Linux Virtualization - Apr 2020 - [PATCH v8 09/19] virtio: stop using legacy struct vring in kernel

struct vring (in the uapi directory) and supporting APIs are kept
around to solely avoid breaking old userspace builds.
It's not actually part of the UAPI - it was kept in the UAPI
header by mistake, and using it in kernel isn't necessary
and prevents us from making changes safely.
In particular, the APIs actually assume the legacy layout.

Add an internal kernel-only struct vring and
switch everyone to use that.

Signed-off-by: Michael S. Tsirkin <mst at redhat.com>
---
 drivers/block/virtio_blk.c       |  1 +
 include/linux/virtio.h           |  1 -
 include/linux/virtio_ring.h      | 10 ++++++++++
 include/linux/vringh.h           |  1 +
 include/uapi/linux/virtio_ring.h | 26 ++++++++++++++++----------
 5 files changed, 28 insertions(+), 11 deletions(-)

diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
index 0736248999b0..dd5732dc4b07 100644
--- a/drivers/block/virtio_blk.c
+++ b/drivers/block/virtio_blk.c
@@ -15,6 +15,7 @@
 #include <linux/blk-mq.h>
 #include <linux/blk-mq-virtio.h>
 #include <linux/numa.h>
+#include <uapi/linux/virtio_ring.h>
 
 #define PART_BITS 4
 #define VQ_NAME_LEN 16
diff --git a/include/linux/virtio.h b/include/linux/virtio.h
index 15f906e4a748..a493eac08393 100644
--- a/include/linux/virtio.h
+++ b/include/linux/virtio.h
@@ -9,7 +9,6 @@
 #include <linux/device.h>
 #include <linux/mod_devicetable.h>
 #include <linux/gfp.h>
-#include <linux/vringh.h>
 
 /**
  * virtqueue - a queue to register buffers for sending or receiving.
diff --git a/include/linux/virtio_ring.h b/include/linux/virtio_ring.h
index 3dc70adfe5f5..11680e74761a 100644
--- a/include/linux/virtio_ring.h
+++ b/include/linux/virtio_ring.h
@@ -60,6 +60,16 @@ static inline void virtio_store_mb(bool weak_barriers,
 struct virtio_device;
 struct virtqueue;
 
+struct vring {
+	unsigned int num;
+
+	struct vring_desc *desc;
+
+	struct vring_avail *avail;
+
+	struct vring_used *used;
+};
+
 /*
  * Creates a virtqueue and allocates the descriptor ring.  If
  * may_reduce_num is set, then this may allocate a smaller ring than
diff --git a/include/linux/vringh.h b/include/linux/vringh.h
index 9e2763d7c159..d71b3710f58e 100644
--- a/include/linux/vringh.h
+++ b/include/linux/vringh.h
@@ -11,6 +11,7 @@
 #ifndef _LINUX_VRINGH_H
 #define _LINUX_VRINGH_H
 #include <uapi/linux/virtio_ring.h>
+#include <linux/virtio_ring.h>
 #include <linux/virtio_byteorder.h>
 #include <linux/uio.h>
 #include <linux/slab.h>
diff --git a/include/uapi/linux/virtio_ring.h b/include/uapi/linux/virtio_ring.h
index 9223c3a5c46a..8961a4adda5c 100644
--- a/include/uapi/linux/virtio_ring.h
+++ b/include/uapi/linux/virtio_ring.h
@@ -118,16 +118,6 @@ struct vring_used {
 	struct vring_used_elem ring[];
 };
 
-struct vring {
-	unsigned int num;
-
-	struct vring_desc *desc;
-
-	struct vring_avail *avail;
-
-	struct vring_used *used;
-};
-
 /* Alignment requirements for vring elements.
  * When using pre-virtio 1.0 layout, these fall out naturally.
  */
@@ -166,6 +156,21 @@ struct vring {
 #define vring_used_event(vr) ((vr)->avail->ring[(vr)->num])
 #define vring_avail_event(vr) (*(__virtio16
*)&(vr)->used->ring[(vr)->num])
 
+#ifndef __KERNEL__
+/*
+ * The following definitions have been put in the UAPI header by mistake. We
+ * keep them around to avoid breaking old userspace builds.
+ */
+struct vring {
+	unsigned int num;
+
+	struct vring_desc *desc;
+
+	struct vring_avail *avail;
+
+	struct vring_used *used;
+};
+
 static inline void vring_init(struct vring *vr, unsigned int num, void *p,
 			      unsigned long align)
 {
@@ -182,6 +187,7 @@ static inline unsigned vring_size(unsigned int num, unsigned
long align)
 		 + align - 1) & ~(align - 1))
 		+ sizeof(__virtio16) * 3 + sizeof(struct vring_used_elem) * num;
 }
+#endif
 
 #endif /* VIRTIO_RING_NO_LEGACY */
 
-- 
MST

On Mon, Apr 06, 2020 at 09:16:46PM -0400, Michael S. Tsirkin
wrote:
> struct vring (in the uapi directory) and supporting APIs are kept
> around to solely avoid breaking old userspace builds.
> It's not actually part of the UAPI - it was kept in the UAPI
> header by mistake, and using it in kernel isn't necessary
> and prevents us from making changes safely.
> In particular, the APIs actually assume the legacy layout.
> 
> Add an internal kernel-only struct vring and
> switch everyone to use that.
> 
> Signed-off-by: Michael S. Tsirkin <mst at redhat.com>
> ---
>  drivers/block/virtio_blk.c       |  1 +
>  include/linux/virtio.h           |  1 -
>  include/linux/virtio_ring.h      | 10 ++++++++++
>  include/linux/vringh.h           |  1 +
>  include/uapi/linux/virtio_ring.h | 26 ++++++++++++++++----------
>  5 files changed, 28 insertions(+), 11 deletions(-)
Reviewed-by: Stefan Hajnoczi <stefanha at redhat.com>
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