[openstack-dev] [nova] Fixing the console.log grows forever bug.

Tony Breeds tony at bakeyournoodle.com
Sat Dec 6 05:38:52 UTC 2014

Hi All,
    In the most recent team meeting we briefly discussed: [1] where the
console.log grows indefinitely, eventually causing guest stalls.  I mentioned
that I was working on a spec to fix this issue.

My original plan was fairly similar to [2]  In that we'd switch libvirt/qemu to
using a unix domain socket and write a simple helper to read from that socket
and write to disk.  That helper would close and reopen the on disk file upon
receiving a HUP (so logrotate just works).   Life would be good. and we could
all move on.

However I was encouraged to investigate fixing this in qemu, such that qemu
could process the HUP and make life better for all.  This is certainly doable
and I'm happy[3] to do this work.  I've floated the idea past qemu-devel and
they seem okay with the idea.  My main concern is in lag and supporting
qemu/libvirt that can't handle this option.

For the sake of discussion  I'll lay out my best guess right now on fixing this
in qemu.

qemu 2.2.0 /should/ release this year the ETA is 2014-12-09[4] so the fix I'm
proposing would be available in qemu 2.3.0 which I think will be available in
June/July 2015.  So we'd be into 'L' development before this fix is available
and possibly 'M' before the community distros (Fedora and  Ubuntu)[5] include
and almost certainly longer for Enterprise distros.  Along with the qemu
development I expect there to be some libvirt development as well but right now
I don't think that's critical to the feature or this discussion.

So if that timeline is approximately correct:

- Can we wait this long to fix the bug?  As opposed to having it squashed in Kilo.
- What do we do in nova for the next ~12 months while know there isn't a qemu to fix this?
- Then once there is a qemu that fixes the issue, do we just say 'thou must use
  qemu 2.3.0' or would nova still need to support old and new qemu's ?

[1] https://bugs.launchpad.net/nova/+bug/832507
[2] https://review.openstack.org/#/c/80865/
[3] For some value of happy ;P
[4] From http://wiki.qemu.org/Planning/2.2
[5] Debian and Gentoo are a little harder to quantify in this scenario but no
    less important.

Yours Tony.

PS: If any of you have a secret laundry list of things qemu should do to make
    life easier for nova.  Put them on a wiki page so we can discuss them.
PPS: If this is going to be a thing we do (write features and fixes in qemu)
     we're going to need a consistent plan on how we cope with that.
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