpy(ni->type, here->nd_type->name);
                  ni->id = ng_node2ID(here);
  
                  /* Cycle through the linked list of hooks */
                  ni->hooks = 0;
                  LIST_FOREACH(hook, &here->nd_hooks, hk_hooks) {
                          struct linkinfo *const link = &hl->link[ni->hooks];
  
                          if (ni->hooks >= nhooks) {
                                  log(LOG_ERR, "%s: number of %s changed\n",
                                      __func__, "hooks");
                                  break;
                          }
                          if (NG_HOOK_NOT_VALID(hook))
                                  continue;
                          strcpy(link->ourhook, NG_HOOK_NAME(hook));
                          strcpy(link->peerhook, NG_PEER_HOOK_NAME(hook));
                          if (NG_PEER_NODE_NAME(hook)[0] != '\0')
                                  strcpy(link->nodeinfo.name,
                                      NG_PEER_NODE_NAME(hook));
                          strcpy(link->nodeinfo.type,
                             NG_PEER_NODE(hook)->nd_type->name);
                          link->nodeinfo.id = ng_node2ID(NG_PEER_NODE(hook));
                          link->nodeinfo.hooks = NG_PEER_NODE(hook)->nd_numhooks;
                          ni->hooks++;
                  }
                  break;
              }
  
          case NGM_LISTNAMES:
          case NGM_LISTNODES:
              {
                  const int unnamed = (msg->header.cmd == NGM_LISTNODES);
                  struct namelist *nl;
                  node_p node;
                  int num = 0;
  
                  mtx_lock(&ng_nodelist_mtx);
                  /* Count number of nodes */
                  LIST_FOREACH(node, &ng_nodelist, nd_nodes) {
                          if (NG_NODE_IS_VALID(node)
                          && (unnamed || NG_NODE_HAS_NAME(node))) {
                                  num++;
                          }
                  }
                  mtx_unlock(&ng_nodelist_mtx);
  
                  /* Get response struct */
                  NG_MKRESPONSE(resp, msg, sizeof(*nl)
                      + (num * sizeof(struct nodeinfo)), M_NOWAIT);
                  if (resp == NULL) {
                          error = ENOMEM;
                          break;
                  }
                  nl = (struct namelist *) resp->data;
  
                  /* Cycle through the linked list of nodes */
                  nl->numnames = 0;
                  mtx_lock(&ng_nodelist_mtx);
                  LIST_FOREACH(node, &ng_nodelist, nd_nodes) {
                          struct nodeinfo *const np = &nl->nodeinfo[nl->numnames];
  
                          if (nl->numnames >= num) {
                                  log(LOG_ERR, "%s: number of %s changed\n",
                                      __func__, "nodes");
                                  break;
                          }
                          if (NG_NODE_NOT_VALID(node))
                                  continue;
                          if (!unnamed && (! NG_NODE_HAS_NAME(node)))
                                  continue;
                          if (NG_NODE_HAS_NAME(node))
                                  strcpy(np->name, NG_NODE_NAME(node));
                          strcpy(np->type, node->nd_type->name);
                          np->id = ng_node2ID(node);
                          np->hooks = node->nd_numhooks;
                          nl->numnames++;
                  }
                  mtx_unlock(&ng_nodelist_mtx);
                  break;
              }
  
          case NGM_LISTTYPES:
              {
                  struct typelist *tl;
                  struct ng_type *type;
                  int num = 0;
  
                  mtx_lock(&ng_typelist_mtx);
                  /* Count number of types */
                  LIST_FOREACH(type, &ng_typelist, types) {
                          num++;
                  }
                  mtx_unlock(&ng_typelist_mtx);
  
                  /* Get response struct */
                  NG_MKRESPONSE(resp, msg, sizeof(*tl)
                      + (num * sizeof(struct typeinfo)), M_NOWAIT);
                  if (resp == NULL) {
                          error = ENOMEM;
                          break;
                  }
                  tl = (struct typelist *) resp->data;
  
                  /* Cycle through the linked list of types */
                  tl->numtypes = 0;
                  mtx_lock(&ng_typelist_mtx);
                  LIST_FOREACH(type, &ng_typelist, types) {
                          struct typeinfo *const tp = &tl->typeinfo[tl->numtypes];
  
                          if (tl->numtypes >= num) {
                                  log(LOG_ERR, "%s: number of %s changed\n",
                                      __func__, "types");
                                  break;
                          }
                          strcpy(tp->type_name, type->name);
                          tp->numnodes = type->refs - 1; /* don't count list */
                          tl->numtypes++;
                  }
                  mtx_unlock(&ng_typelist_mtx);
                  break;
              }
  
          case NGM_BINARY2ASCII:
              {
                  int bufSize = 20 * 1024;        /* XXX hard coded constant */
                  const struct ng_parse_type *argstype;
                  const struct ng_cmdlist *c;
                  struct ng_mesg *binary, *ascii;
  
                  /* Data area must contain a valid netgraph message */
                  binary = (struct ng_mesg *)msg->data;
                  if (msg->header.arglen < sizeof(struct ng_mesg)
                      || (msg->header.arglen - sizeof(struct ng_mesg)
                        < binary->header.arglen)) {
                          TRAP_ERROR();
                          error = EINVAL;
                          break;
                  }
  
                  /* Get a response message with lots of room */
                  NG_MKRESPONSE(resp, msg, sizeof(*ascii) + bufSize, M_NOWAIT);
                  if (resp == NULL) {
                          error = ENOMEM;
                          break;
                  }
                  ascii = (struct ng_mesg *)resp->data;
  
                  /* Copy binary message header to response message payload */
                  bcopy(binary, ascii, sizeof(*binary));
  
                  /* Find command by matching typecookie and command number */
                  for (c = here->nd_type->cmdlist;
                      c != NULL && c->name != NULL; c++) {
                          if (binary->header.typecookie == c->cookie
                              && binary->header.cmd == c->cmd)
                                  break;
                  }
                  if (c == NULL || c->name == NULL) {
                          for (c = ng_generic_cmds; c->name != NULL; c++) {
                                  if (binary->header.typecookie == c->cookie
                                      && binary->header.cmd == c->cmd)
                                          break;
                          }
                          if (c->name == NULL) {
                                  NG_FREE_MSG(resp);
                                  error = ENOSYS;
                                  break;
                          }
                  }
  
                  /* Convert command name to ASCII */
                  snprintf(ascii->header.cmdstr, sizeof(ascii->header.cmdstr),
                      "%s", c->name);
  
                  /* Convert command arguments to ASCII */
                  argstype = (binary->header.flags & NGF_RESP) ?
                      c->respType : c->mesgType;
                  if (argstype == NULL) {
                          *ascii->data = '\0';
                  } else {
                          if ((error = ng_unparse(argstype,
                              (u_char *)binary->data,
                              ascii->data, bufSize)) != 0) {
                                  NG_FREE_MSG(resp);
                                  break;
                          }
                  }
  
                  /* Return the result as struct ng_mesg plus ASCII string */
                  bufSize = strlen(ascii->data) + 1;
                  ascii->header.arglen = bufSize;
                  resp->header.arglen = sizeof(*ascii) + bufSize;
                  break;
              }
  
          case NGM_ASCII2BINARY:
              {
                  int bufSize = 2000;     /* XXX hard coded constant */
                  const struct ng_cmdlist *c;
                  const struct ng_parse_type *argstype;
                  struct ng_mesg *ascii, *binary;
                  int off = 0;
  
                  /* Data area must contain at least a struct ng_mesg + '\0' */
                  ascii = (struct ng_mesg *)msg->data;
                  if ((msg->header.arglen < sizeof(*ascii) + 1)
                      || (ascii->header.arglen < 1)
                      || (msg->header.arglen
                        < sizeof(*ascii) + ascii->header.arglen)) {
                          TRAP_ERROR();
                          error = EINVAL;
                          break;
                  }
                  ascii->data[ascii->header.arglen - 1] = '\0';
  
                  /* Get a response message with lots of room */
                  NG_MKRESPONSE(resp, msg, sizeof(*binary) + bufSize, M_NOWAIT);
                  if (resp == NULL) {
                          error = ENOMEM;
                          break;
                  }
                  binary = (struct ng_mesg *)resp->data;
  
                  /* Copy ASCII message header to response message payload */
                  bcopy(ascii, binary, sizeof(*ascii));
  
                  /* Find command by matching ASCII command string */
                  for (c = here->nd_type->cmdlist;
                      c != NULL && c->name != NULL; c++) {
                          if (strcmp(ascii->header.cmdstr, c->name) == 0)
                                  break;
                  }
                  if (c == NULL || c->name == NULL) {
                          for (c = ng_generic_cmds; c->name != NULL; c++) {
                                  if (strcmp(ascii->header.cmdstr, c->name) == 0)
                                          break;
                          }
                          if (c->name == NULL) {
                                  NG_FREE_MSG(resp);
                                  error = ENOSYS;
                                  break;
                          }
                  }
  
                  /* Convert command name to binary */
                  binary->header.cmd = c->cmd;
                  binary->header.typecookie = c->cookie;
  
                  /* Convert command arguments to binary */
                  argstype = (binary->header.flags & NGF_RESP) ?
                      c->respType : c->mesgType;
                  if (argstype == NULL) {
                          bufSize = 0;
                  } else {
                          if ((error = ng_parse(argstype, ascii->data,
                              &off, (u_char *)binary->data, &bufSize)) != 0) {
                                  NG_FREE_MSG(resp);
                                  break;
                          }
                  }
  
                  /* Return the result */
                  binary->header.arglen = bufSize;
                  resp->header.arglen = sizeof(*binary) + bufSize;
                  break;
              }
  
          case NGM_TEXT_CONFIG:
          case NGM_TEXT_STATUS:
                  /*
                   * This one is tricky as it passes the command down to the
                   * actual node, even though it is a generic type command.
                   * This means we must assume that the item/msg is already freed
                   * when control passes back to us.
                   */
                  if (here->nd_type->rcvmsg != NULL) {
                          NGI_MSG(item) = msg; /* put it back as we found it */
                          return((*here->nd_type->rcvmsg)(here, item, lasthook));
                  }
                  /* Fall through if rcvmsg not supported */
          default:
                  TRAP_ERROR();
                  error = EINVAL;
          }
          /*
           * Sometimes a generic message may be statically allocated
           * to avoid problems with allocating when in tight memeory situations.
           * Don't free it if it is so.
           * I break them appart here, because erros may cause a free if the item
           * in which case we'd be doing it twice.
           * they are kept together above, to simplify freeing.
           */
  out:
          NG_RESPOND_MSG(error, here, item, resp);
          if (msg)
                  NG_FREE_MSG(msg);
          return (error);
  }
  
  /************************************************************************
                          Module routines
  ************************************************************************/
  
  /*
   * Handle the loading/unloading of a netgraph node type module
   */
  int
  ng_mod_event(module_t mod, int event, void *data)
  {
          struct ng_type *const type = data;
          int s, error = 0;
  
          switch (event) {
          case MOD_LOAD:
  
                  /* Register new netgraph node type */
                  s = splnet();
                  if ((error = ng_newtype(type)) != 0) {
                          splx(s);
                          break;
                  }
  
                  /* Call type specific code */
                  if (type->mod_event != NULL)
                          if ((error = (*type->mod_event)(mod, event, data))) {
                                  mtx_lock(&ng_typelist_mtx);
                                  type->refs--;   /* undo it */
                                  LIST_REMOVE(type, types);
                                  mtx_unlock(&ng_typelist_mtx);
                          }
                  splx(s);
                  break;
  
          case MOD_UNLOAD:
                  s = splnet();
                  if (type->refs > 1) {           /* make sure no nodes exist! */
                          error = EBUSY;
                  } else {
                          if (type->refs == 0) {
                                  /* failed load, nothing to undo */
                                  splx(s);
                                  break;
                          }
                          if (type->mod_event != NULL) {  /* check with type */
                                  error = (*type->mod_event)(mod, event, data);
                                  if (error != 0) {       /* type refuses.. */
                                          splx(s);
                                          break;
                                  }
                          }
                          mtx_lock(&ng_typelist_mtx);
                          LIST_REMOVE(type, types);
                          mtx_unlock(&ng_typelist_mtx);
                  }
                  splx(s);
                  break;
  
          default:
                  if (type->mod_event != NULL)
                          error = (*type->mod_event)(mod, event, data);
                  else
                          error = EOPNOTSUPP;             /* XXX ? */
                  break;
          }
          return (error);
  }
  
  /*
   * Handle loading and unloading for this code.
   * The only thing we need to link into is the NETISR strucure.
   */
  static int
  ngb_mod_event(module_t mod, int event, void *data)
  {
          int s, error = 0;
  
          switch (event) {
          case MOD_LOAD:
                  /* Register line discipline */
                  mtx_init(&ng_worklist_mtx, "ng_worklist", NULL, MTX_SPIN);
                  mtx_init(&ng_typelist_mtx, "netgraph types mutex", NULL,
                      MTX_DEF);
                  mtx_init(&ng_nodelist_mtx, "netgraph nodelist mutex", NULL,
                      MTX_DEF);
                  mtx_init(&ng_idhash_mtx, "netgraph idhash mutex", NULL,
                      MTX_DEF);
                  mtx_init(&ngq_mtx, "netgraph free item list mutex", NULL,
                      MTX_DEF);
                  s = splimp();
                  /* XXX could use NETISR_MPSAFE but need to verify code */
                  netisr_register(NETISR_NETGRAPH, (netisr_t *)ngintr, NULL, 0);
                  splx(s);
                  break;
          case MOD_UNLOAD:
                  /* You cant unload it because an interface may be using it.  */
                  error = EBUSY;
                  break;
          default:
                  error = EOPNOTSUPP;
                  break;
          }
          return (error);
  }
  
  static moduledata_t netgraph_mod = {
          "netgraph",
          ngb_mod_event,
          (NULL)
  };
  DECLARE_MODULE(netgraph, netgraph_mod, SI_SUB_DRIVERS, SI_ORDER_MIDDLE);
  SYSCTL_NODE(_net, OID_AUTO, graph, CTLFLAG_RW, 0, "netgraph Family");
  SYSCTL_INT(_net_graph, OID_AUTO, abi_version, CTLFLAG_RD, 0, NG_ABI_VERSION,"");
  SYSCTL_INT(_net_graph, OID_AUTO, msg_version, CTLFLAG_RD, 0, NG_VERSION, "");
  
  /************************************************************************
                          Queue element get/free routines
  ************************************************************************/
  
  
  static int                      allocated;      /* number of items malloc'd */
  
  static int                      maxalloc = 128; /* limit the damage of a leak */
  static int                      ngqfreemax = 64;/* cache at most this many */
  
  TUNABLE_INT("net.graph.maxalloc", &maxalloc);
  SYSCTL_INT(_net_graph, OID_AUTO, maxalloc, CTLFLAG_RDTUN, &maxalloc,
      0, "Maximum number of queue items to allocate");
  
  TUNABLE_INT("net.graph.ngqfreemax", &ngqfreemax);
  SYSCTL_INT(_net_graph, OID_AUTO, ngqfreemax, CTLFLAG_RDTUN, &ngqfreemax,
      0, "Maximum number of free queue items to cache");
  
  static const int                ngqfreelow = 4; /* try malloc if free < this */
  static volatile int             ngqfreesize;    /* number of cached entries */
  static volatile item_p          ngqfree;        /* free ones */
  
  #ifdef  NETGRAPH_DEBUG
  static TAILQ_HEAD(, ng_item) ng_itemlist = TAILQ_HEAD_INITIALIZER(ng_itemlist);
  #endif
  /*
   * Get a queue entry
   * This is usually called when a packet first enters netgraph.
   * By definition, this is usually from an interrupt, or from a user.
   * Users are not so important, but try be quick for the times that it's
   * an interrupt.
   * XXX If reserve is low, we should try to get 2 from malloc as this
   * would indicate it often fails.
   */
  static item_p
  ng_getqblk(void)
  {
          item_p item = NULL;
  
          /*
           * Try get a cached queue block, or else allocate a new one
           * If we are less than our reserve, try malloc. If malloc
           * fails, then that's what the reserve is for...
           * We have our little reserve
           * because we use M_NOWAIT for malloc. This just helps us
           * avoid dropping packets while not increasing the time
           * we take to service the interrupt (on average) (I hope).
           */
          mtx_lock(&ngq_mtx);
  
          if ((ngqfreesize < ngqfreelow) || (ngqfree == NULL)) {
                  if (allocated < maxalloc) {  /* don't leak forever */
                          MALLOC(item, item_p ,
                              sizeof(*item), M_NETGRAPH_ITEM,
                              (M_NOWAIT | M_ZERO));
                          if (item) {
  #ifdef  NETGRAPH_DEBUG
                                  TAILQ_INSERT_TAIL(&ng_itemlist, item, all);
  #endif  /* NETGRAPH_DEBUG */
                                  allocated++;
                          }
                  }
          }
  
          /*
           * We didn't or couldn't malloc.
           * try get one from our cache.
           */
          if (item == NULL && (item = ngqfree) != NULL) {
                  ngqfree = item->el_next;
                  ngqfreesize--;
                  item->el_flags &= ~NGQF_FREE;
          }
  
          mtx_unlock(&ngq_mtx);
          return (item);
  }
  
  /*
   * Release a queue entry
   */
  void
  ng_free_item(item_p item)
  {
  
          /*
           * The item may hold resources on it's own. We need to free
           * these before we can free the item. What they are depends upon
           * what kind of item it is. it is important that nodes zero
           * out pointers to resources that they remove from the item
           * or we release them again here.
           */
          if (item->el_flags & NGQF_FREE) {
                  panic(" Freeing free queue item");
          }
          switch (item->el_flags & NGQF_TYPE) {
          case NGQF_DATA:
                  /* If we have an mbuf still attached.. */
                  NG_FREE_M(_NGI_M(item));
                  break;
          case NGQF_MESG:
                  _NGI_RETADDR(item) = 0;
                  NG_FREE_MSG(_NGI_MSG(item));
                  break;
          case NGQF_FN:
                  /* nothing to free really, */
                  _NGI_FN(item) = NULL;
                  _NGI_ARG1(item) = NULL;
                  _NGI_ARG2(item) = 0;
          case NGQF_UNDEF:
                  break;
          }
          /* If we still have a node or hook referenced... */
          _NGI_CLR_NODE(item);
          _NGI_CLR_HOOK(item);
          item->el_flags |= NGQF_FREE;
  
          mtx_lock(&ngq_mtx);
          if (ngqfreesize < ngqfreemax) {
                  ngqfreesize++;
                  item->el_next = ngqfree;
                  ngqfree = item;
          } else {
  #ifdef  NETGRAPH_DEBUG
                  TAILQ_REMOVE(&ng_itemlist, item, all);
  #endif  /* NETGRAPH_DEBUG */
                  NG_FREE_ITEM_REAL(item);
                  allocated--;
          }
          mtx_unlock(&ngq_mtx);
  }
  
  #ifdef  NETGRAPH_DEBUG
  void
  dumphook (hook_p hook, char *file, int line)
  {
          printf("hook: name %s, %d refs, Last touched:\n",
                  _NG_HOOK_NAME(hook), hook->hk_refs);
          printf("        Last active @ %s, line %d\n",
                  hook->lastfile, hook->lastline);
          if (line) {
                  printf(" problem discovered at file %s, line %d\n", file, line);
          }
  }
  
  void
  dumpnode(node_p node, char *file, int line)
  {
          printf("node: ID [%x]: type '%s', %d hooks, flags 0x%x, %d refs, %s:\n",
                  _NG_NODE_ID(node), node->nd_type->name,
                  node->nd_numhooks, node->nd_flags,
                  node->nd_refs, node->nd_name);
          printf("        Last active @ %s, line %d\n",
                  node->lastfile, node->lastline);
          if (line) {
                  printf(" problem discovered at file %s, line %d\n", file, line);
          }
  }
  
  void
  dumpitem(item_p item, char *file, int line)
  {
          if (item->el_flags & NGQF_FREE) {
                  printf(" Free item, freed at %s, line %d\n",
                          item->lastfile, item->lastline);
          } else {
                  printf(" ACTIVE item, last used at %s, line %d",
                          item->lastfile, item->lastline);
                  switch(item->el_flags & NGQF_TYPE) {
                  case NGQF_DATA:
                          printf(" - [data]\n");
                          break;
                  case NGQF_MESG:
                          printf(" - retaddr[%d]:\n", _NGI_RETADDR(item));
                          break;
                  case NGQF_FN:
                          printf(" - fn@%p (%p, %p, %p, %d (%x))\n",
                                  item->body.fn.fn_fn,
                                  NGI_NODE(item),
                                  NGI_HOOK(item),
                                  item->body.fn.fn_arg1,
                                  item->body.fn.fn_arg2,
                                  item->body.fn.fn_arg2);
                          break;
                  case NGQF_UNDEF:
                          printf(" - UNDEFINED!\n");
                  }
          }
          if (line) {
                  printf(" problem discovered at file %s, line %d\n", file, line);
                  if (NGI_NODE(item)) {
                          printf("node %p ([%x])\n",
                                  NGI_NODE(item), ng_node2ID(NGI_NODE(item)));
                  }
          }
  }
  
  static void
  ng_dumpitems(void)
  {
          item_p item;
          int i = 1;
          TAILQ_FOREACH(item, &ng_itemlist, all) {
                  printf("[%d] ", i++);
                  dumpitem(item, NULL, 0);
          }
  }
  
  static void
  ng_dumpnodes(void)
  {
          node_p node;
          int i = 1;
          mtx_lock(&ng_nodelist_mtx);
          SLIST_FOREACH(node, &ng_allnodes, nd_all) {
                  printf("[%d] ", i++);
                  dumpnode(node, NULL, 0);
          }
          mtx_unlock(&ng_nodelist_mtx);
  }
  
  static void
  ng_dumphooks(void)
  {
          hook_p hook;
          int i = 1;
          mtx_lock(&ng_nodelist_mtx);
          SLIST_FOREACH(hook, &ng_allhooks, hk_all) {
                  printf("[%d] ", i++);
                  dumphook(hook, NULL, 0);
          }
          mtx_unlock(&ng_nodelist_mtx);
  }
  
  static int
  sysctl_debug_ng_dump_items(SYSCTL_HANDLER_ARGS)
  {
          int error;
          int val;
          int i;
  
          val = allocated;
          i = 1;
          error = sysctl_handle_int(oidp, &val, sizeof(int), req);
          if (error != 0 || req->newptr == NULL)
                  return (error);
          if (val == 42) {
                  ng_dumpitems();
                  ng_dumpnodes();
                  ng_dumphooks();
          }
          return (0);
  }
  
  SYSCTL_PROC(_debug, OID_AUTO, ng_dump_items, CTLTYPE_INT | CTLFLAG_RW,
      0, sizeof(int), sysctl_debug_ng_dump_items, "I", "Number of allocated items");
  #endif  /* NETGRAPH_DEBUG */
  
  
  /***********************************************************************
  * Worklist routines
  **********************************************************************/
  /* NETISR thread enters here */
  /*
   * Pick a node off the list of nodes with work,
   * try get an item to process off it.
   * If there are no more, remove the node from the list.
   */
  static void
  ngintr(void)
  {
          item_p item;
          node_p  node = NULL;
  
          for (;;) {
                  mtx_lock_spin(&ng_worklist_mtx);
                  node = TAILQ_FIRST(&ng_worklist);
                  if (!node) {
                          mtx_unlock_spin(&ng_worklist_mtx);
                          break;
                  }
                  node->nd_flags &= ~NGF_WORKQ;   
                  TAILQ_REMOVE(&ng_worklist, node, nd_work);
                  mtx_unlock_spin(&ng_worklist_mtx);
                  /*
                   * We have the node. We also take over the reference
                   * that the list had on it.
                   * Now process as much as you can, until it won't
                   * let you have another item off the queue.
                   * All this time, keep the reference
                   * that lets us be sure that the node still exists.
                   * Let the reference go at the last minute.
                   * ng_dequeue will put us back on the worklist
                   * if there is more too do. This may be of use if there
                   * are Multiple Processors and multiple Net threads in the 
                   * future.
                   */
                  for (;;) {
                          mtx_lock_spin(&node->nd_input_queue.q_mtx);
                          item = ng_dequeue(&node->nd_input_queue);
                          if (item == NULL) {
                                  mtx_unlock_spin(&node->nd_input_queue.q_mtx);
                                  break; /* go look for another node */
                          } else {
                                  mtx_unlock_spin(&node->nd_input_queue.q_mtx);
                                  NGI_GET_NODE(item, node); /* zaps stored node */
                                  ng_apply_item(node, item);
                                  NG_NODE_UNREF(node);
                          }
                  }
                  NG_NODE_UNREF(node);
          }
  }
  
  static void
  ng_worklist_remove(node_p node)
  {
          mtx_lock_spin(&ng_worklist_mtx);
          if (node->nd_flags & NGF_WORKQ) {
                  node->nd_flags &= ~NGF_WORKQ;
                  TAILQ_REMOVE(&ng_worklist, node, nd_work);
                  mtx_unlock_spin(&ng_worklist_mtx);
                  NG_NODE_UNREF(node);
          } else {
                  mtx_unlock_spin(&ng_worklist_mtx);
          }
  }
  
  /*
   * XXX
   * It's posible that a debugging NG_NODE_REF may need
   * to be outside the mutex zone
   */
  static void
  ng_setisr(node_p node)
  {
          mtx_lock_spin(&ng_worklist_mtx);
          if ((node->nd_flags & NGF_WORKQ) == 0) {
                  /*
                   * If we are not already on the work queue,
                   * then put us on.
                   */
                  node->nd_flags |= NGF_WORKQ;
                  TAILQ_INSERT_TAIL(&ng_worklist, node, nd_work);
                  NG_NODE_REF(node); /* XXX fafe in mutex? */
          }
          mtx_unlock_spin(&ng_worklist_mtx);
          schednetisr(NETISR_NETGRAPH);
  }
  
  
  /***********************************************************************
  * Externally useable functions to set up a queue item ready for sending
  ***********************************************************************/
  
  #ifdef  NETGRAPH_DEBUG
  #define ITEM_DEBUG_CHECKS                                               \
          do {                                                            \
                  if (NGI_NODE(item) ) {                                  \
                          printf("item already has node");                \
                          kdb_enter("has node");                          \
                          NGI_CLR_NODE(item);                             \
                  }                                                       \
                  if (NGI_HOOK(item) ) {                                  \
                          printf("item already has hook");                \
                          kdb_enter("has hook");                          \
                          NGI_CLR_HOOK(item);                             \
                  }                                                       \
          } while (0)
  #else
  #define ITEM_DEBUG_CHECKS
  #endif
  
  /*
   * Put mbuf into the item.
   * Hook and node references will be removed when the item is dequeued.
   * (or equivalent)
   * (XXX) Unsafe because no reference held by peer on remote node.
   * remote node might go away in this timescale.
   * We know the hooks can't go away because that would require getting
   * a writer item on both nodes and we must have at least a  reader
   * here to eb able to do this.
   * Note that the hook loaded is the REMOTE hook.
   *
   * This is possibly in the critical path for new data.
   */
  item_p
  ng_package_data(struct mbuf *m, void *dummy)
  {
          item_p item;
  
          if ((item = ng_getqblk()) == NULL) {
                  NG_FREE_M(m);
                  return (NULL);
          }
          ITEM_DEBUG_CHECKS;
          item->el_flags = NGQF_DATA;
          item->el_next = NULL;
          NGI_M(item) = m;
          return (item);
  }
  
  /*
   * Allocate a queue item and put items into it..
   * Evaluate the address as this will be needed to queue it and
   * to work out what some of the fields should be.
   * Hook and node references will be removed when the item is dequeued.
   * (or equivalent)
   */
  item_p
  ng_package_msg(struct ng_mesg *msg)
  {
          item_p item;
  
          if ((item = ng_getqblk()) == NULL) {
                  NG_FREE_MSG(msg);
                  return (NULL);
          }
          ITEM_DEBUG_CHECKS;
          item->el_flags = NGQF_MESG;
          item->el_next = NULL;
          /*
           * Set the current lasthook into the queue item
           */
          NGI_MSG(item) = msg;
          NGI_RETADDR(item) = 0;
          return (item);
  }
  
  
  
  #define SET_RETADDR(item, here, retaddr)                                \
          do {    /* Data or fn items don't have retaddrs */              \
                  if ((item->el_flags & NGQF_TYPE) == NGQF_MESG) {        \
                          if (retaddr) {                                  \
                                  NGI_RETADDR(item) = retaddr;            \
                          } else {                                        \
                                  /*                                      \
                                   * The old return address should be ok. \
                                   * If there isn't one, use the address  \
                                   * here.                                \
                                   */                                     \
                                  if (NGI_RETADDR(item) == 0) {           \
                                          NGI_RETADDR(item)               \
                                                  = ng_node2ID(here);     \
                                  }                                       \
                          }                                               \
                  }                                                       \
          } while (0)
  
  int
  ng_address_hook(node_p here, item_p item, hook_p hook, ng_ID_t retaddr)
  {
          hook_p peer;
          node_p peernode;
          ITEM_DEBUG_CHECKS;
          /*
           * Quick sanity check..
           * Since a hook holds a reference on it's node, once we know
           * that the peer is still connected (even if invalid,) we know
           * that the peer node is present, though maybe invalid.
           */
          if ((hook == NULL)
          || NG_HOOK_NOT_VALID(hook)
          || (NG_HOOK_PEER(hook) == NULL)
          || NG_HOOK_NOT_VALID(NG_HOOK_PEER(hook))
          || NG_NODE_NOT_VALID(NG_PEER_NODE(hook))) {
                  NG_FREE_ITEM(item);
                  TRAP_ERROR();
                  return (ENETDOWN);
          }
  
          /*
           * Transfer our interest to the other (peer) end.
           */
          peer = NG_HOOK_PEER(hook);
          NG_HOOK_REF(peer);
          NGI_SET_HOOK(item, peer);
          peernode = NG_PEER_NODE(hook);
          NG_NODE_REF(peernode);
          NGI_SET_NODE(item, peernode);
          SET_RETADDR(item, here, retaddr);
          return (0);
  }
  
  int
  ng_address_path(node_p here, item_p item, char *address, ng_ID_t retaddr) 
  {
          node_p  dest = NULL;
          hook_p  hook = NULL;
          int     error;
  
          ITEM_DEBUG_CHECKS;
          /*
           * Note that ng_path2noderef increments the reference count
           * on the node for us if it finds one. So we don't have to.
           */
          error = ng_path2noderef(here, address, &dest, &hook);
          if (error) {
                  NG_FREE_ITEM(item);
                  return (error);
          }
          NGI_SET_NODE(item, dest);
          if ( hook) {
                  NG_HOOK_REF(hook);      /* don't let it go while on the queue */
                  NGI_SET_HOOK(item, hook);
          }
          SET_RETADDR(item, here, retaddr);
          return (0);
  }
  
  int
  ng_address_ID(node_p here, item_p item, ng_ID_t ID, ng_ID_t retaddr)
  {
          node_p dest;
  
          ITEM_DEBUG_CHECKS;
          /*
           * Find the target node.
           */
          dest = ng_ID2noderef(ID); /* GETS REFERENCE! */
          if (dest == NULL) {
                  NG_FREE_ITEM(item);
                  TRAP_ERROR();
                  return(EINVAL);
          }
          /* Fill out the contents */
          item->el_flags = NGQF_MESG;
          item->el_next = NULL;
          NGI_SET_NODE(item, dest);
          NGI_CLR_HOOK(item);
          SET_RETADDR(item, here, retaddr);
          return (0);
  }
  
  /*
   * special case to send a message to self (e.g. destroy node)
   * Possibly indicate an arrival hook too.
   * Useful for removing that hook :-)
   */
  item_p
  ng_package_msg_self(node_p here, hook_p hook, struct ng_mesg *msg)
  {
          item_p item;
  
          /*
           * Find the target node.
           * If there is a HOOK argument, then use that in preference
           * to the address.
           */
          if ((item = ng_getqblk()) == NULL) {
                  NG_FREE_MSG(msg);
                  return (NULL);
          }
  
          /* Fill out the contents */
          item->el_flags = NGQF_MESG;
          item->el_next = NULL;
          NG_NODE_REF(here);
          NGI_SET_NODE(item, here);
          if (hook) {
                  NG_HOOK_REF(hook);
                  NGI_SET_HOOK(item, hook);
          }
          NGI_MSG(item) = msg;
          NGI_RETADDR(item) = ng_node2ID(here);
          return (item);
  }
  
  int
  ng_send_fn(node_p node, hook_p hook, ng_item_fn *fn, void * arg1, int arg2)
  {
          item_p item;
  
          if ((item = ng_getqblk()) == NULL) {
                  return (ENOMEM);
          }
          item->el_flags = NGQF_FN | NGQF_WRITER;
          NG_NODE_REF(node); /* and one for the item */
          NGI_SET_NODE(item, node);
          if (hook) {
                  NG_HOOK_REF(hook);
                  NGI_SET_HOOK(item, hook);
          }
          NGI_FN(item) = fn;
          NGI_ARG1(item) = arg1;
          NGI_ARG2(item) = arg2;
          return(ng_snd_item(item, 0));
  }
  
  /* 
   * Official timeout routines for Netgraph nodes.
   */
  static void
  ng_timeout_trapoline(void *arg)
  {
          item_p item = arg;
  
          ng_snd_item(item, 0);
  }
  
  
  struct callout_handle
  ng_timeout(node_p node, hook_p hook, int ticks,
      ng_item_fn *fn, void * arg1, int arg2)
  {
          item_p item;
  
          if ((item = ng_getqblk()) == NULL) {
                  struct callout_handle handle;
                  handle.callout = NULL;
                  return (handle);
          }
          item->el_flags = NGQF_FN | NGQF_WRITER;
          NG_NODE_REF(node);              /* and one for the item */
          NGI_SET_NODE(item, node);
          if (hook) {
                  NG_HOOK_REF(hook);
                  NGI_SET_HOOK(item, hook);
          }
          NGI_FN(item) = fn;
          NGI_ARG1(item) = arg1;
          NGI_ARG2(item) = arg2;
          return (timeout(&ng_timeout_trapoline, item, ticks));
  }
  
  /* A special modified version of untimeout() */
  int 
  ng_untimeout(struct callout_handle handle, node_p node)
  {
          item_p item;
          
          if (handle.callout == NULL)
                  return (0);
          mtx_lock_spin(&callout_lock);
          item = handle.callout->c_arg; /* should be an official way to do this */
          if ((handle.callout->c_func == &ng_timeout_trapoline) &&
              (NGI_NODE(item) == node) &&
              (callout_stop(handle.callout))) {
                  /*
                   * We successfully removed it from the queue before it ran
                   * So now we need to unreference everything that was 
                   * given extra references. (NG_FREE_ITEM does this).
                   */
                  mtx_unlock_spin(&callout_lock);
                  NG_FREE_ITEM(item);
                  return (1);
          }
          mtx_unlock_spin(&callout_lock);
          return (0);
  }
  
  /*
   * Set the address, if none given, give the node here.
   */
  void
  ng_replace_retaddr(node_p here, item_p item, ng_ID_t retaddr)
  {
          if (retaddr) {
                  NGI_RETADDR(item) = retaddr;
          } else {
                  /*
                   * The old return address should be ok.
                   * If there isn't one, use the address here.
                   */
                  NGI_RETADDR(item) = ng_node2ID(here);
          }
  }
  
  #define TESTING
  #ifdef TESTING
  /* just test all the macros */
  void
  ng_macro_test(item_p item);
  void
  ng_macro_test(item_p item)
  {
          node_p node = NULL;
          hook_p hook = NULL;
          struct mbuf *m;
          struct ng_mesg *msg;
          ng_ID_t retaddr;
          int     error;
  
          NGI_GET_M(item, m);
          NGI_GET_MSG(item, msg);
          retaddr = NGI_RETADDR(item);
          NG_SEND_DATA(error, hook, m, NULL);
          NG_SEND_DATA_ONLY(error, hook, m);
          NG_FWD_NEW_DATA(error, item, hook, m);
          NG_FWD_ITEM_HOOK(error, item, hook);
          NG_SEND_MSG_HOOK(error, node, msg, hook, retaddr);
          NG_SEND_MSG_ID(error, node, msg, retaddr, retaddr);
          NG_SEND_MSG_PATH(error, node, msg, ".:", retaddr);
          NG_FWD_MSG_HOOK(error, node, item, hook, retaddr);
  }
  #endif /* TESTING */