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

[Eric Blake]

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;
     }
-- 
2.20.1