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Subject[RFC 1/3] virtio_ring: define flags as shifts consistently
Date
Introduce _SPLIT_ and/or _PACKED_ variants for VRING_DESC_F_*,
VRING_AVAIL_F_NO_INTERRUPT and VRING_USED_F_NO_NOTIFY. These
variants are defined as shifts instead of shifted values for
consistency with other _F_ flags.

Suggested-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Tiwei Bie <tiwei.bie@intel.com>
---
include/uapi/linux/virtio_ring.h | 57 ++++++++++++++++++++++----------
1 file changed, 40 insertions(+), 17 deletions(-)

diff --git a/include/uapi/linux/virtio_ring.h b/include/uapi/linux/virtio_ring.h
index 2414f8af26b3..9b0c0d92ab62 100644
--- a/include/uapi/linux/virtio_ring.h
+++ b/include/uapi/linux/virtio_ring.h
@@ -37,29 +37,52 @@
#include <linux/types.h>
#include <linux/virtio_types.h>

-/* This marks a buffer as continuing via the next field. */
+/*
+ * Notice: unlike other _F_ flags, below flags are defined as shifted
+ * values instead of shifts for compatibility.
+ */
+/* Same as VRING_SPLIT_DESC_F_NEXT. */
#define VRING_DESC_F_NEXT 1
-/* This marks a buffer as write-only (otherwise read-only). */
+/* Same as VRING_SPLIT_DESC_F_WRITE. */
#define VRING_DESC_F_WRITE 2
-/* This means the buffer contains a list of buffer descriptors. */
+/* Same as VRING_SPLIT_DESC_F_INDIRECT. */
#define VRING_DESC_F_INDIRECT 4
-
-/*
- * Mark a descriptor as available or used in packed ring.
- * Notice: they are defined as shifts instead of shifted values.
- */
-#define VRING_PACKED_DESC_F_AVAIL 7
-#define VRING_PACKED_DESC_F_USED 15
-
-/* The Host uses this in used->flags to advise the Guest: don't kick me when
- * you add a buffer. It's unreliable, so it's simply an optimization. Guest
- * will still kick if it's out of buffers. */
+/* Same as VRING_SPLIT_USED_F_NO_NOTIFY. */
#define VRING_USED_F_NO_NOTIFY 1
-/* The Guest uses this in avail->flags to advise the Host: don't interrupt me
- * when you consume a buffer. It's unreliable, so it's simply an
- * optimization. */
+/* Same as VRING_SPLIT_AVAIL_F_NO_INTERRUPT. */
#define VRING_AVAIL_F_NO_INTERRUPT 1

+/* Mark a buffer as continuing via the next field in split ring. */
+#define VRING_SPLIT_DESC_F_NEXT 0
+/* Mark a buffer as write-only (otherwise read-only) in split ring. */
+#define VRING_SPLIT_DESC_F_WRITE 1
+/* Mean the buffer contains a list of buffer descriptors in split ring. */
+#define VRING_SPLIT_DESC_F_INDIRECT 2
+
+/*
+ * The Host uses this in used->flags in split ring to advise the Guest:
+ * don't kick me when you add a buffer. It's unreliable, so it's simply
+ * an optimization. Guest will still kick if it's out of buffers.
+ */
+#define VRING_SPLIT_USED_F_NO_NOTIFY 0
+/*
+ * The Guest uses this in avail->flags in split ring to advise the Host:
+ * don't interrupt me when you consume a buffer. It's unreliable, so it's
+ * simply an optimization.
+ */
+#define VRING_SPLIT_AVAIL_F_NO_INTERRUPT 0
+
+/* Mark a buffer as continuing via the next field in packed ring. */
+#define VRING_PACKED_DESC_F_NEXT 0
+/* Mark a buffer as write-only (otherwise read-only) in packed ring. */
+#define VRING_PACKED_DESC_F_WRITE 1
+/* Mean the buffer contains a list of buffer descriptors in packed ring. */
+#define VRING_PACKED_DESC_F_INDIRECT 2
+
+/* Mark a descriptor as available or used in packed ring. */
+#define VRING_PACKED_DESC_F_AVAIL 7
+#define VRING_PACKED_DESC_F_USED 15
+
/* Enable events in packed ring. */
#define VRING_PACKED_EVENT_FLAG_ENABLE 0x0
/* Disable events in packed ring. */
--
2.17.1
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