Merge remote-tracking branch 'kwolf/for-anthony' into staging

* kwolf/for-anthony: (38 commits)
  qemu-iotests: Fix test 031 for qcow2 v3 support
  qemu-iotests: Add -o and make v3 the default for qcow2
  qcow2: Zero write support
  qemu-iotests: Test backing file COW with zero clusters
  qemu-iotests: add a simple test for write_zeroes
  qcow2: Support for feature table header extension
  qcow2: Support reading zero clusters
  qcow2: Version 3 images
  qcow2: Ignore reserved bits in check_refcounts
  qcow2: Ignore reserved bits in refcount table entries
  qcow2: Simplify count_cow_clusters
  qcow2: Refactor qcow2_free_any_clusters
  qcow2: Ignore reserved bits in L1/L2 entries
  qcow2: Fail write_compressed when overwriting data
  qcow2: Ignore reserved bits in count_contiguous_clusters()
  qcow2: Ignore reserved bits in get_cluster_offset
  qcow2: Save disk size in snapshot header
  Specification for qcow2 version 3
  qcow2: Fix refcount block allocation during qcow2_alloc_cluster_at()
  iotests: Resolve test failures caused by hostname
  ...

diff --cc block/nbd.c
index e0af5b4,524c9cf..56dbf6e
--- 1/block/nbd.c
--- 2/block/nbd.c
+++ b/block/nbd.c
@@@ -203,12 -191,13 +203,12 @@@ static int nbd_co_send_request(BDRVNBDS
      qemu_co_mutex_lock(&s->send_mutex);
      s->send_coroutine = qemu_coroutine_self();
      qemu_aio_set_fd_handler(s->sock, nbd_reply_ready, nbd_restart_write,
-                             nbd_have_request, NULL, s);
+                             nbd_have_request, s);
      rc = nbd_send_request(s->sock, request);
 -    if (rc != -1 && iov) {
 +    if (rc >= 0 && iov) {
          ret = qemu_co_sendv(s->sock, iov, request->len, offset);
          if (ret != request->len) {
 -            errno = -EIO;
 -            rc = -1;
 +            return -EIO;
          }
      }
      qemu_aio_set_fd_handler(s->sock, nbd_reply_ready, NULL,