Merge tag 'pull-nbd-2023-09-07-v2' of https://repo.or.cz/qemu/ericb into staging

NBD patches for 2023-09-07

- Andrey Drobyshev - fix regression in iotest 197 under -nbd
- Stefan Hajnoczi - allow coroutine read and write context to split
across threads
- Philippe Mathieu-Daudé - remove a VLA allocation
- Denis V. Lunev - fix regression in iotest 233 with qemu-nbd -v --fork

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* tag 'pull-nbd-2023-09-07-v2' of https://repo.or.cz/qemu/ericb:
  qemu-nbd: document -v behavior in respect to --fork in man
  qemu-nbd: Restore "qemu-nbd -v --fork" output
  qemu-nbd: invent nbd_client_release_pipe() helper
  qemu-nbd: put saddr into into struct NbdClientOpts
  qemu-nbd: move srcpath into struct NbdClientOpts
  qemu-nbd: define struct NbdClientOpts when HAVE_NBD_DEVICE is not defined
  qemu-nbd: improve error message for dup2 error
  util/iov: Avoid dynamic stack allocation
  io: follow coroutine AioContext in qio_channel_yield()
  io: check there are no qio_channel_yield() coroutines during ->finalize()
  nbd: drop unused nbd_start_negotiate() aio_context argument
  nbd: drop unused nbd_receive_negotiate() aio_context argument
  qemu-iotests/197: use more generic commands for formats other than qcow2

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>