virtio: add feature checking helpers

Add a helper function for checking whether a bit is set in the guest
features for a vdev as well as one that works on a feature bit set.

Convert code that open-coded this: It cleans up the code and makes it
easier to extend the guest feature bits.

Signed-off-by: Cornelia Huck <cornelia.huck@de.ibm.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

1 files changed, 2 insertions, 5 deletions

diff --git a/hw/block/virtio-blk.c b/hw/block/virtio-blk.c
index 6decebf..1e5b918 100644
--- a/hw/block/virtio-blk.c
+++ b/hw/block/virtio-blk.c
@@ -733,7 +733,6 @@ static uint32_t virtio_blk_get_features(VirtIODevice *vdev, uint32_t features)
 static void virtio_blk_set_status(VirtIODevice *vdev, uint8_t status)
 {
     VirtIOBlock *s = VIRTIO_BLK(vdev);
-    uint32_t features;
 
     if (s->dataplane && !(status & (VIRTIO_CONFIG_S_DRIVER |
                                     VIRTIO_CONFIG_S_DRIVER_OK))) {
@@ -744,8 +743,6 @@ static void virtio_blk_set_status(VirtIODevice *vdev, uint8_t status)
         return;
     }
 
-    features = vdev->guest_features;
-
     /* A guest that supports VIRTIO_BLK_F_CONFIG_WCE must be able to send
      * cache flushes.  Thus, the "auto writethrough" behavior is never
      * necessary for guests that support the VIRTIO_BLK_F_CONFIG_WCE feature.
@@ -761,10 +758,10 @@ static void virtio_blk_set_status(VirtIODevice *vdev, uint8_t status)
      *
      * s->blk would erroneously be placed in writethrough mode.
      */
-    if (!(features & (1 << VIRTIO_BLK_F_CONFIG_WCE))) {
+    if (!virtio_has_feature(vdev, VIRTIO_BLK_F_CONFIG_WCE)) {
         aio_context_acquire(blk_get_aio_context(s->blk));
         blk_set_enable_write_cache(s->blk,
-                                   !!(features & (1 << VIRTIO_BLK_F_WCE)));
+                                   virtio_has_feature(vdev, VIRTIO_BLK_F_WCE));
         aio_context_release(blk_get_aio_context(s->blk));
     }
 }