9e052883 |
1 | /* |
2 | * gzlog.c |
3 | * Copyright (C) 2004, 2008, 2012, 2016, 2019 Mark Adler, all rights reserved |
4 | * For conditions of distribution and use, see copyright notice in gzlog.h |
5 | * version 2.3, 25 May 2019 |
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. */ |
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. */ |
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. */ |
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. */ |
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. */ |
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. */ |
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 */ |
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. */ |
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. */ |
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. */ |
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 */ |
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. */ |
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 | free(data); |
760 | log_log(log, op, ".add file read failure"); |
761 | return -1; |
762 | } |
763 | ret = (size_t)read(fd, data, len) != len; |
764 | close(fd); |
765 | if (ret) { |
766 | free(data); |
767 | log_log(log, op, ".add file read failure"); |
768 | return -1; |
769 | } |
770 | log_log(log, op, "loaded .add file"); |
771 | } |
772 | else |
773 | log_log(log, op, "missing .add file!"); |
774 | } |
775 | |
776 | /* recover the interrupted operation */ |
777 | switch (op) { |
778 | case APPEND_OP: |
779 | ret = log_append(log, data, len); |
780 | break; |
781 | case COMPRESS_OP: |
782 | ret = log_compress(log, data, len); |
783 | break; |
784 | case REPLACE_OP: |
785 | ret = log_replace(log); |
786 | } |
787 | |
788 | /* log status */ |
789 | log_log(log, op, ret ? "failure" : "complete"); |
790 | |
791 | /* clean up */ |
792 | if (data != NULL) |
793 | free(data); |
794 | return ret; |
795 | } |
796 | |
797 | /* Close the foo.gz file (if open) and release the lock. */ |
798 | local void log_close(struct log *log) |
799 | { |
800 | if (log->fd >= 0) |
801 | close(log->fd); |
802 | log->fd = -1; |
803 | log_unlock(log); |
804 | } |
805 | |
806 | /* Open foo.gz, verify the header, and load the extra field contents, after |
807 | first creating the foo.lock file to gain exclusive access to the foo.* |
808 | files. If foo.gz does not exist or is empty, then write the initial header, |
809 | extra, and body content of an empty foo.gz log file. If there is an error |
810 | creating the lock file due to access restrictions, or an error reading or |
811 | writing the foo.gz file, or if the foo.gz file is not a proper log file for |
812 | this object (e.g. not a gzip file or does not contain the expected extra |
813 | field), then return true. If there is an error, the lock is released. |
814 | Otherwise, the lock is left in place. */ |
815 | local int log_open(struct log *log) |
816 | { |
817 | int op; |
818 | |
819 | /* release open file resource if left over -- can occur if lock lost |
820 | between gzlog_open() and gzlog_write() */ |
821 | if (log->fd >= 0) |
822 | close(log->fd); |
823 | log->fd = -1; |
824 | |
825 | /* negotiate exclusive access */ |
826 | if (log_lock(log) < 0) |
827 | return -1; |
828 | |
829 | /* open the log file, foo.gz */ |
830 | strcpy(log->end, ".gz"); |
831 | log->fd = open(log->path, O_RDWR | O_CREAT, 0644); |
832 | if (log->fd < 0) { |
833 | log_close(log); |
834 | return -1; |
835 | } |
836 | |
837 | /* if new, initialize foo.gz with an empty log, delete old dictionary */ |
838 | if (lseek(log->fd, 0, SEEK_END) == 0) { |
839 | if (write(log->fd, log_gzhead, HEAD) != HEAD || |
840 | write(log->fd, log_gzext, EXTRA) != EXTRA || |
841 | write(log->fd, log_gzbody, BODY) != BODY) { |
842 | log_close(log); |
843 | return -1; |
844 | } |
845 | strcpy(log->end, ".dict"); |
846 | unlink(log->path); |
847 | } |
848 | |
849 | /* verify log file and load extra field information */ |
850 | if ((op = log_head(log)) < 0) { |
851 | log_close(log); |
852 | return -1; |
853 | } |
854 | |
855 | /* check for interrupted process and if so, recover */ |
856 | if (op != NO_OP && log_recover(log, op)) { |
857 | log_close(log); |
858 | return -1; |
859 | } |
860 | |
861 | /* touch the lock file to prevent another process from grabbing it */ |
862 | log_touch(log); |
863 | return 0; |
864 | } |
865 | |
866 | /* See gzlog.h for the description of the external methods below */ |
867 | gzlog *gzlog_open(char *path) |
868 | { |
869 | size_t n; |
870 | struct log *log; |
871 | |
872 | /* check arguments */ |
873 | if (path == NULL || *path == 0) |
874 | return NULL; |
875 | |
876 | /* allocate and initialize log structure */ |
877 | log = malloc(sizeof(struct log)); |
878 | if (log == NULL) |
879 | return NULL; |
880 | strcpy(log->id, LOGID); |
881 | log->fd = -1; |
882 | |
883 | /* save path and end of path for name construction */ |
884 | n = strlen(path); |
885 | log->path = malloc(n + 9); /* allow for ".repairs" */ |
886 | if (log->path == NULL) { |
887 | free(log); |
888 | return NULL; |
889 | } |
890 | strcpy(log->path, path); |
891 | log->end = log->path + n; |
892 | |
893 | /* gain exclusive access and verify log file -- may perform a |
894 | recovery operation if needed */ |
895 | if (log_open(log)) { |
896 | free(log->path); |
897 | free(log); |
898 | return NULL; |
899 | } |
900 | |
901 | /* return pointer to log structure */ |
902 | return log; |
903 | } |
904 | |
905 | /* gzlog_compress() return values: |
906 | 0: all good |
907 | -1: file i/o error (usually access issue) |
908 | -2: memory allocation failure |
909 | -3: invalid log pointer argument */ |
910 | int gzlog_compress(gzlog *logd) |
911 | { |
912 | int fd, ret; |
913 | uint block; |
914 | size_t len, next; |
915 | unsigned char *data, buf[5]; |
916 | struct log *log = logd; |
917 | |
918 | /* check arguments */ |
919 | if (log == NULL || strcmp(log->id, LOGID)) |
920 | return -3; |
921 | |
922 | /* see if we lost the lock -- if so get it again and reload the extra |
923 | field information (it probably changed), recover last operation if |
924 | necessary */ |
925 | if (log_check(log) && log_open(log)) |
926 | return -1; |
927 | |
928 | /* create space for uncompressed data */ |
929 | len = ((size_t)(log->last - log->first) & ~(((size_t)1 << 10) - 1)) + |
930 | log->stored; |
931 | if ((data = malloc(len)) == NULL) |
932 | return -2; |
933 | |
934 | /* do statement here is just a cheap trick for error handling */ |
935 | do { |
936 | /* read in the uncompressed data */ |
937 | if (lseek(log->fd, log->first - 1, SEEK_SET) < 0) |
938 | break; |
939 | next = 0; |
940 | while (next < len) { |
941 | if (read(log->fd, buf, 5) != 5) |
942 | break; |
943 | block = PULL2(buf + 1); |
944 | if (next + block > len || |
945 | read(log->fd, (char *)data + next, block) != block) |
946 | break; |
947 | next += block; |
948 | } |
949 | if (lseek(log->fd, 0, SEEK_CUR) != log->last + 4 + log->stored) |
950 | break; |
951 | log_touch(log); |
952 | |
953 | /* write the uncompressed data to the .add file */ |
954 | strcpy(log->end, ".add"); |
955 | fd = open(log->path, O_WRONLY | O_CREAT | O_TRUNC, 0644); |
956 | if (fd < 0) |
957 | break; |
958 | ret = (size_t)write(fd, data, len) != len; |
959 | if (ret | close(fd)) |
960 | break; |
961 | log_touch(log); |
962 | |
963 | /* write the dictionary for the next compress to the .temp file */ |
964 | strcpy(log->end, ".temp"); |
965 | fd = open(log->path, O_WRONLY | O_CREAT | O_TRUNC, 0644); |
966 | if (fd < 0) |
967 | break; |
968 | next = DICT > len ? len : DICT; |
969 | ret = (size_t)write(fd, (char *)data + len - next, next) != next; |
970 | if (ret | close(fd)) |
971 | break; |
972 | log_touch(log); |
973 | |
974 | /* roll back to compressed data, mark the compress in progress */ |
975 | log->last = log->first; |
976 | log->stored = 0; |
977 | if (log_mark(log, COMPRESS_OP)) |
978 | break; |
979 | BAIL(7); |
980 | |
981 | /* compress and append the data (clears mark) */ |
982 | ret = log_compress(log, data, len); |
983 | free(data); |
984 | return ret; |
985 | } while (0); |
986 | |
987 | /* broke out of do above on i/o error */ |
988 | free(data); |
989 | return -1; |
990 | } |
991 | |
992 | /* gzlog_write() return values: |
993 | 0: all good |
994 | -1: file i/o error (usually access issue) |
995 | -2: memory allocation failure |
996 | -3: invalid log pointer argument */ |
997 | int gzlog_write(gzlog *logd, void *data, size_t len) |
998 | { |
999 | int fd, ret; |
1000 | struct log *log = logd; |
1001 | |
1002 | /* check arguments */ |
1003 | if (log == NULL || strcmp(log->id, LOGID)) |
1004 | return -3; |
1005 | if (data == NULL || len <= 0) |
1006 | return 0; |
1007 | |
1008 | /* see if we lost the lock -- if so get it again and reload the extra |
1009 | field information (it probably changed), recover last operation if |
1010 | necessary */ |
1011 | if (log_check(log) && log_open(log)) |
1012 | return -1; |
1013 | |
1014 | /* create and write .add file */ |
1015 | strcpy(log->end, ".add"); |
1016 | fd = open(log->path, O_WRONLY | O_CREAT | O_TRUNC, 0644); |
1017 | if (fd < 0) |
1018 | return -1; |
1019 | ret = (size_t)write(fd, data, len) != len; |
1020 | if (ret | close(fd)) |
1021 | return -1; |
1022 | log_touch(log); |
1023 | |
1024 | /* mark log file with append in progress */ |
1025 | if (log_mark(log, APPEND_OP)) |
1026 | return -1; |
1027 | BAIL(8); |
1028 | |
1029 | /* append data (clears mark) */ |
1030 | if (log_append(log, data, len)) |
1031 | return -1; |
1032 | |
1033 | /* check to see if it's time to compress -- if not, then done */ |
1034 | if (((log->last - log->first) >> 10) + (log->stored >> 10) < TRIGGER) |
1035 | return 0; |
1036 | |
1037 | /* time to compress */ |
1038 | return gzlog_compress(log); |
1039 | } |
1040 | |
1041 | /* gzlog_close() return values: |
1042 | 0: ok |
1043 | -3: invalid log pointer argument */ |
1044 | int gzlog_close(gzlog *logd) |
1045 | { |
1046 | struct log *log = logd; |
1047 | |
1048 | /* check arguments */ |
1049 | if (log == NULL || strcmp(log->id, LOGID)) |
1050 | return -3; |
1051 | |
1052 | /* close the log file and release the lock */ |
1053 | log_close(log); |
1054 | |
1055 | /* free structure and return */ |
1056 | if (log->path != NULL) |
1057 | free(log->path); |
1058 | strcpy(log->id, "bad"); |
1059 | free(log); |
1060 | return 0; |
1061 | } |