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zlib/examples/gzlog.c  view on Meta::CPAN

#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);

zlib/examples/gzlog.c  view on Meta::CPAN

        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 ((off_t)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) {
                free(data);
                log_log(log, op, ".add file read failure");
                return -1;
            }
            ret = (size_t)read(fd, data, len) != len;
            close(fd);
            if (ret) {
                free(data);
                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