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#include "config.h"
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#ifdef HAVE_MEMFD_CREATE
36#include <sys/mman.h>
37#endif
38
39#include "os-compatibility.h"
40
41#ifndef HAVE_MKOSTEMP
42static int
43set_cloexec_or_close(int fd)
44{
45 long flags;
46
47 if (fd == -1)
48 return -1;
49
50 flags = fcntl(fd: fd, F_GETFD);
51 if (flags == -1)
52 goto err;
53
54 if (fcntl(fd: fd, F_SETFD, flags | FD_CLOEXEC) == -1)
55 goto err;
56
57 return fd;
58
59err:
60 close(fd: fd);
61 return -1;
62}
63#endif
64
65static int
66create_tmpfile_cloexec(char *tmpname)
67{
68 int fd;
69
70#ifdef HAVE_MKOSTEMP
71 fd = mkostemp(tmpname, O_CLOEXEC);
72 if (fd >= 0)
73 unlink(tmpname);
74#else
75 fd = mkstemp(template: tmpname);
76 if (fd >= 0) {
77 fd = set_cloexec_or_close(fd);
78 unlink(name: tmpname);
79 }
80#endif
81
82 return fd;
83}
84
85/*
86 * Create a new, unique, anonymous file of the given size, and
87 * return the file descriptor for it. The file descriptor is set
88 * CLOEXEC. The file is immediately suitable for mmap()'ing
89 * the given size at offset zero.
90 *
91 * The file should not have a permanent backing store like a disk,
92 * but may have if XDG_RUNTIME_DIR is not properly implemented in OS.
93 *
94 * The file name is deleted from the file system.
95 *
96 * The file is suitable for buffer sharing between processes by
97 * transmitting the file descriptor over Unix sockets using the
98 * SCM_RIGHTS methods.
99 *
100 * If the C library implements posix_fallocate(), it is used to
101 * guarantee that disk space is available for the file at the
102 * given size. If disk space is insufficient, errno is set to ENOSPC.
103 * If posix_fallocate() is not supported, program may receive
104 * SIGBUS on accessing mmap()'ed file contents instead.
105 *
106 * If the C library implements memfd_create(), it is used to create the
107 * file purely in memory, without any backing file name on the file
108 * system, and then sealing off the possibility of shrinking it. This
109 * can then be checked before accessing mmap()'ed file contents, to
110 * make sure SIGBUS can't happen. It also avoids requiring
111 * XDG_RUNTIME_DIR.
112 */
113int
114os_create_anonymous_file(off_t size)
115{
116 static const char template[] = "/wayland-cursor-shared-XXXXXX";
117 const char *path;
118 char *name;
119 int fd;
120 int ret;
121
122#ifdef HAVE_MEMFD_CREATE
123 fd = memfd_create(name: "wayland-cursor", MFD_CLOEXEC | MFD_ALLOW_SEALING);
124 if (fd >= 0) {
125 /* We can add this seal before calling posix_fallocate(), as
126 * the file is currently zero-sized anyway.
127 *
128 * There is also no need to check for the return value, we
129 * couldn't do anything with it anyway.
130 */
131 fcntl(fd: fd, F_ADD_SEALS, F_SEAL_SHRINK | F_SEAL_SEAL);
132 } else
133#endif
134 {
135 path = getenv(name: "XDG_RUNTIME_DIR");
136 if (!path) {
137 errno = ENOENT;
138 return -1;
139 }
140
141 name = malloc(size: strlen(s: path) + sizeof(template));
142 if (!name)
143 return -1;
144
145 strcpy(dest: name, src: path);
146 strcat(dest: name, src: template);
147
148 fd = create_tmpfile_cloexec(tmpname: name);
149
150 free(ptr: name);
151
152 if (fd < 0)
153 return -1;
154 }
155
156#ifdef HAVE_POSIX_FALLOCATE
157 ret = posix_fallocate(fd: fd, offset: 0, len: size);
158 if (ret != 0) {
159 close(fd: fd);
160 errno = ret;
161 return -1;
162 }
163#else
164 ret = ftruncate(fd, size);
165 if (ret < 0) {
166 close(fd);
167 return -1;
168 }
169#endif
170
171 return fd;
172}
173

source code of gtk/gdk/wayland/cursor/os-compatibility.c