Re: [PATCH 1/3] vhost: logging math fix
From: Juan Quintela <hidden>
Date: 2010-02-23 19:26:30
Also in:
kvm, lkml, virtualization
"Michael S. Tsirkin" [off-list ref] wrote:
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>
Reviewed-by: Juan Quintela <redacted>
quoted hunk
--- 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. */
We explain what smp_wmb() does.
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);
Once here, can we add a comment explaining _what_ are we trying to write to the log? michael explains that t is the used element and the index, but nothing states that.
if (vq->log_ctx) eventfd_signal(vq->log_ctx, 1); }