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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.


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