1 /* 2 * gzlog.c 3 * Copyright (C) 2004, 2008 Mark Adler, all rights reserved 4 * For conditions of distribution and use, see copyright notice in gzlog.h 5 * version 2.0, 25 Apr 2008 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 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 (len != st.st_size || (data = malloc(st.st_size)) == NULL) { 754 log_log(log, op, "allocation failure"); 755 return -2; 756 } 757 if ((fd = open(log->path, O_RDONLY, 0)) < 0) { 758 log_log(log, op, ".add file read failure"); 759 return -1; 760 } 761 ret = read(fd, data, len) != len; 762 close(fd); 763 if (ret) { 764 log_log(log, op, ".add file read failure"); 765 return -1; 766 } 767 log_log(log, op, "loaded .add file"); 768 } 769 else 770 log_log(log, op, "missing .add file!"); 771 } 772 773 /* recover the interrupted operation */ 774 switch (op) { 775 case APPEND_OP: 776 ret = log_append(log, data, len); 777 break; 778 case COMPRESS_OP: 779 ret = log_compress(log, data, len); 780 break; 781 case REPLACE_OP: 782 ret = log_replace(log); 783 } 784 785 /* log status */ 786 log_log(log, op, ret ? "failure" : "complete"); 787 788 /* clean up */ 789 if (data != NULL) 790 free(data); 791 return ret; 792 } 793 794 /* Close the foo.gz file (if open) and release the lock. */ 795 local void log_close(struct log *log) 796 { 797 if (log->fd >= 0) 798 close(log->fd); 799 log->fd = -1; 800 log_unlock(log); 801 } 802 803 /* Open foo.gz, verify the header, and load the extra field contents, after 804 first creating the foo.lock file to gain exclusive access to the foo.* 805 files. If foo.gz does not exist or is empty, then write the initial header, 806 extra, and body content of an empty foo.gz log file. If there is an error 807 creating the lock file due to access restrictions, or an error reading or 808 writing the foo.gz file, or if the foo.gz file is not a proper log file for 809 this object (e.g. not a gzip file or does not contain the expected extra 810 field), then return true. If there is an error, the lock is released. 811 Otherwise, the lock is left in place. */ 812 local int log_open(struct log *log) 813 { 814 int op; 815 816 /* release open file resource if left over -- can occur if lock lost 817 between gzlog_open() and gzlog_write() */ 818 if (log->fd >= 0) 819 close(log->fd); 820 log->fd = -1; 821 822 /* negotiate exclusive access */ 823 if (log_lock(log) < 0) 824 return -1; 825 826 /* open the log file, foo.gz */ 827 strcpy(log->end, ".gz"); 828 log->fd = open(log->path, O_RDWR | O_CREAT, 0644); 829 if (log->fd < 0) { 830 log_close(log); 831 return -1; 832 } 833 834 /* if new, initialize foo.gz with an empty log, delete old dictionary */ 835 if (lseek(log->fd, 0, SEEK_END) == 0) { 836 if (write(log->fd, log_gzhead, HEAD) != HEAD || 837 write(log->fd, log_gzext, EXTRA) != EXTRA || 838 write(log->fd, log_gzbody, BODY) != BODY) { 839 log_close(log); 840 return -1; 841 } 842 strcpy(log->end, ".dict"); 843 unlink(log->path); 844 } 845 846 /* verify log file and load extra field information */ 847 if ((op = log_head(log)) < 0) { 848 log_close(log); 849 return -1; 850 } 851 852 /* check for interrupted process and if so, recover */ 853 if (op != NO_OP && log_recover(log, op)) { 854 log_close(log); 855 return -1; 856 } 857 858 /* touch the lock file to prevent another process from grabbing it */ 859 log_touch(log); 860 return 0; 861 } 862 863 /* See gzlog.h for the description of the external methods below */ 864 gzlog *gzlog_open(char *path) 865 { 866 size_t n; 867 struct log *log; 868 869 /* check arguments */ 870 if (path == NULL || *path == 0) 871 return NULL; 872 873 /* allocate and initialize log structure */ 874 log = malloc(sizeof(struct log)); 875 if (log == NULL) 876 return NULL; 877 strcpy(log->id, LOGID); 878 log->fd = -1; 879 880 /* save path and end of path for name construction */ 881 n = strlen(path); 882 log->path = malloc(n + 9); /* allow for ".repairs" */ 883 if (log->path == NULL) { 884 free(log); 885 return NULL; 886 } 887 strcpy(log->path, path); 888 log->end = log->path + n; 889 890 /* gain exclusive access and verify log file -- may perform a 891 recovery operation if needed */ 892 if (log_open(log)) { 893 free(log->path); 894 free(log); 895 return NULL; 896 } 897 898 /* return pointer to log structure */ 899 return log; 900 } 901 902 /* gzlog_compress() return values: 903 0: all good 904 -1: file i/o error (usually access issue) 905 -2: memory allocation failure 906 -3: invalid log pointer argument */ 907 int gzlog_compress(gzlog *logd) 908 { 909 int fd, ret; 910 uint block; 911 size_t len, next; 912 unsigned char *data, buf[5]; 913 struct log *log = logd; 914 915 /* check arguments */ 916 if (log == NULL || strcmp(log->id, LOGID) || len < 0) 917 return -3; 918 919 /* see if we lost the lock -- if so get it again and reload the extra 920 field information (it probably changed), recover last operation if 921 necessary */ 922 if (log_check(log) && log_open(log)) 923 return -1; 924 925 /* create space for uncompressed data */ 926 len = ((size_t)(log->last - log->first) & ~(((size_t)1 << 10) - 1)) + 927 log->stored; 928 if ((data = malloc(len)) == NULL) 929 return -2; 930 931 /* do statement here is just a cheap trick for error handling */ 932 do { 933 /* read in the uncompressed data */ 934 if (lseek(log->fd, log->first - 1, SEEK_SET) < 0) 935 break; 936 next = 0; 937 while (next < len) { 938 if (read(log->fd, buf, 5) != 5) 939 break; 940 block = PULL2(buf + 1); 941 if (next + block > len || 942 read(log->fd, (char *)data + next, block) != block) 943 break; 944 next += block; 945 } 946 if (lseek(log->fd, 0, SEEK_CUR) != log->last + 4 + log->stored) 947 break; 948 log_touch(log); 949 950 /* write the uncompressed data to the .add file */ 951 strcpy(log->end, ".add"); 952 fd = open(log->path, O_WRONLY | O_CREAT | O_TRUNC, 0644); 953 if (fd < 0) 954 break; 955 ret = write(fd, data, len) != len; 956 if (ret | close(fd)) 957 break; 958 log_touch(log); 959 960 /* write the dictionary for the next compress to the .temp file */ 961 strcpy(log->end, ".temp"); 962 fd = open(log->path, O_WRONLY | O_CREAT | O_TRUNC, 0644); 963 if (fd < 0) 964 break; 965 next = DICT > len ? len : DICT; 966 ret = write(fd, (char *)data + len - next, next) != next; 967 if (ret | close(fd)) 968 break; 969 log_touch(log); 970 971 /* roll back to compressed data, mark the compress in progress */ 972 log->last = log->first; 973 log->stored = 0; 974 if (log_mark(log, COMPRESS_OP)) 975 break; 976 BAIL(7); 977 978 /* compress and append the data (clears mark) */ 979 ret = log_compress(log, data, len); 980 free(data); 981 return ret; 982 } while (0); 983 984 /* broke out of do above on i/o error */ 985 free(data); 986 return -1; 987 } 988 989 /* gzlog_write() return values: 990 0: all good 991 -1: file i/o error (usually access issue) 992 -2: memory allocation failure 993 -3: invalid log pointer argument */ 994 int gzlog_write(gzlog *logd, void *data, size_t len) 995 { 996 int fd, ret; 997 struct log *log = logd; 998 999 /* check arguments */ 1000 if (log == NULL || strcmp(log->id, LOGID) || len < 0) 1001 return -3; 1002 if (data == NULL || len == 0) 1003 return 0; 1004 1005 /* see if we lost the lock -- if so get it again and reload the extra 1006 field information (it probably changed), recover last operation if 1007 necessary */ 1008 if (log_check(log) && log_open(log)) 1009 return -1; 1010 1011 /* create and write .add file */ 1012 strcpy(log->end, ".add"); 1013 fd = open(log->path, O_WRONLY | O_CREAT | O_TRUNC, 0644); 1014 if (fd < 0) 1015 return -1; 1016 ret = write(fd, data, len) != len; 1017 if (ret | close(fd)) 1018 return -1; 1019 log_touch(log); 1020 1021 /* mark log file with append in progress */ 1022 if (log_mark(log, APPEND_OP)) 1023 return -1; 1024 BAIL(8); 1025 1026 /* append data (clears mark) */ 1027 if (log_append(log, data, len)) 1028 return -1; 1029 1030 /* check to see if it's time to compress -- if not, then done */ 1031 if (((log->last - log->first) >> 10) + (log->stored >> 10) < TRIGGER) 1032 return 0; 1033 1034 /* time to compress */ 1035 return gzlog_compress(log); 1036 } 1037 1038 /* gzlog_close() return values: 1039 0: ok 1040 -3: invalid log pointer argument */ 1041 int gzlog_close(gzlog *logd) 1042 { 1043 struct log *log = logd; 1044 1045 /* check arguments */ 1046 if (log == NULL || strcmp(log->id, LOGID)) 1047 return -3; 1048 1049 /* close the log file and release the lock */ 1050 log_close(log); 1051 1052 /* free structure and return */ 1053 if (log->path != NULL) 1054 free(log->path); 1055 strcpy(log->id, "bad"); 1056 free(log); 1057 return 0; 1058 } 1059
