Re: [Qemu-devel] [PATCH v6 08/10] qapi: Add transaction support to block-dirty-bitmap-{add, enable, disable}

[Max Reitz]

On 2014-11-24 at 10:41, Paolo Bonzini wrote:
> On 24/11/2014 09:35, Max Reitz wrote:
> > > > But what if the dirty bitmap was enabled before so that this enabling
> > > > transaction was supposed to be a no-op?
> > > Maybe it's not a problem: The only case in which the enable/disable
> > > operation will fail is if it cannot find the device or bitmap -- in
> > > which case, the abort operation isn't going to be able to affect
> > > anything either.
> > Well, it's part of a transaction. As far as I understand it, one groups
> > several operations in one transaction and if any fails, all are aborted.
> > Therefore, the "enable the dirty bitmap" operation can trivially succeed
> > (because it was enabled before), but some different operation may fail,
> > which then results in invocation of this abort function.
> Would it work to do the actual enabling/disabling in the commit
> function, since it cannot fail?

Too easy. :-)

This patch could then no longer reuse qmp_block_dirty_bitmap_enable(), 
but reimplementing it here should be fine (it's short enough).

Max