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Re: [Qemu-block] RFC cdrom in own thread?


From: Peter Lieven
Subject: Re: [Qemu-block] RFC cdrom in own thread?
Date: Thu, 18 Jun 2015 08:03:03 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.7.0

Am 17.06.2015 um 10:35 schrieb Kevin Wolf:
Am 16.06.2015 um 17:34 hat Stefan Hajnoczi geschrieben:
On Tue, Jun 16, 2015 at 3:44 PM, Peter Lieven <address@hidden> wrote:
I wonder how difficult it would be to have the IDE CDROM run in its own
thread?
We usually have ISOs mounted on an NFS share as CDROM. Problem: If the NFS
Share
goes down, it takes down monitor, qmp, vnc etc. with it.

Maybe its already possible to do this via cmdline args?

Any ideas, comments?
If QEMU hangs in the read/write/flush/discard code path due to NFS
downtime it is a bug.

QEMU is expected to hang in open/reopen because those are performed in
a blocking fashion.

Which of these cases applies to what you are seeing?  Maybe it can be fixed.
Don't forget bdrv_drain_all(), which is called a lot by the monitor. So
no matter what you do (and this includes moving to a thread as in a
hypothetical "ATAPI dataplane"), you end up with a hang sooner or later.

I will have a look where qemu hangs. The problem exists with an NFS share
mounted by the kernel and also with libnfs. So it might be a bdrv_drain_all.
I regularly query info block and info blockstats. Do these commands always
call bdrv_drain_all()?.

Peter




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