xf.li | bdd93d5 | 2023-05-12 07:10:14 -0700 | [diff] [blame] | 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 | } |