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Re: [libvirt] New QEMU daemon for persistent reservations

On Mon, Nov 27, 2017 at 07:27:17 +0100, Michal Privoznik wrote:
> On 11/26/2017 09:32 AM, Peter Krempa wrote:
> > On Fri, Nov 24, 2017 at 15:38:54 +0100, Michal Privoznik wrote:
> >> On 08/22/2017 06:27 PM, Paolo Bonzini wrote:


> >> However, we want to be able to turn it on/off or not mention it at all
> >> on per-disk basis. So what has been suggested so far is:
> >>
> >>   <disk type='block' device='disk'>
> >>     <source dev='/dev/sda'>
> >>     <target dev='sda' bus='scsi'/>
> >>     <reservations enable='yes'/>
> >>   </disk>
> > 
> > Note that if the reservation is applied to the image and not the disk
> > the element should become child of the <source> elememt.
> > Especially if
> > there is only a ever so slight chance that it will work with formats
> > supporting backing store (qcow2) and thus there would be a need to
> > configure it per-image.
> The way I understand PRs is that they are format agnostic, so there's
> not (nor there will be) per image configuration. Nevertheless,

In qemu you have two objects representing a disk image (or member of the
backing chain). One is the format driver, and the second is the driver
which accesses the storage itself. So even if it concerns the access to
the physical storage, it may be necessary to track it in the backing
chain and thus under <source>.

Only if we are sure that no member of the backing chain can have
different config, only then it can be made per-disk.

> <reservations/> concern disk image so I will place the element under
> <source/>. Good point.

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