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Bug 791200 - Character device consumers can miss OPENED events
Summary: Character device consumers can miss OPENED events
Keywords:
Status: CLOSED ERRATA
Alias: None
Product: Red Hat Enterprise Linux 6
Classification: Red Hat
Component: qemu-kvm
Version: 6.3
Hardware: x86_64
OS: Linux
unspecified
high
Target Milestone: rc
: ---
Assignee: Kevin Wolf
QA Contact: Virtualization Bugs
URL:
Whiteboard:
: 795661 796115 796203 (view as bug list)
Depends On:
Blocks:
TreeView+ depends on / blocked
 
Reported: 2012-02-16 13:42 UTC by Stefan Hajnoczi
Modified: 2012-06-20 11:43 UTC (History)
14 users (show)

Fixed In Version: qemu-kvm-0.12.1.2-2.234.el6
Doc Type: Bug Fix
Doc Text:
No Documentation Needed
Clone Of:
Environment:
Last Closed: 2012-06-20 11:43:32 UTC
Target Upstream Version:
Embargoed:

Attachments (Terms of Use)


Links
System ID Private Priority Status Summary Last Updated
Red Hat Product Errata RHBA-2012:0746 0 normal SHIPPED_LIVE qemu-kvm bug fix and enhancement update 2012-06-19 19:31:48 UTC

Description Stefan Hajnoczi 2012-02-16 13:42:06 UTC 
Description of problem:

QEMU character devices emit an OPENED event when the device is open or a connection has been accepted.  This is used, for example, to print the QMP monitor greeting.

Because character devices are initialized in vl.c:main() before their consumers care must be taken to deliver the OPENED event reliably.

In Kevin's coroutine backport to RHEL 6.3 I noticed that the QMP monitor does not work on a socket,path=/tmp/qemu-mon UNIX domain socket because the OPENED event is emitted before the QMP monitor is attached.  As a result, the QMP monitor never begins operation and clients do not see the greeting.

Alexander Graf fixed this issue for a different scenario with the s390 virtio-console.  His patch also addresses RHEL 6.3 qemu-kvm with coroutines in the block layer.

Version-Release number of selected component (if applicable):

RHEL 6.3 qemu-kvm with Kevin's coroutines backport series

How reproducible:

Deterministic

Steps to Reproduce:
1. nc -l -U /tmp/qemu-mon
2. In another shell: x86_64-softmmu/qemu-system-x86_64 -cpu host -chardev socket,id=mon,path=/tmp/qemu-mon -mon chardev=mon,mode=control -nographic -drive if=virtio,file=test.img,cache=none,id=virtio0
  
Actual results:

The netcat sessions never receives the QMP monitor greeting.

Expected results:

The QMP monitor should send the greeting to the netcat client.

Additional info:

Please cherry-pick Alexander Graf's fix 73cdf3f2c97703a89b026d3a42c1120ba05fe37d.
Comment 1 Kevin Wolf 2012-02-21 09:10:10 UTC 
*** Bug 795661 has been marked as a duplicate of this bug. ***
Comment 4 Qixiang Wan 2012-02-29 02:16:30 UTC 
*** Bug 796115 has been marked as a duplicate of this bug. ***
Comment 5 Chao Yang 2012-03-02 03:16:27 UTC 
--- Reproduced this bug with qemu-kvm-0.12.1.2-2.233.el6.x86_64.
Scenario 1:
1. listen by nc -lU /path/to/unix-socket
2. boot a guest by two ways:
a. -chardev socket,id=mon,path=/opt/mon.monitor -mon chardev=mon,mode=control
b. -qmp unix:/opt/mon.monitor 

Actual Result:
No greeting printed.
# nc -lU /opt/mon.monitor
{"execute":"qmp_capabilities"}   <--- returns nothing

Scenario 2:
1. listen by nc -lU /path/to/unix-socket
2. boot a guest by -monitor stdio

Actual Result:
No greeting printed like "QEMU 0.12.1 monitor - type 'help' for more information
"

--- Verified with qemu-kvm-0.12.1.2-2.234.el6.x86_64 using same scenarios above.
Scenario 1 actual result:
Greeting printed.
# nc -lU /opt/mon.monitor
 {"QMP": {"version": {"qemu": {"micro": 1, "minor": 12, "major": 0}, "package": "(qemu-kvm-0.12.1.2)"}, "capabilities": []}}
 {"execute":"qmp_capabilities"}
 {"return": {}}

Scenario 2 actual result:
Greeting printed in screen:
QEMU 0.12.1 monitor - type 'help' for more information


--- As per above, this issue has been fixed.
Comment 7 Amit Shah 2012-04-11 08:19:33 UTC 
*** Bug 796203 has been marked as a duplicate of this bug. ***
Comment 9 Michal Novotny 2012-05-04 12:43:08 UTC 
    Technical note added. If any revisions are required, please edit the "Technical Notes" field
    accordingly. All revisions will be proofread by the Engineering Content Services team.
    
    New Contents:
NEEDINFO
Comment 12 Richard W.M. Jones 2012-05-08 10:52:07 UTC 
    Technical note updated. If any revisions are required, please edit the "Technical Notes" field
    accordingly. All revisions will be proofread by the Engineering Content Services team.
    
    Diffed Contents:
@@ -1 +1 @@
-NEEDINFO+No Documentation Needed
Comment 13 errata-xmlrpc 2012-06-20 11:43:32 UTC 
Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.

For information on the advisory, and where to find the updated
files, follow the link below.

If the solution does not work for you, open a new bug report.

http://rhn.redhat.com/errata/RHBA-2012-0746.html
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