diff options
Diffstat (limited to 'include/linux/virtio_ring.h')
| -rw-r--r-- | include/linux/virtio_ring.h | 14 |
1 files changed, 14 insertions, 0 deletions
diff --git a/include/linux/virtio_ring.h b/include/linux/virtio_ring.h index c4eef73deb3f..4a32cb6da425 100644 --- a/include/linux/virtio_ring.h +++ b/include/linux/virtio_ring.h @@ -146,6 +146,20 @@ static inline unsigned vring_size(unsigned int num, unsigned long align) + sizeof(__u16) * 3 + sizeof(struct vring_used_elem) * num; } +/* The following is used with USED_EVENT_IDX and AVAIL_EVENT_IDX */ +/* Assuming a given event_idx value from the other size, if + * we have just incremented index from old to new_idx, + * should we trigger an event? */ +static inline int vring_need_event(__u16 event_idx, __u16 new_idx, __u16 old) +{ + /* Note: Xen has similar logic for notification hold-off + * in include/xen/interface/io/ring.h with req_event and req_prod + * corresponding to event_idx + 1 and new_idx respectively. + * Note also that req_event and req_prod in Xen start at 1, + * event indexes in virtio start at 0. */ + return (__u16)(new_idx - event_idx - 1) < (__u16)(new_idx - old); +} + #ifdef __KERNEL__ #include <linux/irqreturn.h> struct virtio_device; |