1 /* Copyright (C) 2000-2014 Free Software Foundation, Inc.
2 This file is part of the GNU C Library.
4 The GNU C Library is free software; you can redistribute it and/or
5 modify it under the terms of the GNU Lesser General Public
6 License as published by the Free Software Foundation; either
7 version 2.1 of the License, or (at your option) any later version.
9 The GNU C Library is distributed in the hope that it will be useful,
10 but WITHOUT ANY WARRANTY; without even the implied warranty of
11 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
12 Lesser General Public License for more details.
14 You should have received a copy of the GNU Lesser General Public
15 License along with the GNU C Library; if not, see
16 <http://www.gnu.org/licenses/>. */
27 #include <sys/statfs.h>
28 #include <bits/libc-lock.h>
29 #include "linux_fsinfo.h"
32 /* Mount point of the shared memory filesystem. */
39 /* This is the default directory. */
40 static const char defaultdir
[] = "/dev/shm/";
42 /* Protect the `mountpoint' variable above. */
43 __libc_once_define (static, once
);
46 /* Determine where the shmfs is mounted (if at all). */
56 /* The canonical place is /dev/shm. This is at least what the
57 documentation tells everybody to do. */
58 if (__statfs (defaultdir
, &f
) == 0 && (f
.f_type
== SHMFS_SUPER_MAGIC
59 || f
.f_type
== RAMFS_MAGIC
))
61 /* It is in the normal place. */
62 mountpoint
.dir
= (char *) defaultdir
;
63 mountpoint
.dirlen
= sizeof (defaultdir
) - 1;
68 /* OK, do it the hard way. Look through the /proc/mounts file and if
69 this does not exist through /etc/fstab to find the mount point. */
70 fp
= __setmntent ("/proc/mounts", "r");
71 if (__glibc_unlikely (fp
== NULL
))
73 fp
= __setmntent (_PATH_MNTTAB
, "r");
74 if (__glibc_unlikely (fp
== NULL
))
75 /* There is nothing we can do. Blind guesses are not helpful. */
79 /* Now read the entries. */
80 while ((mp
= __getmntent_r (fp
, &resmem
, buf
, sizeof buf
)) != NULL
)
81 /* The original name is "shm" but this got changed in early Linux
83 if (strcmp (mp
->mnt_type
, "tmpfs") == 0
84 || strcmp (mp
->mnt_type
, "shm") == 0)
86 /* Found it. There might be more than one place where the
87 filesystem is mounted but one is enough for us. */
90 /* First make sure this really is the correct entry. At least
91 some versions of the kernel give wrong information because
92 of the implicit mount of the shmfs for SysV IPC. */
93 if (__statfs (mp
->mnt_dir
, &f
) != 0 || (f
.f_type
!= SHMFS_SUPER_MAGIC
94 && f
.f_type
!= RAMFS_MAGIC
))
97 namelen
= strlen (mp
->mnt_dir
);
100 /* Hum, maybe some crippled entry. Keep on searching. */
103 mountpoint
.dir
= (char *) malloc (namelen
+ 2);
104 if (mountpoint
.dir
!= NULL
)
106 char *cp
= __mempcpy (mountpoint
.dir
, mp
->mnt_dir
, namelen
);
110 mountpoint
.dirlen
= cp
- mountpoint
.dir
;
116 /* Close the stream. */
121 /* Open shared memory object. This implementation assumes the shmfs
122 implementation introduced in the late 2.3.x kernel series to be
123 available. Normally the filesystem will be mounted at /dev/shm but
124 we fall back on searching for the actual mount point should opening
127 shm_open (const char *name
, int oflag
, mode_t mode
)
133 /* Determine where the shmfs is mounted. */
134 __libc_once (once
, where_is_shmfs
);
136 /* If we don't know the mount points there is nothing we can do. Ever. */
137 if (mountpoint
.dir
== NULL
)
139 __set_errno (ENOSYS
);
143 /* Construct the filename. */
144 while (name
[0] == '/')
147 namelen
= strlen (name
);
149 /* Validate the filename. */
150 if (name
[0] == '\0' || namelen
> NAME_MAX
|| strchr (name
, '/') != NULL
)
152 __set_errno (EINVAL
);
156 fname
= (char *) alloca (mountpoint
.dirlen
+ namelen
+ 1);
157 __mempcpy (__mempcpy (fname
, mountpoint
.dir
, mountpoint
.dirlen
),
160 /* And get the file descriptor.
161 XXX Maybe we should test each descriptor whether it really is for a
162 file on the shmfs. If this is what should be done the whole function
163 should be revamped since we can determine whether shmfs is available
164 while trying to open the file, all in one turn. */
165 fd
= open (fname
, oflag
| O_CLOEXEC
| O_NOFOLLOW
, mode
);
166 if (fd
== -1 && __glibc_unlikely (errno
== EISDIR
))
167 /* It might be better to fold this error with EINVAL since
168 directory names are just another example for unsuitable shared
169 object names and the standard does not mention EISDIR. */
170 __set_errno (EINVAL
);
176 /* Unlink a shared memory object. */
178 shm_unlink (const char *name
)
183 /* Determine where the shmfs is mounted. */
184 __libc_once (once
, where_is_shmfs
);
186 if (mountpoint
.dir
== NULL
)
188 /* We cannot find the shmfs. If `name' is really a shared
189 memory object it must have been created by another process
190 and we have no idea where that process found the mountpoint. */
191 __set_errno (ENOENT
);
195 /* Construct the filename. */
196 while (name
[0] == '/')
199 namelen
= strlen (name
);
201 /* Validate the filename. */
202 if (name
[0] == '\0' || namelen
> NAME_MAX
|| strchr (name
, '/') != NULL
)
204 __set_errno (ENOENT
);
208 fname
= (char *) alloca (mountpoint
.dirlen
+ namelen
+ 1);
209 __mempcpy (__mempcpy (fname
, mountpoint
.dir
, mountpoint
.dirlen
),
212 /* And remove the file. */
213 int ret
= unlink (fname
);
214 if (ret
< 0 && errno
== EPERM
)
215 __set_errno (EACCES
);
220 /* Make sure the table is freed if we want to free everything before
222 libc_freeres_fn (freeit
)
224 if (mountpoint
.dir
!= defaultdir
)
225 free (mountpoint
.dir
);