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syslogd,logread: get rid of head pointer, fix logread bug in the process

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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
2007-08-12 21:33:06 +00:00
parent 1b9064d535
commit 5f1b149d54
3 changed files with 86 additions and 92 deletions
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113
sysklogd/logread.c
View File

@@ -19,11 +19,10 @@
enum { KEY_ID = 0x414e4547 }; /* "GENA" */
static struct shbuf_ds {
int32_t size; // size of data written
int32_t head; // start of message list
int32_t size; // size of data - 1
int32_t tail; // end of message list
char data[1]; // data/messages
} *buf; // shared memory pointer
char data[1]; // messages
} *shbuf;
// Semaphore operation structures
static struct sembuf SMrup[1] = {{0, -1, IPC_NOWAIT | SEM_UNDO}}; // set SMrup
@@ -34,7 +33,7 @@ static void error_exit(const char *str) ATTRIBUTE_NORETURN;
static void error_exit(const char *str)
{
//release all acquired resources
shmdt(buf);
shmdt(shbuf);
bb_perror_msg_and_die(str);
}
@@ -50,7 +49,7 @@ static void sem_up(int semid)
static void interrupted(int sig ATTRIBUTE_UNUSED)
{
signal(SIGINT, SIG_IGN);
shmdt(buf);
shmdt(shbuf);
exit(0);
}
@@ -66,79 +65,105 @@ int logread_main(int argc, char **argv)
if (log_shmid == -1)
bb_perror_msg_and_die("can't find syslogd buffer");
// Attach shared memory to our char*
buf = shmat(log_shmid, NULL, SHM_RDONLY);
if (buf == NULL)
/* Attach shared memory to our char* */
shbuf = shmat(log_shmid, NULL, SHM_RDONLY);
if (shbuf == NULL)
bb_perror_msg_and_die("can't access syslogd buffer");
log_semid = semget(KEY_ID, 0, 0);
if (log_semid == -1)
error_exit("can't get access to semaphores for syslogd buffer");
// attempt to redefine ^C signal
signal(SIGINT, interrupted);
// Suppose atomic memory move
cur = follow ? buf->tail : buf->head;
/* Suppose atomic memory read */
/* Max possible value for tail is shbuf->size - 1 */
cur = shbuf->tail;
/* Loop for logread -f, one pass if there was no -f */
do {
unsigned shbuf_size;
unsigned shbuf_tail;
const char *shbuf_data;
#if ENABLE_FEATURE_LOGREAD_REDUCED_LOCKING
char *buf_data;
int log_len, j;
int i;
int len_first_part;
int len_total = len_total; /* for gcc */
char *copy = copy; /* for gcc */
#endif
if (semop(log_semid, SMrdn, 2) == -1)
error_exit("semop[SMrdn]");
if (DEBUG)
printf("head:%i cur:%d tail:%i size:%i\n",
buf->head, cur, buf->tail, buf->size);
/* Copy the info, helps gcc to realize that it doesn't change */
shbuf_size = shbuf->size;
shbuf_tail = shbuf->tail;
shbuf_data = shbuf->data; /* pointer! */
if (buf->head == buf->tail || cur == buf->tail) {
if (follow) {
if (DEBUG)
printf("cur:%d tail:%i size:%i\n",
cur, shbuf_tail, shbuf_size);
if (!follow) {
/* advance to oldest complete message */
/* find NUL */
cur += strlen(shbuf_data + cur);
if (cur >= shbuf_size) { /* last byte in buffer? */
cur = strnlen(shbuf_data, shbuf_tail);
if (cur == shbuf_tail)
goto unlock; /* no complete messages */
}
/* advance to first byte of the message */
cur++;
if (cur >= shbuf_size) /* last byte in buffer? */
cur = 0;
} else { /* logread -f */
if (cur == shbuf_tail) {
sem_up(log_semid);
fflush(stdout);
sleep(1); /* TODO: replace me with a sleep_on */
continue;
}
puts("<empty syslog>");
}
// Read Memory
/* Read from cur to tail */
#if ENABLE_FEATURE_LOGREAD_REDUCED_LOCKING
log_len = buf->tail - cur;
if (log_len < 0)
log_len += buf->size;
buf_data = xmalloc(log_len);
if (buf->tail >= cur)
j = log_len;
else
j = buf->size - cur;
memcpy(buf_data, buf->data + cur, j);
if (buf->tail < cur)
memcpy(buf_data + buf->size - cur, buf->data, buf->tail);
cur = buf->tail;
len_first_part = len_total = shbuf_tail - cur;
if (len_total < 0) {
/* message wraps: */
/* [SECOND PART.........FIRST PART] */
/* ^data ^tail ^cur ^size */
len_total += shbuf_size;
}
copy = xmalloc(len_total + 1);
if (len_first_part < 0) {
/* message wraps (see above) */
len_first_part = shbuf_size - cur;
memcpy(copy + len_first_part, shbuf_data, shbuf_tail);
}
memcpy(copy, shbuf_data + cur, len_first_part);
copy[len_total] = '\0';
cur = shbuf_tail;
#else
while (cur != buf->tail) {
fputs(buf->data + cur, stdout);
cur += strlen(buf->data + cur) + 1;
if (cur >= buf->size)
while (cur != shbuf_tail) {
fputs(shbuf_data + cur, stdout);
cur += strlen(shbuf_data + cur) + 1;
if (cur >= shbuf_size)
cur = 0;
}
#endif
// release the lock on the log chain
unlock:
/* release the lock on the log chain */
sem_up(log_semid);
#if ENABLE_FEATURE_LOGREAD_REDUCED_LOCKING
for (j = 0; j < log_len; j += strlen(buf_data+j) + 1) {
fputs(buf_data + j, stdout);
for (i = 0; i < len_total; i += strlen(copy + i) + 1) {
fputs(copy + i, stdout);
}
free(buf_data);
free(copy);
#endif
} while (follow);
shmdt(buf);
shmdt(shbuf);
fflush_stdout_and_exit(EXIT_SUCCESS);
}