Re: [PATCH V3 5/6] block/rbd: add write zeroes support

From: Ilya Dryomov <idryomov@gmail.com>
To: Peter Lieven <pl@kamp.de>
Cc: kwolf@redhat.com, berrange@redhat.com, qemu-block@nongnu.org,
	qemu-devel@nongnu.org, ct@flyingcircus.io,
	Paolo Bonzini <pbonzini@redhat.com>,
	mreitz@redhat.com
Subject: Re: [PATCH V3 5/6] block/rbd: add write zeroes support
Date: Wed, 16 Jun 2021 14:34:25 +0200	[thread overview]
Message-ID: <CAOi1vP8AFWaS7Qwu8DVQP0EGZh48CcsrYnTfCWU2J6ZctGA2EQ@mail.gmail.com> (raw)
In-Reply-To: <20210519142359.23083-6-pl@kamp.de>

On Wed, May 19, 2021 at 4:28 PM Peter Lieven <pl@kamp.de> wrote:
>
> Signed-off-by: Peter Lieven <pl@kamp.de>
> ---
>  block/rbd.c | 37 ++++++++++++++++++++++++++++++++++++-
>  1 file changed, 36 insertions(+), 1 deletion(-)
>
> diff --git a/block/rbd.c b/block/rbd.c
> index 0d8612a988..ee13f08a74 100644
> --- a/block/rbd.c
> +++ b/block/rbd.c
> @@ -63,7 +63,8 @@ typedef enum {
>      RBD_AIO_READ,
>      RBD_AIO_WRITE,
>      RBD_AIO_DISCARD,
> -    RBD_AIO_FLUSH
> +    RBD_AIO_FLUSH,
> +    RBD_AIO_WRITE_ZEROES
>  } RBDAIOCmd;
>
>  typedef struct BDRVRBDState {
> @@ -705,6 +706,10 @@ static int qemu_rbd_open(BlockDriverState *bs, QDict *options, int flags,
>          }
>      }
>
> +#ifdef LIBRBD_SUPPORTS_WRITE_ZEROES
> +    bs->supported_zero_flags = BDRV_REQ_MAY_UNMAP;

I wonder if we should also set BDRV_REQ_NO_FALLBACK here since librbd
does not really have a notion of non-efficient explicit zeroing.

Thanks,

                Ilya