vhost-net: cleanup macros for DMA status tracking

Better document macros for DMA tracking. Add an
explicit one for DMA in progress instead of
relying on user supplying len != 1.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 9 insertions, 3 deletions

diff --git a/drivers/vhost/vhost.h b/drivers/vhost/vhost.h
index 2de4ce2fec40..b6538eef7468 100644
--- a/drivers/vhost/vhost.h
+++ b/drivers/vhost/vhost.h
@@ -13,9 +13,15 @@
 #include <linux/virtio_ring.h>
 #include <linux/atomic.h>
 
-/* This is for zerocopy, used buffer len is set to 1 when lower device DMA
- * done */
-#define VHOST_DMA_DONE_LEN      1
+/*
+ * For transmit, used buffer len is unused; we override it to track buffer
+ * status internally; used for zerocopy tx only.
+ */
+/* Lower device DMA done */
+#define VHOST_DMA_DONE_LEN      2
+/* Lower device DMA in progress */
+#define VHOST_DMA_IN_PROGRESS   1
+/* Buffer unused */
 #define VHOST_DMA_CLEAR_LEN     0
 
 struct vhost_device;