1 | /* Copyright (C) 2002-2016 Free Software Foundation, Inc. |
2 | This file is part of the GNU C Library. |
3 | Contributed by Ulrich Drepper <drepper@redhat.com>, 2002. |
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 | <http://www.gnu.org/licenses/>. */ |
18 | |
19 | #include <errno.h> |
20 | #include <fcntl.h> |
21 | #include <pthread.h> |
22 | #include <search.h> |
23 | #include <semaphore.h> |
24 | #include <stdarg.h> |
25 | #include <stdio.h> |
26 | #include <stdlib.h> |
27 | #include <string.h> |
28 | #include <unistd.h> |
29 | #include <sys/mman.h> |
30 | #include <sys/stat.h> |
31 | #include "semaphoreP.h" |
32 | #include <shm-directory.h> |
33 | #include <futex-internal.h> |
34 | |
35 | |
36 | /* Comparison function for search of existing mapping. */ |
37 | int |
38 | attribute_hidden |
39 | __sem_search (const void *a, const void *b) |
40 | { |
41 | const struct inuse_sem *as = (const struct inuse_sem *) a; |
42 | const struct inuse_sem *bs = (const struct inuse_sem *) b; |
43 | |
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); |
47 | |
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); |
51 | |
52 | return strcmp (as->name, bs->name); |
53 | } |
54 | |
55 | |
56 | /* The search tree for existing mappings. */ |
57 | void *__sem_mappings attribute_hidden; |
58 | |
59 | /* Lock to protect the search tree. */ |
60 | int __sem_mappings_lock attribute_hidden = LLL_LOCK_INITIALIZER; |
61 | |
62 | |
63 | /* Search for existing mapping and if possible add the one provided. */ |
64 | static sem_t * |
65 | check_add_mapping (const char *name, size_t namelen, int fd, sem_t *existing) |
66 | { |
67 | sem_t *result = SEM_FAILED; |
68 | |
69 | /* Get the information about the file. */ |
70 | struct stat64 st; |
71 | if (__fxstat64 (_STAT_VER, fd, &st) == 0) |
72 | { |
73 | /* Get the lock. */ |
74 | lll_lock (__sem_mappings_lock, LLL_PRIVATE); |
75 | |
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; |
82 | |
83 | struct inuse_sem **foundp = __tfind (fake, &__sem_mappings, |
84 | __sem_search); |
85 | if (foundp != NULL) |
86 | { |
87 | /* There is already a mapping. Use it. */ |
88 | result = (*foundp)->sem; |
89 | ++(*foundp)->refcnt; |
90 | } |
91 | else |
92 | { |
93 | /* We haven't found a mapping. Install ione. */ |
94 | struct inuse_sem *newp; |
95 | |
96 | newp = (struct inuse_sem *) malloc (sizeof (*newp) + namelen); |
97 | if (newp != NULL) |
98 | { |
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, |
103 | fd, 0); |
104 | |
105 | newp->dev = st.st_dev; |
106 | newp->ino = st.st_ino; |
107 | newp->refcnt = 1; |
108 | newp->sem = existing; |
109 | memcpy (newp->name, name, namelen); |
110 | |
111 | /* Insert the new value. */ |
112 | if (existing != MAP_FAILED |
113 | && __tsearch (newp, &__sem_mappings, __sem_search) != NULL) |
114 | /* Successful. */ |
115 | result = existing; |
116 | else |
117 | /* Something went wrong while inserting the new |
118 | value. We fail completely. */ |
119 | free (newp); |
120 | } |
121 | } |
122 | |
123 | /* Release the lock. */ |
124 | lll_unlock (__sem_mappings_lock, LLL_PRIVATE); |
125 | } |
126 | |
127 | if (result != existing && existing != SEM_FAILED && existing != MAP_FAILED) |
128 | { |
129 | /* Do not disturb errno. */ |
130 | int save = errno; |
131 | munmap (existing, sizeof (sem_t)); |
132 | errno = save; |
133 | } |
134 | |
135 | return result; |
136 | } |
137 | |
138 | |
139 | sem_t * |
140 | sem_open (const char *name, int oflag, ...) |
141 | { |
142 | int fd; |
143 | sem_t *result; |
144 | |
145 | /* Check that shared futexes are supported. */ |
146 | int err = futex_supports_pshared (PTHREAD_PROCESS_SHARED); |
147 | if (err != 0) |
148 | { |
149 | __set_errno (err); |
150 | return SEM_FAILED; |
151 | } |
152 | |
153 | /* Create the name of the final file in local variable SHM_NAME. */ |
154 | SHM_GET_NAME (EINVAL, SEM_FAILED, SEM_SHM_PREFIX); |
155 | |
156 | /* If the semaphore object has to exist simply open it. */ |
157 | if ((oflag & O_CREAT) == 0 || (oflag & O_EXCL) == 0) |
158 | { |
159 | try_again: |
160 | fd = __libc_open (shm_name, |
161 | (oflag & ~(O_CREAT|O_ACCMODE)) | O_NOFOLLOW | O_RDWR); |
162 | |
163 | if (fd == -1) |
164 | { |
165 | /* If we are supposed to create the file try this next. */ |
166 | if ((oflag & O_CREAT) != 0 && errno == ENOENT) |
167 | goto try_create; |
168 | |
169 | /* Return. errno is already set. */ |
170 | } |
171 | else |
172 | /* Check whether we already have this semaphore mapped and |
173 | create one if necessary. */ |
174 | result = check_add_mapping (name, namelen, fd, SEM_FAILED); |
175 | } |
176 | else |
177 | { |
178 | /* We have to open a temporary file first since it must have the |
179 | correct form before we can start using it. */ |
180 | char *tmpfname; |
181 | mode_t mode; |
182 | unsigned int value; |
183 | va_list ap; |
184 | |
185 | try_create: |
186 | va_start (ap, oflag); |
187 | |
188 | mode = va_arg (ap, mode_t); |
189 | value = va_arg (ap, unsigned int); |
190 | |
191 | va_end (ap); |
192 | |
193 | if (value > SEM_VALUE_MAX) |
194 | { |
195 | __set_errno (EINVAL); |
196 | return SEM_FAILED; |
197 | } |
198 | |
199 | /* Create the initial file content. */ |
200 | union |
201 | { |
202 | sem_t initsem; |
203 | struct new_sem newsem; |
204 | } sem; |
205 | |
206 | #if __HAVE_64B_ATOMICS |
207 | sem.newsem.data = value; |
208 | #else |
209 | sem.newsem.value = value << SEM_VALUE_SHIFT; |
210 | sem.newsem.nwaiters = 0; |
211 | #endif |
212 | /* This always is a shared semaphore. */ |
213 | sem.newsem.private = FUTEX_SHARED; |
214 | |
215 | /* Initialize the remaining bytes as well. */ |
216 | memset ((char *) &sem.initsem + sizeof (struct new_sem), '\0', |
217 | sizeof (sem_t) - sizeof (struct new_sem)); |
218 | |
219 | tmpfname = __alloca (shm_dirlen + sizeof SEM_SHM_PREFIX + 6); |
220 | char *xxxxxx = __mempcpy (tmpfname, shm_dir, shm_dirlen); |
221 | |
222 | int retries = 0; |
223 | #define NRETRIES 50 |
224 | while (1) |
225 | { |
226 | /* Add the suffix for mktemp. */ |
227 | strcpy (xxxxxx, "XXXXXX" ); |
228 | |
229 | /* We really want to use mktemp here. We cannot use mkstemp |
230 | since the file must be opened with a specific mode. The |
231 | mode cannot later be set since then we cannot apply the |
232 | file create mask. */ |
233 | if (__mktemp (tmpfname) == NULL) |
234 | return SEM_FAILED; |
235 | |
236 | /* Open the file. Make sure we do not overwrite anything. */ |
237 | fd = __libc_open (tmpfname, O_RDWR | O_CREAT | O_EXCL, mode); |
238 | if (fd == -1) |
239 | { |
240 | if (errno == EEXIST) |
241 | { |
242 | if (++retries < NRETRIES) |
243 | continue; |
244 | |
245 | __set_errno (EAGAIN); |
246 | } |
247 | |
248 | return SEM_FAILED; |
249 | } |
250 | |
251 | /* We got a file. */ |
252 | break; |
253 | } |
254 | |
255 | if (TEMP_FAILURE_RETRY (__libc_write (fd, &sem.initsem, sizeof (sem_t))) |
256 | == sizeof (sem_t) |
257 | /* Map the sem_t structure from the file. */ |
258 | && (result = (sem_t *) mmap (NULL, sizeof (sem_t), |
259 | PROT_READ | PROT_WRITE, MAP_SHARED, |
260 | fd, 0)) != MAP_FAILED) |
261 | { |
262 | /* Create the file. Don't overwrite an existing file. */ |
263 | if (link (tmpfname, shm_name) != 0) |
264 | { |
265 | /* Undo the mapping. */ |
266 | (void) munmap (result, sizeof (sem_t)); |
267 | |
268 | /* Reinitialize 'result'. */ |
269 | result = SEM_FAILED; |
270 | |
271 | /* This failed. If O_EXCL is not set and the problem was |
272 | that the file exists, try again. */ |
273 | if ((oflag & O_EXCL) == 0 && errno == EEXIST) |
274 | { |
275 | /* Remove the file. */ |
276 | (void) unlink (tmpfname); |
277 | |
278 | /* Close the file. */ |
279 | (void) __libc_close (fd); |
280 | |
281 | goto try_again; |
282 | } |
283 | } |
284 | else |
285 | /* Insert the mapping into the search tree. This also |
286 | determines whether another thread sneaked by and already |
287 | added such a mapping despite the fact that we created it. */ |
288 | result = check_add_mapping (name, namelen, fd, result); |
289 | } |
290 | |
291 | /* Now remove the temporary name. This should never fail. If |
292 | it fails we leak a file name. Better fix the kernel. */ |
293 | (void) unlink (tmpfname); |
294 | } |
295 | |
296 | /* Map the mmap error to the error we need. */ |
297 | if (MAP_FAILED != (void *) SEM_FAILED && result == MAP_FAILED) |
298 | result = SEM_FAILED; |
299 | |
300 | /* We don't need the file descriptor anymore. */ |
301 | if (fd != -1) |
302 | { |
303 | /* Do not disturb errno. */ |
304 | int save = errno; |
305 | __libc_close (fd); |
306 | errno = save; |
307 | } |
308 | |
309 | return result; |
310 | } |
311 | |