Re: [Qemu-devel] [PATCH RFC 1/1] block/rbd: increase dynamically the image size

[Jason Dillaman <jdillama@redhat.com>]

On Thu, Apr 11, 2019 at 7:00 AM Stefano Garzarella <sgarzare@redhat.com> 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 RW operations that exceed the current size.

What's the use-case for storing qcow2 images within a RBD image? RBD
images are already thinly provisioned, they support snapshots, they
can form a parent/child linked image hierarchy.

> Buglink: https://bugzilla.redhat.com/show_bug.cgi?id=1171007
> Signed-off-by: Stefano Garzarella <sgarzare@redhat.com>
> ---
>  block/rbd.c | 25 +++++++++++++++++++++++++
>  1 file changed, 25 insertions(+)
>
> diff --git a/block/rbd.c b/block/rbd.c
> index 0c549c9935..228658e20a 100644
> --- a/block/rbd.c
> +++ b/block/rbd.c
> @@ -102,6 +102,7 @@ typedef struct BDRVRBDState {
>      rbd_image_t image;
>      char *image_name;
>      char *snap;
> +    uint64_t image_size;
>  } BDRVRBDState;
>
>  static int qemu_rbd_connect(rados_t *cluster, rados_ioctx_t *io_ctx,
> @@ -777,6 +778,14 @@ static int qemu_rbd_open(BlockDriverState *bs, QDict *options, int flags,
>          goto failed_open;
>      }
>
> +    r = rbd_get_size(s->image, &s->image_size);
> +    if (r < 0) {
> +        error_setg_errno(errp, -r, "error reading image size from %s",
> +                         s->image_name);
> +        rbd_close(s->image);
> +        goto failed_open;
> +    }
> +
>      /* If we are using an rbd snapshot, we must be r/o, otherwise
>       * leave as-is */
>      if (s->snap != NULL) {
> @@ -921,6 +930,20 @@ static BlockAIOCB *rbd_start_aio(BlockDriverState *bs,
>          rcb->buf = acb->bounce;
>      }
>
> +    /*
> +     * RBD APIs don't allow us to write more than actual size, so in order
> +     * to support growing images, we resize the image before RW operations
> +     * that exceed the current size.
> +     */
> +    if (s->image_size < off + size) {
> +        r = rbd_resize(s->image, off + size);
> +        if (r < 0) {
> +            goto failed;
> +        }
> +
> +        s->image_size = off + size;
> +    }
> +
>      acb->ret = 0;
>      acb->error = 0;
>      acb->s = s;
> @@ -1066,6 +1089,8 @@ static int coroutine_fn qemu_rbd_co_truncate(BlockDriverState *bs,
>          return r;
>      }
>
> +    s->image_size = offset;
> +
>      return 0;
>  }
>
> --
> 2.20.1
>
>


-- 
Jason