diff options
| author | rusty <rusty@0c8fb4dd-22a2-4bb5-bc14-6c75a5f43652> | 2013-08-16 03:17:32 +0000 |
|---|---|---|
| committer | rusty <rusty@0c8fb4dd-22a2-4bb5-bc14-6c75a5f43652> | 2013-08-16 03:17:32 +0000 |
| commit | 49f2dca46e18e7dcf9c54663b6ed2b75b1803878 (patch) | |
| tree | e63580833993623f1538d77fae37039b5c4abbbe /virtio-spec.txt | |
| parent | 9d6033575f5a6129e2150e86d91cf32cbb2962ed (diff) | |
2.1.4 Virtqueues: Clarify vring_size() when VIRTIO_RING_F_EVENT_INDEX.
Ported from draft commit eb9fc84d0d3c46438aaab190e2401a9e5409a052.
Reported-by: Stefan Fritsch <sf@sfritsch.de>
Signed-off-by: Rusty Russell <rusty@au1.ibm.com>
git-svn-id: https://tools.oasis-open.org/version-control/svn/virtio@3 0c8fb4dd-22a2-4bb5-bc14-6c75a5f43652
Diffstat (limited to 'virtio-spec.txt')
| -rw-r--r-- | virtio-spec.txt | 11 |
1 files changed, 6 insertions, 5 deletions
diff --git a/virtio-spec.txt b/virtio-spec.txt index 6a3860e..864c663 100644 --- a/virtio-spec.txt +++ b/virtio-spec.txt @@ -179,11 +179,12 @@ required for the virtqueue according to the following formula: static inline unsigned vring_size(unsigned int qsz) { return ALIGN(sizeof(struct vring_desc)*qsz + sizeof(u16)*(2 + qsz)) - + ALIGN(sizeof(struct vring_used_elem)*qsz); + + ALIGN(sizeof(u16)*2 + sizeof(struct vring_used_elem)*qsz); } -This currently wastes some space with padding, but also allows -future extensions. The virtqueue layout structure looks like this: +This currently wastes some space with padding, but also allows future +extensions such as the VIRTIO_RING_F_EVENT_IDX extension. The +virtqueue layout structure looks like this: struct vring { // The actual descriptors (16 bytes each) @@ -314,7 +315,7 @@ entry (modulo the queue size). This starts at 0, and increases. u16 flags; u16 idx; u16 ring[ /* Queue Size */ ]; - u16 used_event; + u16 used_event; /* Only if VIRTIO_RING_F_EVENT_IDX */ }; 2.1.4.5 The Virtqueue Used Ring @@ -353,7 +354,7 @@ the buffer to ensure no data leakage occurs. u16 flags; u16 idx; struct vring_used_elem ring[ /* Queue Size */]; - u16 avail_event; + u16 avail_event; /* Only if VIRTIO_RING_F_EVENT_IDX */ }; 2.1.4.6 Helpers for Operating Virtqueues |