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1 | /* Determine directory for shm/sem files. Linux version. | |
2 | Copyright (C) 2000-2019 Free Software Foundation, Inc. | |
3 | This file is part of the GNU C Library. | |
4 | ||
5 | The GNU C Library is free software; you can redistribute it and/or | |
6 | modify it under the terms of the GNU Lesser General Public | |
7 | License as published by the Free Software Foundation; either | |
8 | version 2.1 of the License, or (at your option) any later version. | |
9 | ||
10 | The GNU C Library is distributed in the hope that it will be useful, | |
11 | but WITHOUT ANY WARRANTY; without even the implied warranty of | |
12 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU | |
13 | Lesser General Public License for more details. | |
14 | ||
15 | You should have received a copy of the GNU Lesser General Public | |
16 | License along with the GNU C Library; if not, see | |
17 | <https://www.gnu.org/licenses/>. */ | |
18 | ||
19 | #include "shm-directory.h" | |
20 | ||
21 | #include <errno.h> | |
22 | #include <mntent.h> | |
23 | #include <paths.h> | |
24 | #include <stdio.h> | |
25 | #include <string.h> | |
26 | #include <sys/statfs.h> | |
27 | #include <libc-lock.h> | |
28 | #include "linux_fsinfo.h" | |
29 | ||
30 | ||
31 | /* Mount point of the shared memory filesystem. */ | |
32 | static struct | |
33 | { | |
34 | char *dir; | |
35 | size_t dirlen; | |
36 | } mountpoint; | |
37 | ||
38 | /* This is the default directory. */ | |
39 | static const char defaultdir[] = "/dev/shm/"; | |
40 | ||
41 | /* Protect the `mountpoint' variable above. */ | |
42 | __libc_once_define (static, once); | |
43 | ||
44 | ||
45 | /* Determine where the shmfs is mounted (if at all). */ | |
46 | static void | |
47 | where_is_shmfs (void) | |
48 | { | |
49 | char buf[512]; | |
50 | struct statfs f; | |
51 | struct mntent resmem; | |
52 | struct mntent *mp; | |
53 | FILE *fp; | |
54 | ||
55 | /* The canonical place is /dev/shm. This is at least what the | |
56 | documentation tells everybody to do. */ | |
57 | if (__statfs (defaultdir, &f) == 0 && (f.f_type == SHMFS_SUPER_MAGIC | |
58 | || f.f_type == RAMFS_MAGIC)) | |
59 | { | |
60 | /* It is in the normal place. */ | |
61 | mountpoint.dir = (char *) defaultdir; | |
62 | mountpoint.dirlen = sizeof (defaultdir) - 1; | |
63 | ||
64 | return; | |
65 | } | |
66 | ||
67 | /* OK, do it the hard way. Look through the /proc/mounts file and if | |
68 | this does not exist through /etc/fstab to find the mount point. */ | |
69 | fp = __setmntent ("/proc/mounts", "r"); | |
70 | if (__glibc_unlikely (fp == NULL)) | |
71 | { | |
72 | fp = __setmntent (_PATH_MNTTAB, "r"); | |
73 | if (__glibc_unlikely (fp == NULL)) | |
74 | /* There is nothing we can do. Blind guesses are not helpful. */ | |
75 | return; | |
76 | } | |
77 | ||
78 | /* Now read the entries. */ | |
79 | while ((mp = __getmntent_r (fp, &resmem, buf, sizeof buf)) != NULL) | |
80 | /* The original name is "shm" but this got changed in early Linux | |
81 | 2.4.x to "tmpfs". */ | |
82 | if (strcmp (mp->mnt_type, "tmpfs") == 0 | |
83 | || strcmp (mp->mnt_type, "shm") == 0) | |
84 | { | |
85 | /* Found it. There might be more than one place where the | |
86 | filesystem is mounted but one is enough for us. */ | |
87 | size_t namelen; | |
88 | ||
89 | /* First make sure this really is the correct entry. At least | |
90 | some versions of the kernel give wrong information because | |
91 | of the implicit mount of the shmfs for SysV IPC. */ | |
92 | if (__statfs (mp->mnt_dir, &f) != 0 || (f.f_type != SHMFS_SUPER_MAGIC | |
93 | && f.f_type != RAMFS_MAGIC)) | |
94 | continue; | |
95 | ||
96 | namelen = strlen (mp->mnt_dir); | |
97 | ||
98 | if (namelen == 0) | |
99 | /* Hum, maybe some crippled entry. Keep on searching. */ | |
100 | continue; | |
101 | ||
102 | mountpoint.dir = (char *) malloc (namelen + 2); | |
103 | if (mountpoint.dir != NULL) | |
104 | { | |
105 | char *cp = __mempcpy (mountpoint.dir, mp->mnt_dir, namelen); | |
106 | if (cp[-1] != '/') | |
107 | *cp++ = '/'; | |
108 | *cp = '\0'; | |
109 | mountpoint.dirlen = cp - mountpoint.dir; | |
110 | } | |
111 | ||
112 | break; | |
113 | } | |
114 | ||
115 | /* Close the stream. */ | |
116 | __endmntent (fp); | |
117 | } | |
118 | ||
119 | ||
120 | const char * | |
121 | __shm_directory (size_t *len) | |
122 | { | |
123 | /* Determine where the shmfs is mounted. */ | |
124 | __libc_once (once, where_is_shmfs); | |
125 | ||
126 | /* If we don't know the mount points there is nothing we can do. Ever. */ | |
127 | if (__glibc_unlikely (mountpoint.dir == NULL)) | |
128 | { | |
129 | __set_errno (ENOSYS); | |
130 | return NULL; | |
131 | } | |
132 | ||
133 | *len = mountpoint.dirlen; | |
134 | return mountpoint.dir; | |
135 | } | |
136 | #if IS_IN (libpthread) | |
137 | hidden_def (__shm_directory) | |
138 | ||
139 | /* Make sure the table is freed if we want to free everything before | |
140 | exiting. */ | |
141 | void | |
142 | __shm_directory_freeres (void) | |
143 | { | |
144 | if (mountpoint.dir != defaultdir) | |
145 | free (mountpoint.dir); | |
146 | } | |
147 | #endif |