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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
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(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
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

10
include/usage.h
View File

@ -3327,17 +3327,17 @@ USE_FEATURE_RUN_PARTS_FANCY("\n -l Prints names of all matching files even when
"Note that this version of syslogd ignores /etc/syslog.conf." \
"\n\nOptions:" \
"\n -n Run as foreground process" \
"\n -O FILE Use an alternate log file (default=/var/log/messages)" \
"\n -l n Sets the local log level of messages to n" \
"\n -S Make logging output smaller" \
"\n -O FILE Log to given file (default=/var/log/messages)" \
"\n -l n Set local log level" \
"\n -S Smaller logging output" \
USE_FEATURE_ROTATE_LOGFILE( \
"\n -s SIZE Max size (KB) before rotate (default=200KB, 0=off)" \
"\n -b NUM Number of rotated logs to keep (default=1, max=99, 0=purge)") \
USE_FEATURE_REMOTE_LOG( \
"\n -R HOST[:PORT] Log to IP or hostname on PORT (default PORT=514/UDP)" \
"\n -L Log locally and via network logging (default is network only)") \
"\n -L Log locally and via network (default is network only if -R)") \
USE_FEATURE_IPC_SYSLOG( \
"\n -C[size(KiB)] Log to a shared mem buffer (read the buffer using logread)")
"\n -C[size(KiB)] Log to shared mem buffer (read it using logread)")
/* NB: -Csize shouldn't have space (because size is optional) */
/* "\n -m MIN Minutes between MARK lines (default=20, 0=off)" */
#define syslogd_example_usage \

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);
}

55
sysklogd/syslogd.c
View File

@ -46,8 +46,7 @@ enum { MAX_READ = 256 };
/* Semaphore operation structures */
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 */
};
@ -212,8 +211,9 @@ static void ipcsyslog_init(void)
bb_perror_msg_and_die("shmat");
}
G.shbuf->size = G.shm_size - offsetof(struct shbuf_ds, data);
G.shbuf->head = G.shbuf->tail = 0;
memset(G.shbuf, 0, G.shm_size);
G.shbuf->size = G.shm_size - offsetof(struct shbuf_ds, data) - 1;
/*G.shbuf->tail = 0;*/
// we'll trust the OS to set initial semval to 0 (let's hope)
G.s_semid = semget(KEY_ID, 2, IPC_CREAT | IPC_EXCL | 1023);
@ -231,7 +231,6 @@ static void ipcsyslog_init(void)
static void log_to_shmem(const char *msg, int len)
{
int old_tail, new_tail;
char *c;
if (semop(G.s_semid, G.SMwdn, 3) == -1) {
bb_perror_msg_and_die("SMwdn");
@ -240,49 +239,20 @@ static void log_to_shmem(const char *msg, int len)
/* Circular Buffer Algorithm:
* --------------------------
* tail == position where to store next syslog message.
* head == position of next message to retrieve ("print").
* if head == tail, there is no "unprinted" messages left.
* head is typically advanced by separate "reader" program,
* but if there isn't one, we have to do it ourself.
* messages are NUL-separated.
* tail's max value is (shbuf->size - 1)
* Last byte of buffer is never used and remains NUL.
*/
len++; /* length with NUL included */
again:
old_tail = G.shbuf->tail;
new_tail = old_tail + len;
if (new_tail < G.shbuf->size) {
/* No need to move head if shbuf->head <= old_tail,
* else... */
if (old_tail < G.shbuf->head && G.shbuf->head <= new_tail) {
/* ...need to move head forward */
c = memchr(G.shbuf->data + new_tail, '\0',
G.shbuf->size - new_tail);
if (!c) /* no NUL ahead of us, wrap around */
c = memchr(G.shbuf->data, '\0', old_tail);
if (!c) { /* still nothing? point to this msg... */
G.shbuf->head = old_tail;
} else {
/* convert pointer to offset + skip NUL */
G.shbuf->head = c - G.shbuf->data + 1;
}
}
/* store message, set new tail */
memcpy(G.shbuf->data + old_tail, msg, len);
G.shbuf->tail = new_tail;
} else {
/* we need to break up the message and wrap it around */
/* k == available buffer space ahead of old tail */
int k = G.shbuf->size - old_tail - 1;
if (G.shbuf->head > old_tail) {
/* we are going to overwrite head, need to
* move it out of the way */
c = memchr(G.shbuf->data, '\0', old_tail);
if (!c) { /* nothing? point to this msg... */
G.shbuf->head = old_tail;
} else { /* convert pointer to offset + skip NUL */
G.shbuf->head = c - G.shbuf->data + 1;
}
}
int k = G.shbuf->size - old_tail;
/* copy what fits to the end of buffer, and repeat */
memcpy(G.shbuf->data + old_tail, msg, k);
msg += k;
@ -294,7 +264,7 @@ static void log_to_shmem(const char *msg, int len)
bb_perror_msg_and_die("SMwup");
}
if (DEBUG)
printf("head:%d tail:%d\n", G.shbuf->head, G.shbuf->tail);
printf("tail:%d\n", G.shbuf->tail);
}
#else
void ipcsyslog_cleanup(void);
@ -339,11 +309,10 @@ static void log_locally(char *msg)
}
#if ENABLE_FEATURE_ROTATE_LOGFILE
{
struct stat statf;
G.isRegular = (fstat(G.logFD, &statf) == 0 && (statf.st_mode & S_IFREG));
/* bug (mostly harmless): can wrap around if file > 4gb */
G.curFileSize = statf.st_size;
struct stat statf;
G.isRegular = (fstat(G.logFD, &statf) == 0 && S_ISREG(statf.st_mode));
/* bug (mostly harmless): can wrap around if file > 4gb */
G.curFileSize = statf.st_size;
}
#endif
}