[libvirt] [PATCH v2 1/8] Added public API to enable post-copy migration

[Cristian KLEIN]

On 2014-09-30 17:16, Daniel P. Berrange wrote:
> On Tue, Sep 30, 2014 at 05:11:03PM +0200, Jiri Denemark wrote:
>> On Tue, Sep 30, 2014 at 16:39:22 +0200, Cristian Klein wrote:
>>> Signed-off-by: Cristian Klein <cristian.klein at cs.umu.se>
>>> ---
>>>   include/libvirt/libvirt.h.in | 1 +
>>>   src/libvirt.c                | 7 +++++++
>>>   2 files changed, 8 insertions(+)
>>>
>>> diff --git a/include/libvirt/libvirt.h.in b/include/libvirt/libvirt.h.in
>>> index 5217ab3..82f3aeb 100644
>>> --- a/include/libvirt/libvirt.h.in
>>> +++ b/include/libvirt/libvirt.h.in
>>> @@ -1225,6 +1225,7 @@ typedef enum {
>>>       VIR_MIGRATE_ABORT_ON_ERROR    = (1 << 12), /* abort migration on I/O errors happened during migration */
>>>       VIR_MIGRATE_AUTO_CONVERGE     = (1 << 13), /* force convergence */
>>>       VIR_MIGRATE_RDMA_PIN_ALL      = (1 << 14), /* RDMA memory pinning */
>>> +    VIR_MIGRATE_POSTCOPY          = (1 << 15), /* enable (but don't start) post-copy */
>>>   } virDomainMigrateFlags;
>>
>> I still think we should add an extra flag to start post copy
>> immediately. To address your concerns about it, I don't think it's
>> implementing a policy in libvirt. It's for apps that want to make sure
>> migration converges without having to spawn another thread and monitor
>> the progress or wait for a timeout. It's a bit similar to migrating a
>> paused domain vs. migrating a running domain and pausing it when it
>> doesn't seem to converge.
>
> Your point about spawning another thread makes me wonder if we should
> actually look at adding a 'VIR_MIGRATE_ASYNC' method (that would require
> P2P migration of course). If this flag were set, virDomainMigrateXXX would
> only block for long enough to start the migration and then return.
>
> Callers can use the job info API to monitor progress & success/failure.
>
> Then we wouldn't have to keep adding flags like you suggest - apps can
> just easily call the appropriate API right away with no threads needed

This would make a lot of sense. The user would call:

"""
virDomainMigrateXXX(..., VIR_MIGRATE_POSTCOPY | VIR_MIGRATE_ASYNC)
virDomainMigrateStartPostCopy(...)
"""

Would this be seen as more cumbersome than having a dedicated 
VIR_MIGRATE_POSTCOPY_AUTOSTART?

-- 
Cristian Klein, PhD
Post-doc @ Umeå Universitet
http://www8.cs.umu.se/~cklein