Re: [Qemu-devel] drive transactions (was Re: [PATCH 2/2 v2] Add the blockdev-reopen and blockdev-migrate commands)

[Paolo Bonzini]

On 02/27/2012 05:33 PM, Federico Simoncelli wrote:
>> > 
>> >     blockdev-begin-transaction
>> >     drive-reopen device new-image-file
>> >     drive-mirror streaming=false device dest
>> >     blockdev-commit-transaction
>> > 
>> > No strange optional arguments, no proliferation of commands, etc.
>> >  The
>> > only downside is that if someone tries to do (4) without transactions
>> > (or without stopping the VM) they'll get corruption because atomicity
>> > is
>> > required.
> I'm all for the modularity of the commands (I suggested it since the 
> beginning),
> but all this infrastructure goes way beyond what I'd need for oVirt now.
> 
> When I submitted my patches we knew that my work wasn't the definitive 
> solution
> (eg: the future implementation of -blockdev). So I'd suggest to try and settle
> with something that is good enough and that is not preventing a future 
> improvement.
> 
> What about having a (temporary) flag in drive-mirror to accept also a 
> new-image-file
> until we will have the optimal solution?

What if libvirt could simply try blockdev-freeze and, if it's not there,
try passing a new-image-file argument.  Add the new-image-file
downstream if you have time constraints, and leave it out upstream.  Too
ugly?

Paolo