[PATCH 1/3] vhost: logging math fix

Michael S. Tsirkin
2010-02-23T16:57:43Z

vhost was dong some complex math to get
offset to log at, and got it wrong by a couple of bytes,
while in fact it's simple: get address where we write,
subtract start of buffer, add log base.

Do it this way.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
---
drivers/vhost/vhost.c | 10 ++++++----
1 files changed, 6 insertions(+), 4 deletions(-)

diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index 6eb1525..c767279 100644
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c
@@ -1004,10 +1004,12 @@ int vhost_add_used(struct vhost_virtqueue *vq, unsigned int head, int len)
if (unlikely(vq->log_used)) {
/* Make sure data is seen before log. */
smp_wmb();
- log_write(vq->log_base, vq->log_addr + sizeof *vq->used->ring *
- (vq->last_used_idx % vq->num),
- sizeof *vq->used->ring);
- log_write(vq->log_base, vq->log_addr, sizeof *vq->used->ring);
+ log_write(vq->log_base,
+ vq->log_addr + ((void *)used - (void *)vq->used),
+ sizeof *used);
+ log_write(vq->log_base,
+ vq->log_addr + offsetof(struct vring_used, idx),
+ sizeof vq->used->idx);
if (vq->log_ctx)
eventfd_signal(vq->log_ctx, 1);
}
--
1.7.0.18.g0d53a5