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

[Peter Lieven <pl@kamp.de>]

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 <pl@kamp.de> 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