Re: [Qemu-block] [Qemu-devel] [PATCH v2] block/rbd: increase dynamically the image size

[Jason Dillaman]

On Fri, May 3, 2019 at 12:30 PM Stefano Garzarella <address@hidden> 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 <address@hidden>
> ---
> v2:
>   - use bs->total_sectors instead of adding a new field [Kevin]
>   - resize the image only during write operation [Kevin]
>     for read operation, the bdrv_aligned_preadv() already handles reads
>     that exceed the length returned by bdrv_getlength(), so IMHO we can
>     avoid to handle it in the rbd driver
> ---
>  block/rbd.c | 14 +++++++++++++-
>  1 file changed, 13 insertions(+), 1 deletion(-)
>
> diff --git a/block/rbd.c b/block/rbd.c
> index 0c549c9935..613e8f4982 100644
> --- a/block/rbd.c
> +++ b/block/rbd.c
> @@ -934,13 +934,25 @@ static BlockAIOCB *rbd_start_aio(BlockDriverState *bs,
>      }
>
>      switch (cmd) {
> -    case RBD_AIO_WRITE:
> +    case RBD_AIO_WRITE: {
> +        /*
> +         * RBD APIs don't allow us to write more than actual size, so in 
> order
> +         * to support growing images, we resize the image before write
> +         * operations that exceed the current size.
> +         */
> +        if (off + size > bs->total_sectors * BDRV_SECTOR_SIZE) {

When will "bs->total_sectors" be refreshed to represent the correct
current size? You wouldn't want a future write whose extent was
greater than the original image size but less then a previous IO that
expanded the image to attempt to shrink the image.

> +            r = rbd_resize(s->image, off + size);
> +            if (r < 0) {
> +                goto failed_completion;
> +            }
> +        }
>  #ifdef LIBRBD_SUPPORTS_IOVEC
>              r = rbd_aio_writev(s->image, qiov->iov, qiov->niov, off, c);
>  #else
>              r = rbd_aio_write(s->image, off, size, rcb->buf, c);
>  #endif
>          break;
> +    }
>      case RBD_AIO_READ:
>  #ifdef LIBRBD_SUPPORTS_IOVEC
>              r = rbd_aio_readv(s->image, qiov->iov, qiov->niov, off, c);
> --
> 2.20.1
>
>


-- 
Jason