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 size_t 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 ssize_t 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 if (slot->key)
65 slot->match = bufkeylen == slot->keylen &&
66 !memcmp(slot->key, slot->buf, bufkeylen + 1);
67
68 return 0;
69}
70
71/* Close the active cache slot */
72static int close_slot(struct cache_slot *slot)
73{
74 int err = 0;
75 if (slot->cache_fd > 0) {
76 if (close(slot->cache_fd))
77 err = errno;
78 else
79 slot->cache_fd = -1;
80 }
81 return err;
82}
83
84/* Print the content of the active cache slot (but skip the key). */
85static int print_slot(struct cache_slot *slot)
86{
87#ifdef HAVE_LINUX_SENDFILE
88 off_t start_off;
89 int ret;
90
91 start_off = slot->keylen + 1;
92
93 do {
94 ret = sendfile(STDOUT_FILENO, slot->cache_fd, &start_off,
95 slot->cache_st.st_size - start_off);
96 if (ret < 0) {
97 if (errno == EAGAIN || errno == EINTR)
98 continue;
99 return errno;
100 }
101 return 0;
102 } while (1);
103#else
104 ssize_t i, j;
105
106 i = lseek(slot->cache_fd, slot->keylen + 1, SEEK_SET);
107 if (i != slot->keylen + 1)
108 return errno;
109
110 do {
111 i = j = xread(slot->cache_fd, slot->buf, sizeof(slot->buf));
112 if (i > 0)
113 j = xwrite(STDOUT_FILENO, slot->buf, i);
114 } while (i > 0 && j == i);
115
116 if (i < 0 || j != i)
117 return errno;
118 else
119 return 0;
120#endif
121}
122
123/* Check if the slot has expired */
124static int is_expired(struct cache_slot *slot)
125{
126 if (slot->ttl < 0)
127 return 0;
128 else
129 return slot->cache_st.st_mtime + slot->ttl * 60 < time(NULL);
130}
131
132/* Check if the slot has been modified since we opened it.
133 * NB: If stat() fails, we pretend the file is modified.
134 */
135static int is_modified(struct cache_slot *slot)
136{
137 struct stat st;
138
139 if (stat(slot->cache_name, &st))
140 return 1;
141 return (st.st_ino != slot->cache_st.st_ino ||
142 st.st_mtime != slot->cache_st.st_mtime ||
143 st.st_size != slot->cache_st.st_size);
144}
145
146/* Close an open lockfile */
147static int close_lock(struct cache_slot *slot)
148{
149 int err = 0;
150 if (slot->lock_fd > 0) {
151 if (close(slot->lock_fd))
152 err = errno;
153 else
154 slot->lock_fd = -1;
155 }
156 return err;
157}
158
159/* Create a lockfile used to store the generated content for a cache
160 * slot, and write the slot key + \0 into it.
161 * Returns 0 on success and errno otherwise.
162 */
163static int lock_slot(struct cache_slot *slot)
164{
165 struct flock lock = {
166 .l_type = F_WRLCK,
167 .l_whence = SEEK_SET,
168 .l_start = 0,
169 .l_len = 0,
170 };
171
172 slot->lock_fd = open(slot->lock_name, O_RDWR | O_CREAT,
173 S_IRUSR | S_IWUSR);
174 if (slot->lock_fd == -1)
175 return errno;
176 if (fcntl(slot->lock_fd, F_SETLK, &lock) < 0) {
177 int saved_errno = errno;
178 close(slot->lock_fd);
179 slot->lock_fd = -1;
180 return saved_errno;
181 }
182 if (xwrite(slot->lock_fd, slot->key, slot->keylen + 1) < 0)
183 return errno;
184 return 0;
185}
186
187/* Release the current lockfile. If `replace_old_slot` is set the
188 * lockfile replaces the old cache slot, otherwise the lockfile is
189 * just deleted.
190 */
191static int unlock_slot(struct cache_slot *slot, int replace_old_slot)
192{
193 int err;
194
195 if (replace_old_slot)
196 err = rename(slot->lock_name, slot->cache_name);
197 else
198 err = unlink(slot->lock_name);
199
200 if (err)
201 return errno;
202
203 return 0;
204}
205
206/* Generate the content for the current cache slot by redirecting
207 * stdout to the lock-fd and invoking the callback function
208 */
209static int fill_slot(struct cache_slot *slot)
210{
211 int tmp;
212
213 /* Preserve stdout */
214 tmp = dup(STDOUT_FILENO);
215 if (tmp == -1)
216 return errno;
217
218 /* Redirect stdout to lockfile */
219 if (dup2(slot->lock_fd, STDOUT_FILENO) == -1) {
220 close(tmp);
221 return errno;
222 }
223
224 /* Generate cache content */
225 slot->fn();
226
227 /* update stat info */
228 if (fstat(slot->lock_fd, &slot->cache_st)) {
229 close(tmp);
230 return errno;
231 }
232
233 /* Restore stdout */
234 if (dup2(tmp, STDOUT_FILENO) == -1) {
235 close(tmp);
236 return errno;
237 }
238
239 /* Close the temporary filedescriptor */
240 if (close(tmp))
241 return errno;
242
243 return 0;
244}
245
246/* Crude implementation of 32-bit FNV-1 hash algorithm,
247 * see http://www.isthe.com/chongo/tech/comp/fnv/ for details
248 * about the magic numbers.
249 */
250#define FNV_OFFSET 0x811c9dc5
251#define FNV_PRIME 0x01000193
252
253unsigned long hash_str(const char *str)
254{
255 unsigned long h = FNV_OFFSET;
256 unsigned char *s = (unsigned char *)str;
257
258 if (!s)
259 return h;
260
261 while (*s) {
262 h *= FNV_PRIME;
263 h ^= *s++;
264 }
265 return h;
266}
267
268static int process_slot(struct cache_slot *slot)
269{
270 int err;
271
272 err = open_slot(slot);
273 if (!err && slot->match) {
274 if (is_expired(slot)) {
275 if (!lock_slot(slot)) {
276 /* If the cachefile has been replaced between
277 * `open_slot` and `lock_slot`, we'll just
278 * serve the stale content from the original
279 * cachefile. This way we avoid pruning the
280 * newly generated slot. The same code-path
281 * is chosen if fill_slot() fails for some
282 * reason.
283 *
284 * TODO? check if the new slot contains the
285 * same key as the old one, since we would
286 * prefer to serve the newest content.
287 * This will require us to open yet another
288 * file-descriptor and read and compare the
289 * key from the new file, so for now we're
290 * lazy and just ignore the new file.
291 */
292 if (is_modified(slot) || fill_slot(slot)) {
293 unlock_slot(slot, 0);
294 close_lock(slot);
295 } else {
296 close_slot(slot);
297 unlock_slot(slot, 1);
298 slot->cache_fd = slot->lock_fd;
299 }
300 }
301 }
302 if ((err = print_slot(slot)) != 0) {
303 cache_log("[cgit] error printing cache %s: %s (%d)\n",
304 slot->cache_name,
305 strerror(err),
306 err);
307 }
308 close_slot(slot);
309 return err;
310 }
311
312 /* If the cache slot does not exist (or its key doesn't match the
313 * current key), lets try to create a new cache slot for this
314 * request. If this fails (for whatever reason), lets just generate
315 * the content without caching it and fool the caller to belive
316 * everything worked out (but print a warning on stdout).
317 */
318
319 close_slot(slot);
320 if ((err = lock_slot(slot)) != 0) {
321 cache_log("[cgit] Unable to lock slot %s: %s (%d)\n",
322 slot->lock_name, strerror(err), err);
323 slot->fn();
324 return 0;
325 }
326
327 if ((err = fill_slot(slot)) != 0) {
328 cache_log("[cgit] Unable to fill slot %s: %s (%d)\n",
329 slot->lock_name, strerror(err), err);
330 unlock_slot(slot, 0);
331 close_lock(slot);
332 slot->fn();
333 return 0;
334 }
335 // We've got a valid cache slot in the lock file, which
336 // is about to replace the old cache slot. But if we
337 // release the lockfile and then try to open the new cache
338 // slot, we might get a race condition with a concurrent
339 // writer for the same cache slot (with a different key).
340 // Lets avoid such a race by just printing the content of
341 // the lock file.
342 slot->cache_fd = slot->lock_fd;
343 unlock_slot(slot, 1);
344 if ((err = print_slot(slot)) != 0) {
345 cache_log("[cgit] error printing cache %s: %s (%d)\n",
346 slot->cache_name,
347 strerror(err),
348 err);
349 }
350 close_slot(slot);
351 return err;
352}
353
354/* Print cached content to stdout, generate the content if necessary. */
355int cache_process(int size, const char *path, const char *key, int ttl,
356 cache_fill_fn fn)
357{
358 unsigned long hash;
359 int i;
360 struct strbuf filename = STRBUF_INIT;
361 struct strbuf lockname = STRBUF_INIT;
362 struct cache_slot slot;
363 int result;
364
365 /* If the cache is disabled, just generate the content */
366 if (size <= 0 || ttl == 0) {
367 fn();
368 return 0;
369 }
370
371 /* Verify input, calculate filenames */
372 if (!path) {
373 cache_log("[cgit] Cache path not specified, caching is disabled\n");
374 fn();
375 return 0;
376 }
377 if (!key)
378 key = "";
379 hash = hash_str(key) % size;
380 strbuf_addstr(&filename, path);
381 strbuf_ensure_end(&filename, '/');
382 for (i = 0; i < 8; i++) {
383 strbuf_addf(&filename, "%x", (unsigned char)(hash & 0xf));
384 hash >>= 4;
385 }
386 strbuf_addbuf(&lockname, &filename);
387 strbuf_addstr(&lockname, ".lock");
388 slot.fn = fn;
389 slot.ttl = ttl;
390 slot.cache_name = filename.buf;
391 slot.lock_name = lockname.buf;
392 slot.key = key;
393 slot.keylen = strlen(key);
394 result = process_slot(&slot);
395
396 strbuf_release(&filename);
397 strbuf_release(&lockname);
398 return result;
399}
400
401/* Return a strftime formatted date/time
402 * NB: the result from this function is to shared memory
403 */
404static char *sprintftime(const char *format, time_t time)
405{
406 static char buf[64];
407 struct tm *tm;
408
409 if (!time)
410 return NULL;
411 tm = gmtime(&time);
412 strftime(buf, sizeof(buf)-1, format, tm);
413 return buf;
414}
415
416int cache_ls(const char *path)
417{
418 DIR *dir;
419 struct dirent *ent;
420 int err = 0;
421 struct cache_slot slot = { NULL };
422 struct strbuf fullname = STRBUF_INIT;
423 size_t prefixlen;
424
425 if (!path) {
426 cache_log("[cgit] cache path not specified\n");
427 return -1;
428 }
429 dir = opendir(path);
430 if (!dir) {
431 err = errno;
432 cache_log("[cgit] unable to open path %s: %s (%d)\n",
433 path, strerror(err), err);
434 return err;
435 }
436 strbuf_addstr(&fullname, path);
437 strbuf_ensure_end(&fullname, '/');
438 prefixlen = fullname.len;
439 while ((ent = readdir(dir)) != NULL) {
440 if (strlen(ent->d_name) != 8)
441 continue;
442 strbuf_setlen(&fullname, prefixlen);
443 strbuf_addstr(&fullname, ent->d_name);
444 slot.cache_name = fullname.buf;
445 if ((err = open_slot(&slot)) != 0) {
446 cache_log("[cgit] unable to open path %s: %s (%d)\n",
447 fullname.buf, strerror(err), err);
448 continue;
449 }
450 htmlf("%s %s %10"PRIuMAX" %s\n",
451 fullname.buf,
452 sprintftime("%Y-%m-%d %H:%M:%S",
453 slot.cache_st.st_mtime),
454 (uintmax_t)slot.cache_st.st_size,
455 slot.buf);
456 close_slot(&slot);
457 }
458 closedir(dir);
459 strbuf_release(&fullname);
460 return 0;
461}
462
463/* Print a message to stdout */
464void cache_log(const char *format, ...)
465{
466 va_list args;
467 va_start(args, format);
468 vfprintf(stderr, format, args);
469 va_end(args);
470}
471