Re: [Qemu-devel] [PATCH] nbd/server: introduce NBD_CMD_CACHE

[Eric Blake <eblake@redhat.com>]

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On 04/13/2018 09:31 AM, Vladimir Sementsov-Ogievskiy wrote:
> Handle nbd CACHE command. Just do read, without sending read data back.
> Cache mechanism should be done by exported node driver chain.
> 
> Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
> ---
>  include/block/nbd.h |  3 ++-
>  nbd/server.c        | 10 ++++++----
>  2 files changed, 8 insertions(+), 5 deletions(-)
> 
> diff --git a/include/block/nbd.h b/include/block/nbd.h
> index fcdcd54502..b4793d0a29 100644
> --- a/include/block/nbd.h
> +++ b/include/block/nbd.h
> @@ -135,6 +135,7 @@ typedef struct NBDExtent {
>  #define NBD_FLAG_SEND_TRIM         (1 << 5) /* Send TRIM (discard) */
>  #define NBD_FLAG_SEND_WRITE_ZEROES (1 << 6) /* Send WRITE_ZEROES */
>  #define NBD_FLAG_SEND_DF           (1 << 7) /* Send DF (Do not Fragment) */
> +#define NBD_FLAG_SEND_CACHE        (1 << 8) /* Send CACHE (prefetch) */

Hmm, this flag is not documented in the upstream NBD protocol yet; are
we sure it matches the xNBD implementation?  We'll want at least a
documentation patch proposed for the NBD list before taking this.

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org


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