[PATCH v2] virtio_blk: VIRTIO_BLK_F_WCE->VIRTIO_BLK_F_FLUSH

[Michael S. Tsirkin]

Latest virtio spec says the feature bit name is VIRTIO_BLK_F_FLUSH,
VIRTIO_BLK_F_WCE is the legacy name.  virtio blk header says exactly the
reverse - fix that and update driver code to match.

Cc: Paolo Bonzini <pbonz...@redhat.com>
Signed-off-by: Michael S. Tsirkin <m...@redhat.com>
---

Changs from v1:
        comments updated

 include/uapi/linux/virtio_blk.h |  6 +++---
 drivers/block/virtio_blk.c      | 11 ++++++++---
 2 files changed, 11 insertions(+), 6 deletions(-)

diff --git a/include/uapi/linux/virtio_blk.h b/include/uapi/linux/virtio_blk.h
index 19c66fc..9ebe4d9 100644
--- a/include/uapi/linux/virtio_blk.h
+++ b/include/uapi/linux/virtio_blk.h
@@ -43,11 +43,11 @@
 #ifndef VIRTIO_BLK_NO_LEGACY
 #define VIRTIO_BLK_F_BARRIER   0       /* Does host support barriers? */
 #define VIRTIO_BLK_F_SCSI      7       /* Supports scsi command passthru */
-#define VIRTIO_BLK_F_WCE       9       /* Writeback mode enabled after reset */
+#define VIRTIO_BLK_F_FLUSH     9       /* Flush command supported */
 #define VIRTIO_BLK_F_CONFIG_WCE        11      /* Writeback mode available in 
config */
 #ifndef __KERNEL__
-/* Old (deprecated) name for VIRTIO_BLK_F_WCE. */
-#define VIRTIO_BLK_F_FLUSH VIRTIO_BLK_F_WCE
+/* Old (deprecated) name for VIRTIO_BLK_F_FLUSH. */
+#define VIRTIO_BLK_F_WCE VIRTIO_BLK_F_FLUSH
 #endif
 #endif /* !VIRTIO_BLK_NO_LEGACY */
 
diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
index 6ca3549..28cff0d 100644
--- a/drivers/block/virtio_blk.c
+++ b/drivers/block/virtio_blk.c
@@ -477,8 +477,13 @@ static int virtblk_get_cache_mode(struct virtio_device 
*vdev)
        err = virtio_cread_feature(vdev, VIRTIO_BLK_F_CONFIG_WCE,
                                   struct virtio_blk_config, wce,
                                   &writeback);
+
+       /*
+        * If WCE is not configurable and flush is not available,
+        * assume no writeback cache is in use.
+        */
        if (err)
-               writeback = virtio_has_feature(vdev, VIRTIO_BLK_F_WCE);
+               writeback = virtio_has_feature(vdev, VIRTIO_BLK_F_FLUSH);
 
        return writeback;
 }
@@ -833,14 +838,14 @@ static const struct virtio_device_id id_table[] = {
 static unsigned int features_legacy[] = {
        VIRTIO_BLK_F_SEG_MAX, VIRTIO_BLK_F_SIZE_MAX, VIRTIO_BLK_F_GEOMETRY,
        VIRTIO_BLK_F_RO, VIRTIO_BLK_F_BLK_SIZE, VIRTIO_BLK_F_SCSI,
-       VIRTIO_BLK_F_WCE, VIRTIO_BLK_F_TOPOLOGY, VIRTIO_BLK_F_CONFIG_WCE,
+       VIRTIO_BLK_F_FLUSH, VIRTIO_BLK_F_TOPOLOGY, VIRTIO_BLK_F_CONFIG_WCE,
        VIRTIO_BLK_F_MQ,
 }
 ;
 static unsigned int features[] = {
        VIRTIO_BLK_F_SEG_MAX, VIRTIO_BLK_F_SIZE_MAX, VIRTIO_BLK_F_GEOMETRY,
        VIRTIO_BLK_F_RO, VIRTIO_BLK_F_BLK_SIZE,
-       VIRTIO_BLK_F_WCE, VIRTIO_BLK_F_TOPOLOGY, VIRTIO_BLK_F_CONFIG_WCE,
+       VIRTIO_BLK_F_FLUSH, VIRTIO_BLK_F_TOPOLOGY, VIRTIO_BLK_F_CONFIG_WCE,
        VIRTIO_BLK_F_MQ,
 };
 
-- 
MST