1 /* Copyright (C) 2002-2020 Free Software Foundation, Inc.
2 This file is part of the GNU C Library.
3 Contributed by Ulrich Drepper <drepper@redhat.com>, 2002.
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.
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.
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/>. */
23 #include <semaphore.h>
31 #include "semaphoreP.h"
32 #include <shm-directory.h>
33 #include <futex-internal.h>
34 #include <libc-lock.h>
36 /* Comparison function for search of existing mapping. */
39 __sem_search (const void *a
, const void *b
)
41 const struct inuse_sem
*as
= (const struct inuse_sem
*) a
;
42 const struct inuse_sem
*bs
= (const struct inuse_sem
*) b
;
44 if (as
->ino
!= bs
->ino
)
45 /* Cannot return the difference the type is larger than int. */
46 return as
->ino
< bs
->ino
? -1 : (as
->ino
== bs
->ino
? 0 : 1);
48 if (as
->dev
!= bs
->dev
)
49 /* Cannot return the difference the type is larger than int. */
50 return as
->dev
< bs
->dev
? -1 : (as
->dev
== bs
->dev
? 0 : 1);
52 return strcmp (as
->name
, bs
->name
);
56 /* The search tree for existing mappings. */
57 void *__sem_mappings attribute_hidden
;
59 /* Lock to protect the search tree. */
60 int __sem_mappings_lock attribute_hidden
= LLL_LOCK_INITIALIZER
;
63 /* Search for existing mapping and if possible add the one provided. */
65 check_add_mapping (const char *name
, size_t namelen
, int fd
, sem_t
*existing
)
67 sem_t
*result
= SEM_FAILED
;
69 /* Get the information about the file. */
71 if (__fstat64 (fd
, &st
) == 0)
74 lll_lock (__sem_mappings_lock
, LLL_PRIVATE
);
76 /* Search for an existing mapping given the information we have. */
77 struct inuse_sem
*fake
;
78 fake
= (struct inuse_sem
*) alloca (sizeof (*fake
) + namelen
);
79 memcpy (fake
->name
, name
, namelen
);
80 fake
->dev
= st
.st_dev
;
81 fake
->ino
= st
.st_ino
;
83 struct inuse_sem
**foundp
= __tfind (fake
, &__sem_mappings
,
87 /* There is already a mapping. Use it. */
88 result
= (*foundp
)->sem
;
93 /* We haven't found a mapping. Install ione. */
94 struct inuse_sem
*newp
;
96 newp
= (struct inuse_sem
*) malloc (sizeof (*newp
) + namelen
);
99 /* If the caller hasn't provided any map it now. */
100 if (existing
== SEM_FAILED
)
101 existing
= (sem_t
*) mmap (NULL
, sizeof (sem_t
),
102 PROT_READ
| PROT_WRITE
, MAP_SHARED
,
105 newp
->dev
= st
.st_dev
;
106 newp
->ino
= st
.st_ino
;
108 newp
->sem
= existing
;
109 memcpy (newp
->name
, name
, namelen
);
111 /* Insert the new value. */
112 if (existing
!= MAP_FAILED
113 && __tsearch (newp
, &__sem_mappings
, __sem_search
) != NULL
)
117 /* Something went wrong while inserting the new
118 value. We fail completely. */
123 /* Release the lock. */
124 lll_unlock (__sem_mappings_lock
, LLL_PRIVATE
);
127 if (result
!= existing
&& existing
!= SEM_FAILED
&& existing
!= MAP_FAILED
)
129 /* Do not disturb errno. */
131 munmap (existing
, sizeof (sem_t
));
140 sem_open (const char *name
, int oflag
, ...)
145 /* Check that shared futexes are supported. */
146 int err
= futex_supports_pshared (PTHREAD_PROCESS_SHARED
);
153 /* Create the name of the final file in local variable SHM_NAME. */
154 SHM_GET_NAME (EINVAL
, SEM_FAILED
, SEM_SHM_PREFIX
);
156 /* Disable asynchronous cancellation. */
157 #ifdef __libc_ptf_call
159 __libc_ptf_call (__pthread_setcancelstate
,
160 (PTHREAD_CANCEL_DISABLE
, &state
), 0);
163 /* If the semaphore object has to exist simply open it. */
164 if ((oflag
& O_CREAT
) == 0 || (oflag
& O_EXCL
) == 0)
167 fd
= __libc_open (shm_name
,
168 (oflag
& ~(O_CREAT
|O_ACCMODE
)) | O_NOFOLLOW
| O_RDWR
);
172 /* If we are supposed to create the file try this next. */
173 if ((oflag
& O_CREAT
) != 0 && errno
== ENOENT
)
176 /* Return. errno is already set. */
179 /* Check whether we already have this semaphore mapped and
180 create one if necessary. */
181 result
= check_add_mapping (name
, namelen
, fd
, SEM_FAILED
);
185 /* We have to open a temporary file first since it must have the
186 correct form before we can start using it. */
193 va_start (ap
, oflag
);
195 mode
= va_arg (ap
, mode_t
);
196 value
= va_arg (ap
, unsigned int);
200 if (value
> SEM_VALUE_MAX
)
202 __set_errno (EINVAL
);
207 /* Create the initial file content. */
211 struct new_sem newsem
;
214 #if __HAVE_64B_ATOMICS
215 sem
.newsem
.data
= value
;
217 sem
.newsem
.value
= value
<< SEM_VALUE_SHIFT
;
218 sem
.newsem
.nwaiters
= 0;
220 /* pad is used as a mutex on pre-v9 sparc and ignored otherwise. */
223 /* This always is a shared semaphore. */
224 sem
.newsem
.private = FUTEX_SHARED
;
226 /* Initialize the remaining bytes as well. */
227 memset ((char *) &sem
.initsem
+ sizeof (struct new_sem
), '\0',
228 sizeof (sem_t
) - sizeof (struct new_sem
));
230 tmpfname
= __alloca (shm_dirlen
+ sizeof SEM_SHM_PREFIX
+ 6);
231 char *xxxxxx
= __mempcpy (tmpfname
, shm_dir
, shm_dirlen
);
237 /* Add the suffix for mktemp. */
238 strcpy (xxxxxx
, "XXXXXX");
240 /* We really want to use mktemp here. We cannot use mkstemp
241 since the file must be opened with a specific mode. The
242 mode cannot later be set since then we cannot apply the
244 if (__mktemp (tmpfname
) == NULL
)
250 /* Open the file. Make sure we do not overwrite anything. */
251 fd
= __libc_open (tmpfname
, O_RDWR
| O_CREAT
| O_EXCL
, mode
);
256 if (++retries
< NRETRIES
)
259 __set_errno (EAGAIN
);
270 if (TEMP_FAILURE_RETRY (__libc_write (fd
, &sem
.initsem
, sizeof (sem_t
)))
272 /* Map the sem_t structure from the file. */
273 && (result
= (sem_t
*) mmap (NULL
, sizeof (sem_t
),
274 PROT_READ
| PROT_WRITE
, MAP_SHARED
,
275 fd
, 0)) != MAP_FAILED
)
277 /* Create the file. Don't overwrite an existing file. */
278 if (link (tmpfname
, shm_name
) != 0)
280 /* Undo the mapping. */
281 (void) munmap (result
, sizeof (sem_t
));
283 /* Reinitialize 'result'. */
286 /* This failed. If O_EXCL is not set and the problem was
287 that the file exists, try again. */
288 if ((oflag
& O_EXCL
) == 0 && errno
== EEXIST
)
290 /* Remove the file. */
291 (void) unlink (tmpfname
);
293 /* Close the file. */
294 (void) __libc_close (fd
);
300 /* Insert the mapping into the search tree. This also
301 determines whether another thread sneaked by and already
302 added such a mapping despite the fact that we created it. */
303 result
= check_add_mapping (name
, namelen
, fd
, result
);
306 /* Now remove the temporary name. This should never fail. If
307 it fails we leak a file name. Better fix the kernel. */
308 (void) unlink (tmpfname
);
311 /* Map the mmap error to the error we need. */
312 if (MAP_FAILED
!= (void *) SEM_FAILED
&& result
== MAP_FAILED
)
315 /* We don't need the file descriptor anymore. */
318 /* Do not disturb errno. */
325 #ifdef __libc_ptf_call
326 __libc_ptf_call (__pthread_setcancelstate
, (state
, NULL
), 0);