1 /* Copyright (C) 2000, 2001 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 Library General Public License as
6 published by the Free Software Foundation; either version 2 of the
7 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 Library General Public License for more details.
14 You should have received a copy of the GNU Library General Public
15 License along with the GNU C Library; see the file COPYING.LIB. If not,
16 write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
17 Boston, MA 02111-1307, USA. */
28 #include <sys/statfs.h>
29 #include <bits/libc-lock.h>
30 #include "linux_fsinfo.h"
33 /* Mount point of the shared memory filesystem. */
40 /* This is the default directory. */
41 static const char defaultdir
[] = "/dev/shm/";
43 /* Protect the `mountpoint' variable above. */
44 __libc_once_define (static, once
);
47 /* Determine where the shmfs is mounted (if at all). */
57 /* The canonical place is /dev/shm. This is at least what the
58 documentation tells everybody to do. */
59 if (__statfs (defaultdir
, &f
) == 0 && f
.f_type
== SHMFS_SUPER_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 (__builtin_expect (fp
== NULL
, 0))
73 fp
= __setmntent (_PATH_MNTTAB
, "r");
74 if (__builtin_expect (fp
== NULL
, 0))
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 if (strcmp (mp
->mnt_type
, "shm") == 0)
83 /* Found it. There might be more than one place where the
84 filesystem is mounted but one is enough for us. */
87 /* First make sure this really is the correct entry. At least
88 some versions of the kernel give wrong information because
89 of the implicit mount of the shmfs for SysV IPC. */
90 if (__statfs (mp
->mnt_dir
, &f
) != 0 || f
.f_type
!= SHMFS_SUPER_MAGIC
)
93 namelen
= strlen (mp
->mnt_dir
);
96 /* Hum, maybe some crippled entry. Keep on searching. */
99 mountpoint
.dir
= (char *) malloc (namelen
+ 2);
100 if (mountpoint
.dir
!= NULL
)
102 char *cp
= __mempcpy (mountpoint
.dir
, mp
->mnt_dir
, namelen
);
106 mountpoint
.dirlen
= cp
- mountpoint
.dir
;
112 /* Close the stream. */
117 /* Open shared memory object. This implementation assumes the shmfs
118 implementation introduced in the late 2.3.x kernel series to be
119 available. Normally the filesystem will be mounted at /dev/shm but
120 we fall back on searching for the actual mount point should opening
123 shm_open (const char *name
, int oflag
, mode_t mode
)
129 /* Determine where the shmfs is mounted. */
130 __libc_once (once
, where_is_shmfs
);
132 /* If we don't know the mount points there is nothing we can do. Ever. */
133 if (mountpoint
.dir
== NULL
)
135 __set_errno (ENOSYS
);
139 /* Construct the filename. */
140 while (name
[0] == '/')
145 /* The name "/" is not supported. */
146 __set_errno (EINVAL
);
150 namelen
= strlen (name
);
151 fname
= (char *) alloca (mountpoint
.dirlen
+ namelen
+ 1);
152 __mempcpy (__mempcpy (fname
, mountpoint
.dir
, mountpoint
.dirlen
),
155 /* And get the file descriptor.
156 XXX Maybe we should test each descriptor whether it really is for a
157 file on the shmfs. If this is what should be done the whole function
158 should be revamped since we can determine whether shmfs is available
159 while trying to open the file, all in one turn. */
160 fd
= open (fname
, oflag
| O_NOFOLLOW
, mode
);
163 /* We got a descriptor. Now set the FD_CLOEXEC bit. */
164 int flags
= fcntl (fd
, F_GETFD
, 0);
166 if (__builtin_expect (flags
, 0) >= 0)
169 flags
= fcntl (fd
, F_SETFD
, flags
);
174 /* Something went wrong. We cannot return the descriptor. */
175 int save_errno
= errno
;
178 __set_errno (save_errno
);
186 /* Unlink a shared memory object. */
188 shm_unlink (const char *name
)
193 /* Determine where the shmfs is mounted. */
194 __libc_once (once
, where_is_shmfs
);
196 if (mountpoint
.dir
== NULL
)
198 /* We cannot find the shmfs. If `name' is really a shared
199 memory object it must have been created by another process
200 and we have no idea where that process found the mountpoint. */
201 __set_errno (ENOENT
);
205 /* Construct the filename. */
206 while (name
[0] == '/')
211 /* The name "/" is not supported. */
212 __set_errno (ENOENT
);
216 namelen
= strlen (name
);
217 fname
= (char *) alloca (mountpoint
.dirlen
+ namelen
+ 1);
218 __mempcpy (__mempcpy (fname
, mountpoint
.dir
, mountpoint
.dirlen
),
221 /* And remove the file. */
222 return unlink (fname
);
226 static void __attribute__ ((unused
))
229 if (mountpoint
.dir
!= defaultdir
)
230 free (mountpoint
.dir
);
234 /* Make sure the table is freed if we want to free everything before
236 text_set_element (__libc_subfreeres
, freeit
);