On Fri, Nov 30, 2018 at 11:37:37PM +0800, Tiwei Bie wrote:

On Fri, Nov 30, 2018 at 08:52:42AM -0500, Michael S. Tsirkin wrote:

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On Fri, Nov 30, 2018 at 02:01:06PM +0100, Maxime Coquelin wrote:

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On 11/30/18 1:47 PM, Michael S. Tsirkin wrote:

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On Fri, Nov 30, 2018 at 05:53:40PM +0800, Tiwei Bie wrote:

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On Fri, Nov 30, 2018 at 04:10:55PM +0800, Jason Wang wrote:

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On 2018/11/21 下午6:03, Tiwei Bie wrote:

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Add types and macros for packed ring.

Signed-off-by: Tiwei Bie <redacted>
---
   include/uapi/linux/virtio_config.h |  3 +++
   include/uapi/linux/virtio_ring.h   | 52 ++++++++++++++++++++++++++++++++++++++
   2 files changed, 55 insertions(+)

diff --git a/include/uapi/linux/virtio_config.h b/include/uapi/linux/virtio_config.h
index 449132c76b1c..1196e1c1d4f6 100644
--- a/include/uapi/linux/virtio_config.h
+++ b/include/uapi/linux/virtio_config.h

@@ -75,6 +75,9 @@
    */
   #define VIRTIO_F_IOMMU_PLATFORM		33
+/* This feature indicates support for the packed virtqueue layout. */
+#define VIRTIO_F_RING_PACKED		34
+
   /*
    * Does the device support Single Root I/O Virtualization?
    */

diff --git a/include/uapi/linux/virtio_ring.h b/include/uapi/linux/virtio_ring.h
index 6d5d5faa989b..2414f8af26b3 100644
--- a/include/uapi/linux/virtio_ring.h
+++ b/include/uapi/linux/virtio_ring.h

@@ -44,6 +44,13 @@
   /* This means the buffer contains a list of buffer descriptors. */
   #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.

This looks inconsistent to previous flags, any reason for using shifts?

Yeah, it was suggested to use shifts, as _F_ should be a bit
number, not a shifted value:

https://patchwork.ozlabs.org/patch/942296/#1989390

But let's add a _SPLIT_ variant that uses shifts consistently.

Maybe we could avoid adding SPLIT and PACKED, but define as follow:

#define VRING_DESC_F_INDIRECT_SHIFT 2
#define VRING_DESC_F_INDIRECT (1ull <<  VRING_DESC_F_INDIRECT_SHIFT)

#define VRING_DESC_F_AVAIL_SHIFT 7
#define VRING_DESC_F_AVAIL (1ull << VRING_DESC_F_AVAIL_SHIFT)

I think it would be better for consistency.

I don't think that will help. the problem is that
most of the existing virtio code consistently uses _F_ as shifts.
So we just need to do something about these 5 being inconsistent:

include/uapi/linux/virtio_ring.h:#define VRING_DESC_F_NEXT      1
include/uapi/linux/virtio_ring.h:#define VRING_DESC_F_WRITE     2
include/uapi/linux/virtio_ring.h:#define VRING_DESC_F_INDIRECT  4
include/uapi/linux/virtio_ring.h:#define VRING_USED_F_NO_NOTIFY 1
include/uapi/linux/virtio_ring.h:#define VRING_AVAIL_F_NO_INTERRUPT     1

I do not want all of virtio to become verbose with _SHIFT, ergo
we need to change the above 5 to have names which are with _F_ and
have the bit number.

How about something like this:

#define VRING_COMM_DESC_F_NEXT			0
#define VRING_COMM_DESC_F_WRITE			1
#define VRING_COMM_DESC_F_INDIRECT		2

#define VRING_SPLIT_USED_F_NO_NOTIFY		0
#define VRING_SPLIT_AVAIL_F_NO_INTERRUPT	0

or

#define VRING_SPLIT_DESC_F_NEXT			0
#define VRING_SPLIT_DESC_F_WRITE		1
#define VRING_SPLIT_DESC_F_INDIRECT		2

#define VRING_SPLIT_USED_F_NO_NOTIFY		0
#define VRING_SPLIT_AVAIL_F_NO_INTERRUPT	0

#define VRING_PACKED_DESC_F_NEXT		0
#define VRING_PACKED_DESC_F_WRITE		1
#define VRING_PACKED_DESC_F_INDIRECT		2

As we aren't sharing code I think I prefer the second form.
Maybe add VRING_NO_LEGACY so people can audit their code
for assumptions?

We also want to guard layout definitions at the end of that file
I think.

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+ */
+#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. */

@@ -53,6 +60,23 @@
    * optimization.  */
   #define VRING_AVAIL_F_NO_INTERRUPT	1
+/* Enable events in packed ring. */
+#define VRING_PACKED_EVENT_FLAG_ENABLE	0x0
+/* Disable events in packed ring. */
+#define VRING_PACKED_EVENT_FLAG_DISABLE	0x1
+/*
+ * Enable events for a specific descriptor in packed ring.
+ * (as specified by Descriptor Ring Change Event Offset/Wrap Counter).
+ * Only valid if VIRTIO_RING_F_EVENT_IDX has been negotiated.
+ */
+#define VRING_PACKED_EVENT_FLAG_DESC	0x2

Any reason for using _FLAG_ instead of _F_?

Yeah, it was suggested to not use _F_, as these are values,
should not have _F_:

https://patchwork.ozlabs.org/patch/942296/#1989390

Regards,
Tiwei

quoted

Thanks

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+
+/*
+ * Wrap counter bit shift in event suppression structure
+ * of packed ring.
+ */
+#define VRING_PACKED_EVENT_F_WRAP_CTR	15
+
   /* We support indirect buffer descriptors */
   #define VIRTIO_RING_F_INDIRECT_DESC	28

@@ -171,4 +195,32 @@ static inline int vring_need_event(__u16 event_idx, __u16 new_idx, __u16 old)
   	return (__u16)(new_idx - event_idx - 1) < (__u16)(new_idx - old);
   }
+struct vring_packed_desc_event {
+	/* Descriptor Ring Change Event Offset/Wrap Counter. */
+	__le16 off_wrap;
+	/* Descriptor Ring Change Event Flags. */
+	__le16 flags;
+};
+
+struct vring_packed_desc {
+	/* Buffer Address. */
+	__le64 addr;
+	/* Buffer Length. */
+	__le32 len;
+	/* Buffer ID. */
+	__le16 id;
+	/* The flags depending on descriptor type. */
+	__le16 flags;
+};
+
+struct vring_packed {
+	unsigned int num;
+
+	struct vring_packed_desc *desc;
+
+	struct vring_packed_desc_event *driver;
+
+	struct vring_packed_desc_event *device;
+};
+
   #endif /* _UAPI_LINUX_VIRTIO_RING_H */