Since this cannot automatically recover from a crashed QEMU client with an
RBD image, perhaps this RBD locking should not default to enabled.
Additionally, this will conflict with the "exclusive-lock" feature
available since the Ceph Hammer-release since both utilize the same locking
construct.
As a quick background, the optional exclusive-lock feature can be
enabled/disabled on image and safely/automatically handles the case of
recovery from a crashed client. Under normal conditions, the RBD
exclusive-lock feature automatically acquires the lock upon the first
attempt to write to the image and transparently transitions ownership of
the lock between two or more clients -- used for QEMU live-migration.
I'd be happy to add a new librbd API method to explicitly expose acquiring
and releasing the RBD exclusive lock since it certainly solves a couple
compromises in our current QEMU integration.
On Thu, Apr 14, 2016 at 11:27 PM, Fam Zheng <f...@redhat.com> wrote:
> librbd has the locking API that can be used to implement .bdrv_lockf.
>
> Signed-off-by: Fam Zheng <f...@redhat.com>
> ---
> block/rbd.c | 25 +++++++++++++++++++++++++
> 1 file changed, 25 insertions(+)
>
> diff --git a/block/rbd.c b/block/rbd.c
> index 5bc5b32..a495083 100644
> --- a/block/rbd.c
> +++ b/block/rbd.c
> @@ -810,6 +810,30 @@ static int qemu_rbd_truncate(BlockDriverState *bs,
> int64_t offset)
> return 0;
> }
>
> +static int qemu_rbd_lockf(BlockDriverState *bs, BdrvLockfCmd cmd)
> +{
> + int ret;
> + BDRVRBDState *s = bs->opaque;
> +
> + /* XXX: RBD locks are not released automatically when program exits,
> which
> + * means if QEMU dies it cannot open the image next time until
> manually
> + * unlocked. */
> + switch (cmd) {
> + case BDRV_LOCKF_RWLOCK:
> + ret = rbd_lock_exclusive(s->image, NULL);
> + break;
> + case BDRV_LOCKF_ROLOCK:
> + ret = rbd_lock_shared(s->image, NULL, NULL);
> + break;
> + case BDRV_LOCKF_UNLOCK:
> + ret = rbd_unlock(s->image, NULL);
> + break;
> + default:
> + abort();
> + }
> + return ret;
> +}
> +
> static int qemu_rbd_snap_create(BlockDriverState *bs,
> QEMUSnapshotInfo *sn_info)
> {
> @@ -998,6 +1022,7 @@ static BlockDriver bdrv_rbd = {
> .bdrv_aio_discard = qemu_rbd_aio_discard,
> #endif
>
> + .bdrv_lockf = qemu_rbd_lockf,
> .bdrv_snapshot_create = qemu_rbd_snap_create,
> .bdrv_snapshot_delete = qemu_rbd_snap_remove,
> .bdrv_snapshot_list = qemu_rbd_snap_list,
> --
> 2.8.0
>
>
>
--
Jason
