[PATCH 4/6] virtio: VIRTIO_DEVICE_F_MASK for all per-device features

[Si-Wei Liu]

Introduce VIRTIO_DEVICE_F_MASK bitmask used for identification
of per-device features. Feature bits VIRTIO_TRANSPORT_F_START
through VIRTIO_TRANSPORT_F_END are reserved for transport
features hence are not counted as per-device features against
the 64bit feature space.

Signed-off-by: Si-Wei Liu <si-wei.liu@xxxxxxxxxx>
---
 include/uapi/linux/virtio_config.h | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/include/uapi/linux/virtio_config.h b/include/uapi/linux/virtio_config.h
index 3c05162..3bdc7ed 100644
--- a/include/uapi/linux/virtio_config.h
+++ b/include/uapi/linux/virtio_config.h
@@ -54,6 +54,14 @@
 #define VIRTIO_TRANSPORT_F_START	28
 #define VIRTIO_TRANSPORT_F_END		41
 
+/*
+ * Bitmask for all per-device features: feature bits VIRTIO_TRANSPORT_F_START
+ * through VIRTIO_TRANSPORT_F_END are unset, i.e. 0xfffffc000fffffff for
+ * all 64bit features
+ */
+#define VIRTIO_DEVICE_F_MASK (~0ULL << (VIRTIO_TRANSPORT_F_END + 1) | \
+			      ((1ULL << VIRTIO_TRANSPORT_F_START) - 1))
+
 #ifndef VIRTIO_CONFIG_NO_LEGACY
 /* Do we get callbacks when the ring is completely used, even if we've
  * suppressed them? */
-- 
1.8.3.1