[Qemu-devel] [PATCH 1/2] virtio-blk: support VIRTIO_BLK_F_CONFIG_WCE

[Paolo Bonzini <pbonzini@redhat.com>]

Introduce a new feature bit and configuration field that provide
support for toggling the cache mode between writethrough and writeback.

Also rename VIRTIO_BLK_F_WCACHE to VIRTIO_BLK_F_WCE for consistency with
the spec.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 hw/virtio-blk.c |   16 ++++++++++++++--
 hw/virtio-blk.h |    4 +++-
 2 files changed, 17 insertions(+), 3 deletions(-)

diff --git a/hw/virtio-blk.c b/hw/virtio-blk.c
index fe07746..280f96d 100644
--- a/hw/virtio-blk.c
+++ b/hw/virtio-blk.c
@@ -510,9 +510,19 @@ static void virtio_blk_update_config(VirtIODevice *vdev, uint8_t *config)
     blkcfg.size_max = 0;
     blkcfg.physical_block_exp = get_physical_block_exp(s->conf);
     blkcfg.alignment_offset = 0;
+    blkcfg.wce = bdrv_enable_write_cache(s->bs);
     memcpy(config, &blkcfg, sizeof(struct virtio_blk_config));
 }
 
+static void virtio_blk_set_config(VirtIODevice *vdev, const uint8_t *config)
+{
+    VirtIOBlock *s = to_virtio_blk(vdev);
+    struct virtio_blk_config blkcfg;
+
+    memcpy(&blkcfg, config, sizeof(blkcfg));
+    bdrv_set_enable_write_cache(s->bs, blkcfg.wce != 0);
+}
+
 static uint32_t virtio_blk_get_features(VirtIODevice *vdev, uint32_t features)
 {
     VirtIOBlock *s = to_virtio_blk(vdev);
@@ -523,9 +533,10 @@ static uint32_t virtio_blk_get_features(VirtIODevice *vdev, uint32_t features)
     features |= (1 << VIRTIO_BLK_F_BLK_SIZE);
     features |= (1 << VIRTIO_BLK_F_SCSI);
 
+    features |= (1 << VIRTIO_BLK_F_CONFIG_WCE);
     if (bdrv_enable_write_cache(s->bs))
-        features |= (1 << VIRTIO_BLK_F_WCACHE);
-    
+        features |= (1 << VIRTIO_BLK_F_WCE);
+
     if (bdrv_is_read_only(s->bs))
         features |= 1 << VIRTIO_BLK_F_RO;
 
@@ -615,6 +626,7 @@ VirtIODevice *virtio_blk_init(DeviceState *dev, VirtIOBlkConf *blk)
                                           sizeof(VirtIOBlock));
 
     s->vdev.get_config = virtio_blk_update_config;
+    s->vdev.set_config = virtio_blk_set_config;
     s->vdev.get_features = virtio_blk_get_features;
     s->vdev.reset = virtio_blk_reset;
     s->bs = blk->conf.bs;
diff --git a/hw/virtio-blk.h b/hw/virtio-blk.h
index d785001..afea114 100644
--- a/hw/virtio-blk.h
+++ b/hw/virtio-blk.h
@@ -31,8 +31,9 @@
 #define VIRTIO_BLK_F_BLK_SIZE   6       /* Block size of disk is available*/
 #define VIRTIO_BLK_F_SCSI       7       /* Supports scsi command passthru */
 /* #define VIRTIO_BLK_F_IDENTIFY   8       ATA IDENTIFY supported, DEPRECATED */
-#define VIRTIO_BLK_F_WCACHE     9       /* write cache enabled */
+#define VIRTIO_BLK_F_WCE        9       /* write cache enabled */
 #define VIRTIO_BLK_F_TOPOLOGY   10      /* Topology information is available */
+#define VIRTIO_BLK_F_CONFIG_WCE 11      /* write cache configurable */
 
 #define VIRTIO_BLK_ID_BYTES     20      /* ID string length */
 
@@ -49,6 +50,7 @@ struct virtio_blk_config
     uint8_t alignment_offset;
     uint16_t min_io_size;
     uint32_t opt_io_size;
+    uint8_t wce;
 } QEMU_PACKED;
 
 /* These two define direction. */
-- 
1.7.10.2