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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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55
sysklogd/syslogd.c
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@@ -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
}