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/uipc_shm.c

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    1 /*-
    2  * Copyright (c) 2006 Robert N. M. Watson
    3  * All rights reserved.
    4  *
    5  * Redistribution and use in source and binary forms, with or without
    6  * modification, are permitted provided that the following conditions
    7  * are met:
    8  * 1. Redistributions of source code must retain the above copyright
    9  *    notice, this list of conditions and the following disclaimer.
   10  * 2. Redistributions in binary form must reproduce the above copyright
   11  *    notice, this list of conditions and the following disclaimer in the
   12  *    documentation and/or other materials provided with the distribution.
   13  *
   14  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
   15  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   16  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   17  * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
   18  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
   19  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
   20  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
   21  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   22  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
   23  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
   24  * SUCH DAMAGE.
   25  */
   26 
   27 /*
   28  * Support for shared swap-backed anonymous memory objects via
   29  * shm_open(2) and shm_unlink(2).  While most of the implementation is
   30  * here, vm_mmap.c contains mapping logic changes.
   31  *
   32  * TODO:
   33  *
   34  * (2) Need to export data to a userland tool via a sysctl.  Should ipcs(1)
   35  *     and ipcrm(1) be expanded or should new tools to manage both POSIX
   36  *     kernel semaphores and POSIX shared memory be written?
   37  *
   38  * (3) Add support for this file type to fstat(1).
   39  *
   40  * (4) Resource limits?  Does this need its own resource limits or are the
   41  *     existing limits in mmap(2) sufficient?
   42  *
   43  * (5) Partial page truncation.  vnode_pager_setsize() will zero any parts
   44  *     of a partially mapped page as a result of ftruncate(2)/truncate(2).
   45  *     We can do the same (with the same pmap evil), but do we need to
   46  *     worry about the bits on disk if the page is swapped out or will the
   47  *     swapper zero the parts of a page that are invalid if the page is
   48  *     swapped back in for us?
   49  *
   50  * (6) Add MAC support in mac_biba(4) and mac_mls(4).
   51  *
   52  * (7) Add a MAC check_create() hook for creating new named objects.
   53  */
   54 
   55 #include <sys/cdefs.h>
   56 __FBSDID("$FreeBSD: releng/8.3/sys/kern/uipc_shm.c 199583 2009-11-20 15:27:52Z jhb $");
   57 
   58 #include <sys/param.h>
   59 #include <sys/fcntl.h>
   60 #include <sys/file.h>
   61 #include <sys/filedesc.h>
   62 #include <sys/fnv_hash.h>
   63 #include <sys/kernel.h>
   64 #include <sys/lock.h>
   65 #include <sys/malloc.h>
   66 #include <sys/mman.h>
   67 #include <sys/mutex.h>
   68 #include <sys/proc.h>
   69 #include <sys/refcount.h>
   70 #include <sys/resourcevar.h>
   71 #include <sys/stat.h>
   72 #include <sys/sysctl.h>
   73 #include <sys/sysproto.h>
   74 #include <sys/systm.h>
   75 #include <sys/sx.h>
   76 #include <sys/time.h>
   77 #include <sys/vnode.h>
   78 
   79 #include <security/mac/mac_framework.h>
   80 
   81 #include <vm/vm.h>
   82 #include <vm/vm_param.h>
   83 #include <vm/pmap.h>
   84 #include <vm/vm_map.h>
   85 #include <vm/vm_object.h>
   86 #include <vm/vm_page.h>
   87 #include <vm/vm_pager.h>
   88 #include <vm/swap_pager.h>
   89 
   90 struct shm_mapping {
   91         char            *sm_path;
   92         Fnv32_t         sm_fnv;
   93         struct shmfd    *sm_shmfd;
   94         LIST_ENTRY(shm_mapping) sm_link;
   95 };
   96 
   97 static MALLOC_DEFINE(M_SHMFD, "shmfd", "shared memory file descriptor");
   98 static LIST_HEAD(, shm_mapping) *shm_dictionary;
   99 static struct sx shm_dict_lock;
  100 static struct mtx shm_timestamp_lock;
  101 static u_long shm_hash;
  102 
  103 #define SHM_HASH(fnv)   (&shm_dictionary[(fnv) & shm_hash])
  104 
  105 static int      shm_access(struct shmfd *shmfd, struct ucred *ucred, int flags);
  106 static struct shmfd *shm_alloc(struct ucred *ucred, mode_t mode);
  107 static void     shm_dict_init(void *arg);
  108 static void     shm_drop(struct shmfd *shmfd);
  109 static struct shmfd *shm_hold(struct shmfd *shmfd);
  110 static void     shm_insert(char *path, Fnv32_t fnv, struct shmfd *shmfd);
  111 static struct shmfd *shm_lookup(char *path, Fnv32_t fnv);
  112 static int      shm_remove(char *path, Fnv32_t fnv, struct ucred *ucred);
  113 static int      shm_dotruncate(struct shmfd *shmfd, off_t length);
  114 
  115 static fo_rdwr_t        shm_read;
  116 static fo_rdwr_t        shm_write;
  117 static fo_truncate_t    shm_truncate;
  118 static fo_ioctl_t       shm_ioctl;
  119 static fo_poll_t        shm_poll;
  120 static fo_kqfilter_t    shm_kqfilter;
  121 static fo_stat_t        shm_stat;
  122 static fo_close_t       shm_close;
  123 
  124 /* File descriptor operations. */
  125 static struct fileops shm_ops = {
  126         .fo_read = shm_read,
  127         .fo_write = shm_write,
  128         .fo_truncate = shm_truncate,
  129         .fo_ioctl = shm_ioctl,
  130         .fo_poll = shm_poll,
  131         .fo_kqfilter = shm_kqfilter,
  132         .fo_stat = shm_stat,
  133         .fo_close = shm_close,
  134         .fo_flags = DFLAG_PASSABLE
  135 };
  136 
  137 FEATURE(posix_shm, "POSIX shared memory");
  138 
  139 static int
  140 shm_read(struct file *fp, struct uio *uio, struct ucred *active_cred,
  141     int flags, struct thread *td)
  142 {
  143 
  144         return (EOPNOTSUPP);
  145 }
  146 
  147 static int
  148 shm_write(struct file *fp, struct uio *uio, struct ucred *active_cred,
  149     int flags, struct thread *td)
  150 {
  151 
  152         return (EOPNOTSUPP);
  153 }
  154 
  155 static int
  156 shm_truncate(struct file *fp, off_t length, struct ucred *active_cred,
  157     struct thread *td)
  158 {
  159         struct shmfd *shmfd;
  160 #ifdef MAC
  161         int error;
  162 #endif
  163 
  164         shmfd = fp->f_data;
  165 #ifdef MAC
  166         error = mac_posixshm_check_truncate(active_cred, fp->f_cred, shmfd);
  167         if (error)
  168                 return (error);
  169 #endif
  170         return (shm_dotruncate(shmfd, length));
  171 }
  172 
  173 static int
  174 shm_ioctl(struct file *fp, u_long com, void *data,
  175     struct ucred *active_cred, struct thread *td)
  176 {
  177 
  178         return (EOPNOTSUPP);
  179 }
  180 
  181 static int
  182 shm_poll(struct file *fp, int events, struct ucred *active_cred,
  183     struct thread *td)
  184 {
  185 
  186         return (EOPNOTSUPP);
  187 }
  188 
  189 static int
  190 shm_kqfilter(struct file *fp, struct knote *kn)
  191 {
  192 
  193         return (EOPNOTSUPP);
  194 }
  195 
  196 static int
  197 shm_stat(struct file *fp, struct stat *sb, struct ucred *active_cred,
  198     struct thread *td)
  199 {
  200         struct shmfd *shmfd;
  201 #ifdef MAC
  202         int error;
  203 #endif
  204 
  205         shmfd = fp->f_data;
  206 
  207 #ifdef MAC
  208         error = mac_posixshm_check_stat(active_cred, fp->f_cred, shmfd);
  209         if (error)
  210                 return (error);
  211 #endif
  212         
  213         /*
  214          * Attempt to return sanish values for fstat() on a memory file
  215          * descriptor.
  216          */
  217         bzero(sb, sizeof(*sb));
  218         sb->st_mode = S_IFREG | shmfd->shm_mode;                /* XXX */
  219         sb->st_blksize = PAGE_SIZE;
  220         sb->st_size = shmfd->shm_size;
  221         sb->st_blocks = (sb->st_size + sb->st_blksize - 1) / sb->st_blksize;
  222         sb->st_atimespec = shmfd->shm_atime;
  223         sb->st_ctimespec = shmfd->shm_ctime;
  224         sb->st_mtimespec = shmfd->shm_mtime;
  225         sb->st_birthtimespec = shmfd->shm_birthtime;    
  226         sb->st_uid = shmfd->shm_uid;
  227         sb->st_gid = shmfd->shm_gid;
  228 
  229         return (0);
  230 }
  231 
  232 static int
  233 shm_close(struct file *fp, struct thread *td)
  234 {
  235         struct shmfd *shmfd;
  236 
  237         shmfd = fp->f_data;
  238         fp->f_data = NULL;
  239         shm_drop(shmfd);
  240 
  241         return (0);
  242 }
  243 
  244 static int
  245 shm_dotruncate(struct shmfd *shmfd, off_t length)
  246 {
  247         vm_object_t object;
  248         vm_page_t m;
  249         vm_pindex_t nobjsize;
  250         vm_ooffset_t delta;
  251 
  252         object = shmfd->shm_object;
  253         VM_OBJECT_LOCK(object);
  254         if (length == shmfd->shm_size) {
  255                 VM_OBJECT_UNLOCK(object);
  256                 return (0);
  257         }
  258         nobjsize = OFF_TO_IDX(length + PAGE_MASK);
  259 
  260         /* Are we shrinking?  If so, trim the end. */
  261         if (length < shmfd->shm_size) {
  262                 delta = ptoa(object->size - nobjsize);
  263 
  264                 /* Toss in memory pages. */
  265                 if (nobjsize < object->size)
  266                         vm_object_page_remove(object, nobjsize, object->size,
  267                             FALSE);
  268 
  269                 /* Toss pages from swap. */
  270                 if (object->type == OBJT_SWAP)
  271                         swap_pager_freespace(object, nobjsize, delta);
  272 
  273                 /* Free the swap accounted for shm */
  274                 swap_release_by_uid(delta, object->uip);
  275                 object->charge -= delta;
  276 
  277                 /*
  278                  * If the last page is partially mapped, then zero out
  279                  * the garbage at the end of the page.  See comments
  280                  * in vnode_pager_setsize() for more details.
  281                  *
  282                  * XXXJHB: This handles in memory pages, but what about
  283                  * a page swapped out to disk?
  284                  */
  285                 if ((length & PAGE_MASK) &&
  286                     (m = vm_page_lookup(object, OFF_TO_IDX(length))) != NULL &&
  287                     m->valid != 0) {
  288                         int base = (int)length & PAGE_MASK;
  289                         int size = PAGE_SIZE - base;
  290 
  291                         pmap_zero_page_area(m, base, size);
  292 
  293                         /*
  294                          * Update the valid bits to reflect the blocks that
  295                          * have been zeroed.  Some of these valid bits may
  296                          * have already been set.
  297                          */
  298                         vm_page_set_valid(m, base, size);
  299 
  300                         /*
  301                          * Round "base" to the next block boundary so that the
  302                          * dirty bit for a partially zeroed block is not
  303                          * cleared.
  304                          */
  305                         base = roundup2(base, DEV_BSIZE);
  306 
  307                         vm_page_lock_queues();
  308                         vm_page_clear_dirty(m, base, PAGE_SIZE - base);
  309                         vm_page_unlock_queues();
  310                 } else if ((length & PAGE_MASK) &&
  311                     __predict_false(object->cache != NULL)) {
  312                         vm_page_cache_free(object, OFF_TO_IDX(length),
  313                             nobjsize);
  314                 }
  315         } else {
  316 
  317                 /* Attempt to reserve the swap */
  318                 delta = ptoa(nobjsize - object->size);
  319                 if (!swap_reserve_by_uid(delta, object->uip)) {
  320                         VM_OBJECT_UNLOCK(object);
  321                         return (ENOMEM);
  322                 }
  323                 object->charge += delta;
  324         }
  325         shmfd->shm_size = length;
  326         mtx_lock(&shm_timestamp_lock);
  327         vfs_timestamp(&shmfd->shm_ctime);
  328         shmfd->shm_mtime = shmfd->shm_ctime;
  329         mtx_unlock(&shm_timestamp_lock);
  330         object->size = nobjsize;
  331         VM_OBJECT_UNLOCK(object);
  332         return (0);
  333 }
  334 
  335 /*
  336  * shmfd object management including creation and reference counting
  337  * routines.
  338  */
  339 static struct shmfd *
  340 shm_alloc(struct ucred *ucred, mode_t mode)
  341 {
  342         struct shmfd *shmfd;
  343 
  344         shmfd = malloc(sizeof(*shmfd), M_SHMFD, M_WAITOK | M_ZERO);
  345         shmfd->shm_size = 0;
  346         shmfd->shm_uid = ucred->cr_uid;
  347         shmfd->shm_gid = ucred->cr_gid;
  348         shmfd->shm_mode = mode;
  349         shmfd->shm_object = vm_pager_allocate(OBJT_DEFAULT, NULL,
  350             shmfd->shm_size, VM_PROT_DEFAULT, 0, ucred);
  351         KASSERT(shmfd->shm_object != NULL, ("shm_create: vm_pager_allocate"));
  352         VM_OBJECT_LOCK(shmfd->shm_object);
  353         vm_object_clear_flag(shmfd->shm_object, OBJ_ONEMAPPING);
  354         vm_object_set_flag(shmfd->shm_object, OBJ_NOSPLIT);
  355         VM_OBJECT_UNLOCK(shmfd->shm_object);
  356         vfs_timestamp(&shmfd->shm_birthtime);
  357         shmfd->shm_atime = shmfd->shm_mtime = shmfd->shm_ctime =
  358             shmfd->shm_birthtime;
  359         refcount_init(&shmfd->shm_refs, 1);
  360 #ifdef MAC
  361         mac_posixshm_init(shmfd);
  362         mac_posixshm_create(ucred, shmfd);
  363 #endif
  364 
  365         return (shmfd);
  366 }
  367 
  368 static struct shmfd *
  369 shm_hold(struct shmfd *shmfd)
  370 {
  371 
  372         refcount_acquire(&shmfd->shm_refs);
  373         return (shmfd);
  374 }
  375 
  376 static void
  377 shm_drop(struct shmfd *shmfd)
  378 {
  379 
  380         if (refcount_release(&shmfd->shm_refs)) {
  381 #ifdef MAC
  382                 mac_posixshm_destroy(shmfd);
  383 #endif
  384                 vm_object_deallocate(shmfd->shm_object);
  385                 free(shmfd, M_SHMFD);
  386         }
  387 }
  388 
  389 /*
  390  * Determine if the credentials have sufficient permissions for a
  391  * specified combination of FREAD and FWRITE.
  392  */
  393 static int
  394 shm_access(struct shmfd *shmfd, struct ucred *ucred, int flags)
  395 {
  396         accmode_t accmode;
  397 
  398         accmode = 0;
  399         if (flags & FREAD)
  400                 accmode |= VREAD;
  401         if (flags & FWRITE)
  402                 accmode |= VWRITE;
  403         return (vaccess(VREG, shmfd->shm_mode, shmfd->shm_uid, shmfd->shm_gid,
  404             accmode, ucred, NULL));
  405 }
  406 
  407 /*
  408  * Dictionary management.  We maintain an in-kernel dictionary to map
  409  * paths to shmfd objects.  We use the FNV hash on the path to store
  410  * the mappings in a hash table.
  411  */
  412 static void
  413 shm_dict_init(void *arg)
  414 {
  415 
  416         mtx_init(&shm_timestamp_lock, "shm timestamps", NULL, MTX_DEF);
  417         sx_init(&shm_dict_lock, "shm dictionary");
  418         shm_dictionary = hashinit(1024, M_SHMFD, &shm_hash);
  419 }
  420 SYSINIT(shm_dict_init, SI_SUB_SYSV_SHM, SI_ORDER_ANY, shm_dict_init, NULL);
  421 
  422 static struct shmfd *
  423 shm_lookup(char *path, Fnv32_t fnv)
  424 {
  425         struct shm_mapping *map;
  426 
  427         LIST_FOREACH(map, SHM_HASH(fnv), sm_link) {
  428                 if (map->sm_fnv != fnv)
  429                         continue;
  430                 if (strcmp(map->sm_path, path) == 0)
  431                         return (map->sm_shmfd);
  432         }
  433 
  434         return (NULL);
  435 }
  436 
  437 static void
  438 shm_insert(char *path, Fnv32_t fnv, struct shmfd *shmfd)
  439 {
  440         struct shm_mapping *map;
  441 
  442         map = malloc(sizeof(struct shm_mapping), M_SHMFD, M_WAITOK);
  443         map->sm_path = path;
  444         map->sm_fnv = fnv;
  445         map->sm_shmfd = shm_hold(shmfd);
  446         LIST_INSERT_HEAD(SHM_HASH(fnv), map, sm_link);
  447 }
  448 
  449 static int
  450 shm_remove(char *path, Fnv32_t fnv, struct ucred *ucred)
  451 {
  452         struct shm_mapping *map;
  453         int error;
  454 
  455         LIST_FOREACH(map, SHM_HASH(fnv), sm_link) {
  456                 if (map->sm_fnv != fnv)
  457                         continue;
  458                 if (strcmp(map->sm_path, path) == 0) {
  459 #ifdef MAC
  460                         error = mac_posixshm_check_unlink(ucred, map->sm_shmfd);
  461                         if (error)
  462                                 return (error);
  463 #endif
  464                         error = shm_access(map->sm_shmfd, ucred,
  465                             FREAD | FWRITE);
  466                         if (error)
  467                                 return (error);
  468                         LIST_REMOVE(map, sm_link);
  469                         shm_drop(map->sm_shmfd);
  470                         free(map->sm_path, M_SHMFD);
  471                         free(map, M_SHMFD);
  472                         return (0);
  473                 }
  474         }
  475 
  476         return (ENOENT);
  477 }
  478 
  479 /* System calls. */
  480 int
  481 shm_open(struct thread *td, struct shm_open_args *uap)
  482 {
  483         struct filedesc *fdp;
  484         struct shmfd *shmfd;
  485         struct file *fp;
  486         char *path;
  487         Fnv32_t fnv;
  488         mode_t cmode;
  489         int fd, error;
  490 
  491         if ((uap->flags & O_ACCMODE) != O_RDONLY &&
  492             (uap->flags & O_ACCMODE) != O_RDWR)
  493                 return (EINVAL);
  494 
  495         if ((uap->flags & ~(O_ACCMODE | O_CREAT | O_EXCL | O_TRUNC)) != 0)
  496                 return (EINVAL);
  497 
  498         fdp = td->td_proc->p_fd;
  499         cmode = (uap->mode & ~fdp->fd_cmask) & ACCESSPERMS;
  500 
  501         error = falloc(td, &fp, &fd);
  502         if (error)
  503                 return (error);
  504 
  505         /* A SHM_ANON path pointer creates an anonymous object. */
  506         if (uap->path == SHM_ANON) {
  507                 /* A read-only anonymous object is pointless. */
  508                 if ((uap->flags & O_ACCMODE) == O_RDONLY) {
  509                         fdclose(fdp, fp, fd, td);
  510                         fdrop(fp, td);
  511                         return (EINVAL);
  512                 }
  513                 shmfd = shm_alloc(td->td_ucred, cmode);
  514         } else {
  515                 path = malloc(MAXPATHLEN, M_SHMFD, M_WAITOK);
  516                 error = copyinstr(uap->path, path, MAXPATHLEN, NULL);
  517 
  518                 /* Require paths to start with a '/' character. */
  519                 if (error == 0 && path[0] != '/')
  520                         error = EINVAL;
  521                 if (error) {
  522                         fdclose(fdp, fp, fd, td);
  523                         fdrop(fp, td);
  524                         free(path, M_SHMFD);
  525                         return (error);
  526                 }
  527 
  528                 fnv = fnv_32_str(path, FNV1_32_INIT);
  529                 sx_xlock(&shm_dict_lock);
  530                 shmfd = shm_lookup(path, fnv);
  531                 if (shmfd == NULL) {
  532                         /* Object does not yet exist, create it if requested. */
  533                         if (uap->flags & O_CREAT) {
  534                                 shmfd = shm_alloc(td->td_ucred, cmode);
  535                                 shm_insert(path, fnv, shmfd);
  536                         } else {
  537                                 free(path, M_SHMFD);
  538                                 error = ENOENT;
  539                         }
  540                 } else {
  541                         /*
  542                          * Object already exists, obtain a new
  543                          * reference if requested and permitted.
  544                          */
  545                         free(path, M_SHMFD);
  546                         if ((uap->flags & (O_CREAT | O_EXCL)) ==
  547                             (O_CREAT | O_EXCL))
  548                                 error = EEXIST;
  549                         else {
  550 #ifdef MAC
  551                                 error = mac_posixshm_check_open(td->td_ucred,
  552                                     shmfd);
  553                                 if (error == 0)
  554 #endif
  555                                 error = shm_access(shmfd, td->td_ucred,
  556                                     FFLAGS(uap->flags & O_ACCMODE));
  557                         }
  558 
  559                         /*
  560                          * Truncate the file back to zero length if
  561                          * O_TRUNC was specified and the object was
  562                          * opened with read/write.
  563                          */
  564                         if (error == 0 &&
  565                             (uap->flags & (O_ACCMODE | O_TRUNC)) ==
  566                             (O_RDWR | O_TRUNC)) {
  567 #ifdef MAC
  568                                 error = mac_posixshm_check_truncate(
  569                                         td->td_ucred, fp->f_cred, shmfd);
  570                                 if (error == 0)
  571 #endif
  572                                         shm_dotruncate(shmfd, 0);
  573                         }
  574                         if (error == 0)
  575                                 shm_hold(shmfd);
  576                 }
  577                 sx_xunlock(&shm_dict_lock);
  578 
  579                 if (error) {
  580                         fdclose(fdp, fp, fd, td);
  581                         fdrop(fp, td);
  582                         return (error);
  583                 }
  584         }
  585 
  586         finit(fp, FFLAGS(uap->flags & O_ACCMODE), DTYPE_SHM, shmfd, &shm_ops);
  587 
  588         FILEDESC_XLOCK(fdp);
  589         if (fdp->fd_ofiles[fd] == fp)
  590                 fdp->fd_ofileflags[fd] |= UF_EXCLOSE;
  591         FILEDESC_XUNLOCK(fdp);
  592         td->td_retval[0] = fd;
  593         fdrop(fp, td);
  594 
  595         return (0);
  596 }
  597 
  598 int
  599 shm_unlink(struct thread *td, struct shm_unlink_args *uap)
  600 {
  601         char *path;
  602         Fnv32_t fnv;
  603         int error;
  604 
  605         path = malloc(MAXPATHLEN, M_TEMP, M_WAITOK);
  606         error = copyinstr(uap->path, path, MAXPATHLEN, NULL);
  607         if (error) {
  608                 free(path, M_TEMP);
  609                 return (error);
  610         }
  611 
  612         fnv = fnv_32_str(path, FNV1_32_INIT);
  613         sx_xlock(&shm_dict_lock);
  614         error = shm_remove(path, fnv, td->td_ucred);
  615         sx_xunlock(&shm_dict_lock);
  616         free(path, M_TEMP);
  617 
  618         return (error);
  619 }
  620 
  621 /*
  622  * mmap() helper to validate mmap() requests against shm object state
  623  * and give mmap() the vm_object to use for the mapping.
  624  */
  625 int
  626 shm_mmap(struct shmfd *shmfd, vm_size_t objsize, vm_ooffset_t foff,
  627     vm_object_t *obj)
  628 {
  629 
  630         /*
  631          * XXXRW: This validation is probably insufficient, and subject to
  632          * sign errors.  It should be fixed.
  633          */
  634         if (foff >= shmfd->shm_size ||
  635             foff + objsize > round_page(shmfd->shm_size))
  636                 return (EINVAL);
  637 
  638         mtx_lock(&shm_timestamp_lock);
  639         vfs_timestamp(&shmfd->shm_atime);
  640         mtx_unlock(&shm_timestamp_lock);
  641         vm_object_reference(shmfd->shm_object);
  642         *obj = shmfd->shm_object;
  643         return (0);
  644 }

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