Merge branch 't/cleanups'
[dss.git] / ipc.c
1 #include <sys/wait.h>
2 #include <stdio.h>
3 #include <inttypes.h>
4 #include <stdlib.h>
5 #include <unistd.h>
6 #include <errno.h>
7 #include <sys/types.h>
8 #include <sys/ipc.h>
9 #include <sys/sem.h>
10 #include <string.h>
11 #include <assert.h>
12 #include <sys/stat.h>
13 #include <stddef.h>
14 #include <limits.h>
15 #include <sys/param.h>
16
17 #include "gcc-compat.h"
18 #include "string.h"
19 #include "log.h"
20 #include "gcc-compat.h"
21 #include "error.h"
22
23 #if (defined(__GNUC__) && defined(__i386__))
24 #define get16bits(d) (*((const uint16_t *) (d)))
25 #else
26 #define get16bits(d) ((((uint32_t)(((const uint8_t *)(d))[1])) << 8)\
27 +(uint32_t)(((const uint8_t *)(d))[0]) )
28 #endif
29
30 /*
31 * SuperFastHash, by Paul Hsieh.
32 * http://www.azillionmonkeys.com/qed/hash.html
33 */
34 static uint32_t super_fast_hash(const uint8_t *data, uint32_t len, uint32_t hash)
35 {
36 uint32_t tmp;
37 int rem = len & 3;
38
39 len >>= 2;
40
41 for (;len > 0; len--) {
42 hash += get16bits (data);
43 tmp = (get16bits (data+2) << 11) ^ hash;
44 hash = (hash << 16) ^ tmp;
45 data += 2*sizeof (uint16_t);
46 hash += hash >> 11;
47 }
48
49 /* Handle end cases */
50 switch (rem) {
51 case 3:
52 hash += get16bits (data);
53 hash ^= hash << 16;
54 hash ^= data[sizeof (uint16_t)] << 18;
55 hash += hash >> 11;
56 break;
57 case 2:
58 hash += get16bits (data);
59 hash ^= hash << 11;
60 hash += hash >> 17;
61 break;
62 case 1:
63 hash += *data;
64 hash ^= hash << 10;
65 hash += hash >> 1;
66 }
67 /* Force "avalanching" of final 127 bits */
68 hash ^= hash << 3;
69 hash += hash >> 5;
70 hash ^= hash << 4;
71 hash += hash >> 17;
72 hash ^= hash << 25;
73 hash += hash >> 6;
74 return hash;
75 }
76
77 /*
78 * Return the canonical absolute name of a given file name.
79 *
80 * Slightly modified version of glibc's realpath, Copyright (C)
81 * 1996-2002,2004,2005,2006,2008 Free Software Foundation, Inc.
82 *
83 * A canonical name does not contain any `.', `..' components nor any repeated
84 * path separators ('/') or symlinks. All path components must exist. The
85 * result is malloc'd and must be freed by the caller.
86 */
87 static int dss_realpath(const char *name, char **resolved_path)
88 {
89 char *rpath = NULL, *dest, *extra_buf = NULL;
90 const char *start, *end, *rpath_limit;
91 long int path_max;
92 int ret, num_links = 0;
93
94 if (name[0] == '\0') {
95 /*
96 * As per Single Unix Specification V2 we must return an error
97 * if the name argument points to an empty string.
98 */
99 ret = -ERRNO_TO_DSS_ERROR(ENOENT);
100 goto error;
101 }
102 #ifdef PATH_MAX
103 path_max = PATH_MAX;
104 #else
105 /*
106 * From realpath(3): Asking pathconf(3) does not really help, since on
107 * the one hand POSIX warns that the result of pathconf(3) may be
108 * huge and unsuitable for mallocing memory. And on the other hand
109 * pathconf(3) may return -1 to signify that PATH_MAX is not bounded.
110 */
111 path_max = pathconf(name, _PC_PATH_MAX);
112 if (path_max <= 0 || path_max >= 4096)
113 path_max = 4096;
114 #endif
115 rpath = dss_malloc(path_max);
116 rpath_limit = rpath + path_max;
117
118 if (name[0] != '/') {
119 if (!getcwd(rpath, path_max)) {
120 ret = -ERRNO_TO_DSS_ERROR(errno);
121 goto error;
122 }
123 dest = memchr(rpath, '\0', path_max);
124 } else {
125 rpath[0] = '/';
126 dest = rpath + 1;
127 }
128
129 for (start = end = name; *start; start = end) {
130 struct stat st;
131 int n;
132
133 /* Skip sequence of multiple path-separators. */
134 while (*start == '/')
135 ++start;
136
137 /* Find end of path component. */
138 for (end = start; *end && *end != '/'; ++end)
139 /* Nothing. */ ;
140
141 if (end - start == 0)
142 break;
143 else if (end - start == 1 && start[0] == '.')
144 /* nothing */ ;
145 else if (end - start == 2 && start[0] == '.' && start[1] == '.') {
146 /* Back up to previous component, ignore if at root already. */
147 if (dest > rpath + 1)
148 while ((--dest)[-1] != '/') ;
149 } else {
150 size_t new_size;
151
152 if (dest[-1] != '/')
153 *dest++ = '/';
154
155 if (dest + (end - start) >= rpath_limit) {
156 ptrdiff_t dest_offset = dest - rpath;
157
158 new_size = rpath_limit - rpath;
159 if (end - start + 1 > path_max)
160 new_size += end - start + 1;
161 else
162 new_size += path_max;
163 rpath = dss_realloc(rpath, new_size);
164 rpath_limit = rpath + new_size;
165 dest = rpath + dest_offset;
166 }
167
168 memcpy(dest, start, end - start);
169 dest += end - start;
170 *dest = '\0';
171
172 if (stat(rpath, &st) < 0) {
173 ret = -ERRNO_TO_DSS_ERROR(errno);
174 goto error;
175 }
176
177 if (S_ISLNK(st.st_mode)) {
178 char *buf = alloca(path_max);
179 size_t len;
180
181 if (++num_links > MAXSYMLINKS) {
182 ret = -ERRNO_TO_DSS_ERROR(ELOOP);
183 goto error;
184 }
185
186 n = readlink(rpath, buf, path_max - 1);
187 if (n < 0) {
188 ret = -ERRNO_TO_DSS_ERROR(errno);
189 goto error;
190 }
191 buf[n] = '\0';
192
193 if (!extra_buf)
194 extra_buf = alloca(path_max);
195
196 len = strlen(end);
197 if ((long int) (n + len) >= path_max) {
198 ret = -ERRNO_TO_DSS_ERROR(ENAMETOOLONG);
199 goto error;
200 }
201
202 /* Careful here, end may be a pointer into extra_buf... */
203 memmove(&extra_buf[n], end, len + 1);
204 name = end = memcpy(extra_buf, buf, n);
205
206 if (buf[0] == '/') /* It's an absolute symlink */
207 dest = rpath + 1;
208 else /* Back up to previous component, ignore if at root already: */
209 if (dest > rpath + 1)
210 while ((--dest)[-1] != '/')
211 ; /* nothing */
212 } else if (!S_ISDIR(st.st_mode) && *end != '\0') {
213 ret = -ERRNO_TO_DSS_ERROR(ENOTDIR);
214 goto error;
215 }
216 }
217 }
218 if (dest > rpath + 1 && dest[-1] == '/')
219 --dest;
220 *dest = '\0';
221 *resolved_path = rpath;
222 return 1;
223 error:
224 free(rpath);
225 *resolved_path = NULL;
226 return ret;
227 }
228
229 static inline int get_key_or_die(char *config_file)
230 {
231 int ret;
232 struct stat statbuf;
233 char *rpath;
234
235 assert(config_file);
236 if (stat(config_file, &statbuf) == 0) {
237 ret = dss_realpath(config_file, &rpath);
238 if (ret < 0) {
239 DSS_EMERG_LOG("could not resolve path %s: %s\n", config_file,
240 dss_strerror(-ret));
241 exit(EXIT_FAILURE);
242 }
243 DSS_DEBUG_LOG("resolved path: %s\n", rpath);
244 } else
245 /*
246 * This happens if the user did not specify a config file, and
247 * the default config file does not exist. Another (unlikely)
248 * possibility is that the config file was removed between
249 * startup and this call. We don't care about these corner
250 * cases too much and just use the unresolved path in this
251 * case.
252 */
253 rpath = dss_strdup(config_file);
254 ret = super_fast_hash((uint8_t *)rpath, strlen(rpath), 0) >> 1;
255 free(rpath);
256 return ret;
257 }
258
259 static int mutex_get(int key, int flags)
260 {
261 int ret;
262
263 DSS_DEBUG_LOG("getting semaphore 0x%x\n", key);
264 ret = semget(key, 2, flags);
265 if (ret < 0)
266 return -ERRNO_TO_DSS_ERROR(errno);
267 return ret;
268 }
269
270 static int do_semop(int id, struct sembuf *sops, int num)
271 {
272 int ret;
273
274 DSS_DEBUG_LOG("calling semop\n");
275 do {
276 ret = semop(id, sops, num);
277 if (ret >= 0)
278 return 1;
279 } while (errno == EINTR);
280 return -ERRNO_TO_DSS_ERROR(errno);
281 }
282
283 static int mutex_lock(int id)
284 {
285 int ret;
286
287 DSS_DEBUG_LOG("locking\n");
288 struct sembuf sops[4] = {
289 {
290 .sem_num = 0,
291 .sem_op = 0,
292 .sem_flg = SEM_UNDO | IPC_NOWAIT
293 },
294 {
295 .sem_num = 0,
296 .sem_op = 1,
297 .sem_flg = SEM_UNDO | IPC_NOWAIT
298 },
299 {
300 .sem_num = 1,
301 .sem_op = 0,
302 .sem_flg = SEM_UNDO | IPC_NOWAIT
303 },
304 {
305 .sem_num = 1,
306 .sem_op = 1,
307 .sem_flg = SEM_UNDO | IPC_NOWAIT
308 }
309 };
310 ret = do_semop(id, sops, 4);
311 if (ret < 0)
312 return -ERRNO_TO_DSS_ERROR(errno);
313 return 1;
314 }
315
316 static int mutex_try_lock(int id)
317 {
318 int ret;
319
320 DSS_DEBUG_LOG("trying to lock\n");
321 struct sembuf sops[2] = {
322 {
323 .sem_num = 0,
324 .sem_op = 0,
325 .sem_flg = SEM_UNDO | IPC_NOWAIT
326 },
327 {
328 .sem_num = 0,
329 .sem_op = 1,
330 .sem_flg = SEM_UNDO | IPC_NOWAIT
331 }
332 };
333 ret = do_semop(id, sops, 2);
334 if (ret < 0)
335 return -ERRNO_TO_DSS_ERROR(errno);
336 return 1;
337 }
338
339 int lock_dss(char *config_file)
340 {
341 int ret, key = get_key_or_die(config_file);
342
343 ret = mutex_get(key, IPC_CREAT | 0600);
344 if (ret < 0)
345 return ret;
346 return mutex_lock(ret);
347 }
348
349 int get_dss_pid(char *config_file, pid_t *pid)
350 {
351 int ret, semid, key = get_key_or_die(config_file);
352
353 ret = mutex_get(key, 0);
354 if (ret < 0)
355 return ret;
356 semid = ret;
357 ret = semctl(semid, 1, GETPID);
358 if (ret < 0)
359 return -E_NOT_RUNNING;
360 *pid = ret;
361 ret = mutex_try_lock(semid);
362 if (ret >= 0)
363 return -E_NOT_RUNNING;
364 return 1;
365 }