support vhost user without specifying vhostforce

[Liang Chen]

[Impact]

 * vhost-user falls back to virtio-net which causes performance lose without specifying the vhostforce option. But it should be the default behavior for vhost-user, since guests using PMD doesn't support msi-x.

[Test Case]

  create a vhost-user virtio backend without specifying the vhostforce option, i.e. -netdev type=vhost-user,id=mynet1,chardev=<char_dev_for_the_controll_channel>
  start the VM
  vhost-user is not enabled

[Regression Potential]

 * none

vhost user nic doesn't support non msi guests(like pxe stage) by default.
Vhost user nic can't fall back to qemu like normal vhost net nic does. So we should
enable it for non msi guests.

The problem has been fix in qemu upstream - http://git.qemu.org/?p=qemu.git;a=commitdiff;h=24f938a682d934b133863eb421aac33592f7a09e. And the patch needs to be backported to 1:2.2+dfsg-5expubuntu9.8 .

[Ubuntu Foundations Team Bug Bot (crichton)]

The attachment "debian patch for qemu 1:2.2+dfsg" seems to be a debdiff. The ubuntu-sponsors team has been subscribed to the bug report so that they can review and hopefully sponsor the debdiff. If the attachment isn't a patch, please remove the "patch" flag from the attachment, remove the "patch" tag, and if you are member of the ~ubuntu-sponsors, unsubscribe the team.

[This is an automated message performed by a Launchpad user owned by ~brian-murray, for any issue please contact him.]

[James Page (james-page)]

Hello Liang, or anyone else affected,

Accepted qemu into kilo-proposed. The package will build now and be available in the Ubuntu Cloud Archive in a few hours, and then in the -proposed repository.

Please help us by testing this new package. To enable the -proposed repository:

  sudo add-apt-repository cloud-archive:kilo-proposed
  sudo apt-get update

Your feedback will aid us getting this update out to other Ubuntu users.

If this package fixes the bug for you, please add a comment to this bug, mentioning the version of the package you tested, and change the tag from verification-kilo-needed to verification-kilo-done. If it does not fix the bug for you, please add a comment stating that, and change the tag to verification-kilo-failed. In either case, details of your testing will help us make a better decision.

Further information regarding the verification process can be found at https://wiki.ubuntu.com/QATeam/PerformingSRUVerification . Thank you in advance!

[Liang Chen (cbjchen)]

Tested with 1:2.2+dfsg-5expubuntu9.7~cloud2, and the fix works for me.

[Ryan Beisner (1chb1n)]

FYI, following additional regression tests, today we promoted qemu 2.2+dfsg-5expubuntu9.7~cloud2 from kilo-proposed to kilo-updates in the Ubuntu Cloud Archive.