syslogd,logread: get rid of head pointer, fix logread bug in the process
function old new delta logread_main 450 462 +12 syslogd_main 1246 1252 +6 shbuf - 4 +4 buf 34 30 -4 packed_usage 22729 22724 -5 log_locally 957 767 -190 ------------------------------------------------------------------------------ (add/remove: 1/0 grow/shrink: 2/3 up/down: 22/-199) Total: -177 bytes text data bss dec hex filename 773886 1116 11316 786318 bff8e busybox_old 773714 1116 11316 786146 bfee2 busybox_unstripped
This commit is contained in:
Denis Vlasenko
parent
1b9064d535
commit
5f1b149d54
@ -3327,17 +3327,17 @@ USE_FEATURE_RUN_PARTS_FANCY("\n -l Prints names of all matching files even when
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"Note that this version of syslogd ignores /etc/syslog.conf." \
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"\n\nOptions:" \
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"\n -n Run as foreground process" \
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"\n -O FILE Use an alternate log file (default=/var/log/messages)" \
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"\n -l n Sets the local log level of messages to n" \
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"\n -S Make logging output smaller" \
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"\n -O FILE Log to given file (default=/var/log/messages)" \
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"\n -l n Set local log level" \
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"\n -S Smaller logging output" \
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USE_FEATURE_ROTATE_LOGFILE( \
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"\n -s SIZE Max size (KB) before rotate (default=200KB, 0=off)" \
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"\n -b NUM Number of rotated logs to keep (default=1, max=99, 0=purge)") \
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USE_FEATURE_REMOTE_LOG( \
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"\n -R HOST[:PORT] Log to IP or hostname on PORT (default PORT=514/UDP)" \
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"\n -L Log locally and via network logging (default is network only)") \
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"\n -L Log locally and via network (default is network only if -R)") \
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USE_FEATURE_IPC_SYSLOG( \
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"\n -C[size(KiB)] Log to a shared mem buffer (read the buffer using logread)")
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"\n -C[size(KiB)] Log to shared mem buffer (read it using logread)")
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/* NB: -Csize shouldn't have space (because size is optional) */
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/* "\n -m MIN Minutes between MARK lines (default=20, 0=off)" */
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#define syslogd_example_usage \
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@ -19,11 +19,10 @@
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enum { KEY_ID = 0x414e4547 }; /* "GENA" */
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static struct shbuf_ds {
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int32_t size; // size of data written
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int32_t head; // start of message list
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int32_t size; // size of data - 1
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int32_t tail; // end of message list
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char data[1]; // data/messages
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} *buf; // shared memory pointer
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char data[1]; // messages
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} *shbuf;
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// Semaphore operation structures
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static struct sembuf SMrup[1] = {{0, -1, IPC_NOWAIT | SEM_UNDO}}; // set SMrup
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@ -34,7 +33,7 @@ static void error_exit(const char *str) ATTRIBUTE_NORETURN;
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static void error_exit(const char *str)
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{
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//release all acquired resources
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shmdt(buf);
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shmdt(shbuf);
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bb_perror_msg_and_die(str);
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}
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@ -50,7 +49,7 @@ static void sem_up(int semid)
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static void interrupted(int sig ATTRIBUTE_UNUSED)
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{
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signal(SIGINT, SIG_IGN);
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shmdt(buf);
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shmdt(shbuf);
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exit(0);
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}
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@ -66,79 +65,105 @@ int logread_main(int argc, char **argv)
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if (log_shmid == -1)
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bb_perror_msg_and_die("can't find syslogd buffer");
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// Attach shared memory to our char*
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buf = shmat(log_shmid, NULL, SHM_RDONLY);
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if (buf == NULL)
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/* Attach shared memory to our char* */
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shbuf = shmat(log_shmid, NULL, SHM_RDONLY);
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if (shbuf == NULL)
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bb_perror_msg_and_die("can't access syslogd buffer");
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log_semid = semget(KEY_ID, 0, 0);
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if (log_semid == -1)
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error_exit("can't get access to semaphores for syslogd buffer");
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// attempt to redefine ^C signal
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signal(SIGINT, interrupted);
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// Suppose atomic memory move
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cur = follow ? buf->tail : buf->head;
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/* Suppose atomic memory read */
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/* Max possible value for tail is shbuf->size - 1 */
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cur = shbuf->tail;
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/* Loop for logread -f, one pass if there was no -f */
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do {
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unsigned shbuf_size;
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unsigned shbuf_tail;
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const char *shbuf_data;
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#if ENABLE_FEATURE_LOGREAD_REDUCED_LOCKING
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char *buf_data;
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int log_len, j;
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int i;
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int len_first_part;
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int len_total = len_total; /* for gcc */
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char *copy = copy; /* for gcc */
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#endif
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if (semop(log_semid, SMrdn, 2) == -1)
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error_exit("semop[SMrdn]");
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if (DEBUG)
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printf("head:%i cur:%d tail:%i size:%i\n",
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buf->head, cur, buf->tail, buf->size);
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/* Copy the info, helps gcc to realize that it doesn't change */
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shbuf_size = shbuf->size;
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shbuf_tail = shbuf->tail;
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shbuf_data = shbuf->data; /* pointer! */
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if (buf->head == buf->tail || cur == buf->tail) {
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if (follow) {
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if (DEBUG)
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printf("cur:%d tail:%i size:%i\n",
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cur, shbuf_tail, shbuf_size);
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if (!follow) {
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/* advance to oldest complete message */
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/* find NUL */
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cur += strlen(shbuf_data + cur);
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if (cur >= shbuf_size) { /* last byte in buffer? */
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cur = strnlen(shbuf_data, shbuf_tail);
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if (cur == shbuf_tail)
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goto unlock; /* no complete messages */
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}
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/* advance to first byte of the message */
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cur++;
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if (cur >= shbuf_size) /* last byte in buffer? */
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cur = 0;
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} else { /* logread -f */
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if (cur == shbuf_tail) {
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sem_up(log_semid);
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fflush(stdout);
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sleep(1); /* TODO: replace me with a sleep_on */
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continue;
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}
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puts("<empty syslog>");
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}
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// Read Memory
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/* Read from cur to tail */
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#if ENABLE_FEATURE_LOGREAD_REDUCED_LOCKING
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log_len = buf->tail - cur;
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if (log_len < 0)
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log_len += buf->size;
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buf_data = xmalloc(log_len);
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if (buf->tail >= cur)
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j = log_len;
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else
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j = buf->size - cur;
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memcpy(buf_data, buf->data + cur, j);
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if (buf->tail < cur)
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memcpy(buf_data + buf->size - cur, buf->data, buf->tail);
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cur = buf->tail;
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len_first_part = len_total = shbuf_tail - cur;
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if (len_total < 0) {
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/* message wraps: */
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/* [SECOND PART.........FIRST PART] */
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/* ^data ^tail ^cur ^size */
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len_total += shbuf_size;
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}
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copy = xmalloc(len_total + 1);
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if (len_first_part < 0) {
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/* message wraps (see above) */
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len_first_part = shbuf_size - cur;
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memcpy(copy + len_first_part, shbuf_data, shbuf_tail);
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}
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memcpy(copy, shbuf_data + cur, len_first_part);
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copy[len_total] = '\0';
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cur = shbuf_tail;
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#else
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while (cur != buf->tail) {
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fputs(buf->data + cur, stdout);
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cur += strlen(buf->data + cur) + 1;
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if (cur >= buf->size)
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while (cur != shbuf_tail) {
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fputs(shbuf_data + cur, stdout);
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cur += strlen(shbuf_data + cur) + 1;
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if (cur >= shbuf_size)
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cur = 0;
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}
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#endif
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// release the lock on the log chain
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unlock:
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/* release the lock on the log chain */
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sem_up(log_semid);
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#if ENABLE_FEATURE_LOGREAD_REDUCED_LOCKING
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for (j = 0; j < log_len; j += strlen(buf_data+j) + 1) {
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fputs(buf_data + j, stdout);
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for (i = 0; i < len_total; i += strlen(copy + i) + 1) {
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fputs(copy + i, stdout);
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}
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free(buf_data);
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free(copy);
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#endif
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} while (follow);
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shmdt(buf);
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shmdt(shbuf);
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fflush_stdout_and_exit(EXIT_SUCCESS);
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}
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@ -46,8 +46,7 @@ enum { MAX_READ = 256 };
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/* Semaphore operation structures */
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struct shbuf_ds {
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int32_t size; /* size of data written */
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int32_t head; /* start of message list */
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int32_t size; /* size of data - 1 */
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int32_t tail; /* end of message list */
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char data[1]; /* data/messages */
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};
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@ -212,8 +211,9 @@ static void ipcsyslog_init(void)
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bb_perror_msg_and_die("shmat");
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}
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G.shbuf->size = G.shm_size - offsetof(struct shbuf_ds, data);
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G.shbuf->head = G.shbuf->tail = 0;
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memset(G.shbuf, 0, G.shm_size);
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G.shbuf->size = G.shm_size - offsetof(struct shbuf_ds, data) - 1;
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/*G.shbuf->tail = 0;*/
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// we'll trust the OS to set initial semval to 0 (let's hope)
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G.s_semid = semget(KEY_ID, 2, IPC_CREAT | IPC_EXCL | 1023);
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@ -231,7 +231,6 @@ static void ipcsyslog_init(void)
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static void log_to_shmem(const char *msg, int len)
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{
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int old_tail, new_tail;
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char *c;
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if (semop(G.s_semid, G.SMwdn, 3) == -1) {
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bb_perror_msg_and_die("SMwdn");
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@ -240,49 +239,20 @@ static void log_to_shmem(const char *msg, int len)
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/* Circular Buffer Algorithm:
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* --------------------------
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* tail == position where to store next syslog message.
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* head == position of next message to retrieve ("print").
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* if head == tail, there is no "unprinted" messages left.
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* head is typically advanced by separate "reader" program,
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* but if there isn't one, we have to do it ourself.
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* messages are NUL-separated.
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* tail's max value is (shbuf->size - 1)
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* Last byte of buffer is never used and remains NUL.
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*/
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len++; /* length with NUL included */
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again:
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old_tail = G.shbuf->tail;
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new_tail = old_tail + len;
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if (new_tail < G.shbuf->size) {
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/* No need to move head if shbuf->head <= old_tail,
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* else... */
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if (old_tail < G.shbuf->head && G.shbuf->head <= new_tail) {
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/* ...need to move head forward */
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c = memchr(G.shbuf->data + new_tail, '\0',
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G.shbuf->size - new_tail);
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if (!c) /* no NUL ahead of us, wrap around */
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c = memchr(G.shbuf->data, '\0', old_tail);
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if (!c) { /* still nothing? point to this msg... */
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G.shbuf->head = old_tail;
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} else {
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/* convert pointer to offset + skip NUL */
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G.shbuf->head = c - G.shbuf->data + 1;
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}
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}
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/* store message, set new tail */
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memcpy(G.shbuf->data + old_tail, msg, len);
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G.shbuf->tail = new_tail;
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} else {
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/* we need to break up the message and wrap it around */
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/* k == available buffer space ahead of old tail */
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int k = G.shbuf->size - old_tail - 1;
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if (G.shbuf->head > old_tail) {
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/* we are going to overwrite head, need to
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* move it out of the way */
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c = memchr(G.shbuf->data, '\0', old_tail);
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if (!c) { /* nothing? point to this msg... */
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G.shbuf->head = old_tail;
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} else { /* convert pointer to offset + skip NUL */
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G.shbuf->head = c - G.shbuf->data + 1;
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}
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}
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int k = G.shbuf->size - old_tail;
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/* copy what fits to the end of buffer, and repeat */
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memcpy(G.shbuf->data + old_tail, msg, k);
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msg += k;
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@ -294,7 +264,7 @@ static void log_to_shmem(const char *msg, int len)
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bb_perror_msg_and_die("SMwup");
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}
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if (DEBUG)
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printf("head:%d tail:%d\n", G.shbuf->head, G.shbuf->tail);
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printf("tail:%d\n", G.shbuf->tail);
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}
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#else
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void ipcsyslog_cleanup(void);
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@ -340,8 +310,7 @@ static void log_locally(char *msg)
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#if ENABLE_FEATURE_ROTATE_LOGFILE
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{
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struct stat statf;
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G.isRegular = (fstat(G.logFD, &statf) == 0 && (statf.st_mode & S_IFREG));
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G.isRegular = (fstat(G.logFD, &statf) == 0 && S_ISREG(statf.st_mode));
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/* bug (mostly harmless): can wrap around if file > 4gb */
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G.curFileSize = statf.st_size;
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}
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