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Fix #26: handle Linux EPIPE on /dev/kmsg

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When Linux CONFIG_LOG_BUF_SHIFT is set too low, or too many messages are
generated by the kernel, /dev/kmsg will overflow.  This is signaled with
EPIPE to userspace.  We can use the seqnos to figure out how many we've
lost, but seqnos are currently ignored.

> In case records get overwritten while /dev/kmsg is held open, or
> records get faster overwritten than they are read, the next read()
> will return -EPIPE and the current reading position gets updated to
> the next available record. The passed sequence numbers allow the log
> consumer to calculate the amount of lost messages.

-- https://lwn.net/Articles/490690/

Signed-off-by: Joachim Wiberg <troglobit@gmail.com>
This commit is contained in:
Joachim Wiberg 2021-01-24 22:39:27 +01:00
parent 22d26c5945
commit 3e4000b25a
1 changed files with 15 additions and 3 deletions
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18
src/syslogd.c
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@ -469,9 +469,21 @@ static void kernel_cb(int fd, void *arg)
if (i > 0) {
line[i + len] = '\0';
} else {
if (i < 0 && errno != EINTR && errno != EAGAIN) {
ERR("klog read()");
socket_close(fd);
if (i < 0) {
switch (errno) {
case EPIPE: /* linux, log buffer overrun */
ERRX("Kernel log buffer filling up too quick, "
"or too small log buffer, "
"adjust kernel CONFIG_LOG_BUF_SHIFT");
case EINTR:
case EAGAIN:
break;
default:
ERR("klog read()");
socket_close(fd);
break;
}
}
break;
}