[libvirt] [PATCH 04/19] qemu: Allow all query commands to be run during long jobs

[Daniel P. Berrange]

On Fri, Jul 08, 2011 at 01:34:09AM +0200, Jiri Denemark wrote:
> Query commands are safe to be called during long running jobs (such as
> migration). This patch makes them all work without the need to
> special-case every single one of them.
> 
> The patch introduces new job.asyncCond condition and associated
> job.asyncJob which are dedicated to asynchronous (from qemu monitor
> point of view) jobs that can take arbitrarily long time to finish while
> qemu monitor is still usable for other commands.
> 
> The existing job.active (and job.cond condition) is used all other
> synchronous jobs (including the commands run during async job).
> 
> Locking schema is changed to use these two conditions. While asyncJob is
> active, only allowed set of synchronous jobs is allowed (the set can be
> different according to a particular asyncJob) so any method that
> communicates to qemu monitor needs to check if it is allowed to be
> executed during current asyncJob (if any). Once the check passes, the
> method needs to normally acquire job.cond to ensure no other command is
> running. Since domain object lock is released during that time, asyncJob
> could have been started in the meantime so the method needs to recheck
> the first condition. Then, normal jobs set job.active and asynchronous
> jobs set job.asyncJob and optionally change the list of allowed job
> groups.
> 
> Since asynchronous jobs only set job.asyncJob, other allowed commands
> can still be run when domain object is unlocked (when communicating to
> remote libvirtd or sleeping). To protect its own internal synchronous
> commands, the asynchronous job needs to start a special nested job
> before entering qemu monitor. The nested job doesn't check asyncJob, it
> only acquires job.cond and sets job.active to block other jobs.
> ---
>  src/qemu/qemu_domain.c    |  219 +++++++++++++++++++++++++++++++++++++--------
>  src/qemu/qemu_domain.h    |   82 +++++++++++++----
>  src/qemu/qemu_driver.c    |  122 +++++++++++++-------------
>  src/qemu/qemu_hotplug.c   |   38 ++++----
>  src/qemu/qemu_migration.c |  152 ++++++++++++++++++-------------
>  src/qemu/qemu_process.c   |   42 +++++----
>  6 files changed, 439 insertions(+), 216 deletions(-)

ACK

Daniel
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