Re: [PATCH 2/3] nbd: Add new qemu:allocation-depth metacontext

[Vladimir Sementsov-Ogievskiy]

26.09.2020 10:33, Richard W.M. Jones wrote:
> On Fri, Sep 25, 2020 at 03:32:48PM -0500, Eric Blake wrote:
> > +The second is related to exposing the source of various extents within
> > +the image, with a single context named:
> > +
> > +    qemu:allocation-depth
> > +
> > +In the allocation depth context, bits 0 and 1 form a tri-state value:
> > +
> > +    bits 0-1 clear: NBD_STATE_DEPTH_UNALLOC, means the extent is unallocated
> > +    bit 0 set: NBD_STATE_DEPTH_LOCAL, the extent is allocated in this image
> > +    bit 1 set: NBD_STATE_DEPTH_BACKING, the extent is inherited from a
> > +               backing layer
>
>  From the cover description I imagined it would show the actual depth, ie:
>
>           top -> backing -> backing -> backing
>   depth:   1        2         3   ....          (0 = unallocated)
>
> I wonder if that is possible?  (Perhaps there's something I don't
> understand here.)
That's possible if we want it. Probably the best way is to add *depth parameter to 
bdrv_is_allocated_above (and better on top of my "[PATCH v7 0/5] fix & merge 
block_status_above and is_allocated_above")


--
Best regards,
Vladimir