[libvirt] [PATCH] qemu: forbid second blockcommit during active commit

[Peter Krempa]

On Mon, Jan 12, 2015 at 04:20:34PM -0700, Eric Blake wrote:
> https://bugzilla.redhat.com/show_bug.cgi?id=1135339 documents some
> confusing behavior when a user tries to start an inactive block
> commit in a second connection while there is already an on-going
> active commit from a first connection.  Eventually, qemu will
> support multiple simultaneous block jobs, but as of now, it does
> not; furthermore, libvirt also needs an overhaul before we can
> support simultaneous jobs.  So, the best way to avoid confusing
> ourselves is to quit relying on qemu to tell us about the situation
> (where we risk getting in weird states) and instead forbid a
> duplicate block commit ourselves.
> 
> Note that we are still relying on qemu to diagnose attempts to
> interrupt an inactive commit (since we only track XML of an active
> commit), but as inactive commit is less confusing for libvirt to
> manage, there is less that can go wrong by leaving that detection
> up to qemu.
> 
> * src/qemu/qemu_driver.c (qemuDomainBlockCommit): Hoist check for
> active commit to occur earlier outside of conditions.
> 
> Signed-off-by: Eric Blake <eblake at redhat.com>
> ---
>  src/qemu/qemu_driver.c | 14 +++++++-------
>  1 file changed, 7 insertions(+), 7 deletions(-)

ACK,

Peter