cache.c (view raw)
1/* cache.c: cache management
2 *
3 * Copyright (C) 2006-2014 cgit Development Team <cgit@lists.zx2c4.com>
4 *
5 * Licensed under GNU General Public License v2
6 * (see COPYING for full license text)
7 *
8 *
9 * The cache is just a directory structure where each file is a cache slot,
10 * and each filename is based on the hash of some key (e.g. the cgit url).
11 * Each file contains the full key followed by the cached content for that
12 * key.
13 *
14 */
15
16#include "cgit.h"
17#include "cache.h"
18#include "html.h"
19#ifdef HAVE_LINUX_SENDFILE
20#include <sys/sendfile.h>
21#endif
22
23#define CACHE_BUFSIZE (1024 * 4)
24
25struct cache_slot {
26 const char *key;
27 int keylen;
28 int ttl;
29 cache_fill_fn fn;
30 int cache_fd;
31 int lock_fd;
32 const char *cache_name;
33 const char *lock_name;
34 int match;
35 struct stat cache_st;
36 int bufsize;
37 char buf[CACHE_BUFSIZE];
38};
39
40/* Open an existing cache slot and fill the cache buffer with
41 * (part of) the content of the cache file. Return 0 on success
42 * and errno otherwise.
43 */
44static int open_slot(struct cache_slot *slot)
45{
46 char *bufz;
47 int bufkeylen = -1;
48
49 slot->cache_fd = open(slot->cache_name, O_RDONLY);
50 if (slot->cache_fd == -1)
51 return errno;
52
53 if (fstat(slot->cache_fd, &slot->cache_st))
54 return errno;
55
56 slot->bufsize = xread(slot->cache_fd, slot->buf, sizeof(slot->buf));
57 if (slot->bufsize < 0)
58 return errno;
59
60 bufz = memchr(slot->buf, 0, slot->bufsize);
61 if (bufz)
62 bufkeylen = bufz - slot->buf;
63
64 slot->match = bufkeylen == slot->keylen &&
65 !memcmp(slot->key, slot->buf, bufkeylen + 1);
66
67 return 0;
68}
69
70/* Close the active cache slot */
71static int close_slot(struct cache_slot *slot)
72{
73 int err = 0;
74 if (slot->cache_fd > 0) {
75 if (close(slot->cache_fd))
76 err = errno;
77 else
78 slot->cache_fd = -1;
79 }
80 return err;
81}
82
83/* Print the content of the active cache slot (but skip the key). */
84static int print_slot(struct cache_slot *slot)
85{
86#ifdef HAVE_LINUX_SENDFILE
87 off_t start_off;
88 int ret;
89
90 start_off = slot->keylen + 1;
91
92 do {
93 ret = sendfile(STDOUT_FILENO, slot->cache_fd, &start_off,
94 slot->cache_st.st_size - start_off);
95 if (ret < 0) {
96 if (errno == EAGAIN || errno == EINTR)
97 continue;
98 return errno;
99 }
100 return 0;
101 } while (1);
102#else
103 ssize_t i, j;
104
105 i = lseek(slot->cache_fd, slot->keylen + 1, SEEK_SET);
106 if (i != slot->keylen + 1)
107 return errno;
108
109 do {
110 i = j = xread(slot->cache_fd, slot->buf, sizeof(slot->buf));
111 if (i > 0)
112 j = xwrite(STDOUT_FILENO, slot->buf, i);
113 } while (i > 0 && j == i);
114
115 if (i < 0 || j != i)
116 return errno;
117 else
118 return 0;
119#endif
120}
121
122/* Check if the slot has expired */
123static int is_expired(struct cache_slot *slot)
124{
125 if (slot->ttl < 0)
126 return 0;
127 else
128 return slot->cache_st.st_mtime + slot->ttl * 60 < time(NULL);
129}
130
131/* Check if the slot has been modified since we opened it.
132 * NB: If stat() fails, we pretend the file is modified.
133 */
134static int is_modified(struct cache_slot *slot)
135{
136 struct stat st;
137
138 if (stat(slot->cache_name, &st))
139 return 1;
140 return (st.st_ino != slot->cache_st.st_ino ||
141 st.st_mtime != slot->cache_st.st_mtime ||
142 st.st_size != slot->cache_st.st_size);
143}
144
145/* Close an open lockfile */
146static int close_lock(struct cache_slot *slot)
147{
148 int err = 0;
149 if (slot->lock_fd > 0) {
150 if (close(slot->lock_fd))
151 err = errno;
152 else
153 slot->lock_fd = -1;
154 }
155 return err;
156}
157
158/* Create a lockfile used to store the generated content for a cache
159 * slot, and write the slot key + \0 into it.
160 * Returns 0 on success and errno otherwise.
161 */
162static int lock_slot(struct cache_slot *slot)
163{
164 struct flock lock = {
165 .l_type = F_WRLCK,
166 .l_whence = SEEK_SET,
167 .l_start = 0,
168 .l_len = 0,
169 };
170
171 slot->lock_fd = open(slot->lock_name, O_RDWR | O_CREAT,
172 S_IRUSR | S_IWUSR);
173 if (slot->lock_fd == -1)
174 return errno;
175 if (fcntl(slot->lock_fd, F_SETLK, &lock) < 0) {
176 int saved_errno = errno;
177 close(slot->lock_fd);
178 slot->lock_fd = -1;
179 return saved_errno;
180 }
181 if (xwrite(slot->lock_fd, slot->key, slot->keylen + 1) < 0)
182 return errno;
183 return 0;
184}
185
186/* Release the current lockfile. If `replace_old_slot` is set the
187 * lockfile replaces the old cache slot, otherwise the lockfile is
188 * just deleted.
189 */
190static int unlock_slot(struct cache_slot *slot, int replace_old_slot)
191{
192 int err;
193
194 if (replace_old_slot)
195 err = rename(slot->lock_name, slot->cache_name);
196 else
197 err = unlink(slot->lock_name);
198
199 if (err)
200 return errno;
201
202 return 0;
203}
204
205/* Generate the content for the current cache slot by redirecting
206 * stdout to the lock-fd and invoking the callback function
207 */
208static int fill_slot(struct cache_slot *slot)
209{
210 int tmp;
211
212 /* Preserve stdout */
213 tmp = dup(STDOUT_FILENO);
214 if (tmp == -1)
215 return errno;
216
217 /* Redirect stdout to lockfile */
218 if (dup2(slot->lock_fd, STDOUT_FILENO) == -1) {
219 close(tmp);
220 return errno;
221 }
222
223 /* Generate cache content */
224 slot->fn();
225
226 /* update stat info */
227 if (fstat(slot->lock_fd, &slot->cache_st)) {
228 close(tmp);
229 return errno;
230 }
231
232 /* Restore stdout */
233 if (dup2(tmp, STDOUT_FILENO) == -1) {
234 close(tmp);
235 return errno;
236 }
237
238 /* Close the temporary filedescriptor */
239 if (close(tmp))
240 return errno;
241
242 return 0;
243}
244
245/* Crude implementation of 32-bit FNV-1 hash algorithm,
246 * see http://www.isthe.com/chongo/tech/comp/fnv/ for details
247 * about the magic numbers.
248 */
249#define FNV_OFFSET 0x811c9dc5
250#define FNV_PRIME 0x01000193
251
252unsigned long hash_str(const char *str)
253{
254 unsigned long h = FNV_OFFSET;
255 unsigned char *s = (unsigned char *)str;
256
257 if (!s)
258 return h;
259
260 while (*s) {
261 h *= FNV_PRIME;
262 h ^= *s++;
263 }
264 return h;
265}
266
267static int process_slot(struct cache_slot *slot)
268{
269 int err;
270
271 err = open_slot(slot);
272 if (!err && slot->match) {
273 if (is_expired(slot)) {
274 if (!lock_slot(slot)) {
275 /* If the cachefile has been replaced between
276 * `open_slot` and `lock_slot`, we'll just
277 * serve the stale content from the original
278 * cachefile. This way we avoid pruning the
279 * newly generated slot. The same code-path
280 * is chosen if fill_slot() fails for some
281 * reason.
282 *
283 * TODO? check if the new slot contains the
284 * same key as the old one, since we would
285 * prefer to serve the newest content.
286 * This will require us to open yet another
287 * file-descriptor and read and compare the
288 * key from the new file, so for now we're
289 * lazy and just ignore the new file.
290 */
291 if (is_modified(slot) || fill_slot(slot)) {
292 unlock_slot(slot, 0);
293 close_lock(slot);
294 } else {
295 close_slot(slot);
296 unlock_slot(slot, 1);
297 slot->cache_fd = slot->lock_fd;
298 }
299 }
300 }
301 if ((err = print_slot(slot)) != 0) {
302 cache_log("[cgit] error printing cache %s: %s (%d)\n",
303 slot->cache_name,
304 strerror(err),
305 err);
306 }
307 close_slot(slot);
308 return err;
309 }
310
311 /* If the cache slot does not exist (or its key doesn't match the
312 * current key), lets try to create a new cache slot for this
313 * request. If this fails (for whatever reason), lets just generate
314 * the content without caching it and fool the caller to belive
315 * everything worked out (but print a warning on stdout).
316 */
317
318 close_slot(slot);
319 if ((err = lock_slot(slot)) != 0) {
320 cache_log("[cgit] Unable to lock slot %s: %s (%d)\n",
321 slot->lock_name, strerror(err), err);
322 slot->fn();
323 return 0;
324 }
325
326 if ((err = fill_slot(slot)) != 0) {
327 cache_log("[cgit] Unable to fill slot %s: %s (%d)\n",
328 slot->lock_name, strerror(err), err);
329 unlock_slot(slot, 0);
330 close_lock(slot);
331 slot->fn();
332 return 0;
333 }
334 // We've got a valid cache slot in the lock file, which
335 // is about to replace the old cache slot. But if we
336 // release the lockfile and then try to open the new cache
337 // slot, we might get a race condition with a concurrent
338 // writer for the same cache slot (with a different key).
339 // Lets avoid such a race by just printing the content of
340 // the lock file.
341 slot->cache_fd = slot->lock_fd;
342 unlock_slot(slot, 1);
343 if ((err = print_slot(slot)) != 0) {
344 cache_log("[cgit] error printing cache %s: %s (%d)\n",
345 slot->cache_name,
346 strerror(err),
347 err);
348 }
349 close_slot(slot);
350 return err;
351}
352
353/* Print cached content to stdout, generate the content if necessary. */
354int cache_process(int size, const char *path, const char *key, int ttl,
355 cache_fill_fn fn)
356{
357 unsigned long hash;
358 int i;
359 struct strbuf filename = STRBUF_INIT;
360 struct strbuf lockname = STRBUF_INIT;
361 struct cache_slot slot;
362 int result;
363
364 /* If the cache is disabled, just generate the content */
365 if (size <= 0 || ttl == 0) {
366 fn();
367 return 0;
368 }
369
370 /* Verify input, calculate filenames */
371 if (!path) {
372 cache_log("[cgit] Cache path not specified, caching is disabled\n");
373 fn();
374 return 0;
375 }
376 if (!key)
377 key = "";
378 hash = hash_str(key) % size;
379 strbuf_addstr(&filename, path);
380 strbuf_ensure_end(&filename, '/');
381 for (i = 0; i < 8; i++) {
382 strbuf_addf(&filename, "%x", (unsigned char)(hash & 0xf));
383 hash >>= 4;
384 }
385 strbuf_addbuf(&lockname, &filename);
386 strbuf_addstr(&lockname, ".lock");
387 slot.fn = fn;
388 slot.ttl = ttl;
389 slot.cache_name = filename.buf;
390 slot.lock_name = lockname.buf;
391 slot.key = key;
392 slot.keylen = strlen(key);
393 result = process_slot(&slot);
394
395 strbuf_release(&filename);
396 strbuf_release(&lockname);
397 return result;
398}
399
400/* Return a strftime formatted date/time
401 * NB: the result from this function is to shared memory
402 */
403static char *sprintftime(const char *format, time_t time)
404{
405 static char buf[64];
406 struct tm *tm;
407
408 if (!time)
409 return NULL;
410 tm = gmtime(&time);
411 strftime(buf, sizeof(buf)-1, format, tm);
412 return buf;
413}
414
415int cache_ls(const char *path)
416{
417 DIR *dir;
418 struct dirent *ent;
419 int err = 0;
420 struct cache_slot slot = { NULL };
421 struct strbuf fullname = STRBUF_INIT;
422 size_t prefixlen;
423
424 if (!path) {
425 cache_log("[cgit] cache path not specified\n");
426 return -1;
427 }
428 dir = opendir(path);
429 if (!dir) {
430 err = errno;
431 cache_log("[cgit] unable to open path %s: %s (%d)\n",
432 path, strerror(err), err);
433 return err;
434 }
435 strbuf_addstr(&fullname, path);
436 strbuf_ensure_end(&fullname, '/');
437 prefixlen = fullname.len;
438 while ((ent = readdir(dir)) != NULL) {
439 if (strlen(ent->d_name) != 8)
440 continue;
441 strbuf_setlen(&fullname, prefixlen);
442 strbuf_addstr(&fullname, ent->d_name);
443 slot.cache_name = fullname.buf;
444 if ((err = open_slot(&slot)) != 0) {
445 cache_log("[cgit] unable to open path %s: %s (%d)\n",
446 fullname.buf, strerror(err), err);
447 continue;
448 }
449 htmlf("%s %s %10"PRIuMAX" %s\n",
450 fullname.buf,
451 sprintftime("%Y-%m-%d %H:%M:%S",
452 slot.cache_st.st_mtime),
453 (uintmax_t)slot.cache_st.st_size,
454 slot.buf);
455 close_slot(&slot);
456 }
457 closedir(dir);
458 strbuf_release(&fullname);
459 return 0;
460}
461
462/* Print a message to stdout */
463void cache_log(const char *format, ...)
464{
465 va_list args;
466 va_start(args, format);
467 vfprintf(stderr, format, args);
468 va_end(args);
469}
470