Re: [PATCH] virtio: fix size computation according to the definition of struct vring_used in vring_size

On 2011年08月28日 19:31, Michael S. Tsirkin wrote:

On Sat, Aug 27, 2011 at 05:52:02PM +0800, Wang Sheng-Hui wrote:

quoted

On 2011年08月27日 17:34, Wang Sheng-Hui wrote:

quoted

On 2011年08月27日 10:49, Wanlong Gao wrote:

quoted

On Sat, 2011-08-27 at 09:07 +0800, Wang Sheng-Hui wrote:

quoted

The patch is against 3.1-rc3.

struct vring_used has two __u16 fields plus array of struct vring_used_elem.
Current vring_size counts the __u16 fields to 3. Fix it to 2 in the patch.

Signed-off-by: Wang Sheng-Hui <redacted>
---
 include/linux/virtio_ring.h |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/include/linux/virtio_ring.h b/include/linux/virtio_ring.h
index 4a32cb6..fcda152 100644
--- a/include/linux/virtio_ring.h
+++ b/include/linux/virtio_ring.h

@@ -143,7 +143,7 @@ static inline unsigned vring_size(unsigned int num, unsigned long align)
 {
 	return ((sizeof(struct vring_desc) * num + sizeof(__u16) * (2 + num)
 		 + align - 1) & ~(align - 1))
-		+ sizeof(__u16) * 3 + sizeof(struct vring_used_elem) * num;
+		+ sizeof(__u16) * 2 + sizeof(struct vring_used_elem) * num;
 }
 
 /* The following is used with USED_EVENT_IDX and AVAIL_EVENT_IDX */

Hi:
I'm not deep into it, but I think you can see this:
http://marc.info/?l=git-commits-head&m=130687915816130&w=2

Thanks
-Wanlong Gao

Thanks.

I checked the comments, and think we should patch vring_init
and vring_size according to the layout description in the comments.
Right?

New patch generated. Please check it. Thanks,

quoted

[PATCH] virtio: modify vring_init and vring_size to take account of the layout containing *_event_idx

The patch is against 3.1-rc3.

Based on the layout description in the comments, take account of
the *_event_idx in functions vring_init and vring_size.

Signed-off-by: Wang Sheng-Hui <redacted>

Is this a bugfix or just a cleanup?
Alignment makes us get the same values with and without, right?

It's just a cleanup.
For normal case, the value 16 is too small compared with
the alignment, I think.

quoted

---
 include/linux/virtio_ring.h |    6 +++---
 1 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/include/linux/virtio_ring.h b/include/linux/virtio_ring.h
index 4a32cb6..300af76 100644
--- a/include/linux/virtio_ring.h
+++ b/include/linux/virtio_ring.h

@@ -135,13 +135,13 @@ static inline void vring_init(struct vring *vr, unsigned int num, void *p,
 	vr->num = num;
 	vr->desc = p;
 	vr->avail = p + num*sizeof(struct vring_desc);
-	vr->used = (void *)(((unsigned long)&vr->avail->ring[num] + align-1)
-			    & ~(align - 1));
+	vr->used = (void *)(((unsigned long)&vr->avail->ring[num] + 16
+		+ align-1) & ~(align - 1));
 }
 
 static inline unsigned vring_size(unsigned int num, unsigned long align)
 {
-	return ((sizeof(struct vring_desc) * num + sizeof(__u16) * (2 + num)
+	return ((sizeof(struct vring_desc) * num + sizeof(__u16) * (3 + num)
 		 + align - 1) & ~(align - 1))
 		+ sizeof(__u16) * 3 + sizeof(struct vring_used_elem) * num;
 }

-- 
1.7.1

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