virtio-blk: allow toggling host cache between writeback and writethrough
This patch adds support for the new VIRTIO_BLK_F_CONFIG_WCE feature,
which exposes the cache mode in the configuration space and lets the
driver modify it. The cache mode is exposed via sysfs.
Even if the host does not support the new feature, the cache mode is
visible (thanks to the existing VIRTIO_BLK_F_WCE), but not modifiable.
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
diff --git a/include/linux/virtio_blk.h b/include/linux/virtio_blk.h
index e0edb40..e2aba15 100644
--- a/include/linux/virtio_blk.h
+++ b/include/linux/virtio_blk.h
@@ -37,8 +37,9 @@
#define VIRTIO_BLK_F_RO 5 /* Disk is read-only */
#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_FLUSH 9 /* Cache flush command support */
+#define VIRTIO_BLK_F_WCE 9 /* Writeback mode enabled after reset */
#define VIRTIO_BLK_F_TOPOLOGY 10 /* Topology information is available */
+#define VIRTIO_BLK_F_CONFIG_WCE 11 /* Writeback mode available in config */
#define VIRTIO_BLK_ID_BYTES 20 /* ID string length */
@@ -69,6 +70,8 @@
/* optimal sustained I/O size in logical blocks. */
__u32 opt_io_size;
+ /* writeback mode (if VIRTIO_BLK_F_CONFIG_WCE) */
+ __u8 wce;
} __attribute__((packed));
/*