Re: [Qemu-devel] [PATCH 1/3] virtio: introduce virtqueue_unmap_sg()

[Jason Wang <jasowang@redhat.com>]

On 09/25/2015 12:19 AM, Andrew James wrote:
> On 09/18/2015 02:01 AM, Jason Wang wrote:
>> > Factor out sg unmapping logic. This will be reused by the patch that
>> > can discard descriptor.
>> > 
>> > Cc: Michael S. Tsirkin <mst@redhat.com>
>> > Signed-off-by: Jason Wang <jasowang@redhat.com>
>> > ---
>> >  hw/virtio/virtio.c | 15 ++++++++++-----
>> >  1 file changed, 10 insertions(+), 5 deletions(-)
>> > 
>> > diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c
>> > index 0832db9..eb8d5ca 100644
>> > --- a/hw/virtio/virtio.c
>> > +++ b/hw/virtio/virtio.c
>> > @@ -243,15 +243,12 @@ int virtio_queue_empty(VirtQueue *vq)
>> >      return vring_avail_idx(vq) == vq->last_avail_idx;
>> >  }
>> >  
>> > -void virtqueue_fill(VirtQueue *vq, const VirtQueueElement *elem,
>> > -                    unsigned int len, unsigned int idx)
>> > +static void virtqueue_unmap_sg(VirtQueue *vq, const VirtQueueElement *elem,
>> > +                               unsigned int len)
>> >  {
>> >      unsigned int offset;
>> >      int i;
>> >  
>> > -    trace_virtqueue_fill(vq, elem, len, idx);
>> > -
>> > -    offset = 0;
>> >      for (i = 0; i < elem->in_num; i++) {
>> >          size_t size = MIN(len - offset, elem->in_sg[i].iov_len);
>> >  
> Should the "offset = 0" really be dropped here? 

Probably not.

> Seems like it ends
> up uninitialized. GCC thinks it might too.
>

Yes, will keep the offset initialization in V2.

Thanks