Re: [PATCH 04/16] virtio-blk: use virtqueue_start_buf on bio path

[Asias He <asias@redhat.com>]

On 02/19/2013 03:56 PM, Rusty Russell wrote:
> (This is a respin of Paolo Bonzini's patch, but it calls
> virtqueue_add_sgs() instead of his multi-part API).
> 
> Move the creation of the request header and response footer to
> __virtblk_add_req.  vbr->sg only contains the data scatterlist,
> the header/footer are added separately using virtqueue_add_sgs().
> 
> With this change, virtio-blk (with use_bio) is not relying anymore on
> the virtio functions ignoring the end markers in a scatterlist.
> The next patch will do the same for the other path.
> 
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

(This subject needs to be changed to reflect using of virtqueue_add_sgs)


> ---
>  drivers/block/virtio_blk.c |   58 ++++++++++++++++++++++----------------------
>  1 file changed, 29 insertions(+), 29 deletions(-)
> 
> diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
> index fd8a689..e27bc6c 100644
> --- a/drivers/block/virtio_blk.c
> +++ b/drivers/block/virtio_blk.c
> @@ -62,6 +62,7 @@ struct virtblk_req
>  	struct virtio_blk *vblk;
>  	int flags;
>  	u8 status;
> +	int nents;
>  	struct scatterlist sg[];
>  };
>  
> @@ -100,24 +101,36 @@ static inline struct virtblk_req *virtblk_alloc_req(struct virtio_blk *vblk,
>  	return vbr;
>  }
>  
> -static inline int __virtblk_add_req(struct virtqueue *vq,
> -			     struct virtblk_req *vbr,
> -			     unsigned long out,
> -			     unsigned long in)
> +static int __virtblk_add_req(struct virtqueue *vq,
> +			     struct virtblk_req *vbr)
>  {
> -	return virtqueue_add_buf(vq, vbr->sg, out, in, vbr, GFP_ATOMIC);
> +	struct scatterlist hdr, tailer, *sgs[3];

'status' might be better than 'tailer'. We are using status in other
places.


> +	unsigned int num_out = 0, num_in = 0;
> +
> +	sg_init_one(&hdr, &vbr->out_hdr, sizeof(vbr->out_hdr));
> +	sgs[num_out++] = &hdr;
> +
> +	if (vbr->nents) {
> +		if (vbr->out_hdr.type & VIRTIO_BLK_T_OUT)
> +			sgs[num_out++] = vbr->sg;
> +		else
> +			sgs[num_out + num_in++] = vbr->sg;
> +	}
> +
> +	sg_init_one(&tailer, &vbr->status, sizeof(vbr->status));
> +	sgs[num_out + num_in++] = &tailer;
> +
> +	return virtqueue_add_sgs(vq, sgs, num_out, num_in, vbr, GFP_ATOMIC);
>  }
>  
> -static void virtblk_add_req(struct virtblk_req *vbr,
> -			    unsigned int out, unsigned int in)
> +static void virtblk_add_req(struct virtblk_req *vbr)
>  {
>  	struct virtio_blk *vblk = vbr->vblk;
>  	DEFINE_WAIT(wait);
>  	int ret;
>  
>  	spin_lock_irq(vblk->disk->queue->queue_lock);
> -	while (unlikely((ret = __virtblk_add_req(vblk->vq, vbr,
> -						 out, in)) < 0)) {
> +	while (unlikely((ret = __virtblk_add_req(vblk->vq, vbr)) < 0)) {
>  		prepare_to_wait_exclusive(&vblk->queue_wait, &wait,
>  					  TASK_UNINTERRUPTIBLE);
>  
> @@ -134,22 +147,18 @@ static void virtblk_add_req(struct virtblk_req *vbr,
>  
>  static void virtblk_bio_send_flush(struct virtblk_req *vbr)
>  {
> -	unsigned int out = 0, in = 0;
> -
>  	vbr->flags |= VBLK_IS_FLUSH;
>  	vbr->out_hdr.type = VIRTIO_BLK_T_FLUSH;
>  	vbr->out_hdr.sector = 0;
>  	vbr->out_hdr.ioprio = 0;
> -	sg_set_buf(&vbr->sg[out++], &vbr->out_hdr, sizeof(vbr->out_hdr));
> -	sg_set_buf(&vbr->sg[out + in++], &vbr->status, sizeof(vbr->status));
> +	vbr->nents = 0;
>  
> -	virtblk_add_req(vbr, out, in);
> +	virtblk_add_req(vbr);
>  }
>  
>  static void virtblk_bio_send_data(struct virtblk_req *vbr)
>  {
>  	struct virtio_blk *vblk = vbr->vblk;
> -	unsigned int num, out = 0, in = 0;
>  	struct bio *bio = vbr->bio;
>  
>  	vbr->flags &= ~VBLK_IS_FLUSH;
> @@ -157,24 +166,15 @@ static void virtblk_bio_send_data(struct virtblk_req *vbr)
>  	vbr->out_hdr.sector = bio->bi_sector;
>  	vbr->out_hdr.ioprio = bio_prio(bio);
>  
> -	sg_set_buf(&vbr->sg[out++], &vbr->out_hdr, sizeof(vbr->out_hdr));
> -
> -	num = blk_bio_map_sg(vblk->disk->queue, bio, vbr->sg + out);
> -
> -	sg_set_buf(&vbr->sg[num + out + in++], &vbr->status,
> -		   sizeof(vbr->status));
> -
> -	if (num) {
> -		if (bio->bi_rw & REQ_WRITE) {
> +	vbr->nents = blk_bio_map_sg(vblk->disk->queue, bio, vbr->sg);
> +	if (vbr->nents) {
> +		if (bio->bi_rw & REQ_WRITE)
>  			vbr->out_hdr.type |= VIRTIO_BLK_T_OUT;
> -			out += num;
> -		} else {
> +		else
>  			vbr->out_hdr.type |= VIRTIO_BLK_T_IN;
> -			in += num;
> -		}
>  	}
>  
> -	virtblk_add_req(vbr, out, in);
> +	virtblk_add_req(vbr);
>  }
>  
>  static void virtblk_bio_send_data_work(struct work_struct *work)
> 


Reviewed-by: Asias He <asias@redhat.com>

-- 
Asias