Not all subsystems use the fact that we may have the same _IOC_NR for
different _IOC_DIR, as in the end it'll result in a different ioctl
number.

So, for instance, vhost virtio has:

  #define VHOST_GET_FEATURES      _IOR(VHOST_VIRTIO, 0x00, __u64)
  #define VHOST_SET_FEATURES      _IOW(VHOST_VIRTIO, 0x00, __u64)

So same _IOC_NR (0x00) but different _IOC_DIR (R versus W), but it also
have:

  #define VHOST_SET_VRING_ENDIAN _IOW(VHOST_VIRTIO, 0x13, struct vhost_vring_state)
  #define VHOST_GET_VRING_ENDIAN _IOW(VHOST_VIRTIO, 0x14, struct vhost_vring_state)

A "get" operation that uses a "W" _IOC_DIR, and its implementation, uses
copy_to_user, it should've probably been _IOR().

Then:

  /* Base value where queue looks for available descriptors */
  #define VHOST_SET_VRING_BASE _IOW(VHOST_VIRTIO, 0x12, struct vhost_vring_state)
  /* Get accessor: reads index, writes value in num */
  #define VHOST_GET_VRING_BASE _IOWR(VHOST_VIRTIO, 0x12, struct vhost_vring_state)

So we'll need to use _IOC_DIR() to disambiguate the VHOST_VIRTIO ioctl
bautifier.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Radim Krčmář <rkrcmar@redhat.com>
Cc: Wang Nan <wangnan0@huawei.com>
Link: http://lkml.kernel.org/n/tip-rq6q717ql7j2z7kuccafgq84@git.kernel.org


Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>