NBD_CMD_CACHE carries no payload in either direction, yet the server
rejects any effect length above the advertised maximum payload size.
The specification explicitly allows the oversize request, and we
already accept it for NBD_CMD_TRIM and NBD_CMD_WRITE_ZEROES. Patch 2
drops the check.

The rest of the series adds tests/qemu-iotests/tests/nbd-commands, a
small client which speaks the NBD transmission phase itself. Nothing
in the tree does that today, so the protocol surface of the server -
reply modes, command flags, error codes, sparse and extended replies -
is covered only as far as our own client happens to exercise it. It is
useful both as coverage and as a regression tool.

Signed-off-by: Denis V. Lunev <den@openvz.org>
CC: Eric Blake <eblake@redhat.com>
CC: Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru>

Denis V. Lunev (5):
  iotests: add coverage for NBD transmission commands
  nbd/server: accept NBD_CMD_CACHE above the maximum payload size
  iotests/nbd-commands: exercise the simple and structured reply modes
  iotests/nbd-commands: cover NBD_CMD_BLOCK_STATUS with a payload
  iotests/nbd-commands: cover the command flags and sparse replies

 nbd/server.c                              |   4 +-
 tests/qemu-iotests/tests/nbd-commands     | 269 ++++++++++++++++++++++
 tests/qemu-iotests/tests/nbd-commands.out |   5 +
 3 files changed, 275 insertions(+), 3 deletions(-)
 create mode 100755 tests/qemu-iotests/tests/nbd-commands
 create mode 100644 tests/qemu-iotests/tests/nbd-commands.out


base-commit: bde2492aace2b5acb755a5b057013e915163a77f
-- 
2.53.0