Re: [PATCH 1/2] nbd: enable replace socket if only one connection is configured

[Hou Pu <houpu.main@gmail.com>]

On Wed, Mar 4, 2020 at 5:48 AM Mike Christie <mchristi@redhat.com> wrote:
>
> On 03/03/2020 03:12 PM, Josef Bacik wrote:
> > On 2/28/20 1:40 AM, Hou Pu wrote:
> >> Nbd server with multiple connections could be upgraded since
> >> 560bc4b (nbd: handle dead connections). But if only one conncection
> >> is configured, after we take down nbd server, all inflight IO
> >> would finally timeout and return error. We could requeue them
> >> like what we do with multiple connections and wait for new socket
> >> in submit path.
> >>
> >> Signed-off-by: Hou Pu <houpu@bytedance.com>
> >> ---
> >>   drivers/block/nbd.c | 17 +++++++++--------
> >>   1 file changed, 9 insertions(+), 8 deletions(-)
> >>
> >> diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c
> >> index 78181908f0df..83070714888b 100644
> >> --- a/drivers/block/nbd.c
> >> +++ b/drivers/block/nbd.c
> >> @@ -395,16 +395,19 @@ static enum blk_eh_timer_return
> >> nbd_xmit_timeout(struct request *req,
> >>       }
> >>       config = nbd->config;
> >>   -    if (config->num_connections > 1) {
> >> +    if (config->num_connections > 1 ||
> >> +        (config->num_connections == 1 && nbd->tag_set.timeout)) {
> >
> > This is every connection, do you mean to couple this with
> > dead_conn_timeout? Thanks,
> >

Except this case tag_set.timeout==0 and num_connections == 1. As Mike
said below.

Regards.
Hou.

>
> In
>
> commit 2da22da573481cc4837e246d0eee4d518b3f715e
> Author: Mike Christie <mchristi@redhat.com>
> Date:   Tue Aug 13 11:39:52 2019 -0500
>
>     nbd: fix zero cmd timeout handling v2
>
> we can set tag_set.timeout=0 again.
>
> So if timeout != 0 and num_connections = 1, we requeue here and let
> nbd_handle_cmd->wait_for_reconnect decide to wait or fail the command if
> dead_conn_timeout is not set.
>
> If timeout = 0, then we give it more time because it might have just
> been a slow server or connection. I think this behavior is wrong for the
> case Hou is fixing. See comment in the next patch.
>

Yes. While we are waiting for a slow connection, we also take care if the
socket is reconfigured.

Regards.
Hou.