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shm.c revision 1.2 
      1 /*	$NetBSD: shm.c,v 1.2 2015/06/30 11:46:47 martin 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 1.2 2015/06/30 11:46:47 martin 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 static char			_shmfs_path_buf[PATH_MAX];
     62 
     63 static bool
     64 _shm_check_fs(void)
     65 {
     66 	const char *shmfs = SHMFS_DIR_PATH;
     67 	struct statvfs sv;
     68 	struct stat st;
     69 	char buf[PATH_MAX];
     70 	ssize_t cnt;
     71 
     72 	if ((cnt = readlink(shmfs, buf, sizeof(buf))) > 0) {
     73 		if ((size_t)cnt >= sizeof(buf))
     74 			return false;
     75 		buf[cnt] = 0;
     76 		shmfs = buf;
     77 	}
     78 	if (statvfs1(shmfs, &sv, ST_NOWAIT) == -1) {
     79 		return false;
     80 	}
     81 	if (strncmp(sv.f_fstypename, MOUNT_SHMFS, sizeof(sv.f_fstypename))) {
     82 		return false;
     83 	}
     84 
     85 	if (lstat(shmfs, &st) == -1) {
     86 		return false;
     87 	}
     88 	if ((st.st_mode & SHMFS_DIR_MODE) != SHMFS_DIR_MODE) {
     89 		return false;
     90 	}
     91 
     92 	if (shmfs == buf) {
     93 		strcpy(_shmfs_path_buf, buf);
     94 		_shmfs_path = _shmfs_path_buf;
     95 	} else {
     96 		_shmfs_path = shmfs;
     97 	}
     98 	return true;
     99 }
    100 
    101 static bool
    102 _shm_get_path(char *buf, size_t len, const char *name)
    103 {
    104 	int ret;
    105 
    106 	if (__predict_false(!_shmfs_path) && !_shm_check_fs()) {
    107 		errno = ENOTSUP;
    108 		return false;
    109 	}
    110 
    111 	/*
    112 	 * As per POSIX: the name should begin with a slash character.
    113 	 * We may disallow other slashes (implementation-defined behaviour).
    114 	 */
    115 	if (*name++ != '/' || strchr(name, '/') != NULL) {
    116 		errno = EINVAL;
    117 		return false;
    118 	}
    119 
    120 	ret = snprintf(buf, len, "%s/%s%s",
    121 	    _shmfs_path, SHMFS_OBJ_PREFIX, name);
    122 
    123 	if ((size_t)ret >= PATH_MAX) {
    124 		errno = ENAMETOOLONG;
    125 		return false;
    126 	}
    127 	return ret != -1;
    128 }
    129 
    130 int
    131 shm_open(const char *name, int oflag, mode_t mode)
    132 {
    133 	char path[PATH_MAX + 1];
    134 
    135 	if (!_shm_get_path(path, sizeof(path), name)) {
    136 		return -1;
    137 	}
    138 	return open(path, oflag | O_CLOEXEC | O_NOFOLLOW, mode);
    139 }
    140 
    141 int
    142 shm_unlink(const char *name)
    143 {
    144 	char path[PATH_MAX + 1];
    145 
    146 	if (!_shm_get_path(path, sizeof(path), name)) {
    147 		return -1;
    148 	}
    149 	return unlink(path);
    150 }
    151