Re: [Qemu-devel] [PATCH v2 1/2] rbd: use the higher level librbd instead of just librados

[Josh Durgin]

On 04/08/2011 01:43 AM, Stefan Hajnoczi wrote:
> On Mon, Mar 28, 2011 at 04:15:57PM -0700, Josh Durgin wrote:
> > librbd stacks on top of librados to provide access
> > to rbd images.
> >
> > Using librbd simplifies the qemu code, and allows
> > qemu to use new versions of the rbd format
> > with few (if any) changes.
> >
> > Signed-off-by: Josh Durgin<address@hidden>
> > Signed-off-by: Yehuda Sadeh<address@hidden>
> > ---
> >   block/rbd.c       |  785 +++++++++++++++--------------------------------------
> >   block/rbd_types.h |   71 -----
> >   configure         |   33 +--
> >   3 files changed, 221 insertions(+), 668 deletions(-)
> >   delete mode 100644 block/rbd_types.h
>
> Hi Josh,
> I have applied your patches onto qemu.git/master and am running
> ceph.git/master.
>
> Unfortunately qemu-iotests fails for me.
>
>
> Test 016 seems to hang in qemu-io -g -c write -P 66 128M 512
> rbd:rbd/t.raw.  I can reproduce this consistently.  Here is the
> backtrace of the hung process (not consuming CPU, probably deadlocked):

This hung because it wasn't checking the return value of rbd_aio_write.
I've fixed this in the for-qemu branch of 
http://ceph.newdream.net/git/qemu-kvm.git. Also, the existing rbd 
implementation is not 'growable' - writing to a large offset will not 
expand the rbd image correctly. Should we implement bdrv_truncate to 
support this (librbd has a resize operation)? Is bdrv_truncate useful 
outside of qemu-img and qemu-io?

> Test 008 failed with an assertion but succeeded when run again.  I think
> this is a race condition:

This is likely a use-after-free, but I haven't been able to find the 
race condition yet (or reproduce it). Could you get a backtrace from the 
core file?

Thanks,
Josh