The Design and Implementation of the FreeBSD Operating System, Second Edition
Now available: The Design and Implementation of the FreeBSD Operating System (Second Edition)


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

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    1 /*-
    2  * SPDX-License-Identifier: BSD-2-Clause-FreeBSD
    3  *
    4  * Copyright (c) 1999 Michael Smith <msmith@freebsd.org>
    5  * All rights reserved.
    6  *
    7  * Redistribution and use in source and binary forms, with or without
    8  * modification, are permitted provided that the following conditions
    9  * are met:
   10  * 1. Redistributions of source code must retain the above copyright
   11  *    notice, this list of conditions and the following disclaimer.
   12  * 2. Redistributions in binary form must reproduce the above copyright
   13  *    notice, this list of conditions and the following disclaimer in the
   14  *    documentation and/or other materials provided with the distribution.
   15  *
   16  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
   17  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   18  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   19  * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
   20  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
   21  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
   22  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
   23  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   24  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
   25  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
   26  * SUCH DAMAGE.
   27  */
   28 
   29 #include <sys/cdefs.h>
   30 __FBSDID("$FreeBSD$");
   31 
   32 #include <sys/param.h>
   33 #include <sys/kernel.h>
   34 #include <sys/ktr.h>
   35 #include <sys/lock.h>
   36 #include <sys/malloc.h>
   37 #include <sys/mutex.h>
   38 #include <sys/proc.h>
   39 #include <sys/systm.h>
   40 #include <sys/eventhandler.h>
   41 
   42 static MALLOC_DEFINE(M_EVENTHANDLER, "eventhandler", "Event handler records");
   43 
   44 /* List of all eventhandler lists */
   45 static TAILQ_HEAD(, eventhandler_list)  eventhandler_lists;
   46 static int                              eventhandler_lists_initted = 0;
   47 static struct mtx                       eventhandler_mutex;
   48 
   49 struct eventhandler_entry_generic 
   50 {
   51     struct eventhandler_entry   ee;
   52     void                        (* func)(void);
   53 };
   54 
   55 static struct eventhandler_list *_eventhandler_find_list(const char *name);
   56 
   57 /*
   58  * Initialize the eventhandler mutex and list.
   59  */
   60 static void
   61 eventhandler_init(void *dummy __unused)
   62 {
   63     TAILQ_INIT(&eventhandler_lists);
   64     mtx_init(&eventhandler_mutex, "eventhandler", NULL, MTX_DEF);
   65     atomic_store_rel_int(&eventhandler_lists_initted, 1);
   66 }
   67 SYSINIT(eventhandlers, SI_SUB_EVENTHANDLER, SI_ORDER_FIRST, eventhandler_init,
   68     NULL);
   69 
   70 static struct eventhandler_list *
   71 eventhandler_find_or_create_list(const char *name)
   72 {
   73         struct eventhandler_list *list, *new_list;
   74 
   75         /* look for a matching, existing list */
   76         list = _eventhandler_find_list(name);
   77 
   78         /* Do we need to create the list? */
   79         if (list == NULL) {
   80             mtx_unlock(&eventhandler_mutex);
   81 
   82             new_list = malloc(sizeof(*new_list) + strlen(name) + 1,
   83                 M_EVENTHANDLER, M_WAITOK | M_ZERO);
   84 
   85             /* If someone else created it already, then use that one. */
   86             mtx_lock(&eventhandler_mutex);
   87             list = _eventhandler_find_list(name);
   88             if (list != NULL) {
   89                 free(new_list, M_EVENTHANDLER);
   90             } else {
   91                 CTR2(KTR_EVH, "%s: creating list \"%s\"", __func__, name);
   92                 list = new_list;
   93                 TAILQ_INIT(&list->el_entries);
   94                 list->el_name = (char *)(list + 1);
   95                 strcpy(list->el_name, name);
   96                 mtx_init(&list->el_lock, list->el_name, "eventhandler list",
   97                     MTX_DEF);
   98                 TAILQ_INSERT_HEAD(&eventhandler_lists, list, el_link);
   99             }
  100         }
  101         return (list);
  102 }
  103 
  104 /* 
  105  * Insertion is O(n) due to the priority scan, but optimises to O(1)
  106  * if all priorities are identical.
  107  */
  108 static eventhandler_tag
  109 eventhandler_register_internal(struct eventhandler_list *list,
  110     const char *name, eventhandler_tag epn)
  111 {
  112     struct eventhandler_entry           *ep;
  113     
  114     KASSERT(eventhandler_lists_initted, ("eventhandler registered too early"));
  115     KASSERT(epn != NULL, ("%s: cannot register NULL event", __func__));
  116 
  117     /* Do we need to find/create the list? */
  118     if (list == NULL) {
  119             mtx_lock(&eventhandler_mutex);
  120             list = eventhandler_find_or_create_list(name);
  121             mtx_unlock(&eventhandler_mutex);
  122     }
  123 
  124     KASSERT(epn->ee_priority != EHE_DEAD_PRIORITY,
  125         ("%s: handler for %s registered with dead priority", __func__, name));
  126 
  127     /* sort it into the list */
  128     CTR4(KTR_EVH, "%s: adding item %p (function %p) to \"%s\"", __func__, epn,
  129         ((struct eventhandler_entry_generic *)epn)->func, name);
  130     EHL_LOCK(list);
  131     TAILQ_FOREACH(ep, &list->el_entries, ee_link) {
  132         if (ep->ee_priority != EHE_DEAD_PRIORITY &&
  133             epn->ee_priority < ep->ee_priority) {
  134             TAILQ_INSERT_BEFORE(ep, epn, ee_link);
  135             break;
  136         }
  137     }
  138     if (ep == NULL)
  139         TAILQ_INSERT_TAIL(&list->el_entries, epn, ee_link);
  140     EHL_UNLOCK(list);
  141     return(epn);
  142 }
  143 
  144 eventhandler_tag
  145 eventhandler_register(struct eventhandler_list *list, const char *name, 
  146                       void *func, void *arg, int priority)
  147 {
  148     struct eventhandler_entry_generic   *eg;
  149     
  150     /* allocate an entry for this handler, populate it */
  151     eg = malloc(sizeof(struct eventhandler_entry_generic), M_EVENTHANDLER,
  152         M_WAITOK | M_ZERO);
  153     eg->func = func;
  154     eg->ee.ee_arg = arg;
  155     eg->ee.ee_priority = priority;
  156 
  157     return (eventhandler_register_internal(list, name, &eg->ee));
  158 }
  159 
  160 #ifdef VIMAGE
  161 struct eventhandler_entry_generic_vimage
  162 {
  163     struct eventhandler_entry           ee;
  164     vimage_iterator_func_t              func;           /* Vimage iterator function. */
  165     struct eventhandler_entry_vimage    v_ee;           /* Original func, arg. */
  166 };
  167 
  168 eventhandler_tag
  169 vimage_eventhandler_register(struct eventhandler_list *list, const char *name, 
  170     void *func, void *arg, int priority, vimage_iterator_func_t iterfunc)
  171 {
  172     struct eventhandler_entry_generic_vimage    *eg;
  173     
  174     /* allocate an entry for this handler, populate it */
  175     eg = malloc(sizeof(struct eventhandler_entry_generic_vimage),
  176         M_EVENTHANDLER, M_WAITOK | M_ZERO);
  177     eg->func = iterfunc;
  178     eg->v_ee.func = func;
  179     eg->v_ee.ee_arg = arg;
  180     eg->ee.ee_arg = &eg->v_ee;
  181     eg->ee.ee_priority = priority;
  182 
  183     return (eventhandler_register_internal(list, name, &eg->ee));
  184 }
  185 #endif
  186 
  187 static void
  188 _eventhandler_deregister(struct eventhandler_list *list, eventhandler_tag tag,
  189     bool wait)
  190 {
  191     struct eventhandler_entry   *ep = tag;
  192 
  193     EHL_LOCK_ASSERT(list, MA_OWNED);
  194     if (ep != NULL) {
  195         /* remove just this entry */
  196         if (list->el_runcount == 0) {
  197             CTR3(KTR_EVH, "%s: removing item %p from \"%s\"", __func__, ep,
  198                 list->el_name);
  199             TAILQ_REMOVE(&list->el_entries, ep, ee_link);
  200             free(ep, M_EVENTHANDLER);
  201         } else {
  202             CTR3(KTR_EVH, "%s: marking item %p from \"%s\" as dead", __func__,
  203                 ep, list->el_name);
  204             ep->ee_priority = EHE_DEAD_PRIORITY;
  205         }
  206     } else {
  207         /* remove entire list */
  208         if (list->el_runcount == 0) {
  209             CTR2(KTR_EVH, "%s: removing all items from \"%s\"", __func__,
  210                 list->el_name);
  211             while (!TAILQ_EMPTY(&list->el_entries)) {
  212                 ep = TAILQ_FIRST(&list->el_entries);
  213                 TAILQ_REMOVE(&list->el_entries, ep, ee_link);
  214                 free(ep, M_EVENTHANDLER);
  215             }
  216         } else {
  217             CTR2(KTR_EVH, "%s: marking all items from \"%s\" as dead",
  218                 __func__, list->el_name);
  219             TAILQ_FOREACH(ep, &list->el_entries, ee_link)
  220                 ep->ee_priority = EHE_DEAD_PRIORITY;
  221         }
  222     }
  223     while (wait && list->el_runcount > 0)
  224             mtx_sleep(list, &list->el_lock, 0, "evhrm", 0);
  225     EHL_UNLOCK(list);
  226 }
  227 
  228 void
  229 eventhandler_deregister(struct eventhandler_list *list, eventhandler_tag tag)
  230 {
  231 
  232         _eventhandler_deregister(list, tag, true);
  233 }
  234 
  235 void
  236 eventhandler_deregister_nowait(struct eventhandler_list *list,
  237     eventhandler_tag tag)
  238 {
  239 
  240         _eventhandler_deregister(list, tag, false);
  241 }
  242 
  243 /*
  244  * Internal version for use when eventhandler list is already locked.
  245  */
  246 static struct eventhandler_list *
  247 _eventhandler_find_list(const char *name)
  248 {
  249     struct eventhandler_list    *list;
  250 
  251     mtx_assert(&eventhandler_mutex, MA_OWNED);
  252     TAILQ_FOREACH(list, &eventhandler_lists, el_link) {
  253         if (!strcmp(name, list->el_name))
  254             break;
  255     }
  256     return (list);
  257 }
  258 
  259 /*
  260  * Lookup a "slow" list by name.  Returns with the list locked.
  261  */
  262 struct eventhandler_list *
  263 eventhandler_find_list(const char *name)
  264 {
  265     struct eventhandler_list    *list;
  266 
  267     if (!eventhandler_lists_initted)
  268         return(NULL);
  269     
  270     /* scan looking for the requested list */
  271     mtx_lock(&eventhandler_mutex);
  272     list = _eventhandler_find_list(name);
  273     if (list != NULL)
  274         EHL_LOCK(list);
  275     mtx_unlock(&eventhandler_mutex);
  276     
  277     return(list);
  278 }
  279 
  280 /*
  281  * Prune "dead" entries from an eventhandler list.
  282  */
  283 void
  284 eventhandler_prune_list(struct eventhandler_list *list)
  285 {
  286     struct eventhandler_entry *ep, *en;
  287     int pruned = 0;
  288 
  289     CTR2(KTR_EVH, "%s: pruning list \"%s\"", __func__, list->el_name);
  290     EHL_LOCK_ASSERT(list, MA_OWNED);
  291     TAILQ_FOREACH_SAFE(ep, &list->el_entries, ee_link, en) {
  292         if (ep->ee_priority == EHE_DEAD_PRIORITY) {
  293             TAILQ_REMOVE(&list->el_entries, ep, ee_link);
  294             free(ep, M_EVENTHANDLER);
  295             pruned++;
  296         }
  297     }
  298     if (pruned > 0)
  299             wakeup(list);
  300 }
  301 
  302 /*
  303  * Create (or get the existing) list so the pointer can be stored by
  304  * EVENTHANDLER_LIST_DEFINE.
  305  */
  306 struct eventhandler_list *
  307 eventhandler_create_list(const char *name)
  308 {
  309         struct eventhandler_list *list;
  310 
  311         KASSERT(eventhandler_lists_initted,
  312             ("eventhandler list created too early"));
  313 
  314         mtx_lock(&eventhandler_mutex);
  315         list = eventhandler_find_or_create_list(name);
  316         mtx_unlock(&eventhandler_mutex);
  317 
  318         return (list);
  319 }

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