Re: [Qemu-block] Enable debugging in a running vServer

[Kevin Wolf]

Am 27.03.2015 um 09:12 hat Peter Lieven geschrieben:
> Am 26.03.2015 um 16:02 schrieb Kevin Wolf:
> > Am 26.03.2015 um 15:54 hat Peter Lieven geschrieben:
> >> Hi Block people,
> >>
> >> we recently observed some strange I/O stalls on some vServers. I suspect a 
> >> bug in the target and
> >> already added some debugging output to libiscsi that could have helped to 
> >> track the issue.
> >>
> >> However, to enable this debugging I would need to call
> >>
> >> iscsi_set_log_level
> >>
> >> during runtime from the hmp or qmp.
> >>
> >> I wonder what would be the best way to do this and/or if it would be 
> >> interesting to have a generic
> >> way to tell a block backend to enter debugging whereas I would leave it up 
> >> to the backend driver
> >> what exactly that means?
> >>
> >> Other option would be to set an enviroment variable during runtime. But as 
> >> far as I know thats
> >> not possible.
> > I think debugging should be controlled with driver-specific options to
> > bdrv_open(). For changing the debugging options at runtime, we'd need to
> > provide a way to directly call bdrv_reopen() from the monitor.
> >
> > Before this can work, we need some more infrastructure work that even
> > introduces the concept of QDict *options to bdrv_reopen(). I have
> > patches to do this, but even though that branch mostly works, it is
> > still rather messy and not in a mergable state. If you're interested
> > anyway, it's the blockdev branch in my tree.
> >
> > For your immediate case, you'll probably want a downstream ad-hoc hack
> > rather than waiting for the real thing.
> 
> That sounds like the best approach. Would it make sense to already
> introduce a debug option in the options and honour it at least in bdrv_open?

Yes, I would think so. That part should stay unchanged even if we add
the bdrv_reopen() part later.

Kevin