Re: [Qemu-devel] [PATCH] nbd/client: Relax handling of large NBD_CMD_BLOCK_STATUS reply

[Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>]

04.05.2018 01:26, Eric Blake wrote:
> The NBD spec is proposing a relaxation of NBD_CMD_BLOCK_STATUS
> where a server may have the final extent per context give a
> length beyond the original request, if it can easily prove that
> subsequent bytes have the same status, on the grounds that a
> client can take advantage of this information for fewer block
> status requests.  Since qemu 2.12 as a client always sends
> NBD_CMD_FLAG_REQ_ONE, and rejects a server that sends extra
> length, the upstream NBD spec will probably limit this behavior
> to clients that don't request REQ_ONE semantics; but it doesn't
> hurt to relax qemu to always be permissive of this server
> behavior, even if it continues to use REQ_ONE.

Hi!

Patch is applied, are you going to make a patch for NBD spec?

>
> Signed-off-by: Eric Blake <eblake@redhat.com>
> ---
>   block/nbd-client.c | 10 +++++++---
>   1 file changed, 7 insertions(+), 3 deletions(-)
>
> diff --git a/block/nbd-client.c b/block/nbd-client.c
> index e7caf49fbb4..25d34631fe7 100644
> --- a/block/nbd-client.c
> +++ b/block/nbd-client.c
> @@ -259,14 +259,18 @@ static int nbd_parse_blockstatus_payload(NBDClientSession *client,
>
>       if (extent->length == 0 ||
>           (client->info.min_block && !QEMU_IS_ALIGNED(extent->length,
> -                                                    client->info.min_block)) ||
> -        extent->length > orig_length)
> -    {
> +                                                    client->info.min_block))) {
>           error_setg(errp, "Protocol error: server sent status chunk with "
>                      "invalid length");
>           return -EINVAL;
>       }
>
> +    /* The server is allowed to send us extra information on the final
> +     * extent; just clamp it to the length we requested. */
> +    if (extent->length > orig_length) {
> +        extent->length == orig_length;
> +    }
> +
>       return 0;
>   }
>


-- 
Best regards,
Vladimir