| /* |
| * gzlog.c |
| * Copyright (C) 2004, 2008 Mark Adler, all rights reserved |
| * For conditions of distribution and use, see copyright notice in gzlog.h |
| * version 2.0, 25 Apr 2008 |
| */ |
| |
| /* |
| 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 */ |
| |
| #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 |
| |
| /* 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 fd; |
| struct stat st; |
| |
| 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; |
| } |
| |
| /* 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; |
| } |
| |
| /* 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) |
| { |
| struct stat st; |
| |
| strcpy(log->end, ".lock"); |
| if (stat(log->path, &st) || st.st_mtime != log->lock) |
| return 1; |
| log_touch(log); |
| return 0; |
| } |
| |
| /* Unlock a previously acquired lock, but only if it's ours. */ |
| local void log_unlock(struct log *log) |
| { |
| if (log_check(log)) |
| return; |
| strcpy(log->end, ".lock"); |
| unlink(log->path); |
| log->lock = 0; |
| } |
| |
| /* 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 op; |
| unsigned char buf[HEAD + EXTRA]; |
| |
| 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; |
| } |
| |
| /* 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 ret; |
| unsigned char ext[EXTRA]; |
| |
| 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; |
| } |
| |
| /* 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 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); |
| |
| /* 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; |
| } |
| |
| /* 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 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); |
| |
| /* 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); |
| } |
| |
| /* log a repair record to the .repairs file */ |
| local void log_log(struct log *log, int op, char *record) |
| { |
| time_t now; |
| FILE *rec; |
| |
| 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) |
| { |
| int fd, ret = 0; |
| unsigned char *data = NULL; |
| size_t len = 0; |
| struct stat st; |
| |
| /* 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); |
| } |
| |
| /* 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); |
| 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 new, initialize foo.gz with an empty log, delete old dictionary */ |
| if (lseek(log->fd, 0, SEEK_END) == 0) { |
| 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); |
| } |
| |
| /* verify log file and load extra field information */ |
| if ((op = log_head(log)) < 0) { |
| log_close(log); |
| return -1; |
| } |
| |
| /* check for interrupted process and if so, recover */ |
| if (op != NO_OP && log_recover(log, op)) { |
| log_close(log); |
| return -1; |
| } |
| |
| /* 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; |
| |
| /* 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; |
| } |
| 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; |
| } |
| |
| /* return pointer to log structure */ |
| return log; |
| } |
| |
| /* 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) |
| { |
| int fd, ret; |
| uint block; |
| size_t len, next; |
| unsigned char *data, buf[5]; |
| struct log *log = logd; |
| |
| /* check arguments */ |
| if (log == NULL || strcmp(log->id, LOGID) || len < 0) |
| return -3; |
| |
| /* 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; |
| |
| /* 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; |
| |
| /* 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; |
| next = 0; |
| while (next < len) { |
| if (read(log->fd, buf, 5) != 5) |
| break; |
| block = PULL2(buf + 1); |
| if (next + block > len || |
| read(log->fd, (char *)data + next, block) != block) |
| break; |
| next += block; |
| } |
| if (lseek(log->fd, 0, SEEK_CUR) != log->last + 4 + log->stored) |
| break; |
| log_touch(log); |
| |
| /* 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); |
| |
| /* 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); |
| |
| /* 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); |
| |
| /* broke out of do above on i/o error */ |
| free(data); |
| return -1; |
| } |
| |
| /* 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) |
| { |
| int fd, ret; |
| struct log *log = logd; |
| |
| /* check arguments */ |
| if (log == NULL || strcmp(log->id, LOGID) || len < 0) |
| return -3; |
| if (data == NULL || len == 0) |
| 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; |
| |
| /* 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); |
| |
| /* mark log file with append in progress */ |
| if (log_mark(log, APPEND_OP)) |
| return -1; |
| BAIL(8); |
| |
| /* append data (clears mark) */ |
| if (log_append(log, data, len)) |
| 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; |
| |
| /* 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; |
| } |
