Re: [Qemu-devel] [PATCH 4/4] block/nbd-client: use non-blocking io channel for nbd negotiation

[Eric Blake <eblake@redhat.com>]

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On 2/11/19 6:56 AM, Vladimir Sementsov-Ogievskiy wrote:
> Now negotiation is done in coroutine, so to take benefit of it let's
> use non-blocking model.
> 
> Note that QIOChannel handle synchronous io calls correctly anyway, so

s/handle/handles/

> it's not a problem to send final NBD_CMD_DISC to non-blocking channel
> but using sync qio interface, even not in coroutine.

s/not in/when not in a/

> 
> Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
> ---
>  block/nbd-client.c | 10 +++-------
>  1 file changed, 3 insertions(+), 7 deletions(-)

This fixes qemu as NBD client for use in block devices, but what about
qemu as NBD client in qemu-nbd?  Does that need any updates?  Then
again, your observation about QIO doing the right thing for both
blocking (qemu-nbd) and non-blocking (block layer) channels seems to
cover that.

> @@ -1072,9 +1072,6 @@ static int nbd_client_connect(BlockDriverState *bs,
>          object_ref(OBJECT(client->ioc));
>      }
>  
> -    /* Now that we're connected, set the socket to be non-blocking and
> -     * kick the reply mechanism.  */
> -    qio_channel_set_blocking(QIO_CHANNEL(sioc), false, NULL);
>      client->connection_co = qemu_coroutine_create(nbd_connection_entry, client);
>      nbd_client_attach_aio_context(bs, bdrv_get_aio_context(bs));
>  
> @@ -1083,9 +1080,8 @@ static int nbd_client_connect(BlockDriverState *bs,
>  
>   fail:
>      /*
> -     * We have connected, but must fail for other reasons. The
> -     * connection is still blocking; send NBD_CMD_DISC as a courtesy
> -     * to the server.
> +     * We have connected, but must fail for other reasons.
> +     * Send NBD_CMD_DISC as a courtesy to the server.
>       */
>      {
>          NBDRequest request = { .type = NBD_CMD_DISC };
> 

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3226
Virtualization:  qemu.org | libvirt.org


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