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

[Max Reitz <mreitz@redhat.com>]

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On 25.06.19 16:47, Stefano Garzarella wrote:
> 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 <sgarzare@redhat.com>
>>> ---
>>> 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/qemu-devel@nongnu.org/msg615195.html

Ah, right!  Yeah, sure, now that I think about it, the block layer must
have general code for successful writes beyond EOF...  (Read: Now that
I’m pointed towards it...)

OK then; thanks for the patch, applied to my block branch:

https://git.xanclic.moe/XanClic/qemu/commits/branch/block

Max


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