Re: [Qemu-devel] [PATCH 1/3] block: prohibit migration during BlockJobs

[John Snow <jsnow@redhat.com>]

On 10/01/2015 02:03 PM, Paolo Bonzini wrote:
> 
> 
> On 01/10/2015 18:34, John Snow wrote:
>> Unless we can prove this to be safe for specific cases,
>> the default should be to prohibit migration during BlockJobs.
> 
> Block jobs do not affect the current block, only other block device,
> hence they *are* safe for migration.
> 

Can you elaborate for me here?

> What you want, I think, is the target not to be garbage when migration
> ends.  Based on this you can block specific cases, namely mirror which
> you already do allow (patch 2) and backup except for sync='none'.
> 
> Paolo
> 

It would be nice if the target wasn't garbage, yes :)

I allow mirror in specific circumstances -- you can't start a mirror,
but if an existing mirror has hit the sync phase, that's OK.

I can try to do a more exhaustive audit of what should and should not
work, but my thought was "guilty before proven innocent."

>> In conjunction with
>> "migration: disallow_migrate_add_blocker during migration",
>> this should be sufficient to disallow the blockjob from starting
>> in the event of an in-progress migration.
>