diff options
Diffstat (limited to 'zlib/examples/gzlog.c')
| -rw-r--r-- | zlib/examples/gzlog.c | 1303 |
1 files changed, 974 insertions, 329 deletions
diff --git a/zlib/examples/gzlog.c b/zlib/examples/gzlog.c index f71f817c8..d70aacaba 100644 --- a/zlib/examples/gzlog.c +++ b/zlib/examples/gzlog.c @@ -1,413 +1,1058 @@ /* * gzlog.c - * Copyright (C) 2004 Mark Adler + * Copyright (C) 2004, 2008 Mark Adler, all rights reserved * For conditions of distribution and use, see copyright notice in gzlog.h - * version 1.0, 26 Nov 2004 - * + * version 2.0, 25 Apr 2008 */ -#include <string.h> /* memcmp() */ -#include <stdlib.h> /* malloc(), free(), NULL */ -#include <sys/types.h> /* size_t, off_t */ -#include <unistd.h> /* read(), close(), sleep(), ftruncate(), */ - /* lseek() */ -#include <fcntl.h> /* open() */ -#include <sys/file.h> /* flock() */ -#include "zlib.h" /* deflateInit2(), deflate(), deflateEnd() */ +/* + gzlog provides a mechanism for frequently appending short strings to a gzip + file that is efficient both in execution time and compression ratio. The + strategy is to write the short strings in an uncompressed form to the end of + the gzip file, only compressing when the amount of uncompressed data has + reached a given threshold. + + gzlog also provides protection against interruptions in the process due to + system crashes. The status of the operation is recorded in an extra field + in the gzip file, and is only updated once the gzip file is brought to a + valid state. The last data to be appended or compressed is saved in an + auxiliary file, so that if the operation is interrupted, it can be completed + the next time an append operation is attempted. + + gzlog maintains another auxiliary file with the last 32K of data from the + compressed portion, which is preloaded for the compression of the subsequent + data. This minimizes the impact to the compression ratio of appending. + */ + +/* + Operations Concept: + + Files (log name "foo"): + foo.gz -- gzip file with the complete log + foo.add -- last message to append or last data to compress + foo.dict -- dictionary of the last 32K of data for next compression + foo.temp -- temporary dictionary file for compression after this one + foo.lock -- lock file for reading and writing the other files + foo.repairs -- log file for log file recovery operations (not compressed) + + gzip file structure: + - fixed-length (no file name) header with extra field (see below) + - compressed data ending initially with empty stored block + - uncompressed data filling out originally empty stored block and + subsequent stored blocks as needed (16K max each) + - gzip trailer + - no junk at end (no other gzip streams) + + When appending data, the information in the first three items above plus the + foo.add file are sufficient to recover an interrupted append operation. The + extra field has the necessary information to restore the start of the last + stored block and determine where to append the data in the foo.add file, as + well as the crc and length of the gzip data before the append operation. + + The foo.add file is created before the gzip file is marked for append, and + deleted after the gzip file is marked as complete. So if the append + operation is interrupted, the data to add will still be there. If due to + some external force, the foo.add file gets deleted between when the append + operation was interrupted and when recovery is attempted, the gzip file will + still be restored, but without the appended data. + + When compressing data, the information in the first two items above plus the + foo.add file are sufficient to recover an interrupted compress operation. + The extra field has the necessary information to find the end of the + compressed data, and contains both the crc and length of just the compressed + data and of the complete set of data including the contents of the foo.add + file. + + Again, the foo.add file is maintained during the compress operation in case + of an interruption. If in the unlikely event the foo.add file with the data + to be compressed is missing due to some external force, a gzip file with + just the previous compressed data will be reconstructed. In this case, all + of the data that was to be compressed is lost (approximately one megabyte). + This will not occur if all that happened was an interruption of the compress + operation. + + The third state that is marked is the replacement of the old dictionary with + the new dictionary after a compress operation. Once compression is + complete, the gzip file is marked as being in the replace state. This + completes the gzip file, so an interrupt after being so marked does not + result in recompression. Then the dictionary file is replaced, and the gzip + file is marked as completed. This state prevents the possibility of + restarting compression with the wrong dictionary file. + + All three operations are wrapped by a lock/unlock procedure. In order to + gain exclusive access to the log files, first a foo.lock file must be + exclusively created. When all operations are complete, the lock is + released by deleting the foo.lock file. If when attempting to create the + lock file, it already exists and the modify time of the lock file is more + than five minutes old (set by the PATIENCE define below), then the old + lock file is considered stale and deleted, and the exclusive creation of + the lock file is retried. To assure that there are no false assessments + of the staleness of the lock file, the operations periodically touch the + lock file to update the modified date. + + Following is the definition of the extra field with all of the information + required to enable the above append and compress operations and their + recovery if interrupted. Multi-byte values are stored little endian + (consistent with the gzip format). File pointers are eight bytes long. + The crc's and lengths for the gzip trailer are four bytes long. (Note that + the length at the end of a gzip file is used for error checking only, and + for large files is actually the length modulo 2^32.) The stored block + length is two bytes long. The gzip extra field two-byte identification is + "ap" for append. It is assumed that writing the extra field to the file is + an "atomic" operation. That is, either all of the extra field is written + to the file, or none of it is, if the operation is interrupted right at the + point of updating the extra field. This is a reasonable assumption, since + the extra field is within the first 52 bytes of the file, which is smaller + than any expected block size for a mass storage device (usually 512 bytes or + larger). + + Extra field (35 bytes): + - Pointer to first stored block length -- this points to the two-byte length + of the first stored block, which is followed by the two-byte, one's + complement of that length. The stored block length is preceded by the + three-bit header of the stored block, which is the actual start of the + stored block in the deflate format. See the bit offset field below. + - Pointer to the last stored block length. This is the same as above, but + for the last stored block of the uncompressed data in the gzip file. + Initially this is the same as the first stored block length pointer. + When the stored block gets to 16K (see the MAX_STORE define), then a new + stored block as added, at which point the last stored block length pointer + is different from the first stored block length pointer. When they are + different, the first bit of the last stored block header is eight bits, or + one byte back from the block length. + - Compressed data crc and length. This is the crc and length of the data + that is in the compressed portion of the deflate stream. These are used + only in the event that the foo.add file containing the data to compress is + lost after a compress operation is interrupted. + - Total data crc and length. This is the crc and length of all of the data + stored in the gzip file, compressed and uncompressed. It is used to + reconstruct the gzip trailer when compressing, as well as when recovering + interrupted operations. + - Final stored block length. This is used to quickly find where to append, + and allows the restoration of the original final stored block state when + an append operation is interrupted. + - First stored block start as the number of bits back from the final stored + block first length byte. This value is in the range of 3..10, and is + stored as the low three bits of the final byte of the extra field after + subtracting three (0..7). This allows the last-block bit of the stored + block header to be updated when a new stored block is added, for the case + when the first stored block and the last stored block are the same. (When + they are different, the numbers of bits back is known to be eight.) This + also allows for new compressed data to be appended to the old compressed + data in the compress operation, overwriting the previous first stored + block, or for the compressed data to be terminated and a valid gzip file + reconstructed on the off chance that a compression operation was + interrupted and the data to compress in the foo.add file was deleted. + - The operation in process. This is the next two bits in the last byte (the + bits under the mask 0x18). The are interpreted as 0: nothing in process, + 1: append in process, 2: compress in process, 3: replace in process. + - The top three bits of the last byte in the extra field are reserved and + are currently set to zero. + + Main procedure: + - Exclusively create the foo.lock file using the O_CREAT and O_EXCL modes of + the system open() call. If the modify time of an existing lock file is + more than PATIENCE seconds old, then the lock file is deleted and the + exclusive create is retried. + - Load the extra field from the foo.gz file, and see if an operation was in + progress but not completed. If so, apply the recovery procedure below. + - Perform the append procedure with the provided data. + - If the uncompressed data in the foo.gz file is 1MB or more, apply the + compress procedure. + - Delete the foo.lock file. + + Append procedure: + - Put what to append in the foo.add file so that the operation can be + restarted if this procedure is interrupted. + - Mark the foo.gz extra field with the append operation in progress. + + Restore the original last-block bit and stored block length of the last + stored block from the information in the extra field, in case a previous + append operation was interrupted. + - Append the provided data to the last stored block, creating new stored + blocks as needed and updating the stored blocks last-block bits and + lengths. + - Update the crc and length with the new data, and write the gzip trailer. + - Write over the extra field (with a single write operation) with the new + pointers, lengths, and crc's, and mark the gzip file as not in process. + Though there is still a foo.add file, it will be ignored since nothing + is in process. If a foo.add file is leftover from a previously + completed operation, it is truncated when writing new data to it. + - Delete the foo.add file. + + Compress and replace procedures: + - Read all of the uncompressed data in the stored blocks in foo.gz and write + it to foo.add. Also write foo.temp with the last 32K of that data to + provide a dictionary for the next invocation of this procedure. + - Rewrite the extra field marking foo.gz with a compression in process. + * If there is no data provided to compress (due to a missing foo.add file + when recovering), reconstruct and truncate the foo.gz file to contain + only the previous compressed data and proceed to the step after the next + one. Otherwise ... + - Compress the data with the dictionary in foo.dict, and write to the + foo.gz file starting at the bit immediately following the last previously + compressed block. If there is no foo.dict, proceed anyway with the + compression at slightly reduced efficiency. (For the foo.dict file to be + missing requires some external failure beyond simply the interruption of + a compress operation.) During this process, the foo.lock file is + periodically touched to assure that that file is not considered stale by + another process before we're done. The deflation is terminated with a + non-last empty static block (10 bits long), that is then located and + written over by a last-bit-set empty stored block. + - Append the crc and length of the data in the gzip file (previously + calculated during the append operations). + - Write over the extra field with the updated stored block offsets, bits + back, crc's, and lengths, and mark foo.gz as in process for a replacement + of the dictionary. + @ Delete the foo.add file. + - Replace foo.dict with foo.temp. + - Write over the extra field, marking foo.gz as complete. + + Recovery procedure: + - If not a replace recovery, read in the foo.add file, and provide that data + to the appropriate recovery below. If there is no foo.add file, provide + a zero data length to the recovery. In that case, the append recovery + restores the foo.gz to the previous compressed + uncompressed data state. + For the the compress recovery, a missing foo.add file results in foo.gz + being restored to the previous compressed-only data state. + - Append recovery: + - Pick up append at + step above + - Compress recovery: + - Pick up compress at * step above + - Replace recovery: + - Pick up compress at @ step above + - Log the repair with a date stamp in foo.repairs + */ + +#include <sys/types.h> +#include <stdio.h> /* rename, fopen, fprintf, fclose */ +#include <stdlib.h> /* malloc, free */ +#include <string.h> /* strlen, strrchr, strcpy, strncpy, strcmp */ +#include <fcntl.h> /* open */ +#include <unistd.h> /* lseek, read, write, close, unlink, sleep, */ + /* ftruncate, fsync */ +#include <errno.h> /* errno */ +#include <time.h> /* time, ctime */ +#include <sys/stat.h> /* stat */ +#include <sys/time.h> /* utimes */ +#include "zlib.h" /* crc32 */ + +#include "gzlog.h" /* header for external access */ -#include "gzlog.h" /* interface */ #define local static +typedef unsigned int uint; +typedef unsigned long ulong; + +/* Macro for debugging to deterministically force recovery operations */ +#ifdef DEBUG + #include <setjmp.h> /* longjmp */ + jmp_buf gzlog_jump; /* where to go back to */ + int gzlog_bail = 0; /* which point to bail at (1..8) */ + int gzlog_count = -1; /* number of times through to wait */ +# define BAIL(n) do { if (n == gzlog_bail && gzlog_count-- == 0) \ + longjmp(gzlog_jump, gzlog_bail); } while (0) +#else +# define BAIL(n) +#endif + +/* how old the lock file can be in seconds before considering it stale */ +#define PATIENCE 300 + +/* maximum stored block size in Kbytes -- must be in 1..63 */ +#define MAX_STORE 16 -/* log object structure */ -typedef struct { - int id; /* object identifier */ - int fd; /* log file descriptor */ - off_t extra; /* offset of extra "ap" subfield */ - off_t mark_off; /* offset of marked data */ - off_t last_off; /* offset of last block */ - unsigned long crc; /* uncompressed crc */ - unsigned long len; /* uncompressed length (modulo 2^32) */ - unsigned stored; /* length of current stored block */ -} gz_log; - -#define GZLOGID 19334 /* gz_log object identifier */ - -#define LOCK_RETRY 1 /* retry lock once a second */ -#define LOCK_PATIENCE 1200 /* try about twenty minutes before forcing */ - -/* acquire a lock on a file */ -local int lock(int fd) +/* number of stored Kbytes to trigger compression (must be >= 32 to allow + dictionary construction, and <= 204 * MAX_STORE, in order for >> 10 to + discard the stored block headers contribution of five bytes each) */ +#define TRIGGER 1024 + +/* size of a deflate dictionary (this cannot be changed) */ +#define DICT 32768U + +/* values for the operation (2 bits) */ +#define NO_OP 0 +#define APPEND_OP 1 +#define COMPRESS_OP 2 +#define REPLACE_OP 3 + +/* macros to extract little-endian integers from an unsigned byte buffer */ +#define PULL2(p) ((p)[0]+((uint)((p)[1])<<8)) +#define PULL4(p) (PULL2(p)+((ulong)PULL2(p+2)<<16)) +#define PULL8(p) (PULL4(p)+((off_t)PULL4(p+4)<<32)) + +/* macros to store integers into a byte buffer in little-endian order */ +#define PUT2(p,a) do {(p)[0]=a;(p)[1]=(a)>>8;} while(0) +#define PUT4(p,a) do {PUT2(p,a);PUT2(p+2,a>>16);} while(0) +#define PUT8(p,a) do {PUT4(p,a);PUT4(p+4,a>>32);} while(0) + +/* internal structure for log information */ +#define LOGID "\106\035\172" /* should be three non-zero characters */ +struct log { + char id[4]; /* contains LOGID to detect inadvertent overwrites */ + int fd; /* file descriptor for .gz file, opened read/write */ + char *path; /* allocated path, e.g. "/var/log/foo" or "foo" */ + char *end; /* end of path, for appending suffices such as ".gz" */ + off_t first; /* offset of first stored block first length byte */ + int back; /* location of first block id in bits back from first */ + uint stored; /* bytes currently in last stored block */ + off_t last; /* offset of last stored block first length byte */ + ulong ccrc; /* crc of compressed data */ + ulong clen; /* length (modulo 2^32) of compressed data */ + ulong tcrc; /* crc of total data */ + ulong tlen; /* length (modulo 2^32) of total data */ + time_t lock; /* last modify time of our lock file */ +}; + +/* gzip header for gzlog */ +local unsigned char log_gzhead[] = { + 0x1f, 0x8b, /* magic gzip id */ + 8, /* compression method is deflate */ + 4, /* there is an extra field (no file name) */ + 0, 0, 0, 0, /* no modification time provided */ + 0, 0xff, /* no extra flags, no OS specified */ + 39, 0, 'a', 'p', 35, 0 /* extra field with "ap" subfield */ + /* 35 is EXTRA, 39 is EXTRA + 4 */ +}; + +#define HEAD sizeof(log_gzhead) /* should be 16 */ + +/* initial gzip extra field content (52 == HEAD + EXTRA + 1) */ +local unsigned char log_gzext[] = { + 52, 0, 0, 0, 0, 0, 0, 0, /* offset of first stored block length */ + 52, 0, 0, 0, 0, 0, 0, 0, /* offset of last stored block length */ + 0, 0, 0, 0, 0, 0, 0, 0, /* compressed data crc and length */ + 0, 0, 0, 0, 0, 0, 0, 0, /* total data crc and length */ + 0, 0, /* final stored block data length */ + 5 /* op is NO_OP, last bit 8 bits back */ +}; + +#define EXTRA sizeof(log_gzext) /* should be 35 */ + +/* initial gzip data and trailer */ +local unsigned char log_gzbody[] = { + 1, 0, 0, 0xff, 0xff, /* empty stored block (last) */ + 0, 0, 0, 0, /* crc */ + 0, 0, 0, 0 /* uncompressed length */ +}; + +#define BODY sizeof(log_gzbody) + +/* Exclusively create foo.lock in order to negotiate exclusive access to the + foo.* files. If the modify time of an existing lock file is greater than + PATIENCE seconds in the past, then consider the lock file to have been + abandoned, delete it, and try the exclusive create again. Save the lock + file modify time for verification of ownership. Return 0 on success, or -1 + on failure, usually due to an access restriction or invalid path. Note that + if stat() or unlink() fails, it may be due to another process noticing the + abandoned lock file a smidge sooner and deleting it, so those are not + flagged as an error. */ +local int log_lock(struct log *log) { - int patience; + int fd; + struct stat st; - /* try to lock every LOCK_RETRY seconds for LOCK_PATIENCE seconds */ - patience = LOCK_PATIENCE; - do { - if (flock(fd, LOCK_EX + LOCK_NB) == 0) - return 0; - (void)sleep(LOCK_RETRY); - patience -= LOCK_RETRY; - } while (patience > 0); + strcpy(log->end, ".lock"); + while ((fd = open(log->path, O_CREAT | O_EXCL, 0644)) < 0) { + if (errno != EEXIST) + return -1; + if (stat(log->path, &st) == 0 && time(NULL) - st.st_mtime > PATIENCE) { + unlink(log->path); + continue; + } + sleep(2); /* relinquish the CPU for two seconds while waiting */ + } + close(fd); + if (stat(log->path, &st) == 0) + log->lock = st.st_mtime; + return 0; +} - /* we've run out of patience -- give up */ - return -1; +/* Update the modify time of the lock file to now, in order to prevent another + task from thinking that the lock is stale. Save the lock file modify time + for verification of ownership. */ +local void log_touch(struct log *log) +{ + struct stat st; + + strcpy(log->end, ".lock"); + utimes(log->path, NULL); + if (stat(log->path, &st) == 0) + log->lock = st.st_mtime; } -/* release lock */ -local void unlock(int fd) +/* Check the log file modify time against what is expected. Return true if + this is not our lock. If it is our lock, touch it to keep it. */ +local int log_check(struct log *log) { - (void)flock(fd, LOCK_UN); + struct stat st; + + strcpy(log->end, ".lock"); + if (stat(log->path, &st) || st.st_mtime != log->lock) + return 1; + log_touch(log); + return 0; } -/* release a log object */ -local void log_clean(gz_log *log) +/* Unlock a previously acquired lock, but only if it's ours. */ +local void log_unlock(struct log *log) { - unlock(log->fd); - (void)close(log->fd); - free(log); + if (log_check(log)) + return; + strcpy(log->end, ".lock"); + unlink(log->path); + log->lock = 0; } -/* read an unsigned long from a byte buffer little-endian */ -local unsigned long make_ulg(unsigned char *buf) +/* Check the gzip header and read in the extra field, filling in the values in + the log structure. Return op on success or -1 if the gzip header was not as + expected. op is the current operation in progress last written to the extra + field. This assumes that the gzip file has already been opened, with the + file descriptor log->fd. */ +local int log_head(struct log *log) { - int n; - unsigned long val; + int op; + unsigned char buf[HEAD + EXTRA]; - val = (unsigned long)(*buf++); - for (n = 8; n < 32; n += 8) - val += (unsigned long)(*buf++) << n; - return val; + if (lseek(log->fd, 0, SEEK_SET) < 0 || + read(log->fd, buf, HEAD + EXTRA) != HEAD + EXTRA || + memcmp(buf, log_gzhead, HEAD)) { + return -1; + } + log->first = PULL8(buf + HEAD); + log->last = PULL8(buf + HEAD + 8); + log->ccrc = PULL4(buf + HEAD + 16); + log->clen = PULL4(buf + HEAD + 20); + log->tcrc = PULL4(buf + HEAD + 24); + log->tlen = PULL4(buf + HEAD + 28); + log->stored = PULL2(buf + HEAD + 32); + log->back = 3 + (buf[HEAD + 34] & 7); + op = (buf[HEAD + 34] >> 3) & 3; + return op; } -/* read an off_t from a byte buffer little-endian */ -local off_t make_off(unsigned char *buf) +/* Write over the extra field contents, marking the operation as op. Use fsync + to assure that the device is written to, and in the requested order. This + operation, and only this operation, is assumed to be atomic in order to + assure that the log is recoverable in the event of an interruption at any + point in the process. Return -1 if the write to foo.gz failed. */ +local int log_mark(struct log *log, int op) { - int n; - off_t val; + int ret; + unsigned char ext[EXTRA]; - val = (off_t)(*buf++); - for (n = 8; n < 64; n += 8) - val += (off_t)(*buf++) << n; - return val; + PUT8(ext, log->first); + PUT8(ext + 8, log->last); + PUT4(ext + 16, log->ccrc); + PUT4(ext + 20, log->clen); + PUT4(ext + 24, log->tcrc); + PUT4(ext + 28, log->tlen); + PUT2(ext + 32, log->stored); + ext[34] = log->back - 3 + (op << 3); + fsync(log->fd); + ret = lseek(log->fd, HEAD, SEEK_SET) < 0 || + write(log->fd, ext, EXTRA) != EXTRA ? -1 : 0; + fsync(log->fd); + return ret; } -/* write an unsigned long little-endian to byte buffer */ -local void dice_ulg(unsigned long val, unsigned char *buf) +/* Rewrite the last block header bits and subsequent zero bits to get to a byte + boundary, setting the last block bit if last is true, and then write the + remainder of the stored block header (length and one's complement). Leave + the file pointer after the end of the last stored block data. Return -1 if + there is a read or write failure on the foo.gz file */ +local int log_last(struct log *log, int last) { - int n; + int back, len, mask; + unsigned char buf[6]; + + /* determine the locations of the bytes and bits to modify */ + back = log->last == log->first ? log->back : 8; + len = back > 8 ? 2 : 1; /* bytes back from log->last */ + mask = 0x80 >> ((back - 1) & 7); /* mask for block last-bit */ + + /* get the byte to modify (one or two back) into buf[0] -- don't need to + read the byte if the last-bit is eight bits back, since in that case + the entire byte will be modified */ + buf[0] = 0; + if (back != 8 && (lseek(log->fd, log->last - len, SEEK_SET) < 0 || + read(log->fd, buf, 1) != 1)) + return -1; + + /* change the last-bit of the last stored block as requested -- note + that all bits above the last-bit are set to zero, per the type bits + of a stored block being 00 and per the convention that the bits to + bring the stream to a byte boundary are also zeros */ + buf[1] = 0; + buf[2 - len] = (*buf & (mask - 1)) + (last ? mask : 0); - for (n = 0; n < 4; n++) { - *buf++ = val & 0xff; - val >>= 8; + /* write the modified stored block header and lengths, move the file + pointer to after the last stored block data */ + PUT2(buf + 2, log->stored); + PUT2(buf + 4, log->stored ^ 0xffff); + return lseek(log->fd, log->last - len, SEEK_SET) < 0 || + write(log->fd, buf + 2 - len, len + 4) != len + 4 || + lseek(log->fd, log->stored, SEEK_CUR) < 0 ? -1 : 0; +} + +/* Append len bytes from data to the locked and open log file. len may be zero + if recovering and no .add file was found. In that case, the previous state + of the foo.gz file is restored. The data is appended uncompressed in + deflate stored blocks. Return -1 if there was an error reading or writing + the foo.gz file. */ +local int log_append(struct log *log, unsigned char *data, size_t len) +{ + uint put; + off_t end; + unsigned char buf[8]; + + /* set the last block last-bit and length, in case recovering an + interrupted append, then position the file pointer to append to the + block */ + if (log_last(log, 1)) + return -1; + + /* append, adding stored blocks and updating the offset of the last stored + block as needed, and update the total crc and length */ + while (len) { + /* append as much as we can to the last block */ + put = (MAX_STORE << 10) - log->stored; + if (put > len) + put = (uint)len; + if (put) { + if (write(log->fd, data, put) != put) + return -1; + BAIL(1); + log->tcrc = crc32(log->tcrc, data, put); + log->tlen += put; + log->stored += put; + data += put; + len -= put; + } + + /* if we need to, add a new empty stored block */ + if (len) { + /* mark current block as not last */ + if (log_last(log, 0)) + return -1; + + /* point to new, empty stored block */ + log->last += 4 + log->stored + 1; + log->stored = 0; + } + + /* mark last block as last, update its length */ + if (log_last(log, 1)) + return -1; + BAIL(2); } + + /* write the new crc and length trailer, and truncate just in case (could + be recovering from partial append with a missing foo.add file) */ + PUT4(buf, log->tcrc); + PUT4(buf + 4, log->tlen); + if (write(log->fd, buf, 8) != 8 || + (end = lseek(log->fd, 0, SEEK_CUR)) < 0 || ftruncate(log->fd, end)) + return -1; + + /* write the extra field, marking the log file as done, delete .add file */ + if (log_mark(log, NO_OP)) + return -1; + strcpy(log->end, ".add"); + unlink(log->path); /* ignore error, since may not exist */ + return 0; } -/* write an off_t little-endian to byte buffer */ -local void dice_off(off_t val, unsigned char *buf) +/* Replace the foo.dict file with the foo.temp file. Also delete the foo.add + file, since the compress operation may have been interrupted before that was + done. Returns 1 if memory could not be allocated, or -1 if reading or + writing foo.gz fails, or if the rename fails for some reason other than + foo.temp not existing. foo.temp not existing is a permitted error, since + the replace operation may have been interrupted after the rename is done, + but before foo.gz is marked as complete. */ +local int log_replace(struct log *log) { - int n; + int ret; + char *dest; + + /* delete foo.add file */ + strcpy(log->end, ".add"); + unlink(log->path); /* ignore error, since may not exist */ + BAIL(3); + + /* rename foo.name to foo.dict, replacing foo.dict if it exists */ + strcpy(log->end, ".dict"); + dest = malloc(strlen(log->path) + 1); + if (dest == NULL) + return -2; + strcpy(dest, log->path); + strcpy(log->end, ".temp"); + ret = rename(log->path, dest); + free(dest); + if (ret && errno != ENOENT) + return -1; + BAIL(4); - for (n = 0; n < 8; n++) { - *buf++ = val & 0xff; - val >>= 8; + /* mark the foo.gz file as done */ + return log_mark(log, NO_OP); +} + +/* Compress the len bytes at data and append the compressed data to the + foo.gz deflate data immediately after the previous compressed data. This + overwrites the previous uncompressed data, which was stored in foo.add + and is the data provided in data[0..len-1]. If this operation is + interrupted, it picks up at the start of this routine, with the foo.add + file read in again. If there is no data to compress (len == 0), then we + simply terminate the foo.gz file after the previously compressed data, + appending a final empty stored block and the gzip trailer. Return -1 if + reading or writing the log.gz file failed, or -2 if there was a memory + allocation failure. */ +local int log_compress(struct log *log, unsigned char *data, size_t len) +{ + int fd; + uint got, max; + ssize_t dict; + off_t end; + z_stream strm; + unsigned char buf[DICT]; + + /* compress and append compressed data */ + if (len) { + /* set up for deflate, allocating memory */ + strm.zalloc = Z_NULL; + strm.zfree = Z_NULL; + strm.opaque = Z_NULL; + if (deflateInit2(&strm, Z_DEFAULT_COMPRESSION, Z_DEFLATED, -15, 8, + Z_DEFAULT_STRATEGY) != Z_OK) + return -2; + + /* read in dictionary (last 32K of data that was compressed) */ + strcpy(log->end, ".dict"); + fd = open(log->path, O_RDONLY, 0); + if (fd >= 0) { + dict = read(fd, buf, DICT); + close(fd); + if (dict < 0) { + deflateEnd(&strm); + return -1; + } + if (dict) + deflateSetDictionary(&strm, buf, (uint)dict); + } + log_touch(log); + + /* prime deflate with last bits of previous block, position write + pointer to write those bits and overwrite what follows */ + if (lseek(log->fd, log->first - (log->back > 8 ? 2 : 1), + SEEK_SET) < 0 || + read(log->fd, buf, 1) != 1 || lseek(log->fd, -1, SEEK_CUR) < 0) { + deflateEnd(&strm); + return -1; + } + deflatePrime(&strm, (8 - log->back) & 7, *buf); + + /* compress, finishing with a partial non-last empty static block */ + strm.next_in = data; + max = (((uint)0 - 1) >> 1) + 1; /* in case int smaller than size_t */ + do { + strm.avail_in = len > max ? max : (uint)len; + len -= strm.avail_in; + do { + strm.avail_out = DICT; + strm.next_out = buf; + deflate(&strm, len ? Z_NO_FLUSH : Z_PARTIAL_FLUSH); + got = DICT - strm.avail_out; + if (got && write(log->fd, buf, got) != got) { + deflateEnd(&strm); + return -1; + } + log_touch(log); + } while (strm.avail_out == 0); + } while (len); + deflateEnd(&strm); + BAIL(5); + + /* find start of empty static block -- scanning backwards the first one + bit is the second bit of the block, if the last byte is zero, then + we know the byte before that has a one in the top bit, since an + empty static block is ten bits long */ + if ((log->first = lseek(log->fd, -1, SEEK_CUR)) < 0 || + read(log->fd, buf, 1) != 1) + return -1; + log->first++; + if (*buf) { + log->back = 1; + while ((*buf & ((uint)1 << (8 - log->back++))) == 0) + ; /* guaranteed to terminate, since *buf != 0 */ + } + else + log->back = 10; + + /* update compressed crc and length */ + log->ccrc = log->tcrc; + log->clen = log->tlen; + } + else { + /* no data to compress -- fix up existing gzip stream */ + log->tcrc = log->ccrc; + log->tlen = log->clen; } + + /* complete and truncate gzip stream */ + log->last = log->first; + log->stored = 0; + PUT4(buf, log->tcrc); + PUT4(buf + 4, log->tlen); + if (log_last(log, 1) || write(log->fd, buf, 8) != 8 || + (end = lseek(log->fd, 0, SEEK_CUR)) < 0 || ftruncate(log->fd, end)) + return -1; + BAIL(6); + + /* mark as being in the replace operation */ + if (log_mark(log, REPLACE_OP)) + return -1; + + /* execute the replace operation and mark the file as done */ + return log_replace(log); } -/* initial, empty gzip file for appending */ -local char empty_gz[] = { - 0x1f, 0x8b, /* magic gzip id */ - 8, /* compression method is deflate */ - 4, /* there is an extra field */ - 0, 0, 0, 0, /* no modification time provided */ - 0, 0xff, /* no extra flags, no OS */ - 20, 0, 'a', 'p', 16, 0, /* extra field with "ap" subfield */ - 32, 0, 0, 0, 0, 0, 0, 0, /* offset of uncompressed data */ - 32, 0, 0, 0, 0, 0, 0, 0, /* offset of last block */ - 1, 0, 0, 0xff, 0xff, /* empty stored block (last) */ - 0, 0, 0, 0, /* crc */ - 0, 0, 0, 0 /* uncompressed length */ -}; +/* log a repair record to the .repairs file */ +local void log_log(struct log *log, int op, char *record) +{ + time_t now; + FILE *rec; -/* initialize a log object with locking */ -void *gzlog_open(char *path) + now = time(NULL); + strcpy(log->end, ".repairs"); + rec = fopen(log->path, "a"); + if (rec == NULL) + return; + fprintf(rec, "%.24s %s recovery: %s\n", ctime(&now), op == APPEND_OP ? + "append" : (op == COMPRESS_OP ? "compress" : "replace"), record); + fclose(rec); + return; +} + +/* Recover the interrupted operation op. First read foo.add for recovering an + append or compress operation. Return -1 if there was an error reading or + writing foo.gz or reading an existing foo.add, or -2 if there was a memory + allocation failure. */ +local int log_recover(struct log *log, int op) { - unsigned xlen; - unsigned char temp[20]; - unsigned sub_len; - int good; - gz_log *log; - - /* allocate log structure */ - log = malloc(sizeof(gz_log)); - if (log == NULL) - return NULL; - log->id = GZLOGID; + int fd, ret = 0; + unsigned char *data = NULL; + size_t len = 0; + struct stat st; - /* open file, creating it if necessary, and locking it */ - log->fd = open(path, O_RDWR | O_CREAT, 0600); - if (log->fd < 0) { - free(log); - return NULL; + /* log recovery */ + log_log(log, op, "start"); + + /* load foo.add file if expected and present */ + if (op == APPEND_OP || op == COMPRESS_OP) { + strcpy(log->end, ".add"); + if (stat(log->path, &st) == 0 && st.st_size) { + len = (size_t)(st.st_size); + if (len != st.st_size || (data = malloc(st.st_size)) == NULL) { + log_log(log, op, "allocation failure"); + return -2; + } + if ((fd = open(log->path, O_RDONLY, 0)) < 0) { + log_log(log, op, ".add file read failure"); + return -1; + } + ret = read(fd, data, len) != len; + close(fd); + if (ret) { + log_log(log, op, ".add file read failure"); + return -1; + } + log_log(log, op, "loaded .add file"); + } + else + log_log(log, op, "missing .add file!"); + } + + /* recover the interrupted operation */ + switch (op) { + case APPEND_OP: + ret = log_append(log, data, len); + break; + case COMPRESS_OP: + ret = log_compress(log, data, len); + break; + case REPLACE_OP: + ret = log_replace(log); } - if (lock(log->fd)) { + + /* log status */ + log_log(log, op, ret ? "failure" : "complete"); + + /* clean up */ + if (data != NULL) + free(data); + return ret; +} + +/* Close the foo.gz file (if open) and release the lock. */ +local void log_close(struct log *log) +{ + if (log->fd >= 0) close(log->fd); - free(log); - return NULL; + log->fd = -1; + log_unlock(log); +} + +/* Open foo.gz, verify the header, and load the extra field contents, after + first creating the foo.lock file to gain exclusive access to the foo.* + files. If foo.gz does not exist or is empty, then write the initial header, + extra, and body content of an empty foo.gz log file. If there is an error + creating the lock file due to access restrictions, or an error reading or + writing the foo.gz file, or if the foo.gz file is not a proper log file for + this object (e.g. not a gzip file or does not contain the expected extra + field), then return true. If there is an error, the lock is released. + Otherwise, the lock is left in place. */ +local int log_open(struct log *log) +{ + int op; + + /* release open file resource if left over -- can occur if lock lost + between gzlog_open() and gzlog_write() */ + if (log->fd >= 0) + close(log->fd); + log->fd = -1; + + /* negotiate exclusive access */ + if (log_lock(log) < 0) + return -1; + + /* open the log file, foo.gz */ + strcpy(log->end, ".gz"); + log->fd = open(log->path, O_RDWR | O_CREAT, 0644); + if (log->fd < 0) { + log_close(log); + return -1; } - /* if file is empty, write new gzip stream */ + /* if new, initialize foo.gz with an empty log, delete old dictionary */ if (lseek(log->fd, 0, SEEK_END) == 0) { - if (write(log->fd, empty_gz, sizeof(empty_gz)) != sizeof(empty_gz)) { - log_clean(log); - return NULL; + if (write(log->fd, log_gzhead, HEAD) != HEAD || + write(log->fd, log_gzext, EXTRA) != EXTRA || + write(log->fd, log_gzbody, BODY) != BODY) { + log_close(log); + return -1; } + strcpy(log->end, ".dict"); + unlink(log->path); } - /* check gzip header */ - (void)lseek(log->fd, 0, SEEK_SET); - if (read(log->fd, temp, 12) != 12 || temp[0] != 0x1f || - temp[1] != 0x8b || temp[2] != 8 || (temp[3] & 4) == 0) { - log_clean(log); - return NULL; + /* verify log file and load extra field information */ + if ((op = log_head(log)) < 0) { + log_close(log); + return -1; } - /* process extra field to find "ap" sub-field */ - xlen = temp[10] + (temp[11] << 8); - good = 0; - while (xlen) { - if (xlen < 4 || read(log->fd, temp, 4) != 4) - break; - sub_len = temp[2]; - sub_len += temp[3] << 8; - xlen -= 4; - if (memcmp(temp, "ap", 2) == 0 && sub_len == 16) { - good = 1; - break; - } - if (xlen < sub_len) - break; - (void)lseek(log->fd, sub_len, SEEK_CUR); - xlen -= sub_len; + /* check for interrupted process and if so, recover */ + if (op != NO_OP && log_recover(log, op)) { + log_close(log); + return -1; } - if (!good) { - log_clean(log); + + /* touch the lock file to prevent another process from grabbing it */ + log_touch(log); + return 0; +} + +/* See gzlog.h for the description of the external methods below */ +gzlog *gzlog_open(char *path) +{ + size_t n; + struct log *log; + + /* check arguments */ + if (path == NULL || *path == 0) return NULL; - } - /* read in "ap" sub-field */ - log->extra = lseek(log->fd, 0, SEEK_CUR); - if (read(log->fd, temp, 16) != 16) { - log_clean(log); + /* allocate and initialize log structure */ + log = malloc(sizeof(struct log)); + if (log == NULL) + return NULL; + strcpy(log->id, LOGID); + log->fd = -1; + + /* save path and end of path for name construction */ + n = strlen(path); + log->path = malloc(n + 9); /* allow for ".repairs" */ + if (log->path == NULL) { + free(log); return NULL; } - log->mark_off = make_off(temp); - log->last_off = make_off(temp + 8); - - /* get crc, length of gzip file */ - (void)lseek(log->fd, log->last_off, SEEK_SET); - if (read(log->fd, temp, 13) != 13 || - memcmp(temp, "\001\000\000\377\377", 5) != 0) { - log_clean(log); + strcpy(log->path, path); + log->end = log->path + n; + + /* gain exclusive access and verify log file -- may perform a + recovery operation if needed */ + if (log_open(log)) { + free(log->path); + free(log); return NULL; } - log->crc = make_ulg(temp + 5); - log->len = make_ulg(temp + 9); - /* set up to write over empty last block */ - (void)lseek(log->fd, log->last_off + 5, SEEK_SET); - log->stored = 0; - return (void *)log; + /* return pointer to log structure */ + return log; } -/* maximum amount to put in a stored block before starting a new one */ -#define MAX_BLOCK 16384 - -/* write a block to a log object */ -int gzlog_write(void *obj, char *data, size_t len) +/* gzlog_compress() return values: + 0: all good + -1: file i/o error (usually access issue) + -2: memory allocation failure + -3: invalid log pointer argument */ +int gzlog_compress(gzlog *logd) { - size_t some; - unsigned char temp[5]; - gz_log *log; + int fd, ret; + uint block; + size_t len, next; + unsigned char *data, buf[5]; + struct log *log = logd; - /* check object */ - log = (gz_log *)obj; - if (log == NULL || log->id != GZLOGID) - return 1; + /* check arguments */ + if (log == NULL || strcmp(log->id, LOGID) || len < 0) + return -3; - /* write stored blocks until all of the input is written */ - do { - some = MAX_BLOCK - log->stored; - if (some > len) - some = len; - if (write(log->fd, data, some) != some) - return 1; - log->crc = crc32(log->crc, data, some); - log->len += some; - len -= some; - data += some; - log->stored += some; - - /* if the stored block is full, end it and start another */ - if (log->stored == MAX_BLOCK) { - (void)lseek(log->fd, log->last_off, SEEK_SET); - temp[0] = 0; - dice_ulg(log->stored + ((unsigned long)(~log->stored) << 16), - temp + 1); - if (write(log->fd, temp, 5) != 5) - return 1; - log->last_off = lseek(log->fd, log->stored, SEEK_CUR); - (void)lseek(log->fd, 5, SEEK_CUR); - log->stored = 0; - } - } while (len); - return 0; -} + /* see if we lost the lock -- if so get it again and reload the extra + field information (it probably changed), recover last operation if + necessary */ + if (log_check(log) && log_open(log)) + return -1; -/* recompress the remaining stored deflate data in place */ -local int recomp(gz_log *log) -{ - z_stream strm; - size_t len, max; - unsigned char *in; - unsigned char *out; - unsigned char temp[16]; - - /* allocate space and read it all in (it's around 1 MB) */ - len = log->last_off - log->mark_off; - max = len + (len >> 12) + (len >> 14) + 11; - out = malloc(max); - if (out == NULL) - return 1; - in = malloc(len); - if (in == NULL) { - free(out); - return 1; - } - (void)lseek(log->fd, log->mark_off, SEEK_SET); - if (read(log->fd, in, len) != len) { - free(in); - free(out); - return 1; - } + /* create space for uncompressed data */ + len = ((size_t)(log->last - log->first) & ~(((size_t)1 << 10) - 1)) + + log->stored; + if ((data = malloc(len)) == NULL) + return -2; - /* recompress in memory, decoding stored data as we go */ - /* note: this assumes that unsigned is four bytes or more */ - /* consider not making that assumption */ - strm.zalloc = Z_NULL; - strm.zfree = Z_NULL; - strm.opaque = Z_NULL; - if (deflateInit2(&strm, Z_BEST_COMPRESSION, Z_DEFLATED, -15, 8, - Z_DEFAULT_STRATEGY) != Z_OK) { - free(in); - free(out); - return 1; - } - strm.next_in = in; - strm.avail_out = max; - strm.next_out = out; - while (len >= 5) { - if (strm.next_in[0] != 0) + /* do statement here is just a cheap trick for error handling */ + do { + /* read in the uncompressed data */ + if (lseek(log->fd, log->first - 1, SEEK_SET) < 0) break; - strm.avail_in = strm.next_in[1] + (strm.next_in[2] << 8); - strm.next_in += 5; - len -= 5; - if (strm.avail_in != 0) { - if (len < strm.avail_in) + next = 0; + while (next < len) { + if (read(log->fd, buf, 5) != 5) break; - len -= strm.avail_in; - (void)deflate(&strm, Z_NO_FLUSH); - if (strm.avail_in != 0 || strm.avail_out == 0) + block = PULL2(buf + 1); + if (next + block > len || + read(log->fd, (char *)data + next, block) != block) break; + next += block; } - } - (void)deflate(&strm, Z_SYNC_FLUSH); - (void)deflateEnd(&strm); - free(in); - if (len != 0 || strm.avail_out == 0) { - free(out); - return 1; - } + if (lseek(log->fd, 0, SEEK_CUR) != log->last + 4 + log->stored) + break; + log_touch(log); - /* overwrite stored data with compressed data */ - (void)lseek(log->fd, log->mark_off, SEEK_SET); - len = max - strm.avail_out; - if (write(log->fd, out, len) != len) { - free(out); - return 1; - } - free(out); - - /* write last empty block, crc, and length */ - log->mark_off = log->last_off = lseek(log->fd, 0, SEEK_CUR); - temp[0] = 1; - dice_ulg(0xffffL << 16, temp + 1); - dice_ulg(log->crc, temp + 5); - dice_ulg(log->len, temp + 9); - if (write(log->fd, temp, 13) != 13) - return 1; + /* write the uncompressed data to the .add file */ + strcpy(log->end, ".add"); + fd = open(log->path, O_WRONLY | O_CREAT | O_TRUNC, 0644); + if (fd < 0) + break; + ret = write(fd, data, len) != len; + if (ret | close(fd)) + break; + log_touch(log); - /* truncate file to discard remaining stored data and old trailer */ - ftruncate(log->fd, lseek(log->fd, 0, SEEK_CUR)); + /* write the dictionary for the next compress to the .temp file */ + strcpy(log->end, ".temp"); + fd = open(log->path, O_WRONLY | O_CREAT | O_TRUNC, 0644); + if (fd < 0) + break; + next = DICT > len ? len : DICT; + ret = write(fd, (char *)data + len - next, next) != next; + if (ret | close(fd)) + break; + log_touch(log); - /* update extra field to point to new last empty block */ - (void)lseek(log->fd, log->extra, SEEK_SET); - dice_off(log->mark_off, temp); - dice_off(log->last_off, temp + 8); - if (write(log->fd, temp, 16) != 16) - return 1; - return 0; -} + /* roll back to compressed data, mark the compress in progress */ + log->last = log->first; + log->stored = 0; + if (log_mark(log, COMPRESS_OP)) + break; + BAIL(7); + + /* compress and append the data (clears mark) */ + ret = log_compress(log, data, len); + free(data); + return ret; + } while (0); -/* maximum accumulation of stored blocks before compressing */ -#define MAX_STORED 1048576 + /* broke out of do above on i/o error */ + free(data); + return -1; +} -/* close log object */ -int gzlog_close(void *obj) +/* gzlog_write() return values: + 0: all good + -1: file i/o error (usually access issue) + -2: memory allocation failure + -3: invalid log pointer argument */ +int gzlog_write(gzlog *logd, void *data, size_t len) { - unsigned char temp[8]; - gz_log *log; + int fd, ret; + struct log *log = logd; - /* check object */ - log = (gz_log *)obj; - if (log == NULL || log->id != GZLOGID) - return 1; + /* check arguments */ + if (log == NULL || strcmp(log->id, LOGID) || len < 0) + return -3; + if (data == NULL || len == 0) + return 0; - /* go to start of most recent block being written */ - (void)lseek(log->fd, log->last_off, SEEK_SET); - - /* if some stuff was put there, update block */ - if (log->stored) { - temp[0] = 0; - dice_ulg(log->stored + ((unsigned long)(~log->stored) << 16), - temp + 1); - if (write(log->fd, temp, 5) != 5) - return 1; - log->last_off = lseek(log->fd, log->stored, SEEK_CUR); - } + /* see if we lost the lock -- if so get it again and reload the extra + field information (it probably changed), recover last operation if + necessary */ + if (log_check(log) && log_open(log)) + return -1; - /* write last block (empty) */ - if (write(log->fd, "\001\000\000\377\377", 5) != 5) - return 1; + /* create and write .add file */ + strcpy(log->end, ".add"); + fd = open(log->path, O_WRONLY | O_CREAT | O_TRUNC, 0644); + if (fd < 0) + return -1; + ret = write(fd, data, len) != len; + if (ret | close(fd)) + return -1; + log_touch(log); - /* write updated crc and uncompressed length */ - dice_ulg(log->crc, temp); - dice_ulg(log->len, temp + 4); - if (write(log->fd, temp, 8) != 8) - return 1; + /* mark log file with append in progress */ + if (log_mark(log, APPEND_OP)) + return -1; + BAIL(8); - /* put offset of that last block in gzip extra block */ - (void)lseek(log->fd, log->extra + 8, SEEK_SET); - dice_off(log->last_off, temp); - if (write(log->fd, temp, 8) != 8) - return 1; + /* append data (clears mark) */ + if (log_append(log, data, len)) + return -1; - /* if more than 1 MB stored, then time to compress it */ - if (log->last_off - log->mark_off > MAX_STORED) { - if (recomp(log)) - return 1; - } + /* check to see if it's time to compress -- if not, then done */ + if (((log->last - log->first) >> 10) + (log->stored >> 10) < TRIGGER) + return 0; + + /* time to compress */ + return gzlog_compress(log); +} + +/* gzlog_close() return values: + 0: ok + -3: invalid log pointer argument */ +int gzlog_close(gzlog *logd) +{ + struct log *log = logd; - /* unlock and close file */ - log_clean(log); + /* check arguments */ + if (log == NULL || strcmp(log->id, LOGID)) + return -3; + + /* close the log file and release the lock */ + log_close(log); + + /* free structure and return */ + if (log->path != NULL) + free(log->path); + strcpy(log->id, "bad"); + free(log); return 0; } |