[Libguestfs] [libnbd PATCH] opt_go: Tolerate unplanned server death

[Eric Blake]

While debugging some experimental nbdkit code that was triggering an
assertion failure in nbdkit, I noticed a secondary failure of nbdsh
also dying from an assertion:

libnbd: debug: nbdsh: nbd_opt_go: transition: NEWSTYLE.OPT_GO.SEND -> DEAD
libnbd: debug: nbdsh: nbd_opt_go: option queued, ignoring state machine failure
nbdsh: opt.c:86: nbd_unlocked_opt_go: Assertion `nbd_internal_is_state_negotiating (get_next_state (h))' failed.

Although my trigger was from non-production nbdkit code, libnbd should
never die from an assertion failure merely because a server
disappeared at the wrong moment during an incomplete reply to
NBD_OPT_GO or NBD_OPT_INFO.

Fixes: bbf1c51392 (api: Give aio_opt_go a completion callback)
---
 lib/opt.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/lib/opt.c b/lib/opt.c
index 2317b72..e5802f4 100644
--- a/lib/opt.c
+++ b/lib/opt.c
@@ -1,5 +1,5 @@
 /* NBD client library in userspace
- * Copyright (C) 2020 Red Hat Inc.
+ * Copyright (C) 2020-2021 Red Hat Inc.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Lesser General Public
@@ -83,7 +83,8 @@ nbd_unlocked_opt_go (struct nbd_handle *h)

   r = wait_for_option (h);
   if (r == 0 && err) {
-    assert (nbd_internal_is_state_negotiating (get_next_state (h)));
+    assert (nbd_internal_is_state_negotiating (get_next_state (h)) ||
+            nbd_internal_is_state_dead (get_next_state (h)));
     set_error (err, "server replied with error to opt_go request");
     return -1;
   }
@@ -105,7 +106,8 @@ nbd_unlocked_opt_info (struct nbd_handle *h)

   r = wait_for_option (h);
   if (r == 0 && err) {
-    assert (nbd_internal_is_state_negotiating (get_next_state (h)));
+    assert (nbd_internal_is_state_negotiating (get_next_state (h)) ||
+            nbd_internal_is_state_dead (get_next_state (h)));
     set_error (err, "server replied with error to opt_info request");
     return -1;
   }
-- 
2.30.1