Re: [PATCH] virtio: fix size computation according to the definitionof struct vring_used in vring_size
From: Wang Sheng-Hui
Date: Mon Aug 29 2011 - 03:56:20 EST
On 2011å08æ29æ 10:53, Rusty Russell wrote:
> On Sat, 27 Aug 2011 17:52:02 +0800, Wang Sheng-Hui <shhuiw@xxxxxxxxx> wrote:
>> On 2011å08æ27æ 17:34, Wang Sheng-Hui wrote:
>> 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));
>> }
>
> This + 16 should be + sizeof(__u16), right? It's just the
> used_event_idx which has been added:
>
> * __u16 available[num];
> * __u16 used_event_idx;
> *
> * // Padding to the next align boundary.
> * char pad[];
> *
> * [USED]
>
>> 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;
>
> This is correct.
>
> And, yes, since align is always 4096, it's currently just a cleanup, but
> it makes things much less confusing!
>
> Thanks,
> Rusty.
Patch regerated to use sizeof(__u16) instead of 16 in vring_init.
Please check it.
[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 <shhuiw@xxxxxxxxx>
---
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..2a731bd 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] + sizeof(__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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