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journal: include kmsg lines from the systemd process which exec()d us (#8078)

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Let the journal capture messages emitted by systemd, before it ran
exec("/usr/lib/systemd/systemd-journald").  Usually such messages will only
appear with `systemd.log_level=debug`.  kmsg lines written after the exec()
will be ignored as before.

In other words, we are avoiding reading our own lines, which start
"systemd-journald[100]: " assuming we are PID 100.  But now we will start
allowing ourself to read lines which start "systemd[100]: ", or any other
prefix which is not "systemd-journald[100]: ".

So this can't help you see messages when we fail to exec() journald :). But,
it makes it easier to see what the pre-exec() messages look like in
the successful case.  Comparing messages like this can be useful when
debugging.  Noticing weird omissions of messages, otoh, makes me anxious.
This commit is contained in:
Alan Jenkins 2018-02-05 16:53:40 +00:00 committed by Zbigniew Jędrzejewski-Szmek
parent 0e3c6bf0ce
commit fe16729868
1 changed files with 9 additions and 7 deletions
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16
src/journal/journald-kmsg.c
View file

@ -98,15 +98,17 @@ void server_forward_kmsg(
log_debug_errno(errno, "Failed to write to /dev/kmsg for logging: %m");
}
static bool is_us(const char *pid) {
pid_t t;
static bool is_us(const char *identifier, const char *pid) {
pid_t pid_num;
assert(pid);
if (parse_pid(pid, &t) < 0)
if (!identifier || !pid)
return false;
return t == getpid_cached();
if (parse_pid(pid, &pid_num) < 0)
return false;
return pid_num == getpid_cached() &&
streq(identifier, program_invocation_short_name);
}
static void dev_kmsg_record(Server *s, const char *p, size_t l) {
@ -292,7 +294,7 @@ static void dev_kmsg_record(Server *s, const char *p, size_t l) {
/* Avoid any messages we generated ourselves via
* log_info() and friends. */
if (pid && is_us(pid))
if (is_us(identifier, pid))
goto finish;
if (identifier) {