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Re: [Qemu-block] Enable debugging in a running vServer
From: |
Kevin Wolf |
Subject: |
Re: [Qemu-block] Enable debugging in a running vServer |
Date: |
Thu, 26 Mar 2015 16:02:15 +0100 |
User-agent: |
Mutt/1.5.21 (2010-09-15) |
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.
Kevin