Re: [Qemu-devel] [Qemu-block] [PATCH] rbd: Detect rbd image resizes and propagate them

[Adam Wolfe Gordon]

On Wed, Sep 13, 2017 at 3:21 PM, Jason Dillaman <address@hidden> wrote:
> On Wed, 2017-09-13 at 10:44 -0600, Adam Wolfe Gordon wrote:
>> +    parent = bs->inherits_from;
>> +    if (parent == NULL) {
>> +        error_report("bs %s does not have parent", 
>> bdrv_get_device_or_node_name(bs));
>> +        return;
>> +    }
>> +
>> +    /* Force parents to re-read our size. */
>
> Can you just invoke blk_truncate instead?

blk_truncate will end up calling qemu_rbd_truncate, which does an
rbd_resize. The goal of this patch is to avoid calling rbd_resize from
qemu, since we do resizes from an external orchestration service.

That said, this patch also introduces a cache of the size (in
BDRVRBDState.size_bytes), so it would be possible for
qemu_rbd_truncate to avoid calling rbd_resize when the image is
already the right size. If I did that, we could use blk_truncate when
we detect a resize as well. Would that be a desirable change?