On 01/20/2015 06:41 AM, Ilya Dryomov wrote:
> If the clone is resized down to 0, it becomes standalone. If such
> resize is carried over while an image is mapped we would detect this
> and call rbd_dev_parent_put() which means "let go of all parent state,
> including the spec(s) of parent images(s)". This leads to a mismatch
> between "rbd info" and sysfs parent fields, so a fix is in order.
>
> # rbd create --image-format 2 --size 1 foo
> # rbd snap create foo@snap
> # rbd snap protect foo@snap
> # rbd clone foo@snap bar
> # DEV=$(rbd map bar)
> # rbd resize --allow-shrink --size 0 bar
> # rbd resize --size 1 bar
> # rbd info bar | grep parent
> parent: rbd/foo@snap
>
> Before:
>
> # cat /sys/bus/rbd/devices/0/parent
> (no parent image)
>
> After:
>
> # cat /sys/bus/rbd/devices/0/parent
> pool_id 0
> pool_name rbd
> image_id 10056b8b4567
> image_name foo
> snap_id 2
> snap_name snap
> overlap 0
>
> Signed-off-by: Ilya Dryomov <idryomov@xxxxxxxxxx>
Hmm. Interesting.
I think that a parent with an overlap of 0 is of no
real use. So in the last patch I was suggesting it
should just go away.
But now, looking at it from this perspective, the fact
that an image *came from* a particular parent, but which
has no more overlap, could be useful information. The
parent shouldn't simply go away without the user requesting
that.
I haven't completely followed through the logic of keeping
the reference around but I understand what you're doing and
it looks OK to me.
Reviewed-by: Alex Elder <elder@xxxxxxxxxx>
> ---
> drivers/block/rbd.c | 30 ++++++++++--------------------
> 1 file changed, 10 insertions(+), 20 deletions(-)
>
> diff --git a/drivers/block/rbd.c b/drivers/block/rbd.c
> index b85d52005a21..e818c2a6ffb1 100644
> --- a/drivers/block/rbd.c
> +++ b/drivers/block/rbd.c
> @@ -4273,32 +4273,22 @@ static int rbd_dev_v2_parent_info(struct rbd_device *rbd_dev)
> }
>
> /*
> - * We always update the parent overlap. If it's zero we
> - * treat it specially.
> + * We always update the parent overlap. If it's zero we issue
> + * a warning, as we will proceed as if there was no parent.
> */
> - rbd_dev->parent_overlap = overlap;
> if (!overlap) {
> -
> - /* A null parent_spec indicates it's the initial probe */
> -
> if (parent_spec) {
> - /*
> - * The overlap has become zero, so the clone
> - * must have been resized down to 0 at some
> - * point. Treat this the same as a flatten.
> - */
> - rbd_dev_parent_put(rbd_dev);
> - pr_info("%s: clone image now standalone\n",
> - rbd_dev->disk->disk_name);
> + /* refresh, careful to warn just once */
> + if (rbd_dev->parent_overlap)
> + rbd_warn(rbd_dev,
> + "clone now standalone (overlap became 0)");
> } else {
> - /*
> - * For the initial probe, if we find the
> - * overlap is zero we just pretend there was
> - * no parent image.
> - */
> - rbd_warn(rbd_dev, "ignoring parent with overlap 0");
> + /* initial probe */
> + rbd_warn(rbd_dev, "clone is standalone (overlap 0)");
> }
> }
> + rbd_dev->parent_overlap = overlap;
> +
> out:
> ret = 0;
> out_err:
>
--
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