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      1 /*
      2  * Copyright  2012 Collabora, Ltd.
      3  *
      4  * Permission is hereby granted, free of charge, to any person obtaining
      5  * a copy of this software and associated documentation files (the
      6  * "Software"), to deal in the Software without restriction, including
      7  * without limitation the rights to use, copy, modify, merge, publish,
      8  * distribute, sublicense, and/or sell copies of the Software, and to
      9  * permit persons to whom the Software is furnished to do so, subject to
     10  * the following conditions:
     11  *
     12  * The above copyright notice and this permission notice (including the
     13  * next paragraph) shall be included in all copies or substantial
     14  * portions of the Software.
     15  *
     16  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
     17  * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
     18  * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
     19  * NONINFRINGEMENT.  IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
     20  * BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
     21  * ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
     22  * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
     23  * SOFTWARE.
     24  */
     25 
     26 #define _GNU_SOURCE
     27 
     28 #include <sys/types.h>
     29 #include <unistd.h>
     30 #include <fcntl.h>
     31 #include <errno.h>
     32 #include <string.h>
     33 #include <stdlib.h>
     34 
     35 #include "config.h"
     36 #include "os-compatibility.h"
     37 
     38 #ifndef HAVE_MKOSTEMP
     39 static int
     40 set_cloexec_or_close(int fd)
     41 {
     42 	long flags;
     43 
     44 	if (fd == -1)
     45 		return -1;
     46 
     47 	flags = fcntl(fd, F_GETFD);
     48 	if (flags == -1)
     49 		goto err;
     50 
     51 	if (fcntl(fd, F_SETFD, flags | FD_CLOEXEC) == -1)
     52 		goto err;
     53 
     54 	return fd;
     55 
     56 err:
     57 	close(fd);
     58 	return -1;
     59 }
     60 #endif
     61 
     62 static int
     63 create_tmpfile_cloexec(char *tmpname)
     64 {
     65 	int fd;
     66 
     67 #ifdef HAVE_MKOSTEMP
     68 	fd = mkostemp(tmpname, O_CLOEXEC);
     69 	if (fd >= 0)
     70 		unlink(tmpname);
     71 #else
     72 	fd = mkstemp(tmpname);
     73 	if (fd >= 0) {
     74 		fd = set_cloexec_or_close(fd);
     75 		unlink(tmpname);
     76 	}
     77 #endif
     78 
     79 	return fd;
     80 }
     81 
     82 /*
     83  * Create a new, unique, anonymous file of the given size, and
     84  * return the file descriptor for it. The file descriptor is set
     85  * CLOEXEC. The file is immediately suitable for mmap()'ing
     86  * the given size at offset zero.
     87  *
     88  * The file should not have a permanent backing store like a disk,
     89  * but may have if XDG_RUNTIME_DIR is not properly implemented in OS.
     90  *
     91  * The file name is deleted from the file system.
     92  *
     93  * The file is suitable for buffer sharing between processes by
     94  * transmitting the file descriptor over Unix sockets using the
     95  * SCM_RIGHTS methods.
     96  *
     97  * If the C library implements posix_fallocate(), it is used to
     98  * guarantee that disk space is available for the file at the
     99  * given size. If disk space is insufficent, errno is set to ENOSPC.
    100  * If posix_fallocate() is not supported, program may receive
    101  * SIGBUS on accessing mmap()'ed file contents instead.
    102  */
    103 int
    104 os_create_anonymous_file(off_t size)
    105 {
    106 	static const char template[] = "/weston-shared-XXXXXX";
    107 	const char *path;
    108 	char *name;
    109 	int fd;
    110 	int ret;
    111 
    112 	path = getenv("XDG_RUNTIME_DIR");
    113 	if (!path) {
    114 		errno = ENOENT;
    115 		return -1;
    116 	}
    117 
    118 	name = malloc(strlen(path) + sizeof(template));
    119 	if (!name)
    120 		return -1;
    121 
    122 	strcpy(name, path);
    123 	strcat(name, template);
    124 
    125 	fd = create_tmpfile_cloexec(name);
    126 
    127 	free(name);
    128 
    129 	if (fd < 0)
    130 		return -1;
    131 
    132 #ifdef HAVE_POSIX_FALLOCATE
    133 	ret = posix_fallocate(fd, 0, size);
    134 	if (ret != 0) {
    135 		close(fd);
    136 		errno = ret;
    137 		return -1;
    138 	}
    139 #else
    140 	ret = ftruncate(fd, size);
    141 	if (ret < 0) {
    142 		close(fd);
    143 		return -1;
    144 	}
    145 #endif
    146 
    147 	return fd;
    148 }
    149