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shm.c revision 1.1.4.2 
      1 /*	$NetBSD: shm.c,v 1.1.4.2 2014/05/22 11:36:59 yamt Exp $	*/
      2 
      3 /*-
      4  * Copyright (c) 2013 The NetBSD Foundation, Inc.
      5  * All rights reserved.
      6  *
      7  * This code is derived from software contributed to The NetBSD Foundation
      8  * by Mindaugas Rasiukevicius.
      9  *
     10  * Redistribution and use in source and binary forms, with or without
     11  * modification, are permitted provided that the following conditions
     12  * are met:
     13  * 1. Redistributions of source code must retain the above copyright
     14  *    notice, this list of conditions and the following disclaimer.
     15  * 2. Redistributions in binary form must reproduce the above copyright
     16  *    notice, this list of conditions and the following disclaimer in the
     17  *    documentation and/or other materials provided with the distribution.
     18  *
     19  * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
     20  * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
     21  * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
     22  * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
     23  * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
     24  * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
     25  * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
     26  * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
     27  * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
     28  * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
     29  * POSSIBILITY OF SUCH DAMAGE.
     30  */
     31 
     32 /*
     33  * Interface for POSIX shared memory objects.
     34  */
     35 
     36 #include <sys/cdefs.h>
     37 __RCSID("$NetBSD: shm.c,v 1.1.4.2 2014/05/22 11:36:59 yamt Exp $");
     38 
     39 #include <sys/mman.h>
     40 #include <sys/mount.h>
     41 #include <sys/stat.h>
     42 
     43 #include <stdio.h>
     44 #include <stdbool.h>
     45 #include <string.h>
     46 #include <unistd.h>
     47 #include <fcntl.h>
     48 #include <errno.h>
     49 #include <limits.h>
     50 
     51 /*
     52  * Shared memory objects are supported using tmpfs.
     53  */
     54 #define	SHMFS_DIR_PATH		"/var/shm"
     55 #define	SHMFS_DIR_MODE		(S_ISVTX | S_IRWXU | S_IRWXG | S_IRWXO)
     56 #define	SHMFS_OBJ_PREFIX	".shmobj_"
     57 
     58 #define	MOUNT_SHMFS		MOUNT_TMPFS
     59 
     60 static const char *		_shmfs_path = NULL;
     61 
     62 static bool
     63 _shm_check_fs(void)
     64 {
     65 	const char *shmfs = SHMFS_DIR_PATH;
     66 	struct statvfs sv;
     67 	struct stat st;
     68 
     69 	if (statvfs1(shmfs, &sv, ST_NOWAIT) == -1) {
     70 		return false;
     71 	}
     72 	if (strncmp(sv.f_fstypename, MOUNT_SHMFS, sizeof(sv.f_fstypename))) {
     73 		return false;
     74 	}
     75 
     76 	if (lstat(shmfs, &st) == -1) {
     77 		return false;
     78 	}
     79 	if ((st.st_mode & SHMFS_DIR_MODE) != SHMFS_DIR_MODE) {
     80 		return false;
     81 	}
     82 
     83 	_shmfs_path = shmfs;
     84 	return true;
     85 }
     86 
     87 static bool
     88 _shm_get_path(char *buf, size_t len, const char *name)
     89 {
     90 	int ret;
     91 
     92 	if (__predict_false(!_shmfs_path) && !_shm_check_fs()) {
     93 		errno = ENOTSUP;
     94 		return false;
     95 	}
     96 
     97 	/*
     98 	 * As per POSIX: the name should begin with a slash character.
     99 	 * We may disallow other slashes (implementation-defined behaviour).
    100 	 */
    101 	if (*name++ != '/' || strchr(name, '/') != NULL) {
    102 		errno = EINVAL;
    103 		return false;
    104 	}
    105 
    106 	ret = snprintf(buf, len, "%s/%s%s",
    107 	    _shmfs_path, SHMFS_OBJ_PREFIX, name);
    108 
    109 	if ((size_t)ret >= PATH_MAX) {
    110 		errno = ENAMETOOLONG;
    111 		return false;
    112 	}
    113 	return ret != -1;
    114 }
    115 
    116 int
    117 shm_open(const char *name, int oflag, mode_t mode)
    118 {
    119 	char path[PATH_MAX + 1];
    120 
    121 	if (!_shm_get_path(path, sizeof(path), name)) {
    122 		return -1;
    123 	}
    124 	return open(path, oflag | O_CLOEXEC | O_NOFOLLOW, mode);
    125 }
    126 
    127 int
    128 shm_unlink(const char *name)
    129 {
    130 	char path[PATH_MAX + 1];
    131 
    132 	if (!_shm_get_path(path, sizeof(path), name)) {
    133 		return -1;
    134 	}
    135 	return unlink(path);
    136 }
    137