The Design and Implementation of the FreeBSD Operating System, Second Edition
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FreeBSD/Linux Kernel Cross Reference
sys/kern/uipc_sem.c

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    1 /*-
    2  * Copyright (c) 2002 Alfred Perlstein <alfred@FreeBSD.org>
    3  * Copyright (c) 2003-2005 SPARTA, Inc.
    4  * Copyright (c) 2005 Robert N. M. Watson
    5  * All rights reserved.
    6  *
    7  * This software was developed for the FreeBSD Project in part by Network
    8  * Associates Laboratories, the Security Research Division of Network
    9  * Associates, Inc. under DARPA/SPAWAR contract N66001-01-C-8035 ("CBOSS"),
   10  * as part of the DARPA CHATS research program.
   11  *
   12  * Redistribution and use in source and binary forms, with or without
   13  * modification, are permitted provided that the following conditions
   14  * are met:
   15  * 1. Redistributions of source code must retain the above copyright
   16  *    notice, this list of conditions and the following disclaimer.
   17  * 2. Redistributions in binary form must reproduce the above copyright
   18  *    notice, this list of conditions and the following disclaimer in the
   19  *    documentation and/or other materials provided with the distribution.
   20  *
   21  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
   22  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   23  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   24  * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
   25  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
   26  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
   27  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
   28  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   29  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
   30  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
   31  * SUCH DAMAGE.
   32  */
   33 
   34 #include <sys/cdefs.h>
   35 __FBSDID("$FreeBSD: releng/6.2/sys/kern/uipc_sem.c 164286 2006-11-14 20:42:41Z cvs2svn $");
   36 
   37 #include "opt_mac.h"
   38 #include "opt_posix.h"
   39 
   40 #include <sys/param.h>
   41 #include <sys/systm.h>
   42 #include <sys/sysproto.h>
   43 #include <sys/eventhandler.h>
   44 #include <sys/kernel.h>
   45 #include <sys/proc.h>
   46 #include <sys/lock.h>
   47 #include <sys/mutex.h>
   48 #include <sys/module.h>
   49 #include <sys/condvar.h>
   50 #include <sys/sem.h>
   51 #include <sys/uio.h>
   52 #include <sys/syscall.h>
   53 #include <sys/stat.h>
   54 #include <sys/sysent.h>
   55 #include <sys/sysctl.h>
   56 #include <sys/time.h>
   57 #include <sys/mac.h>
   58 #include <sys/malloc.h>
   59 #include <sys/fcntl.h>
   60 
   61 #include <posix4/ksem.h>
   62 #include <posix4/posix4.h>
   63 #include <posix4/semaphore.h>
   64 #include <posix4/_semaphore.h>
   65 
   66 static int sem_count_proc(struct proc *p);
   67 static struct ksem *sem_lookup_byname(const char *name);
   68 static int sem_create(struct thread *td, const char *name,
   69     struct ksem **ksret, mode_t mode, unsigned int value);
   70 static void sem_free(struct ksem *ksnew);
   71 static int sem_perm(struct thread *td, struct ksem *ks);
   72 static void sem_enter(struct proc *p, struct ksem *ks);
   73 static int sem_leave(struct proc *p, struct ksem *ks);
   74 static void sem_exithook(void *arg, struct proc *p);
   75 static void sem_forkhook(void *arg, struct proc *p1, struct proc *p2,
   76     int flags);
   77 static int sem_hasopen(struct thread *td, struct ksem *ks);
   78 
   79 static int kern_sem_close(struct thread *td, semid_t id);
   80 static int kern_sem_post(struct thread *td, semid_t id);
   81 static int kern_sem_wait(struct thread *td, semid_t id, int tryflag,
   82     struct timespec *abstime);
   83 static int kern_sem_init(struct thread *td, int dir, unsigned int value,
   84     semid_t *idp);
   85 static int kern_sem_open(struct thread *td, int dir, const char *name,
   86     int oflag, mode_t mode, unsigned int value, semid_t *idp);
   87 static int kern_sem_unlink(struct thread *td, const char *name);
   88 
   89 #ifndef SEM_MAX
   90 #define SEM_MAX 30
   91 #endif
   92 
   93 #define SEM_MAX_NAMELEN 14
   94 
   95 #define SEM_TO_ID(x)    ((intptr_t)(x))
   96 #define ID_TO_SEM(x)    id_to_sem(x)
   97 
   98 /*
   99  * available semaphores go here, this includes sem_init and any semaphores
  100  * created via sem_open that have not yet been unlinked.
  101  */
  102 LIST_HEAD(, ksem) ksem_head = LIST_HEAD_INITIALIZER(&ksem_head);
  103 /*
  104  * semaphores still in use but have been sem_unlink()'d go here.
  105  */
  106 LIST_HEAD(, ksem) ksem_deadhead = LIST_HEAD_INITIALIZER(&ksem_deadhead);
  107 
  108 static struct mtx sem_lock;
  109 static MALLOC_DEFINE(M_SEM, "sems", "semaphore data");
  110 
  111 static int nsems = 0;
  112 SYSCTL_DECL(_p1003_1b);
  113 SYSCTL_INT(_p1003_1b, OID_AUTO, nsems, CTLFLAG_RD, &nsems, 0, "");
  114 
  115 static eventhandler_tag sem_exit_tag, sem_exec_tag, sem_fork_tag;
  116 
  117 #ifdef SEM_DEBUG
  118 #define DP(x)   printf x
  119 #else
  120 #define DP(x)
  121 #endif
  122 
  123 static __inline
  124 void
  125 sem_ref(struct ksem *ks)
  126 {
  127 
  128         mtx_assert(&sem_lock, MA_OWNED);
  129         ks->ks_ref++;
  130         DP(("sem_ref: ks = %p, ref = %d\n", ks, ks->ks_ref));
  131 }
  132 
  133 static __inline
  134 void
  135 sem_rel(struct ksem *ks)
  136 {
  137 
  138         mtx_assert(&sem_lock, MA_OWNED);
  139         DP(("sem_rel: ks = %p, ref = %d\n", ks, ks->ks_ref - 1));
  140         if (--ks->ks_ref == 0)
  141                 sem_free(ks);
  142 }
  143 
  144 static __inline struct ksem *id_to_sem(semid_t id);
  145 
  146 static __inline
  147 struct ksem *
  148 id_to_sem(semid_t id)
  149 {
  150         struct ksem *ks;
  151 
  152         mtx_assert(&sem_lock, MA_OWNED);
  153         DP(("id_to_sem: id = %0x,%p\n", id, (struct ksem *)id));
  154         LIST_FOREACH(ks, &ksem_head, ks_entry) {
  155                 DP(("id_to_sem: ks = %p\n", ks));
  156                 if (ks == (struct ksem *)id)
  157                         return (ks);
  158         }
  159         return (NULL);
  160 }
  161 
  162 static struct ksem *
  163 sem_lookup_byname(const char *name)
  164 {
  165         struct ksem *ks;
  166 
  167         mtx_assert(&sem_lock, MA_OWNED);
  168         LIST_FOREACH(ks, &ksem_head, ks_entry)
  169                 if (ks->ks_name != NULL && strcmp(ks->ks_name, name) == 0)
  170                         return (ks);
  171         return (NULL);
  172 }
  173 
  174 static int
  175 sem_create(struct thread *td, const char *name, struct ksem **ksret,
  176     mode_t mode, unsigned int value)
  177 {
  178         struct ksem *ret;
  179         struct proc *p;
  180         struct ucred *uc;
  181         size_t len;
  182         int error;
  183 
  184         DP(("sem_create\n"));
  185         p = td->td_proc;
  186         uc = td->td_ucred;
  187         if (value > SEM_VALUE_MAX)
  188                 return (EINVAL);
  189         ret = malloc(sizeof(*ret), M_SEM, M_WAITOK | M_ZERO);
  190         if (name != NULL) {
  191                 len = strlen(name);
  192                 if (len > SEM_MAX_NAMELEN) {
  193                         free(ret, M_SEM);
  194                         return (ENAMETOOLONG);
  195                 }
  196                 /* name must start with a '/' but not contain one. */
  197                 if (*name != '/' || len < 2 || index(name + 1, '/') != NULL) {
  198                         free(ret, M_SEM);
  199                         return (EINVAL);
  200                 }
  201                 ret->ks_name = malloc(len + 1, M_SEM, M_WAITOK);
  202                 strcpy(ret->ks_name, name);
  203         } else {
  204                 ret->ks_name = NULL;
  205         }
  206         ret->ks_mode = mode;
  207         ret->ks_value = value;
  208         ret->ks_ref = 1;
  209         ret->ks_waiters = 0;
  210         ret->ks_uid = uc->cr_uid;
  211         ret->ks_gid = uc->cr_gid;
  212         ret->ks_onlist = 0;
  213         cv_init(&ret->ks_cv, "sem");
  214         LIST_INIT(&ret->ks_users);
  215 #ifdef MAC
  216         mac_init_posix_sem(ret);
  217         mac_create_posix_sem(uc, ret);
  218 #endif
  219         if (name != NULL)
  220                 sem_enter(td->td_proc, ret);
  221         *ksret = ret;
  222         mtx_lock(&sem_lock);
  223         if (nsems >= p31b_getcfg(CTL_P1003_1B_SEM_NSEMS_MAX)) {
  224                 sem_leave(td->td_proc, ret);
  225                 sem_free(ret);
  226                 error = ENFILE;
  227         } else {
  228                 nsems++;
  229                 error = 0;
  230         }
  231         mtx_unlock(&sem_lock);
  232         return (error);
  233 }
  234 
  235 #ifndef _SYS_SYSPROTO_H_
  236 struct ksem_init_args {
  237         unsigned int value;
  238         semid_t *idp;
  239 };
  240 int ksem_init(struct thread *td, struct ksem_init_args *uap);
  241 #endif
  242 int
  243 ksem_init(struct thread *td, struct ksem_init_args *uap)
  244 {
  245         int error;
  246 
  247         error = kern_sem_init(td, UIO_USERSPACE, uap->value, uap->idp);
  248         return (error);
  249 }
  250 
  251 static int
  252 kern_sem_init(struct thread *td, int dir, unsigned int value, semid_t *idp)
  253 {
  254         struct ksem *ks;
  255         semid_t id;
  256         int error;
  257 
  258         error = sem_create(td, NULL, &ks, S_IRWXU | S_IRWXG, value);
  259         if (error)
  260                 return (error);
  261         id = SEM_TO_ID(ks);
  262         if (dir == UIO_USERSPACE) {
  263                 error = copyout(&id, idp, sizeof(id));
  264                 if (error) {
  265                         mtx_lock(&sem_lock);
  266                         sem_rel(ks);
  267                         mtx_unlock(&sem_lock);
  268                         return (error);
  269                 }
  270         } else {
  271                 *idp = id;
  272         }
  273         mtx_lock(&sem_lock);
  274         LIST_INSERT_HEAD(&ksem_head, ks, ks_entry);
  275         ks->ks_onlist = 1;
  276         mtx_unlock(&sem_lock);
  277         return (error);
  278 }
  279 
  280 #ifndef _SYS_SYSPROTO_H_
  281 struct ksem_open_args {
  282         char *name;
  283         int oflag;
  284         mode_t mode;
  285         unsigned int value;
  286         semid_t *idp;   
  287 };
  288 int ksem_open(struct thread *td, struct ksem_open_args *uap);
  289 #endif
  290 int
  291 ksem_open(struct thread *td, struct ksem_open_args *uap)
  292 {
  293         char name[SEM_MAX_NAMELEN + 1];
  294         size_t done;
  295         int error;
  296 
  297         error = copyinstr(uap->name, name, SEM_MAX_NAMELEN + 1, &done);
  298         if (error)
  299                 return (error);
  300         DP((">>> sem_open start\n"));
  301         error = kern_sem_open(td, UIO_USERSPACE,
  302             name, uap->oflag, uap->mode, uap->value, uap->idp);
  303         DP(("<<< sem_open end\n"));
  304         return (error);
  305 }
  306 
  307 static int
  308 kern_sem_open(struct thread *td, int dir, const char *name, int oflag,
  309     mode_t mode, unsigned int value, semid_t *idp)
  310 {
  311         struct ksem *ksnew, *ks;
  312         int error;
  313         semid_t id;
  314 
  315         ksnew = NULL;
  316         mtx_lock(&sem_lock);
  317         ks = sem_lookup_byname(name);
  318         /*
  319          * If we found it but O_EXCL is set, error.
  320          */
  321         if (ks != NULL && (oflag & O_EXCL) != 0) {
  322                 mtx_unlock(&sem_lock);
  323                 return (EEXIST);
  324         }
  325         /*
  326          * If we didn't find it...
  327          */
  328         if (ks == NULL) {
  329                 /*
  330                  * didn't ask for creation? error.
  331                  */
  332                 if ((oflag & O_CREAT) == 0) {
  333                         mtx_unlock(&sem_lock);
  334                         return (ENOENT);
  335                 }
  336                 /*
  337                  * We may block during creation, so drop the lock.
  338                  */
  339                 mtx_unlock(&sem_lock);
  340                 error = sem_create(td, name, &ksnew, mode, value);
  341                 if (error != 0)
  342                         return (error);
  343                 id = SEM_TO_ID(ksnew);
  344                 if (dir == UIO_USERSPACE) {
  345                         DP(("about to copyout! %d to %p\n", id, idp));
  346                         error = copyout(&id, idp, sizeof(id));
  347                         if (error) {
  348                                 mtx_lock(&sem_lock);
  349                                 sem_leave(td->td_proc, ksnew);
  350                                 sem_rel(ksnew);
  351                                 mtx_unlock(&sem_lock);
  352                                 return (error);
  353                         }
  354                 } else {
  355                         DP(("about to set! %d to %p\n", id, idp));
  356                         *idp = id;
  357                 }
  358                 /*
  359                  * We need to make sure we haven't lost a race while
  360                  * allocating during creation.
  361                  */
  362                 mtx_lock(&sem_lock);
  363                 ks = sem_lookup_byname(name);
  364                 if (ks != NULL) {
  365                         /* we lost... */
  366                         sem_leave(td->td_proc, ksnew);
  367                         sem_rel(ksnew);
  368                         /* we lost and we can't loose... */
  369                         if ((oflag & O_EXCL) != 0) {
  370                                 mtx_unlock(&sem_lock);
  371                                 return (EEXIST);
  372                         }
  373                 } else {
  374                         DP(("sem_create: about to add to list...\n"));
  375                         LIST_INSERT_HEAD(&ksem_head, ksnew, ks_entry); 
  376                         DP(("sem_create: setting list bit...\n"));
  377                         ksnew->ks_onlist = 1;
  378                         DP(("sem_create: done, about to unlock...\n"));
  379                 }
  380         } else {
  381 #ifdef MAC
  382                 error = mac_check_posix_sem_open(td->td_ucred, ks);
  383                 if (error)
  384                         goto err_open;
  385 #endif
  386                 /*
  387                  * if we aren't the creator, then enforce permissions.
  388                  */
  389                 error = sem_perm(td, ks);
  390                 if (error)
  391                         goto err_open;
  392                 sem_ref(ks);
  393                 mtx_unlock(&sem_lock);
  394                 id = SEM_TO_ID(ks);
  395                 if (dir == UIO_USERSPACE) {
  396                         error = copyout(&id, idp, sizeof(id));
  397                         if (error) {
  398                                 mtx_lock(&sem_lock);
  399                                 sem_rel(ks);
  400                                 mtx_unlock(&sem_lock);
  401                                 return (error);
  402                         }
  403                 } else {
  404                         *idp = id;
  405                 }
  406                 sem_enter(td->td_proc, ks);
  407                 mtx_lock(&sem_lock);
  408                 sem_rel(ks);
  409         }
  410 err_open:
  411         mtx_unlock(&sem_lock);
  412         return (error);
  413 }
  414 
  415 static int
  416 sem_perm(struct thread *td, struct ksem *ks)
  417 {
  418         struct ucred *uc;
  419 
  420         uc = td->td_ucred;
  421         DP(("sem_perm: uc(%d,%d) ks(%d,%d,%o)\n",
  422             uc->cr_uid, uc->cr_gid,
  423              ks->ks_uid, ks->ks_gid, ks->ks_mode));
  424         if ((uc->cr_uid == ks->ks_uid && (ks->ks_mode & S_IWUSR) != 0) ||
  425             (uc->cr_gid == ks->ks_gid && (ks->ks_mode & S_IWGRP) != 0) ||
  426             (ks->ks_mode & S_IWOTH) != 0 || suser(td) == 0)
  427                 return (0);
  428         return (EPERM);
  429 }
  430 
  431 static void
  432 sem_free(struct ksem *ks)
  433 {
  434 
  435         nsems--;
  436         if (ks->ks_onlist)
  437                 LIST_REMOVE(ks, ks_entry);
  438         if (ks->ks_name != NULL)
  439                 free(ks->ks_name, M_SEM);
  440         cv_destroy(&ks->ks_cv);
  441         free(ks, M_SEM);
  442 }
  443 
  444 static __inline struct kuser *sem_getuser(struct proc *p, struct ksem *ks);
  445 
  446 static __inline struct kuser *
  447 sem_getuser(struct proc *p, struct ksem *ks)
  448 {
  449         struct kuser *k;
  450 
  451         LIST_FOREACH(k, &ks->ks_users, ku_next)
  452                 if (k->ku_pid == p->p_pid)
  453                         return (k);
  454         return (NULL);
  455 }
  456 
  457 static int
  458 sem_hasopen(struct thread *td, struct ksem *ks)
  459 {
  460         
  461         return ((ks->ks_name == NULL && sem_perm(td, ks) == 0)
  462             || sem_getuser(td->td_proc, ks) != NULL);
  463 }
  464 
  465 static int
  466 sem_leave(struct proc *p, struct ksem *ks)
  467 {
  468         struct kuser *k;
  469 
  470         DP(("sem_leave: ks = %p\n", ks));
  471         k = sem_getuser(p, ks);
  472         DP(("sem_leave: ks = %p, k = %p\n", ks, k));
  473         if (k != NULL) {
  474                 LIST_REMOVE(k, ku_next);
  475                 sem_rel(ks);
  476                 DP(("sem_leave: about to free k\n"));
  477                 free(k, M_SEM);
  478                 DP(("sem_leave: returning\n"));
  479                 return (0);
  480         }
  481         return (EINVAL);
  482 }
  483 
  484 static void
  485 sem_enter(p, ks)
  486         struct proc *p;
  487         struct ksem *ks;
  488 {
  489         struct kuser *ku, *k;
  490 
  491         ku = malloc(sizeof(*ku), M_SEM, M_WAITOK);
  492         ku->ku_pid = p->p_pid;
  493         mtx_lock(&sem_lock);
  494         k = sem_getuser(p, ks);
  495         if (k != NULL) {
  496                 mtx_unlock(&sem_lock);
  497                 free(ku, M_TEMP);
  498                 return;
  499         }
  500         LIST_INSERT_HEAD(&ks->ks_users, ku, ku_next);
  501         sem_ref(ks);
  502         mtx_unlock(&sem_lock);
  503 }
  504 
  505 #ifndef _SYS_SYSPROTO_H_
  506 struct ksem_unlink_args {
  507         char *name;
  508 };
  509 int ksem_unlink(struct thread *td, struct ksem_unlink_args *uap);
  510 #endif
  511         
  512 int
  513 ksem_unlink(struct thread *td, struct ksem_unlink_args *uap)
  514 {
  515         char name[SEM_MAX_NAMELEN + 1];
  516         size_t done;
  517         int error;
  518 
  519         error = copyinstr(uap->name, name, SEM_MAX_NAMELEN + 1, &done);
  520         return (error ? error :
  521             kern_sem_unlink(td, name));
  522 }
  523 
  524 static int
  525 kern_sem_unlink(struct thread *td, const char *name)
  526 {
  527         struct ksem *ks;
  528         int error;
  529 
  530         mtx_lock(&sem_lock);
  531         ks = sem_lookup_byname(name);
  532         if (ks != NULL) {
  533 #ifdef MAC
  534                 error = mac_check_posix_sem_unlink(td->td_ucred, ks);
  535                 if (error) {
  536                         mtx_unlock(&sem_lock);
  537                         return (error);
  538                 }
  539 #endif
  540                 error = sem_perm(td, ks);
  541         } else
  542                 error = ENOENT;
  543         DP(("sem_unlink: '%s' ks = %p, error = %d\n", name, ks, error));
  544         if (error == 0) {
  545                 LIST_REMOVE(ks, ks_entry);
  546                 LIST_INSERT_HEAD(&ksem_deadhead, ks, ks_entry); 
  547                 sem_rel(ks);
  548         }
  549         mtx_unlock(&sem_lock);
  550         return (error);
  551 }
  552 
  553 #ifndef _SYS_SYSPROTO_H_
  554 struct ksem_close_args {
  555         semid_t id;
  556 };
  557 int ksem_close(struct thread *td, struct ksem_close_args *uap);
  558 #endif
  559 
  560 int
  561 ksem_close(struct thread *td, struct ksem_close_args *uap)
  562 {
  563 
  564         return (kern_sem_close(td, uap->id));
  565 }
  566 
  567 static int
  568 kern_sem_close(struct thread *td, semid_t id)
  569 {
  570         struct ksem *ks;
  571         int error;
  572 
  573         error = EINVAL;
  574         mtx_lock(&sem_lock);
  575         ks = ID_TO_SEM(id);
  576         /* this is not a valid operation for unnamed sems */
  577         if (ks != NULL && ks->ks_name != NULL)
  578                 error = sem_leave(td->td_proc, ks);
  579         mtx_unlock(&sem_lock);
  580         return (error);
  581 }
  582 
  583 #ifndef _SYS_SYSPROTO_H_
  584 struct ksem_post_args {
  585         semid_t id;
  586 };
  587 int ksem_post(struct thread *td, struct ksem_post_args *uap);
  588 #endif
  589 int
  590 ksem_post(struct thread *td, struct ksem_post_args *uap)
  591 {
  592 
  593         return (kern_sem_post(td, uap->id));
  594 }
  595 
  596 static int
  597 kern_sem_post(struct thread *td, semid_t id)
  598 {
  599         struct ksem *ks;
  600         int error;
  601 
  602         mtx_lock(&sem_lock);
  603         ks = ID_TO_SEM(id);
  604         if (ks == NULL || !sem_hasopen(td, ks)) {
  605                 error = EINVAL;
  606                 goto err;
  607         }
  608 #ifdef MAC
  609         error = mac_check_posix_sem_post(td->td_ucred, ks);
  610         if (error)
  611                 goto err;
  612 #endif
  613         if (ks->ks_value == SEM_VALUE_MAX) {
  614                 error = EOVERFLOW;
  615                 goto err;
  616         }
  617         ++ks->ks_value;
  618         if (ks->ks_waiters > 0)
  619                 cv_signal(&ks->ks_cv);
  620         error = 0;
  621 err:
  622         mtx_unlock(&sem_lock);
  623         return (error);
  624 }
  625 
  626 #ifndef _SYS_SYSPROTO_H_
  627 struct ksem_wait_args {
  628         semid_t id;
  629 };
  630 int ksem_wait(struct thread *td, struct ksem_wait_args *uap);
  631 #endif
  632 
  633 int
  634 ksem_wait(struct thread *td, struct ksem_wait_args *uap)
  635 {
  636 
  637         return (kern_sem_wait(td, uap->id, 0, NULL));
  638 }
  639 
  640 #ifndef _SYS_SYSPROTO_H_
  641 struct ksem_timedwait_args {
  642         semid_t id;
  643         struct timespec *abstime;
  644 };
  645 int ksem_timedwait(struct thread *td, struct ksem_timedwait_args *uap);
  646 #endif
  647 int
  648 ksem_timedwait(struct thread *td, struct ksem_timedwait_args *uap)
  649 {
  650         struct timespec abstime;
  651         struct timespec *ts;
  652         int error;
  653 
  654         /* We allow a null timespec (wait forever). */
  655         if (uap->abstime == NULL)
  656                 ts = NULL;
  657         else {
  658                 error = copyin(uap->abstime, &abstime, sizeof(abstime));
  659                 if (error != 0)
  660                         return (error);
  661                 if (abstime.tv_nsec >= 1000000000 || abstime.tv_nsec < 0)
  662                         return (EINVAL);
  663                 ts = &abstime;
  664         }
  665         return (kern_sem_wait(td, uap->id, 0, ts));
  666 }
  667 
  668 #ifndef _SYS_SYSPROTO_H_
  669 struct ksem_trywait_args {
  670         semid_t id;
  671 };
  672 int ksem_trywait(struct thread *td, struct ksem_trywait_args *uap);
  673 #endif
  674 int
  675 ksem_trywait(struct thread *td, struct ksem_trywait_args *uap)
  676 {
  677 
  678         return (kern_sem_wait(td, uap->id, 1, NULL));
  679 }
  680 
  681 static int
  682 kern_sem_wait(struct thread *td, semid_t id, int tryflag,
  683     struct timespec *abstime)
  684 {
  685         struct timespec ts1, ts2;
  686         struct timeval tv;
  687         struct ksem *ks;
  688         int error;
  689 
  690         DP((">>> kern_sem_wait entered!\n"));
  691         mtx_lock(&sem_lock);
  692         ks = ID_TO_SEM(id);
  693         if (ks == NULL) {
  694                 DP(("kern_sem_wait ks == NULL\n"));
  695                 error = EINVAL;
  696                 goto err;
  697         }
  698         sem_ref(ks);
  699         if (!sem_hasopen(td, ks)) {
  700                 DP(("kern_sem_wait hasopen failed\n"));
  701                 error = EINVAL;
  702                 goto err;
  703         }
  704 #ifdef MAC
  705         error = mac_check_posix_sem_wait(td->td_ucred, ks);
  706         if (error) {
  707                 DP(("kern_sem_wait mac failed\n"));
  708                 goto err;
  709         }
  710 #endif
  711         DP(("kern_sem_wait value = %d, tryflag %d\n", ks->ks_value, tryflag));
  712         if (ks->ks_value == 0) {
  713                 ks->ks_waiters++;
  714                 if (tryflag != 0)
  715                         error = EAGAIN;
  716                 else if (abstime == NULL)
  717                         error = cv_wait_sig(&ks->ks_cv, &sem_lock);
  718                 else {
  719                         for (;;) {
  720                                 ts1 = *abstime;
  721                                 getnanotime(&ts2);
  722                                 timespecsub(&ts1, &ts2);
  723                                 TIMESPEC_TO_TIMEVAL(&tv, &ts1);
  724                                 if (tv.tv_sec < 0) {
  725                                         error = ETIMEDOUT;
  726                                         break;
  727                                 }
  728                                 error = cv_timedwait_sig(&ks->ks_cv,
  729                                     &sem_lock, tvtohz(&tv));
  730                                 if (error != EWOULDBLOCK)
  731                                         break;
  732                         }
  733                 }
  734                 ks->ks_waiters--;
  735                 if (error)
  736                         goto err;
  737         }
  738         ks->ks_value--;
  739         error = 0;
  740 err:
  741         if (ks != NULL)
  742                 sem_rel(ks);
  743         mtx_unlock(&sem_lock);
  744         DP(("<<< kern_sem_wait leaving, error = %d\n", error));
  745         return (error);
  746 }
  747 
  748 #ifndef _SYS_SYSPROTO_H_
  749 struct ksem_getvalue_args {
  750         semid_t id;
  751         int *val;
  752 };
  753 int ksem_getvalue(struct thread *td, struct ksem_getvalue_args *uap);
  754 #endif
  755 int
  756 ksem_getvalue(struct thread *td, struct ksem_getvalue_args *uap)
  757 {
  758         struct ksem *ks;
  759         int error, val;
  760 
  761         mtx_lock(&sem_lock);
  762         ks = ID_TO_SEM(uap->id);
  763         if (ks == NULL || !sem_hasopen(td, ks)) {
  764                 mtx_unlock(&sem_lock);
  765                 return (EINVAL);
  766         }
  767 #ifdef MAC
  768         error = mac_check_posix_sem_getvalue(td->td_ucred, ks);
  769         if (error) {
  770                 mtx_unlock(&sem_lock);
  771                 return (error);
  772         }
  773 #endif
  774         val = ks->ks_value;
  775         mtx_unlock(&sem_lock);
  776         error = copyout(&val, uap->val, sizeof(val));
  777         return (error);
  778 }
  779 
  780 #ifndef _SYS_SYSPROTO_H_
  781 struct ksem_destroy_args {
  782         semid_t id;
  783 };
  784 int ksem_destroy(struct thread *td, struct ksem_destroy_args *uap);
  785 #endif
  786 int
  787 ksem_destroy(struct thread *td, struct ksem_destroy_args *uap)
  788 {
  789         struct ksem *ks;
  790         int error;
  791 
  792         mtx_lock(&sem_lock);
  793         ks = ID_TO_SEM(uap->id);
  794         if (ks == NULL || !sem_hasopen(td, ks) ||
  795             ks->ks_name != NULL) {
  796                 error = EINVAL;
  797                 goto err;
  798         }
  799 #ifdef MAC
  800         error = mac_check_posix_sem_destroy(td->td_ucred, ks);
  801         if (error)
  802                 goto err;
  803 #endif
  804         if (ks->ks_waiters != 0) {
  805                 error = EBUSY;
  806                 goto err;
  807         }
  808         sem_rel(ks);
  809         error = 0;
  810 err:
  811         mtx_unlock(&sem_lock);
  812         return (error);
  813 }
  814 
  815 /*
  816  * Count the number of kusers associated with a proc, so as to guess at how
  817  * many to allocate when forking.
  818  */
  819 static int
  820 sem_count_proc(struct proc *p)
  821 {
  822         struct ksem *ks;
  823         struct kuser *ku;
  824         int count;
  825 
  826         mtx_assert(&sem_lock, MA_OWNED);
  827 
  828         count = 0;
  829         LIST_FOREACH(ks, &ksem_head, ks_entry) {
  830                 LIST_FOREACH(ku, &ks->ks_users, ku_next) {
  831                         if (ku->ku_pid == p->p_pid)
  832                                 count++;
  833                 }
  834         }
  835         LIST_FOREACH(ks, &ksem_deadhead, ks_entry) {
  836                 LIST_FOREACH(ku, &ks->ks_users, ku_next) {
  837                         if (ku->ku_pid == p->p_pid)
  838                                 count++;
  839                 }
  840         }
  841         return (count);
  842 }
  843 
  844 /*
  845  * When a process forks, the child process must gain a reference to each open
  846  * semaphore in the parent process, whether it is unlinked or not.  This
  847  * requires allocating a kuser structure for each semaphore reference in the
  848  * new process.  Because the set of semaphores in the parent can change while
  849  * the fork is in progress, we have to handle races -- first we attempt to
  850  * allocate enough storage to acquire references to each of the semaphores,
  851  * then we enter the semaphores and release the temporary references.
  852  */
  853 static void
  854 sem_forkhook(void *arg, struct proc *p1, struct proc *p2, int flags)
  855 {
  856         struct ksem *ks, **sem_array;
  857         int count, i, new_count;
  858         struct kuser *ku;
  859 
  860         mtx_lock(&sem_lock);
  861         count = sem_count_proc(p1);
  862         if (count == 0) {
  863                 mtx_unlock(&sem_lock);
  864                 return;
  865         }
  866 race_lost:
  867         mtx_assert(&sem_lock, MA_OWNED);
  868         mtx_unlock(&sem_lock);
  869         sem_array = malloc(sizeof(struct ksem *) * count, M_TEMP, M_WAITOK);
  870         mtx_lock(&sem_lock);
  871         new_count = sem_count_proc(p1);
  872         if (count < new_count) {
  873                 /* Lost race, repeat and allocate more storage. */
  874                 free(sem_array, M_TEMP);
  875                 count = new_count;
  876                 goto race_lost;
  877         }
  878         /*
  879          * Given an array capable of storing an adequate number of semaphore
  880          * references, now walk the list of semaphores and acquire a new
  881          * reference for any semaphore opened by p1.
  882          */
  883         count = new_count;
  884         i = 0;
  885         LIST_FOREACH(ks, &ksem_head, ks_entry) {
  886                 LIST_FOREACH(ku, &ks->ks_users, ku_next) {
  887                         if (ku->ku_pid == p1->p_pid) {
  888                                 sem_ref(ks);
  889                                 sem_array[i] = ks;
  890                                 i++;
  891                                 break;
  892                         }
  893                 }
  894         }
  895         LIST_FOREACH(ks, &ksem_deadhead, ks_entry) {
  896                 LIST_FOREACH(ku, &ks->ks_users, ku_next) {
  897                         if (ku->ku_pid == p1->p_pid) {
  898                                 sem_ref(ks);
  899                                 sem_array[i] = ks;
  900                                 i++;
  901                                 break;
  902                         }
  903                 }
  904         }
  905         mtx_unlock(&sem_lock);
  906         KASSERT(i == count, ("sem_forkhook: i != count (%d, %d)", i, count));
  907         /*
  908          * Now cause p2 to enter each of the referenced semaphores, then
  909          * release our temporary reference.  This is pretty inefficient.
  910          * Finally, free our temporary array.
  911          */
  912         for (i = 0; i < count; i++) {
  913                 sem_enter(p2, sem_array[i]);
  914                 mtx_lock(&sem_lock);
  915                 sem_rel(sem_array[i]);
  916                 mtx_unlock(&sem_lock);
  917         }
  918         free(sem_array, M_TEMP);
  919 }
  920 
  921 static void
  922 sem_exithook(void *arg, struct proc *p)
  923 {
  924         struct ksem *ks, *ksnext;
  925 
  926         mtx_lock(&sem_lock);
  927         ks = LIST_FIRST(&ksem_head);
  928         while (ks != NULL) {
  929                 ksnext = LIST_NEXT(ks, ks_entry);
  930                 sem_leave(p, ks);
  931                 ks = ksnext;
  932         }
  933         ks = LIST_FIRST(&ksem_deadhead);
  934         while (ks != NULL) {
  935                 ksnext = LIST_NEXT(ks, ks_entry);
  936                 sem_leave(p, ks);
  937                 ks = ksnext;
  938         }
  939         mtx_unlock(&sem_lock);
  940 }
  941 
  942 static int
  943 sem_modload(struct module *module, int cmd, void *arg)
  944 {
  945         int error = 0;
  946 
  947         switch (cmd) {
  948         case MOD_LOAD:
  949                 mtx_init(&sem_lock, "sem", "semaphore", MTX_DEF);
  950                 p31b_setcfg(CTL_P1003_1B_SEM_NSEMS_MAX, SEM_MAX);
  951                 p31b_setcfg(CTL_P1003_1B_SEM_VALUE_MAX, SEM_VALUE_MAX);
  952                 sem_exit_tag = EVENTHANDLER_REGISTER(process_exit, sem_exithook,
  953                     NULL, EVENTHANDLER_PRI_ANY);
  954                 sem_exec_tag = EVENTHANDLER_REGISTER(process_exec, sem_exithook,
  955                     NULL, EVENTHANDLER_PRI_ANY);
  956                 sem_fork_tag = EVENTHANDLER_REGISTER(process_fork, sem_forkhook, NULL, EVENTHANDLER_PRI_ANY);
  957                 break;
  958         case MOD_UNLOAD:
  959                 if (nsems != 0) {
  960                         error = EOPNOTSUPP;
  961                         break;
  962                 }
  963                 EVENTHANDLER_DEREGISTER(process_exit, sem_exit_tag);
  964                 EVENTHANDLER_DEREGISTER(process_exec, sem_exec_tag);
  965                 EVENTHANDLER_DEREGISTER(process_fork, sem_fork_tag);
  966                 mtx_destroy(&sem_lock);
  967                 break;
  968         case MOD_SHUTDOWN:
  969                 break;
  970         default:
  971                 error = EINVAL;
  972                 break;
  973         }
  974         return (error);
  975 }
  976 
  977 static moduledata_t sem_mod = {
  978         "sem",
  979         &sem_modload,
  980         NULL
  981 };
  982 
  983 SYSCALL_MODULE_HELPER(ksem_init);
  984 SYSCALL_MODULE_HELPER(ksem_open);
  985 SYSCALL_MODULE_HELPER(ksem_unlink);
  986 SYSCALL_MODULE_HELPER(ksem_close);
  987 SYSCALL_MODULE_HELPER(ksem_post);
  988 SYSCALL_MODULE_HELPER(ksem_wait);
  989 SYSCALL_MODULE_HELPER(ksem_timedwait);
  990 SYSCALL_MODULE_HELPER(ksem_trywait);
  991 SYSCALL_MODULE_HELPER(ksem_getvalue);
  992 SYSCALL_MODULE_HELPER(ksem_destroy);
  993 
  994 DECLARE_MODULE(sem, sem_mod, SI_SUB_SYSV_SEM, SI_ORDER_FIRST);
  995 MODULE_VERSION(sem, 1);

Cache object: d63248f61cfeb09f30a7c05bb9ca4ad4


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