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Date: Mon, 24 Oct 2011 11:58:27 +0100
From: Chris Webb <chris@arachsys.com>
Message-ID: <20111024105826.GT9917@arachsys.com>
References: <20111024100037.GS9917@arachsys.com> <4EA54104.7000001@redhat.com>
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Subject: Re: [Qemu-devel] qemu-kvm guest which won't 'cont' (emulation
 failure?)
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To: Kevin Wolf <kwolf@redhat.com>
Cc: qemu-devel@nongnu.org, kvm@vger.kernel.org

Kevin Wolf <kwolf@redhat.com> writes:

> Am 24.10.2011 12:00, schrieb Chris Webb:
> > I have qemu monitor access and can even strace the relevant qemu process if
> > necessary: is it possible to use this to diagnose what's caused this guest
> > to stop, e.g. the unsupported instruction if it's an emulation failure?
> 
> Another common cause for stopped VMs are I/O errors, for example writes
> to a sparse image when the disk is full.

This guest are backed by LVM LVs so I don't think they can return EFULL, but I
could imagine read errors, so I've just done a trivial test to make sure I can
read them end-to-end:

  0015# dd if=/dev/mapper/guest\:e549f8e1-4c0e-4dea-826a-e4b877282c07\:ide\:0\:0 of=/dev/null bs=1M
  3136+0 records in
  3136+0 records out
  3288334336 bytes (3.3 GB) copied, 20.898 s, 157 MB/s

  0015# dd if=/dev/mapper/guest\:e549f8e1-4c0e-4dea-826a-e4b877282c07\:ide\:0\:1 of=/dev/null bs=1M
  276+0 records in
  276+0 records out
  289406976 bytes (289 MB) copied, 1.85218 s, 156 MB/s

Is there any way to ask qemu why a guest has stopped, so I can distinguish IO
problems from emulation problems from anything else?

Cheers,

Chris.