Re: [Qemu-devel] [PATCH v3] block/rbd: increase dynamically the image size

[Stefano Garzarella]

On Tue, Jun 25, 2019 at 04:02:04PM +0200, Max Reitz wrote:
> On 09.05.19 16:59, Stefano Garzarella wrote:
> > RBD APIs don't allow us to write more than the size set with
> > rbd_create() or rbd_resize().
> > In order to support growing images (eg. qcow2), we resize the
> > image before write operations that exceed the current size.
> > 
> > Signed-off-by: Stefano Garzarella <address@hidden>
> > ---
> > v3:
> >   - add 'image_size' field in the BDRVRBDState to keep track of the
> >     current size of the RBD image [Jason, Kevin]
> > ---
> >  block/rbd.c | 42 +++++++++++++++++++++++++++++++++++++++---
> >  1 file changed, 39 insertions(+), 3 deletions(-)
> > 
> > diff --git a/block/rbd.c b/block/rbd.c
> > index 0c549c9935..b0355a2ce0 100644
> > --- a/block/rbd.c
> > +++ b/block/rbd.c
> 
> [...]
> 
> > @@ -833,6 +842,22 @@ static void qemu_rbd_close(BlockDriverState *bs)
> >      rados_shutdown(s->cluster);
> >  }
> >  
> > +/* Resize the RBD image and update the 'image_size' with the current size 
> > */
> > +static int qemu_rbd_resize(BlockDriverState *bs, uint64_t size)
> > +{
> > +    BDRVRBDState *s = bs->opaque;
> > +    int r;
> > +
> > +    r = rbd_resize(s->image, size);
> > +    if (r < 0) {
> > +        return r;
> > +    }
> > +
> > +    s->image_size = size;
> 
> I think this should update bs->total_sectors, too.  In fact, I’m
> wondering why you don’t just use bs->total_sectors (or bdrv_getlength(),
> which returns bs->total_sectors * 512) instead of adding this new field?
> 

Hi Max,
thanks for taking a look!

I used bs->total_sectors in the v2, but Jason pointed out a possible
issue with this, so I proposed to add a variable in the BDRVRBDState to
track the latest resize and Kevin acked [1].

IIUC what Kevin said on his comment, the 'bs->total_sectors' should be
updated by bdrv_co_write_req_finish(), for this reason I didn't update
it.

[1] https://www.mail-archive.com/address@hidden/msg615195.html

Thanks,
Stefano