Re: [Qemu-devel] [Qemu-block] [PATCH v2 06/16] backup: Request BLK_PERM_AIO_CONTEXT_CHANGE on target

[Stefan Hajnoczi]

On Wed, May 24, 2017 at 10:18:44AM +0800, Fam Zheng wrote:
> On Thu, 05/11 15:41, Stefan Hajnoczi wrote:
> > On Wed, Apr 19, 2017 at 05:43:46PM +0800, Fam Zheng wrote:
> > > What's done in the source's context change notifier is moving the
> > > target's context to follow the new one, so we request this permission
> > > here.
> > 
> > It's true that the backup block job must be able to set target's
> > AioContext, but does this change also allow other users to set target's
> > AioContext while the backup job is running?  If yes, then we need to
> > handle that.
> 
> If through job->target, yes, but I don't think there is any user of 
> job->target.
> Otherwise, it's not allowed, because the second parameter of blk_new doesn't
> have BLK_PERM_AIO_CONTEXT_CHANGE.
> 
> So it's okay.

What about blockdev-backup?  It allows the user to specify 'target'.
Therefore the user can also run other monitor commands on target.  Some
of them could change the AioContext and the backup job wouldn't know!

Stefan

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