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Re: [libvirt] [PATCH] qemu: Transition domain to PAUSED after 'stop' command



On 19.09.2012 11:43, Michal Privoznik wrote:
> Currently, we mark domain PAUSED (but not emit an event)
> just before we issue 'stop' on monitor; This command can
> take ages to finish, esp. when domain's doing a lot of
> IO - users can enforce qemu to open files with O_DIRECT
> which doesn't return from write() until data reaches the
> block device. Having said that, we report PAUSED even if
> domain is not paused yet.
> ---
> 
> The event is emitted correctly after all operations returns though.
> But if mgmt app would 'virsh domstate $dom' as we are issuing 'stop'
> monitor command it could get spurious results.

Just for the record, qemu 'stop' command is guaranteed to NOT return
until after all disks are synced. It is not that kind of command which
just requests an operation an returns immediately (like 'shutdown' or
something).

This bug really confuses the enemy - esp. when mgmt application asks
from another thread, it may get PAUSED domain state even though qemu is
still syncing the disks or monitor command hasn't been issued at all or
is about to fail.

Michal


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