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Re: [Qemu-devel] Possible bug in monitor code


From: Apollon Oikonomopoulos
Subject: Re: [Qemu-devel] Possible bug in monitor code
Date: Fri, 24 Jan 2014 12:52:52 +0200
User-agent: Mutt/1.5.21 (2010-09-15)

Hi all,

On 12:14 Fri 24 Jan     , Stratos Psomadakis wrote:
> On 01/23/2014 08:28 PM, Luiz Capitulino wrote:
> > Not yet, I may have some time tomorrow. How reproducible is it for 
> > you?
> 
> We can trigger it (by following the steps described in the first mail)
> consistently.
> 
> > Another question: have you tried to reproduce with an old qemu version
> > (say v1.0) to see if this bug always existed? If the bug was introduced
> > in some recent QEMU version you could try to bisect it.
> 
> v1.1 is not affected. I checked the code and it seems the monitor code
> has been refactored since v1.1.
> 
> > Maybe you could try to reproduce with a different subsystem so that we
> > can rule out or confirm monitor's involvement? Like -serial?
> 
> It's actually a fault of the monitor_flush() function. As far as I can
> understand, monitor_flush() calls qemu_chr_fe_write() and doesn't handle
> all of the return codes / error cases properly (as I described in a
> previous mail). If you check the function, you'll see that the final
> case (where it set ups a watch / callback) always assumes an EAGAIN /
> EWOULDBLOCK error.
> 
> If you can verify / confirm that this is the case and that the patch
> sent resolves the issue in a sane / correct way, I'll resubmit it
> properly (with git-format-patch, a git log msg etc).

Please see the attached testcase (python script) that programmatically 
reproduces this. Sample output with qemu 1.7.0:

------------------------------------------------------------------------
$ ./test-qmp.py 
Spawning qemu

Connecting client 1

Monitor output:
{"QMP": {"version": {"qemu": {"micro": 0, "minor": 7, "major": 1}, "package": " 
(Debian 1.7.0+dfsg-2)"}, "capabilities": []}}


Connecting client 2

Monitor output:
(timeout, disconnecting)

Disconnecting client 1

Connecting client 3

Monitor output
{"QMP": {"version": {"qemu": {"micro": 0, "minor": 7, "major": 1}, "package": " 
(Debian 1.7.0+dfsg-2)"}, "capabilities": []}}
{"QMP": {"version": {"qemu": {"micro": 0, "minor": 7, "major": 1}, "package": " 
(Debian 1.7.0+dfsg-2)"}, "capabilities": []}}

Terminating qemu
qemu: terminating on signal 15 from pid 11269
------------------------------------------------------------------------

Regards,
Apollon

Attachment: test-qmp.py
Description: Text Data


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