qemu-nbd: Allow users to adjust handshake limit

Although defaulting the handshake limit to 10 seconds was a nice QoI
change to weed out intentionally slow clients, it can interfere with
integration testing done with manual NBD_OPT commands over 'nbdsh
--opt-mode'.  Expose a command line option to allow the user to alter
the timeout away from the default.  This option is unlikely to be used
in enough scenarios to warrant a short option letter.

The option --handshake-limit intentionally differs from the name of
the constant added in commit fb1c2aaa98 (limit instead of max_secs)
and the QMP name to be added in the next commit; this is because
typing a longer command-line name is undesirable and there is
sufficient --help text to document the units.

Signed-off-by: Eric Blake <eblake@redhat.com>
Message-ID: <20250203222722.650694-5-eblake@redhat.com>
Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru>

1 files changed, 5 insertions, 0 deletions

diff --git a/docs/tools/qemu-nbd.rst b/docs/tools/qemu-nbd.rst
index 4f21b7904a..f82ea5fd77 100644
--- a/docs/tools/qemu-nbd.rst
+++ b/docs/tools/qemu-nbd.rst
@@ -156,6 +156,11 @@ driver options if :option:`--image-opts` is specified.
   Set the NBD volume export description, as a human-readable
   string.
 
+.. option:: --handshake-limit=N
+
+  Set the timeout for a client to successfully complete its handshake
+  to N seconds (default 10), or 0 for no limit.
+
 .. option:: -L, --list
 
   Connect as a client and list all details about the exports exposed by