[libvirt] [PATCH] qemu: fix migration with local and VIR_STORAGE_TYPE_NETWORK disks

[Chris Friesen]

On 02/07/2018 12:05 PM, Daniel P. Berrangé wrote:
> On Wed, Feb 07, 2018 at 11:57:19AM -0600, Chris Friesen wrote:
>> In the current implementation of qemuMigrateDisk() the value of the
>> "nmigrate_disks" parameter wrongly impacts the decision whether or not
>> to migrate a disk that is not a member of "migrate_disks":
>>
>> 1) If "nmigrate_disks" is zero, "disk" is migrated if it's non-shared
>> non-readonly with source.
>>
>> 2) If "nmigrate_disks" is non-zero and "disk" is not a member of
>> "migrate_disks" then "disk" is not migrated.  This should instead proceed
>> with checking conditions as per 1) and allow migration of non-shared
>> non-readonly disks with source.
>
> Huh, this doesn't make sense. If an app has passed a list of disks
> in migrate_disks, we must *never* touch any disk that is not present
> in this list. If the app wanted the other disk(s) migrated, it would
> have included it in the list of disks it passed in.

Okay, that makes sense.  I can restore the "return false" here.

Are you okay with the other change?

Our original problem scenario was where the root disk is rbd and there is a 
read-only ISO config-drive, and "nmigrate_disks" is zero.  What we see in this 
case is that qemuMigrateDisk() returns "true" for the rbd disk, which then 
causes qemuMigrationPrecreateStorage() to fail with "pre-creation of storage 
targets for incremental storage migration is not supported".

Chris