[Libguestfs] [Qemu-devel] [PATCH 3/5] nbd: Implement client use of NBD FAST_ZERO

[Vladimir Sementsov-Ogievskiy]

23.08.2019 17:37, Eric Blake wrote:
> The client side is fairly straightforward: if the server advertised
> fast zero support, then we can map that to BDRV_REQ_NO_FALLBACK
> support.  A server that advertises FAST_ZERO but not WRITE_ZEROES
> is technically broken, but we can ignore that situation as it does
> not change our behavior.
> 
> Signed-off-by: Eric Blake <eblake at redhat.com>

Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov at virtuozzo.com>

> 
> ---
> 
> Perhaps this is worth merging with the previous patch.
> ---
>   block/nbd.c | 7 +++++++
>   1 file changed, 7 insertions(+)
> 
> diff --git a/block/nbd.c b/block/nbd.c
> index beed46fb3414..8339d7106366 100644
> --- a/block/nbd.c
> +++ b/block/nbd.c
> @@ -1044,6 +1044,10 @@ static int nbd_client_co_pwrite_zeroes(BlockDriverState *bs, int64_t offset,
>       if (!(flags & BDRV_REQ_MAY_UNMAP)) {
>           request.flags |= NBD_CMD_FLAG_NO_HOLE;
>       }
> +    if (flags & BDRV_REQ_NO_FALLBACK) {
> +        assert(s->info.flags & NBD_FLAG_SEND_FAST_ZERO);
> +        request.flags |= NBD_CMD_FLAG_FAST_ZERO;
> +    }
> 
>       if (!bytes) {
>           return 0;
> @@ -1239,6 +1243,9 @@ static int nbd_client_connect(BlockDriverState *bs, Error **errp)
>       }
>       if (s->info.flags & NBD_FLAG_SEND_WRITE_ZEROES) {
>           bs->supported_zero_flags |= BDRV_REQ_MAY_UNMAP;
> +        if (s->info.flags & NBD_FLAG_SEND_FAST_ZERO) {
> +            bs->supported_zero_flags |= BDRV_REQ_NO_FALLBACK;
> +        }
>       }
> 
>       s->sioc = sioc;
> 


-- 
Best regards,
Vladimir