Google Summer of Code 2010/QMP

Summary

qemu has many commands attached to the monitor interface that are currently inaccessible over QMP (QEMU Machine Protocol). I intend to give continuity to this effort, converting the remaining functions to the QObject API. While doing this conversion, the QObject API can be updated to improve its functionality when required.

More details about the protocol: http://www.linux-kvm.org/page/MonitorProtocol

Team

Student

• Name: Miguel Di Ciurcio Filho
• Email: miguel.filho@gmail.com

Mentor

• Name: Luiz Capitulino
• Email: lcapitulino@redhat.com

Subsystems being worked on

Handler	Status	Who I should CC
do_info_netdev	Sent to qemu-devel and mentor for review on June 10. Waiting feedback.	Markus Armbruster <armbru@redhat.com>
do_savevm/do_loadvm	Sent RFC to qemu-devel. Still no feedback.	Kevin Wolf <kwolf@redhat.com>, Juan Quintela <quintela@redhat.com>, Christoph Hellwig <hch@infradead.org>
do_info_qdm	Need to confirm libvirt's needs/priority about this.

do_info_netdev

TODO:

• Nothing :-D

do_savevm/do_loadvm

TODO:

• Cook a separate patch that shows all devices snapshots in Monitor output (almost done, need to take the UUID part out).
• Get do_savevm() UUID stuff more in shape for sending an RFC.
• Update do_loadvm() do load an snapshot using an UUID.
• Update do_delvm() do delete an snapshot using an UUID.

Day by Day

June 10

• Finished the new query-netdev patch. Sent to qemu-devel. FYI, this is the 5th try. http://www.mail-archive.com/qemu-devel@nongnu.org/msg35464.html

June 9

• Coded and tested the new query-netdev.
• Wrestled with git rebase, now I understand it. How could I leave without?

June 8

• Sent to qemu-devel the RFC for the new QMP command query-snapshots.

June 7

• A lot of back and forth over email from all sorts of people about query-netdevices and some chat with Anthony on IRC.
• Resolutions about it:
  • Rename the command to query-netdev
  • Show only the backend information (user, tap, socket, vde)
  • Guest devices (frontend) are already available via info qtree, don't need to show them.

Result:

-> { "execute": "query-netdev" }
<- {
     "return": [
        {
           "device": "tap.0",
           "vlan": 0,
           "type": "tap",
           "info": {
              "script": "/etc/qemu-ifup",
              "downscript": "/etc/qemu-ifdown",
              "ifname": "tap0",
           },
        {
           "device": "user.0",
           "type": "user",
           "peer": "e1000.0",
           "info": {
              "net": "10.0.2.0",
              "netmask": "255.255.255.0"
           },
        },

June 4

• Chat with mentor and Kevin Wolf.
• Sent to qemu-devel the RFC for the new QMP command query-netdevices. I will wait for feedback before coding. http://www.mail-archive.com/qemu-devel@nongnu.org/msg34634.html
• Sent to mentor the RFC for the new QMP command query-snapshots before sending to qemu-devel. This might avoid some noise in the list.
• Lesson learned: compile qemu without --enable-debug before submitting anything, damn it! The do_savevm() v3 patch had an warning that was not caught by me and latter on caught by Kevin Wolf: http://www.mail-archive.com/qemu-devel@nongnu.org/msg34707.html After a few minutes chatting with him on IRC we figured that --enable-debug disables -O2, then some warnings could not be seen. Fixed and resent v4. I hope that know this think gets merged :-D

June 3

• Fixed Kevin's suggestions and resent the do_savevm() patch to qemu-devel (now version 3): http://www.mail-archive.com/qemu-devel@nongnu.org/msg34510.html

May 31 thru June 2

• Studied and toke some exams. Classes are over :-D

May 29

• Fixed Markus and Kevin's suggestions and resent the do_savevm() patch to qemu-devel: http://www.mail-archive.com/qemu-devel@nongnu.org/msg33867.html Fingers crossed, this could be my first merge!

May 28

• Some chat with mentor.

• I've submitted a patch to qemu-devel that verifies the snapshot capabilities of all devices in do_savevm() before trying to save anything at all. More details: http://www.mail-archive.com/qemu-devel@nongnu.org/msg33751.html

May 27

• Got mentor's review about last do_info_netdevices(). Will begin fixing things after finishing some more do_savevm/do_loadvm work.
• do_info_snapshots() now displays snapshot information of all devices.

qemu -hda ../a.qcow2 -hdb ../b.qcow2

QEMU 0.12.50 monitor - type 'help' for more information
(qemu) info snapshots 
Snapshot list from ide0-hd0:
ID   TAG       VM SIZE                DATE       VM CLOCK                                 UUID                          PARENT UUID
1                 1.5M 2010-05-27 12:24:45   00:00:05.640 f89787ea-c39e-4531-90cc-19d73abbc50e 00000000-0000-0000-0000-000000000000
2                 1.5M 2010-05-27 12:24:52   00:00:12.258 4fb1f028-febb-464a-8e61-8abdfde9adc8 f89787ea-c39e-4531-90cc-19d73abbc50e
3                  1.5M 2010-05-27 12:25:05   00:00:24.921 faeb873c-f3fd-40ab-97de-67c6f12fd5ff 4fb1f028-febb-464a-8e61-8abdfde9adc8

Snapshot list from ide0-hd1:
ID   TAG       VM SIZE                DATE       VM CLOCK                                 UUID                          PARENT UUID
1                    0 2010-05-27 11:33:11   00:00:02.781 8f5d24a0-9a92-4650-8b56-babaa7790700 00000000-0000-0000-0000-000000000000
2                    0 2010-05-27 11:53:39   00:00:12.073 9e471508-f9d9-46d6-815b-2c25b15152f3 00000000-0000-0000-0000-000000000000
3                    0 2010-05-27 11:53:40   00:00:12.867 c5a75fd0-2cea-433b-bd21-37025dff3cbd 9e471508-f9d9-46d6-815b-2c25b15152f3

May 26

• Got parent snapshot saving working. Using global variable, not sure if it is best option.
• Updated bdrv_snapshot_dump() to properly show the UUID information. It looks really big.

QEMU 0.12.50 monitor - type 'help' for more information
(qemu) info snapshots 
Snapshot devices: ide0-hd0
Snapshot list (from ide0-hd0):
ID   TAG       VM SIZE                DATE       VM CLOCK                                 UUID                          PARENT UUID
1                 1.5M 2010-05-26 21:51:02   00:00:03.263 ce7cb390-f5d8-4633-9c83-e2c651d5aecf 00000000-0000-0000-0000-000000000000
2                 1.5M 2010-05-26 21:51:09   00:00:08.844 1f80df59-470e-4de6-a0a1-cf6a2a721e0e ce7cb390-f5d8-4633-9c83-e2c651d5aecf
3                 1.5M 2010-05-26 21:51:24   00:00:23.274 63ce278d-26fe-4790-ab13-6643bf9ddf90 1f80df59-470e-4de6-a0a1-cf6a2a721e0e
4                 1.5M 2010-05-26 21:53:17   00:00:03.595 0199cdd9-1c8f-4c53-b711-684110078960 00000000-0000-0000-0000-000000000000
5                 1.5M 2010-05-26 21:53:25   00:00:10.750 6b753c35-8939-477b-a7f5-10ff45e34e93 0199cdd9-1c8f-4c53-b711-684110078960
6                 1.5M 2010-05-26 21:53:27   00:00:12.071 7a127832-7259-4b41-9400-64804b755b0c 6b753c35-8939-477b-a7f5-10ff45e34e93

• Fixed extra_data_size offset handling when loading a qcow2 image with an empty extra area.

May 22

I was actually not saving anything. After closing the VM the UUID information was not written to disk. After hours pulling some hair I figured it as a typo and a wrong offset calculation when saving the QCowSnapshotHeader to disk.

May 21

• Got saving UUID information in a qcow2 file, using QCowSnapshot->extra_data_size and displaying it on 'info snapshots'. It seams we can have snapshot inheritance without breaking the file format or any old code. Now time to actually save the inheritance.

Helpful references:

• http://people.gnome.org/~markmc/qcow-image-format.html
• http://www.mail-archive.com/qemu-devel@nongnu.org/msg11663.html

May 19

After talking with Chris Lalancette from libvirt, we need snapshot inheritance in qemu, before converting do_savevm/do_loadvm to QMP. I've analyzed the code and I there is some hairy things to do. There are more people working on this code, so I will try to get a go before starting coding.

From late March thru May 18

Sent patch v4 to qemu-devel.

We were struggling to get the output of 'info network' exactly the same and juggling to work around the lack of a pattern when formatting VLANClientState.info_str. So we decided to add a new and clean command, and leave 'info network' as it is.

This is the v4 patch:

http://lists.gnu.org/archive/html/qemu-devel/2010-05/msg01567.html

The work on this area has begun late March, as a test if I could do something in GSoC. And here I am :-D There were a lot of interactions before the v4 patch.

Previous attempts:

• First try on 2010-04-03: http://www.mail-archive.com/qemu-devel@nongnu.org/msg28815.html
• Second try on 2010-04-08: http://www.mail-archive.com/qemu-devel@nongnu.org/msg29202.html
• Third try on 2010-04-15: http://www.mail-archive.com/qemu-devel@nongnu.org/msg29768.html