1 /*
2 * gzlog.c
3 * Copyright (C) 2004, 2008, 2012, 2016 Mark Adler, all rights reserved
4 * For conditions of distribution and use, see copyright notice in gzlog.h
5 * version 2.2, 14 Aug 2012
6 */
7
8 /*
9 gzlog provides a mechanism for frequently appending short strings to a gzip
10 file that is efficient both in execution time and compression ratio. The
11 strategy is to write the short strings in an uncompressed form to the end of
12 the gzip file, only compressing when the amount of uncompressed data has
13 reached a given threshold.
14
15 gzlog also provides protection against interruptions in the process due to
16 system crashes. The status of the operation is recorded in an extra field
17 in the gzip file, and is only updated once the gzip file is brought to a
18 valid state. The last data to be appended or compressed is saved in an
19 auxiliary file, so that if the operation is interrupted, it can be completed
20 the next time an append operation is attempted.
21
22 gzlog maintains another auxiliary file with the last 32K of data from the
23 compressed portion, which is preloaded for the compression of the subsequent
24 data. This minimizes the impact to the compression ratio of appending.
25 */
26
27 /*
28 Operations Concept:
29
30 Files (log name "foo"):
31 foo.gz -- gzip file with the complete log
32 foo.add -- last message to append or last data to compress
33 foo.dict -- dictionary of the last 32K of data for next compression
34 foo.temp -- temporary dictionary file for compression after this one
35 foo.lock -- lock file for reading and writing the other files
36 foo.repairs -- log file for log file recovery operations (not compressed)
37
38 gzip file structure:
39 - fixed-length (no file name) header with extra field (see below)
40 - compressed data ending initially with empty stored block
41 - uncompressed data filling out originally empty stored block and
42 subsequent stored blocks as needed (16K max each)
43 - gzip trailer
44 - no junk at end (no other gzip streams)
45
46 When appending data, the information in the first three items above plus the
47 foo.add file are sufficient to recover an interrupted append operation. The
48 extra field has the necessary information to restore the start of the last
49 stored block and determine where to append the data in the foo.add file, as
50 well as the crc and length of the gzip data before the append operation.
51
52 The foo.add file is created before the gzip file is marked for append, and
53 deleted after the gzip file is marked as complete. So if the append
54 operation is interrupted, the data to add will still be there. If due to
55 some external force, the foo.add file gets deleted between when the append
56 operation was interrupted and when recovery is attempted, the gzip file will
57 still be restored, but without the appended data.
58
59 When compressing data, the information in the first two items above plus the
60 foo.add file are sufficient to recover an interrupted compress operation.
61 The extra field has the necessary information to find the end of the
62 compressed data, and contains both the crc and length of just the compressed
63 data and of the complete set of data including the contents of the foo.add
64 file.
65
66 Again, the foo.add file is maintained during the compress operation in case
67 of an interruption. If in the unlikely event the foo.add file with the data
68 to be compressed is missing due to some external force, a gzip file with
69 just the previous compressed data will be reconstructed. In this case, all
70 of the data that was to be compressed is lost (approximately one megabyte).
71 This will not occur if all that happened was an interruption of the compress
72 operation.
73
74 The third state that is marked is the replacement of the old dictionary with
75 the new dictionary after a compress operation. Once compression is
76 complete, the gzip file is marked as being in the replace state. This
77 completes the gzip file, so an interrupt after being so marked does not
78 result in recompression. Then the dictionary file is replaced, and the gzip
79 file is marked as completed. This state prevents the possibility of
80 restarting compression with the wrong dictionary file.
81
82 All three operations are wrapped by a lock/unlock procedure. In order to
83 gain exclusive access to the log files, first a foo.lock file must be
84 exclusively created. When all operations are complete, the lock is
85 released by deleting the foo.lock file. If when attempting to create the
86 lock file, it already exists and the modify time of the lock file is more
87 than five minutes old (set by the PATIENCE define below), then the old
88 lock file is considered stale and deleted, and the exclusive creation of
89 the lock file is retried. To assure that there are no false assessments
90 of the staleness of the lock file, the operations periodically touch the
91 lock file to update the modified date.
92
93 Following is the definition of the extra field with all of the information
94 required to enable the above append and compress operations and their
95 recovery if interrupted. Multi-byte values are stored little endian
96 (consistent with the gzip format). File pointers are eight bytes long.
97 The crc's and lengths for the gzip trailer are four bytes long. (Note that
98 the length at the end of a gzip file is used for error checking only, and
99 for large files is actually the length modulo 2^32.) The stored block
100 length is two bytes long. The gzip extra field two-byte identification is
101 "ap" for append. It is assumed that writing the extra field to the file is
102 an "atomic" operation. That is, either all of the extra field is written
103 to the file, or none of it is, if the operation is interrupted right at the
104 point of updating the extra field. This is a reasonable assumption, since
105 the extra field is within the first 52 bytes of the file, which is smaller
106 than any expected block size for a mass storage device (usually 512 bytes or
107 larger).
108
109 Extra field (35 bytes):
110 - Pointer to first stored block length -- this points to the two-byte length
111 of the first stored block, which is followed by the two-byte, one's
112 complement of that length. The stored block length is preceded by the
113 three-bit header of the stored block, which is the actual start of the
114 stored block in the deflate format. See the bit offset field below.
115 - Pointer to the last stored block length. This is the same as above, but
116 for the last stored block of the uncompressed data in the gzip file.
117 Initially this is the same as the first stored block length pointer.
118 When the stored block gets to 16K (see the MAX_STORE define), then a new
119 stored block as added, at which point the last stored block length pointer
120 is different from the first stored block length pointer. When they are
121 different, the first bit of the last stored block header is eight bits, or
122 one byte back from the block length.
123 - Compressed data crc and length. This is the crc and length of the data
124 that is in the compressed portion of the deflate stream. These are used
125 only in the event that the foo.add file containing the data to compress is
126 lost after a compress operation is interrupted.
127 - Total data crc and length. This is the crc and length of all of the data
128 stored in the gzip file, compressed and uncompressed. It is used to
129 reconstruct the gzip trailer when compressing, as well as when recovering
130 interrupted operations.
131 - Final stored block length. This is used to quickly find where to append,
132 and allows the restoration of the original final stored block state when
133 an append operation is interrupted.
134 - First stored block start as the number of bits back from the final stored
135 block first length byte. This value is in the range of 3..10, and is
136 stored as the low three bits of the final byte of the extra field after
137 subtracting three (0..7). This allows the last-block bit of the stored
138 block header to be updated when a new stored block is added, for the case
139 when the first stored block and the last stored block are the same. (When
140 they are different, the numbers of bits back is known to be eight.) This
141 also allows for new compressed data to be appended to the old compressed
142 data in the compress operation, overwriting the previous first stored
143 block, or for the compressed data to be terminated and a valid gzip file
144 reconstructed on the off chance that a compression operation was
145 interrupted and the data to compress in the foo.add file was deleted.
146 - The operation in process. This is the next two bits in the last byte (the
147 bits under the mask 0x18). The are interpreted as 0: nothing in process,
148 1: append in process, 2: compress in process, 3: replace in process.
149 - The top three bits of the last byte in the extra field are reserved and
150 are currently set to zero.
151
152 Main procedure:
153 - Exclusively create the foo.lock file using the O_CREAT and O_EXCL modes of
154 the system open() call. If the modify time of an existing lock file is
155 more than PATIENCE seconds old, then the lock file is deleted and the
156 exclusive create is retried.
157 - Load the extra field from the foo.gz file, and see if an operation was in
158 progress but not completed. If so, apply the recovery procedure below.
159 - Perform the append procedure with the provided data.
160 - If the uncompressed data in the foo.gz file is 1MB or more, apply the
161 compress procedure.
162 - Delete the foo.lock file.
163
164 Append procedure:
165 - Put what to append in the foo.add file so that the operation can be
166 restarted if this procedure is interrupted.
167 - Mark the foo.gz extra field with the append operation in progress.
168 + Restore the original last-block bit and stored block length of the last
169 stored block from the information in the extra field, in case a previous
170 append operation was interrupted.
171 - Append the provided data to the last stored block, creating new stored
172 blocks as needed and updating the stored blocks last-block bits and
173 lengths.
174 - Update the crc and length with the new data, and write the gzip trailer.
175 - Write over the extra field (with a single write operation) with the new
176 pointers, lengths, and crc's, and mark the gzip file as not in process.
177 Though there is still a foo.add file, it will be ignored since nothing
178 is in process. If a foo.add file is leftover from a previously
179 completed operation, it is truncated when writing new data to it.
180 - Delete the foo.add file.
181
182 Compress and replace procedures:
183 - Read all of the uncompressed data in the stored blocks in foo.gz and write
184 it to foo.add. Also write foo.temp with the last 32K of that data to
185 provide a dictionary for the next invocation of this procedure.
186 - Rewrite the extra field marking foo.gz with a compression in process.
187 * If there is no data provided to compress (due to a missing foo.add file
188 when recovering), reconstruct and truncate the foo.gz file to contain
189 only the previous compressed data and proceed to the step after the next
190 one. Otherwise ...
191 - Compress the data with the dictionary in foo.dict, and write to the
192 foo.gz file starting at the bit immediately following the last previously
193 compressed block. If there is no foo.dict, proceed anyway with the
194 compression at slightly reduced efficiency. (For the foo.dict file to be
195 missing requires some external failure beyond simply the interruption of
196 a compress operation.) During this process, the foo.lock file is
197 periodically touched to assure that that file is not considered stale by
198 another process before we're done. The deflation is terminated with a
199 non-last empty static block (10 bits long), that is then located and
200 written over by a last-bit-set empty stored block.
201 - Append the crc and length of the data in the gzip file (previously
202 calculated during the append operations).
203 - Write over the extra field with the updated stored block offsets, bits
204 back, crc's, and lengths, and mark foo.gz as in process for a replacement
205 of the dictionary.
206 @ Delete the foo.add file.
207 - Replace foo.dict with foo.temp.
208 - Write over the extra field, marking foo.gz as complete.
209
210 Recovery procedure:
211 - If not a replace recovery, read in the foo.add file, and provide that data
212 to the appropriate recovery below. If there is no foo.add file, provide
213 a zero data length to the recovery. In that case, the append recovery
214 restores the foo.gz to the previous compressed + uncompressed data state.
215 For the the compress recovery, a missing foo.add file results in foo.gz
216 being restored to the previous compressed-only data state.
217 - Append recovery:
218 - Pick up append at + step above
219 - Compress recovery:
220 - Pick up compress at * step above
221 - Replace recovery:
222 - Pick up compress at @ step above
223 - Log the repair with a date stamp in foo.repairs
224 */
225
226 #include <sys/types.h>
227 #include <stdio.h> /* rename, fopen, fprintf, fclose */
228 #include <stdlib.h> /* malloc, free */
229 #include <string.h> /* strlen, strrchr, strcpy, strncpy, strcmp */
230 #include <fcntl.h> /* open */
231 #include <unistd.h> /* lseek, read, write, close, unlink, sleep, */
232 /* ftruncate, fsync */
233 #include <errno.h> /* errno */
234 #include <time.h> /* time, ctime */
235 #include <sys/stat.h> /* stat */
236 #include <sys/time.h> /* utimes */
237 #include "zlib.h" /* crc32 */
238
239 #include "gzlog.h" /* header for external access */
240
241 #define local static
242 typedef unsigned int uint;
243 typedef unsigned long ulong;
244
245 /* Macro for debugging to deterministically force recovery operations */
246 #ifdef GZLOG_DEBUG
247 #include <setjmp.h> /* longjmp */
248 jmp_buf gzlog_jump; /* where to go back to */
249 int gzlog_bail = 0; /* which point to bail at (1..8) */
250 int gzlog_count = -1; /* number of times through to wait */
251 # define BAIL(n) do { if (n == gzlog_bail && gzlog_count-- == 0) \
252 longjmp(gzlog_jump, gzlog_bail); } while (0)
253 #else
254 # define BAIL(n)
255 #endif
256
257 /* how old the lock file can be in seconds before considering it stale */
258 #define PATIENCE 300
259
260 /* maximum stored block size in Kbytes -- must be in 1..63 */
261 #define MAX_STORE 16
262
263 /* number of stored Kbytes to trigger compression (must be >= 32 to allow
264 dictionary construction, and <= 204 * MAX_STORE, in order for >> 10 to
265 discard the stored block headers contribution of five bytes each) */
266 #define TRIGGER 1024
267
268 /* size of a deflate dictionary (this cannot be changed) */
269 #define DICT 32768U
270
271 /* values for the operation (2 bits) */
272 #define NO_OP 0
273 #define APPEND_OP 1
274 #define COMPRESS_OP 2
275 #define REPLACE_OP 3
276
277 /* macros to extract little-endian integers from an unsigned byte buffer */
278 #define PULL2(p) ((p)[0]+((uint)((p)[1])<<8))
279 #define PULL4(p) (PULL2(p)+((ulong)PULL2(p+2)<<16))
280 #define PULL8(p) (PULL4(p)+((off_t)PULL4(p+4)<<32))
281
282 /* macros to store integers into a byte buffer in little-endian order */
283 #define PUT2(p,a) do {(p)[0]=a;(p)[1]=(a)>>8;} while(0)
284 #define PUT4(p,a) do {PUT2(p,a);PUT2(p+2,a>>16);} while(0)
285 #define PUT8(p,a) do {PUT4(p,a);PUT4(p+4,a>>32);} while(0)
286
287 /* internal structure for log information */
288 #define LOGID "\106\035\172" /* should be three non-zero characters */
289 struct log {
290 char id[4]; /* contains LOGID to detect inadvertent overwrites */
291 int fd; /* file descriptor for .gz file, opened read/write */
292 char *path; /* allocated path, e.g. "/var/log/foo" or "foo" */
293 char *end; /* end of path, for appending suffices such as ".gz" */
294 off_t first; /* offset of first stored block first length byte */
295 int back; /* location of first block id in bits back from first */
296 uint stored; /* bytes currently in last stored block */
297 off_t last; /* offset of last stored block first length byte */
298 ulong ccrc; /* crc of compressed data */
299 ulong clen; /* length (modulo 2^32) of compressed data */
300 ulong tcrc; /* crc of total data */
301 ulong tlen; /* length (modulo 2^32) of total data */
302 time_t lock; /* last modify time of our lock file */
303 };
304
305 /* gzip header for gzlog */
306 local unsigned char log_gzhead[] = {
307 0x1f, 0x8b, /* magic gzip id */
308 8, /* compression method is deflate */
309 4, /* there is an extra field (no file name) */
310 0, 0, 0, 0, /* no modification time provided */
311 0, 0xff, /* no extra flags, no OS specified */
312 39, 0, 'a', 'p', 35, 0 /* extra field with "ap" subfield */
313 /* 35 is EXTRA, 39 is EXTRA + 4 */
314 };
315
316 #define HEAD sizeof(log_gzhead) /* should be 16 */
317
318 /* initial gzip extra field content (52 == HEAD + EXTRA + 1) */
319 local unsigned char log_gzext[] = {
320 52, 0, 0, 0, 0, 0, 0, 0, /* offset of first stored block length */
321 52, 0, 0, 0, 0, 0, 0, 0, /* offset of last stored block length */
322 0, 0, 0, 0, 0, 0, 0, 0, /* compressed data crc and length */
323 0, 0, 0, 0, 0, 0, 0, 0, /* total data crc and length */
324 0, 0, /* final stored block data length */
325 5 /* op is NO_OP, last bit 8 bits back */
326 };
327
328 #define EXTRA sizeof(log_gzext) /* should be 35 */
329
330 /* initial gzip data and trailer */
331 local unsigned char log_gzbody[] = {
332 1, 0, 0, 0xff, 0xff, /* empty stored block (last) */
333 0, 0, 0, 0, /* crc */
334 0, 0, 0, 0 /* uncompressed length */
335 };
336
337 #define BODY sizeof(log_gzbody)
338
339 /* Exclusively create foo.lock in order to negotiate exclusive access to the
340 foo.* files. If the modify time of an existing lock file is greater than
341 PATIENCE seconds in the past, then consider the lock file to have been
342 abandoned, delete it, and try the exclusive create again. Save the lock
343 file modify time for verification of ownership. Return 0 on success, or -1
344 on failure, usually due to an access restriction or invalid path. Note that
345 if stat() or unlink() fails, it may be due to another process noticing the
346 abandoned lock file a smidge sooner and deleting it, so those are not
347 flagged as an error. */
log_lock(struct log * log)348 local int log_lock(struct log *log)
349 {
350 int fd;
351 struct stat st;
352
353 strcpy(log->end, ".lock");
354 while ((fd = open(log->path, O_CREAT | O_EXCL, 0644)) < 0) {
355 if (errno != EEXIST)
356 return -1;
357 if (stat(log->path, &st) == 0 && time(NULL) - st.st_mtime > PATIENCE) {
358 unlink(log->path);
359 continue;
360 }
361 sleep(2); /* relinquish the CPU for two seconds while waiting */
362 }
363 close(fd);
364 if (stat(log->path, &st) == 0)
365 log->lock = st.st_mtime;
366 return 0;
367 }
368
369 /* Update the modify time of the lock file to now, in order to prevent another
370 task from thinking that the lock is stale. Save the lock file modify time
371 for verification of ownership. */
log_touch(struct log * log)372 local void log_touch(struct log *log)
373 {
374 struct stat st;
375
376 strcpy(log->end, ".lock");
377 utimes(log->path, NULL);
378 if (stat(log->path, &st) == 0)
379 log->lock = st.st_mtime;
380 }
381
382 /* Check the log file modify time against what is expected. Return true if
383 this is not our lock. If it is our lock, touch it to keep it. */
log_check(struct log * log)384 local int log_check(struct log *log)
385 {
386 struct stat st;
387
388 strcpy(log->end, ".lock");
389 if (stat(log->path, &st) || st.st_mtime != log->lock)
390 return 1;
391 log_touch(log);
392 return 0;
393 }
394
395 /* Unlock a previously acquired lock, but only if it's ours. */
log_unlock(struct log * log)396 local void log_unlock(struct log *log)
397 {
398 if (log_check(log))
399 return;
400 strcpy(log->end, ".lock");
401 unlink(log->path);
402 log->lock = 0;
403 }
404
405 /* Check the gzip header and read in the extra field, filling in the values in
406 the log structure. Return op on success or -1 if the gzip header was not as
407 expected. op is the current operation in progress last written to the extra
408 field. This assumes that the gzip file has already been opened, with the
409 file descriptor log->fd. */
log_head(struct log * log)410 local int log_head(struct log *log)
411 {
412 int op;
413 unsigned char buf[HEAD + EXTRA];
414
415 if (lseek(log->fd, 0, SEEK_SET) < 0 ||
416 read(log->fd, buf, HEAD + EXTRA) != HEAD + EXTRA ||
417 memcmp(buf, log_gzhead, HEAD)) {
418 return -1;
419 }
420 log->first = PULL8(buf + HEAD);
421 log->last = PULL8(buf + HEAD + 8);
422 log->ccrc = PULL4(buf + HEAD + 16);
423 log->clen = PULL4(buf + HEAD + 20);
424 log->tcrc = PULL4(buf + HEAD + 24);
425 log->tlen = PULL4(buf + HEAD + 28);
426 log->stored = PULL2(buf + HEAD + 32);
427 log->back = 3 + (buf[HEAD + 34] & 7);
428 op = (buf[HEAD + 34] >> 3) & 3;
429 return op;
430 }
431
432 /* Write over the extra field contents, marking the operation as op. Use fsync
433 to assure that the device is written to, and in the requested order. This
434 operation, and only this operation, is assumed to be atomic in order to
435 assure that the log is recoverable in the event of an interruption at any
436 point in the process. Return -1 if the write to foo.gz failed. */
log_mark(struct log * log,int op)437 local int log_mark(struct log *log, int op)
438 {
439 int ret;
440 unsigned char ext[EXTRA];
441
442 PUT8(ext, log->first);
443 PUT8(ext + 8, log->last);
444 PUT4(ext + 16, log->ccrc);
445 PUT4(ext + 20, log->clen);
446 PUT4(ext + 24, log->tcrc);
447 PUT4(ext + 28, log->tlen);
448 PUT2(ext + 32, log->stored);
449 ext[34] = log->back - 3 + (op << 3);
450 fsync(log->fd);
451 ret = lseek(log->fd, HEAD, SEEK_SET) < 0 ||
452 write(log->fd, ext, EXTRA) != EXTRA ? -1 : 0;
453 fsync(log->fd);
454 return ret;
455 }
456
457 /* Rewrite the last block header bits and subsequent zero bits to get to a byte
458 boundary, setting the last block bit if last is true, and then write the
459 remainder of the stored block header (length and one's complement). Leave
460 the file pointer after the end of the last stored block data. Return -1 if
461 there is a read or write failure on the foo.gz file */
log_last(struct log * log,int last)462 local int log_last(struct log *log, int last)
463 {
464 int back, len, mask;
465 unsigned char buf[6];
466
467 /* determine the locations of the bytes and bits to modify */
468 back = log->last == log->first ? log->back : 8;
469 len = back > 8 ? 2 : 1; /* bytes back from log->last */
470 mask = 0x80 >> ((back - 1) & 7); /* mask for block last-bit */
471
472 /* get the byte to modify (one or two back) into buf[0] -- don't need to
473 read the byte if the last-bit is eight bits back, since in that case
474 the entire byte will be modified */
475 buf[0] = 0;
476 if (back != 8 && (lseek(log->fd, log->last - len, SEEK_SET) < 0 ||
477 read(log->fd, buf, 1) != 1))
478 return -1;
479
480 /* change the last-bit of the last stored block as requested -- note
481 that all bits above the last-bit are set to zero, per the type bits
482 of a stored block being 00 and per the convention that the bits to
483 bring the stream to a byte boundary are also zeros */
484 buf[1] = 0;
485 buf[2 - len] = (*buf & (mask - 1)) + (last ? mask : 0);
486
487 /* write the modified stored block header and lengths, move the file
488 pointer to after the last stored block data */
489 PUT2(buf + 2, log->stored);
490 PUT2(buf + 4, log->stored ^ 0xffff);
491 return lseek(log->fd, log->last - len, SEEK_SET) < 0 ||
492 write(log->fd, buf + 2 - len, len + 4) != len + 4 ||
493 lseek(log->fd, log->stored, SEEK_CUR) < 0 ? -1 : 0;
494 }
495
496 /* Append len bytes from data to the locked and open log file. len may be zero
497 if recovering and no .add file was found. In that case, the previous state
498 of the foo.gz file is restored. The data is appended uncompressed in
499 deflate stored blocks. Return -1 if there was an error reading or writing
500 the foo.gz file. */
log_append(struct log * log,unsigned char * data,size_t len)501 local int log_append(struct log *log, unsigned char *data, size_t len)
502 {
503 uint put;
504 off_t end;
505 unsigned char buf[8];
506
507 /* set the last block last-bit and length, in case recovering an
508 interrupted append, then position the file pointer to append to the
509 block */
510 if (log_last(log, 1))
511 return -1;
512
513 /* append, adding stored blocks and updating the offset of the last stored
514 block as needed, and update the total crc and length */
515 while (len) {
516 /* append as much as we can to the last block */
517 put = (MAX_STORE << 10) - log->stored;
518 if (put > len)
519 put = (uint)len;
520 if (put) {
521 if (write(log->fd, data, put) != put)
522 return -1;
523 BAIL(1);
524 log->tcrc = crc32(log->tcrc, data, put);
525 log->tlen += put;
526 log->stored += put;
527 data += put;
528 len -= put;
529 }
530
531 /* if we need to, add a new empty stored block */
532 if (len) {
533 /* mark current block as not last */
534 if (log_last(log, 0))
535 return -1;
536
537 /* point to new, empty stored block */
538 log->last += 4 + log->stored + 1;
539 log->stored = 0;
540 }
541
542 /* mark last block as last, update its length */
543 if (log_last(log, 1))
544 return -1;
545 BAIL(2);
546 }
547
548 /* write the new crc and length trailer, and truncate just in case (could
549 be recovering from partial append with a missing foo.add file) */
550 PUT4(buf, log->tcrc);
551 PUT4(buf + 4, log->tlen);
552 if (write(log->fd, buf, 8) != 8 ||
553 (end = lseek(log->fd, 0, SEEK_CUR)) < 0 || ftruncate(log->fd, end))
554 return -1;
555
556 /* write the extra field, marking the log file as done, delete .add file */
557 if (log_mark(log, NO_OP))
558 return -1;
559 strcpy(log->end, ".add");
560 unlink(log->path); /* ignore error, since may not exist */
561 return 0;
562 }
563
564 /* Replace the foo.dict file with the foo.temp file. Also delete the foo.add
565 file, since the compress operation may have been interrupted before that was
566 done. Returns 1 if memory could not be allocated, or -1 if reading or
567 writing foo.gz fails, or if the rename fails for some reason other than
568 foo.temp not existing. foo.temp not existing is a permitted error, since
569 the replace operation may have been interrupted after the rename is done,
570 but before foo.gz is marked as complete. */
log_replace(struct log * log)571 local int log_replace(struct log *log)
572 {
573 int ret;
574 char *dest;
575
576 /* delete foo.add file */
577 strcpy(log->end, ".add");
578 unlink(log->path); /* ignore error, since may not exist */
579 BAIL(3);
580
581 /* rename foo.name to foo.dict, replacing foo.dict if it exists */
582 strcpy(log->end, ".dict");
583 dest = malloc(strlen(log->path) + 1);
584 if (dest == NULL)
585 return -2;
586 strcpy(dest, log->path);
587 strcpy(log->end, ".temp");
588 ret = rename(log->path, dest);
589 free(dest);
590 if (ret && errno != ENOENT)
591 return -1;
592 BAIL(4);
593
594 /* mark the foo.gz file as done */
595 return log_mark(log, NO_OP);
596 }
597
598 /* Compress the len bytes at data and append the compressed data to the
599 foo.gz deflate data immediately after the previous compressed data. This
600 overwrites the previous uncompressed data, which was stored in foo.add
601 and is the data provided in data[0..len-1]. If this operation is
602 interrupted, it picks up at the start of this routine, with the foo.add
603 file read in again. If there is no data to compress (len == 0), then we
604 simply terminate the foo.gz file after the previously compressed data,
605 appending a final empty stored block and the gzip trailer. Return -1 if
606 reading or writing the log.gz file failed, or -2 if there was a memory
607 allocation failure. */
log_compress(struct log * log,unsigned char * data,size_t len)608 local int log_compress(struct log *log, unsigned char *data, size_t len)
609 {
610 int fd;
611 uint got, max;
612 ssize_t dict;
613 off_t end;
614 z_stream strm;
615 unsigned char buf[DICT];
616
617 /* compress and append compressed data */
618 if (len) {
619 /* set up for deflate, allocating memory */
620 strm.zalloc = Z_NULL;
621 strm.zfree = Z_NULL;
622 strm.opaque = Z_NULL;
623 if (deflateInit2(&strm, Z_DEFAULT_COMPRESSION, Z_DEFLATED, -15, 8,
624 Z_DEFAULT_STRATEGY) != Z_OK)
625 return -2;
626
627 /* read in dictionary (last 32K of data that was compressed) */
628 strcpy(log->end, ".dict");
629 fd = open(log->path, O_RDONLY, 0);
630 if (fd >= 0) {
631 dict = read(fd, buf, DICT);
632 close(fd);
633 if (dict < 0) {
634 deflateEnd(&strm);
635 return -1;
636 }
637 if (dict)
638 deflateSetDictionary(&strm, buf, (uint)dict);
639 }
640 log_touch(log);
641
642 /* prime deflate with last bits of previous block, position write
643 pointer to write those bits and overwrite what follows */
644 if (lseek(log->fd, log->first - (log->back > 8 ? 2 : 1),
645 SEEK_SET) < 0 ||
646 read(log->fd, buf, 1) != 1 || lseek(log->fd, -1, SEEK_CUR) < 0) {
647 deflateEnd(&strm);
648 return -1;
649 }
650 deflatePrime(&strm, (8 - log->back) & 7, *buf);
651
652 /* compress, finishing with a partial non-last empty static block */
653 strm.next_in = data;
654 max = (((uint)0 - 1) >> 1) + 1; /* in case int smaller than size_t */
655 do {
656 strm.avail_in = len > max ? max : (uint)len;
657 len -= strm.avail_in;
658 do {
659 strm.avail_out = DICT;
660 strm.next_out = buf;
661 deflate(&strm, len ? Z_NO_FLUSH : Z_PARTIAL_FLUSH);
662 got = DICT - strm.avail_out;
663 if (got && write(log->fd, buf, got) != got) {
664 deflateEnd(&strm);
665 return -1;
666 }
667 log_touch(log);
668 } while (strm.avail_out == 0);
669 } while (len);
670 deflateEnd(&strm);
671 BAIL(5);
672
673 /* find start of empty static block -- scanning backwards the first one
674 bit is the second bit of the block, if the last byte is zero, then
675 we know the byte before that has a one in the top bit, since an
676 empty static block is ten bits long */
677 if ((log->first = lseek(log->fd, -1, SEEK_CUR)) < 0 ||
678 read(log->fd, buf, 1) != 1)
679 return -1;
680 log->first++;
681 if (*buf) {
682 log->back = 1;
683 while ((*buf & ((uint)1 << (8 - log->back++))) == 0)
684 ; /* guaranteed to terminate, since *buf != 0 */
685 }
686 else
687 log->back = 10;
688
689 /* update compressed crc and length */
690 log->ccrc = log->tcrc;
691 log->clen = log->tlen;
692 }
693 else {
694 /* no data to compress -- fix up existing gzip stream */
695 log->tcrc = log->ccrc;
696 log->tlen = log->clen;
697 }
698
699 /* complete and truncate gzip stream */
700 log->last = log->first;
701 log->stored = 0;
702 PUT4(buf, log->tcrc);
703 PUT4(buf + 4, log->tlen);
704 if (log_last(log, 1) || write(log->fd, buf, 8) != 8 ||
705 (end = lseek(log->fd, 0, SEEK_CUR)) < 0 || ftruncate(log->fd, end))
706 return -1;
707 BAIL(6);
708
709 /* mark as being in the replace operation */
710 if (log_mark(log, REPLACE_OP))
711 return -1;
712
713 /* execute the replace operation and mark the file as done */
714 return log_replace(log);
715 }
716
717 /* log a repair record to the .repairs file */
log_log(struct log * log,int op,char * record)718 local void log_log(struct log *log, int op, char *record)
719 {
720 time_t now;
721 FILE *rec;
722
723 now = time(NULL);
724 strcpy(log->end, ".repairs");
725 rec = fopen(log->path, "a");
726 if (rec == NULL)
727 return;
728 fprintf(rec, "%.24s %s recovery: %s\n", ctime(&now), op == APPEND_OP ?
729 "append" : (op == COMPRESS_OP ? "compress" : "replace"), record);
730 fclose(rec);
731 return;
732 }
733
734 /* Recover the interrupted operation op. First read foo.add for recovering an
735 append or compress operation. Return -1 if there was an error reading or
736 writing foo.gz or reading an existing foo.add, or -2 if there was a memory
737 allocation failure. */
log_recover(struct log * log,int op)738 local int log_recover(struct log *log, int op)
739 {
740 int fd, ret = 0;
741 unsigned char *data = NULL;
742 size_t len = 0;
743 struct stat st;
744
745 /* log recovery */
746 log_log(log, op, "start");
747
748 /* load foo.add file if expected and present */
749 if (op == APPEND_OP || op == COMPRESS_OP) {
750 strcpy(log->end, ".add");
751 if (stat(log->path, &st) == 0 && st.st_size) {
752 len = (size_t)(st.st_size);
753 if ((off_t)len != st.st_size ||
754 (data = malloc(st.st_size)) == NULL) {
755 log_log(log, op, "allocation failure");
756 return -2;
757 }
758 if ((fd = open(log->path, O_RDONLY, 0)) < 0) {
759 log_log(log, op, ".add file read failure");
760 return -1;
761 }
762 ret = (size_t)read(fd, data, len) != len;
763 close(fd);
764 if (ret) {
765 log_log(log, op, ".add file read failure");
766 return -1;
767 }
768 log_log(log, op, "loaded .add file");
769 }
770 else
771 log_log(log, op, "missing .add file!");
772 }
773
774 /* recover the interrupted operation */
775 switch (op) {
776 case APPEND_OP:
777 ret = log_append(log, data, len);
778 break;
779 case COMPRESS_OP:
780 ret = log_compress(log, data, len);
781 break;
782 case REPLACE_OP:
783 ret = log_replace(log);
784 }
785
786 /* log status */
787 log_log(log, op, ret ? "failure" : "complete");
788
789 /* clean up */
790 if (data != NULL)
791 free(data);
792 return ret;
793 }
794
795 /* Close the foo.gz file (if open) and release the lock. */
log_close(struct log * log)796 local void log_close(struct log *log)
797 {
798 if (log->fd >= 0)
799 close(log->fd);
800 log->fd = -1;
801 log_unlock(log);
802 }
803
804 /* Open foo.gz, verify the header, and load the extra field contents, after
805 first creating the foo.lock file to gain exclusive access to the foo.*
806 files. If foo.gz does not exist or is empty, then write the initial header,
807 extra, and body content of an empty foo.gz log file. If there is an error
808 creating the lock file due to access restrictions, or an error reading or
809 writing the foo.gz file, or if the foo.gz file is not a proper log file for
810 this object (e.g. not a gzip file or does not contain the expected extra
811 field), then return true. If there is an error, the lock is released.
812 Otherwise, the lock is left in place. */
log_open(struct log * log)813 local int log_open(struct log *log)
814 {
815 int op;
816
817 /* release open file resource if left over -- can occur if lock lost
818 between gzlog_open() and gzlog_write() */
819 if (log->fd >= 0)
820 close(log->fd);
821 log->fd = -1;
822
823 /* negotiate exclusive access */
824 if (log_lock(log) < 0)
825 return -1;
826
827 /* open the log file, foo.gz */
828 strcpy(log->end, ".gz");
829 log->fd = open(log->path, O_RDWR | O_CREAT, 0644);
830 if (log->fd < 0) {
831 log_close(log);
832 return -1;
833 }
834
835 /* if new, initialize foo.gz with an empty log, delete old dictionary */
836 if (lseek(log->fd, 0, SEEK_END) == 0) {
837 if (write(log->fd, log_gzhead, HEAD) != HEAD ||
838 write(log->fd, log_gzext, EXTRA) != EXTRA ||
839 write(log->fd, log_gzbody, BODY) != BODY) {
840 log_close(log);
841 return -1;
842 }
843 strcpy(log->end, ".dict");
844 unlink(log->path);
845 }
846
847 /* verify log file and load extra field information */
848 if ((op = log_head(log)) < 0) {
849 log_close(log);
850 return -1;
851 }
852
853 /* check for interrupted process and if so, recover */
854 if (op != NO_OP && log_recover(log, op)) {
855 log_close(log);
856 return -1;
857 }
858
859 /* touch the lock file to prevent another process from grabbing it */
860 log_touch(log);
861 return 0;
862 }
863
864 /* See gzlog.h for the description of the external methods below */
gzlog_open(char * path)865 gzlog *gzlog_open(char *path)
866 {
867 size_t n;
868 struct log *log;
869
870 /* check arguments */
871 if (path == NULL || *path == 0)
872 return NULL;
873
874 /* allocate and initialize log structure */
875 log = malloc(sizeof(struct log));
876 if (log == NULL)
877 return NULL;
878 strcpy(log->id, LOGID);
879 log->fd = -1;
880
881 /* save path and end of path for name construction */
882 n = strlen(path);
883 log->path = malloc(n + 9); /* allow for ".repairs" */
884 if (log->path == NULL) {
885 free(log);
886 return NULL;
887 }
888 strcpy(log->path, path);
889 log->end = log->path + n;
890
891 /* gain exclusive access and verify log file -- may perform a
892 recovery operation if needed */
893 if (log_open(log)) {
894 free(log->path);
895 free(log);
896 return NULL;
897 }
898
899 /* return pointer to log structure */
900 return log;
901 }
902
903 /* gzlog_compress() return values:
904 0: all good
905 -1: file i/o error (usually access issue)
906 -2: memory allocation failure
907 -3: invalid log pointer argument */
gzlog_compress(gzlog * logd)908 int gzlog_compress(gzlog *logd)
909 {
910 int fd, ret;
911 uint block;
912 size_t len, next;
913 unsigned char *data, buf[5];
914 struct log *log = logd;
915
916 /* check arguments */
917 if (log == NULL || strcmp(log->id, LOGID))
918 return -3;
919
920 /* see if we lost the lock -- if so get it again and reload the extra
921 field information (it probably changed), recover last operation if
922 necessary */
923 if (log_check(log) && log_open(log))
924 return -1;
925
926 /* create space for uncompressed data */
927 len = ((size_t)(log->last - log->first) & ~(((size_t)1 << 10) - 1)) +
928 log->stored;
929 if ((data = malloc(len)) == NULL)
930 return -2;
931
932 /* do statement here is just a cheap trick for error handling */
933 do {
934 /* read in the uncompressed data */
935 if (lseek(log->fd, log->first - 1, SEEK_SET) < 0)
936 break;
937 next = 0;
938 while (next < len) {
939 if (read(log->fd, buf, 5) != 5)
940 break;
941 block = PULL2(buf + 1);
942 if (next + block > len ||
943 read(log->fd, (char *)data + next, block) != block)
944 break;
945 next += block;
946 }
947 if (lseek(log->fd, 0, SEEK_CUR) != log->last + 4 + log->stored)
948 break;
949 log_touch(log);
950
951 /* write the uncompressed data to the .add file */
952 strcpy(log->end, ".add");
953 fd = open(log->path, O_WRONLY | O_CREAT | O_TRUNC, 0644);
954 if (fd < 0)
955 break;
956 ret = (size_t)write(fd, data, len) != len;
957 if (ret | close(fd))
958 break;
959 log_touch(log);
960
961 /* write the dictionary for the next compress to the .temp file */
962 strcpy(log->end, ".temp");
963 fd = open(log->path, O_WRONLY | O_CREAT | O_TRUNC, 0644);
964 if (fd < 0)
965 break;
966 next = DICT > len ? len : DICT;
967 ret = (size_t)write(fd, (char *)data + len - next, next) != next;
968 if (ret | close(fd))
969 break;
970 log_touch(log);
971
972 /* roll back to compressed data, mark the compress in progress */
973 log->last = log->first;
974 log->stored = 0;
975 if (log_mark(log, COMPRESS_OP))
976 break;
977 BAIL(7);
978
979 /* compress and append the data (clears mark) */
980 ret = log_compress(log, data, len);
981 free(data);
982 return ret;
983 } while (0);
984
985 /* broke out of do above on i/o error */
986 free(data);
987 return -1;
988 }
989
990 /* gzlog_write() return values:
991 0: all good
992 -1: file i/o error (usually access issue)
993 -2: memory allocation failure
994 -3: invalid log pointer argument */
gzlog_write(gzlog * logd,void * data,size_t len)995 int gzlog_write(gzlog *logd, void *data, size_t len)
996 {
997 int fd, ret;
998 struct log *log = logd;
999
1000 /* check arguments */
1001 if (log == NULL || strcmp(log->id, LOGID))
1002 return -3;
1003 if (data == NULL || len <= 0)
1004 return 0;
1005
1006 /* see if we lost the lock -- if so get it again and reload the extra
1007 field information (it probably changed), recover last operation if
1008 necessary */
1009 if (log_check(log) && log_open(log))
1010 return -1;
1011
1012 /* create and write .add file */
1013 strcpy(log->end, ".add");
1014 fd = open(log->path, O_WRONLY | O_CREAT | O_TRUNC, 0644);
1015 if (fd < 0)
1016 return -1;
1017 ret = (size_t)write(fd, data, len) != len;
1018 if (ret | close(fd))
1019 return -1;
1020 log_touch(log);
1021
1022 /* mark log file with append in progress */
1023 if (log_mark(log, APPEND_OP))
1024 return -1;
1025 BAIL(8);
1026
1027 /* append data (clears mark) */
1028 if (log_append(log, data, len))
1029 return -1;
1030
1031 /* check to see if it's time to compress -- if not, then done */
1032 if (((log->last - log->first) >> 10) + (log->stored >> 10) < TRIGGER)
1033 return 0;
1034
1035 /* time to compress */
1036 return gzlog_compress(log);
1037 }
1038
1039 /* gzlog_close() return values:
1040 0: ok
1041 -3: invalid log pointer argument */
gzlog_close(gzlog * logd)1042 int gzlog_close(gzlog *logd)
1043 {
1044 struct log *log = logd;
1045
1046 /* check arguments */
1047 if (log == NULL || strcmp(log->id, LOGID))
1048 return -3;
1049
1050 /* close the log file and release the lock */
1051 log_close(log);
1052
1053 /* free structure and return */
1054 if (log->path != NULL)
1055 free(log->path);
1056 strcpy(log->id, "bad");
1057 free(log);
1058 return 0;
1059 }
1060