[Libguestfs] [libnbd PATCH v3 4/7] disconnect: Allow shutdown during processing

[Richard W.M. Jones]

On Wed, May 22, 2019 at 04:29:04PM -0500, Eric Blake wrote:
> Although most of our synchronous commands are fine doing a round-robin
> for the first ready connection, and will leave the connection back in
> the ready state on conclusion, shutdown is a different beast. Once
> handshake has finished, we want a shutdown request to reach all
> connections, even if it has to be queued behind other commands already
> being processed on that connection.
> 
> In the future, we may want to consider a flags argument on whether to
> wait for the connection to have no in-flight commands, and/or to force
> a disconnect request to the front of the queue of commands to issue,
> depending on whether the client wants a fast shutdown vs. completion
> of outstanding requests to avoid data corruption.  The NBD spec
> recommends that NBD_CMD_DISC not be sent while any other commands are
> in flight, but similarly that a server should not shut down due to
> NBD_CMD_DISC until all other responses have been flushed. We may also
> want to update the state machine to track that once NBD_CMD_DISC has
> been sent, it is not valid to queue or send any further commands on
> that connection, even if it is still up to receive replies to previous
> in-flight commands.
> ---
>  lib/disconnect.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/lib/disconnect.c b/lib/disconnect.c
> index 9706835..0b8fea0 100644
> --- a/lib/disconnect.c
> +++ b/lib/disconnect.c
> @@ -31,7 +31,8 @@ nbd_unlocked_shutdown (struct nbd_handle *h)
>    size_t i;
> 
>    for (i = 0; i < h->multi_conn; ++i) {
> -    if (nbd_unlocked_aio_is_ready (h->conns[i])) {
> +    if (nbd_unlocked_aio_is_ready (h->conns[i]) ||
> +        nbd_unlocked_aio_is_processing (h->conns[i])) {
>        if (nbd_unlocked_aio_disconnect (h->conns[i]) == -1)
>          return -1;
>      }

ACK

Rich.

-- 
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