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lib: fix possible assert() fail in zlog_fd() 

If the last message in a batched logging operation isn't printed due to
priority, this skips the code that flushes prepared messages through
writev() and can trigger the assert() at the end of zlog_fd().

Since any logmsg above info priority triggers a buffer flush, running
into this situation requires a log file target configured for info
priority, at least 1 message of info priority buffered, a debug message
buffered after that, and then a buffer flush (explicit or due to buffer
full).

I haven't seen this chain of events happen in the wild, but it needs
fixing anyway.

Signed-off-by: David Lamparter <equinox@diac24.net>
This commit is contained in:
David Lamparter 2021-04-10 21:02:06 +02:00 committed by David Lamparter
parent bf6005d5f4
commit db2baed166
1 changed files with 35 additions and 27 deletions
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62
lib/zlog_targets.c
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@ -78,40 +78,48 @@ void zlog_fd(struct zlog_target *zt, struct zlog_msg *msgs[], size_t nmsgs)
struct zlog_msg *msg = msgs[i];
int prio = zlog_msg_prio(msg);
if (prio > zt->prio_min)
continue;
if (prio <= zt->prio_min) {
iov[iovpos].iov_base = ts_pos;
if (iovpos > 0)
*ts_pos++ = '\n';
ts_pos += zlog_msg_ts(msg, ts_pos,
sizeof(ts_buf) - 1
- (ts_pos - ts_buf),
ZLOG_TS_LEGACY | zte->ts_subsec);
*ts_pos++ = ' ';
iov[iovpos].iov_len =
ts_pos - (char *)iov[iovpos].iov_base;
iov[iovpos].iov_base = ts_pos;
if (iovpos > 0)
*ts_pos++ = '\n';
ts_pos += zlog_msg_ts(msg, ts_pos, sizeof(ts_buf) - 1
- (ts_pos - ts_buf),
ZLOG_TS_LEGACY | zte->ts_subsec);
*ts_pos++ = ' ';
iov[iovpos].iov_len = ts_pos - (char *)iov[iovpos].iov_base;
iovpos++;
iovpos++;
if (zte->record_priority) {
iov[iovpos].iov_base = (char *)prionames[prio];
iov[iovpos].iov_len =
strlen(iov[iovpos].iov_base);
if (zte->record_priority) {
iov[iovpos].iov_base = (char *)prionames[prio];
iov[iovpos].iov_len = strlen(iov[iovpos].iov_base);
iovpos++;
}
iov[iovpos].iov_base = zlog_prefix;
iov[iovpos].iov_len = zlog_prefixsz;
iovpos++;
iov[iovpos].iov_base =
(char *)zlog_msg_text(msg, &textlen);
iov[iovpos].iov_len = textlen;
iovpos++;
}
iov[iovpos].iov_base = zlog_prefix;
iov[iovpos].iov_len = zlog_prefixsz;
iovpos++;
iov[iovpos].iov_base = (char *)zlog_msg_text(msg, &textlen);
iov[iovpos].iov_len = textlen;
iovpos++;
if (ts_buf + sizeof(ts_buf) - ts_pos < TS_LEN
|| i + 1 == nmsgs
|| array_size(iov) - iovpos < 5) {
/* conditions that trigger writing:
* - out of space for more timestamps/headers
* - this being the last message in the batch
* - not enough remaining iov entries
*/
if (iovpos > 0 && (ts_buf + sizeof(ts_buf) - ts_pos < TS_LEN
|| i + 1 == nmsgs
|| array_size(iov) - iovpos < 5)) {
iov[iovpos].iov_base = (char *)"\n";
iov[iovpos].iov_len = 1;