Re: [PATCH 1/4] block: fix detect-zeroes= with BDRV_REQ_REGISTERED_BUF

[Fiona Ebner]

Am 26.01.23 um 21:13 schrieb Stefan Hajnoczi:
> When a write request is converted into a write zeroes request by the
> detect-zeroes= feature, it is no longer associated with an I/O buffer.
> The BDRV_REQ_REGISTERED_BUF flag doesn't make sense without an I/O
> buffer and must be cleared because bdrv_co_do_pwrite_zeroes() fails with
> -EINVAL when it's set.
> 
> Fiona Ebner <f.ebner@proxmox.com> bisected and diagnosed this QEMU 7.2
> regression where writes containing zeroes to a blockdev with
> discard=unmap,detect-zeroes=unmap fail.
> 
> Buglink: https://gitlab.com/qemu-project/qemu/-/issues/1404
> Fixes: e8b6535533be ("block: add BDRV_REQ_REGISTERED_BUF request flag")
> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
> ---
>  block/io.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/block/io.c b/block/io.c
> index a09a19f7a7..24a2bc42d3 100644
> --- a/block/io.c
> +++ b/block/io.c
> @@ -1926,6 +1926,9 @@ static int coroutine_fn bdrv_aligned_pwritev(BdrvChild 
> *child,
>          if (bs->detect_zeroes == BLOCKDEV_DETECT_ZEROES_OPTIONS_UNMAP) {
>              flags |= BDRV_REQ_MAY_UNMAP;
>          }
> +
> +        /* Can't use optimization hint with bufferless zero write */
> +        flags &= ~BDRV_REQ_REGISTERED_BUF;
>      }
>  
>      if (ret < 0) {

Tested-by: Fiona Ebner <f.ebner@proxmox.com>

CC-ing stable, because it fixes a regression.