process_event function in journald
(http://cgit.freedesktop.org/systemd/systemd/tree/src/journal/journald-server.c#n987)
handles events differently depending on descriptor type.
Debugging with gdb showed that /dev/kmsg being a symlink triggers
"invalid event" error at line 1032
(http://cgit.freedesktop.org/systemd/systemd/tree/src/journal/journald-server.c#n1032)
and terminates journald immediately.
I asked about that error on #systemd and Kay told me that symlinking
is wrong because /dev/kmsg has specific semantics, that cannot be
reproduced by /dev/console symlink. Journald has config option to
forward messages to console other way around and other logging systems
should be able to do that too.
2013/1/7 Serge Hallyn <serge.hal...@canonical.com>:
> Quoting Alexander Vladimirov (alexander.idkfa.vladimi...@gmail.com):
>> Symlink cannot resemble /dev/kmsg semantics, so symlinking it is wrong.
>
> Hm. It works fine in my containers, and gives me nice startup messages
> on console.
>
>> Guests probably should not use /dev/kmsg at all.
>> Fixes journald crashes and journal corruption in systemd guests.
>
> Can you show exactly what causes the crashes?
>
> I'm not entirely opposed, since eventually (probably soon) we'll
> (at least conditionally) remove it anyway, when /dev/kmsg can be
> protected by user namespace (or even better be namespaced in
> syslogns).
>
> -serge
>
>
>> ---
>> src/lxc/conf.c | 30 ------------------------------
>> 1 file changed, 30 deletions(-)
>>
>> diff --git a/src/lxc/conf.c b/src/lxc/conf.c
>> index 4f041dc..85d72c9 100644
>> --- a/src/lxc/conf.c
>> +++ b/src/lxc/conf.c
>> @@ -1313,33 +1313,6 @@ static int setup_console(const struct lxc_rootfs
>> *rootfs,
>> return setup_ttydir_console(rootfs, console, ttydir);
>> }
>>
>> -static int setup_kmsg(const struct lxc_rootfs *rootfs,
>> - const struct lxc_console *console)
>> -{
>> - char kpath[MAXPATHLEN];
>> - int ret;
>> -
>> - if (!rootfs->path)
>> - return 0;
>> - ret = snprintf(kpath, sizeof(kpath), "%s/dev/kmsg", rootfs->mount);
>> - if (ret < 0 || ret >= sizeof(kpath))
>> - return -1;
>> -
>> - ret = unlink(kpath);
>> - if (ret && errno != ENOENT) {
>> - SYSERROR("error unlinking %s\n", kpath);
>> - return -1;
>> - }
>> -
>> - ret = symlink("console", kpath);
>> - if (ret) {
>> - SYSERROR("failed to create symlink for kmsg");
>> - return -1;
>> - }
>> -
>> - return 0;
>> -}
>> -
>> int setup_cgroup(const char *name, struct lxc_list *cgroups)
>> {
>> struct lxc_list *iterator;
>> @@ -2566,9 +2539,6 @@ int lxc_setup(const char *name, struct lxc_conf
>> *lxc_conf)
>> return -1;
>> }
>>
>> - if (setup_kmsg(&lxc_conf->rootfs, &lxc_conf->console)) // don't fail
>> - ERROR("failed to setup kmsg for '%s'", name);
>> -
>> if (setup_tty(&lxc_conf->rootfs, &lxc_conf->tty_info,
>> lxc_conf->ttydir)) {
>> ERROR("failed to setup the ttys for '%s'", name);
>> return -1;
>> --
>> 1.8.1
>>
>>
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