[RFC PATCH] virtio-blk: advertise F_WCE (F_FLUSH) if F_CONFIG_WCE is also advertised

[Evgeny Yakovlev]

Virtio spec 1.1 (and earlier), 5.2.5.1 Driver Requirements: Device
Initialization:

"Devices SHOULD always offer VIRTIO_BLK_F_FLUSH, and MUST offer it if
they offer VIRTIO_BLK_F_CONFIG_WCE.

It looks like currently F_CONFIG_WCE and F_WCE are not connected to each
other. qemu will advertise F_CONFIG_WCE if config-wce argument is
set for virtio-blk device. While F_WCE is advertised if underlying block
backend actually has it's caching enabled.
Those two things are not related to each other.

Signed-off-by: Evgeny Yakovlev <address@hidden>
---
 hw/block/virtio-blk.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/hw/block/virtio-blk.c b/hw/block/virtio-blk.c
index 1885160..b45dc0c 100644
--- a/hw/block/virtio-blk.c
+++ b/hw/block/virtio-blk.c
@@ -990,7 +990,8 @@ static uint64_t virtio_blk_get_features(VirtIODevice *vdev, 
uint64_t features,
         virtio_add_feature(&features, VIRTIO_BLK_F_SCSI);
     }
 
-    if (blk_enable_write_cache(s->blk)) {
+    if (blk_enable_write_cache(s->blk) ||
+        virtio_has_feature(features, VIRTIO_BLK_F_CONFIG_WCE)) {
         virtio_add_feature(&features, VIRTIO_BLK_F_WCE);
     }
     if (blk_is_read_only(s->blk)) {
-- 
2.7.4