Re: [Qemu-devel] [PATCH RFC 0/6] migration: enable return-path for precopy

[Peter Xu]

On Fri, May 19, 2017 at 02:43:26PM +0800, Peter Xu wrote:
> This idea derives from the bug reported:
> 
>   https://bugzilla.redhat.com/show_bug.cgi?id=1439147
> 
> It is not a extremely critical bug, since as long as the user uses
> libvirt to migrate, we won't have such an issue at all (we'll have
> identical command line parameters for QEMU). However it can be an
> severe one, since it caused data loss (source VM will quit assuming
> that destination VM is good, while it is not). So it would be good we
> fix it. Meanwhile, imho the return path may be used for other things
> as well in the future.
> 
> This series proposed a solution for the bug - let's enable return path
> even for precopy when possible, then source can know whether dest is
> good or not, then it can decide to do something better than quit.
> 
> The series is marked as RFC for two reasons:
> 
> One point for RFC is the idea in general that whether we would like to
> enable return path for precopy. I see it okay since after all it's
> optional (so it greatly reduces the chance that QEMU command line user
> will lose the data, and this feature will be automatically off when we
> are using e.g. "exec:" to migrate to a file).
> 
> The other one point is that I converted MigrationState into a QObject
> (actually a QDevice) to let migration codes benefits from some general
> framework advantages.
> 
> I got at least one positive feedback on each of the RFC elements
> mentioned above, so dare I post this to public. Though I guess some
> migration reviewers may be on PTO recently (I just know it :), I still
> decided to post this out for a broader rfc review.
> 
> Smoke test done, and of course I verified this series to fix the bug
> mentioned.
> 
> Please review. Thanks.
> 
> Peter Xu (6):
>   io: only allow return path for socket typed
>   migration: isolate return path on src
>   migration: fix leak of src file on dst
>   migration: shut src return path unconditionally
>   migration: let MigrationState be an QObject
>   migration: enable return path for precopy
> 
>  include/hw/compat.h           |   4 ++
>  include/io/channel.h          |   1 +
>  include/migration/migration.h |  27 ++++++++-
>  include/qemu/typedefs.h       |   1 -
>  io/channel-socket.c           |   1 +
>  migration/migration.c         | 133 
> +++++++++++++++++++++++++++++++-----------
>  migration/postcopy-ram.c      |   1 -
>  migration/qemu-file-channel.c |   9 +++
>  migration/trace-events        |   4 +-
>  9 files changed, 140 insertions(+), 41 deletions(-)
> 
> -- 
> 2.7.4
> 

CC Laurent as well. Sorry!

-- 
Peter Xu