Re: [Qemu-devel] [PATCH v3] block/rbd: implement .bdrv_get_allocated_file_size callback

[Stefano Garzarella]

On Tue, Jul 09, 2019 at 09:42:14PM -0400, Jason Dillaman wrote:
> On Tue, Jul 9, 2019 at 11:32 AM Max Reitz <address@hidden> wrote:
> > On 09.07.19 15:09, Stefano Garzarella wrote:
> > >
> > > Max, Jason, thanks for the details!
> > >
> > > If you agree, I'll try to implement something similar, iterating on all
> > > snapshots.
> >
> > Yes, that should work.
> >
> > > What about metadata?
> > > I saw some APIs (e.g. rbd_metadata_list()) that allow us to get the 
> > > metadata.
> > > An idea could be to iterate over them and sum the keys-values size 
> > > returned,
> > > but I'm not sure they are returned in the same format as they are stored.
> >
> > I wouldn’t mind ignoring metadata too much.  If you can get something to
> > work, even better, but I don’t consider that too important.
> 
> I don't think it's a good idea to attempt to estimate it. If there is
> enough desire, we can always add a supported "disk-usage" API method
> that takes into account things like the image metadata, object-map,
> journaling, etc overhead. However, I wouldn't expect it to be anywhere
> near the actual block usage (unless something has gone terribly wrong
> w/ journaling and it fails to trim your log).

Okay, so for now, I'll skip the metadata and if you think can be useful
to add "disk-usage" API in RBD, I'll use it later.

Thanks,
Stefano