[ClusterLabs Developers] --verbose breaks stonithd + some fencing agents

Andrew Beekhof andrew at beekhof.net
Wed Oct 14 21:52:07 EDT 2015

> On 15 Oct 2015, at 12:10 PM, Adam Spiers <aspiers at suse.com> wrote:
> Hi all,
> I'm certainly no expert on stonithd or the way it interfaces with
> fence-agents, but I think I found a bug in either stonithd or
> fencing.py.
> If a fencing agent is invoked with the --verbose CLI argument (or
> something like 'verbose=1' via STDIN), then any invocations of
> logging.debug() will cause output to STDERR:
>  https://github.com/ClusterLabs/fence-agents/blob/master/fence/agents/lib/fencing.py.py#L640
> This confuses stonithd, because it dup(2)s STDOUT and STDERR to the
> same fd which is the writeable end of a pipe used by stonithd to read
> output from the forked child which runs the fencing agent:
>  https://github.com/ClusterLabs/pacemaker/blob/master/lib/fencing/st_client.c#L782
> Therefore from the point of view of stonithd, debug output on STDERR
> gets intermingled with "real" output on STDOUT,

That seems like a mistake.
We shouldn’t be duping them to the same descriptor - it should be like the lrmd which captures stderr but only logs it if there is an error (we can’t necessarily assume agents are already logging to syslog).

Some trawling through git suggests that we inherited this from libfence back in 2009.
Time to modernise it.

> and when it comes to
> parse this, the result is warnings in the logs beginning:
>  stonith-ng[5399]:  warning: Could not parse ...
> Since we already log to syslog, I wonder if it's not needed to also
> log to STDERR, so my first instinct was this fix:
>  https://github.com/aspiers/fence-agents/commit/4c7148b8046eb9cef950811c26fab73672f403bc
> However, subsequently I realised that the root cause is the way
> stonithd mixes STDOUT and STDERR from the child fencing agent process
> together, so now I'm wondering if it would be better to change
> lib/fencing/st_client.c to create a third pipe for handling STDERR
> independently.
> Thoughts?

Exactly :)

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