[dm-devel] RFC for multipath queue_if_no_path timeout.

[Mike Snitzer]

On Thu, Oct 17 2013 at  4:45pm -0400,
Frank Mayhar <fmayhar at google.com> wrote:

> On Thu, 2013-10-17 at 15:15 -0400, Mike Snitzer wrote:
> > Shouldn't you wait for the application to shutdown before ripping the
> > network out?  Seems odd to just throw away queued IO.
> 
> In general, yes, and we do that, but there's still the occasional
> shutdown that doesn't go through those extra steps.
> 
> > A proper shutdown sequence really should avoid this problem in general,
> > the multipath daemon would only be shutdown once all mpath devices are
> > deactivated.
> > 
> > Then, if you still want to gracefully handle the case where there is no
> > network (and hence no paths) on shutdown the multipathd would still be
> > around to transition to a table that doesn't have queue_if_no_path.
> 
> Of course, this still depends on the daemon surviving everything else
> circumstances can throw at it.
> 
> In our particular case, changing the shutdown sequence is far more
> difficult than using the kernel mechanism I've already provided.  This
> would also simplify things for other folks who use queue_if_no_path.

Cannot say that argument wins me over but I will say that if you intend
to take the approach to have the kernel have a timeout; please pursue
the approach Hannes offered:

https://patchwork.kernel.org/patch/2953231/

It is much cleaner and if it works for your needs we can see about
getting a tested version upstream.