Re: [RFC-V3 4/7] [net/9p] Add gup/zero_copy support to VirtIO transport layer.

["Aneesh Kumar K. V" <aneesh.kumar@linux.vnet.ibm.com>]

On Thu, 10 Feb 2011 17:25:08 -0800, "Venkateswararao Jujjuri (JV)" <jvrao@linux.vnet.ibm.com> wrote:
> Signed-off-by: Venkateswararao Jujjuri <jvrao@linux.vnet.ibm.com>
> ---
>  net/9p/trans_virtio.c |  107 ++++++++++++++++++++++++++++++++++++++++++++++---
>  1 files changed, 101 insertions(+), 6 deletions(-)
> 
> diff --git a/net/9p/trans_virtio.c b/net/9p/trans_virtio.c
> index c8f3f72..e0c301f 100644
> --- a/net/9p/trans_virtio.c
> +++ b/net/9p/trans_virtio.c
> @@ -45,6 +45,7 @@
>  #include <linux/scatterlist.h>
>  #include <linux/virtio.h>
>  #include <linux/virtio_9p.h>
> +#include "trans_common.h"
> 
>  #define VIRTQUEUE_NUM	128
> 
> @@ -155,6 +156,14 @@ static void req_done(struct virtqueue *vq)
>  					rc->tag);
>  			req = p9_tag_lookup(chan->client, rc->tag);
>  			req->status = REQ_STATUS_RCVD;
> +			if (req->tc->private) {
> +				struct trans_rpage_info *rp = req->tc->private;
> +				/*Release pages */
> +				p9_release_req_pages(rp);
> +				if (rp->rp_alloc)
> +					kfree(rp);
> +				req->tc->private = NULL;
> +			}
>  			p9_client_cb(chan->client, req);
>  		} else {
>  			spin_unlock_irqrestore(&chan->lock, flags);
> @@ -202,6 +211,30 @@ static int p9_virtio_cancel(struct p9_client *client, struct p9_req_t *req)
>  	return 1;
>  }
> 
> +static int
> +pack_sg_list_p(struct scatterlist *sg, int start, int limit, size_t pdata_off,
> +		struct page **pdata, int count)
> +{
> +	int s;
> +	int i = 0;
> +	int index = start;
> +
> +	if (pdata_off) {
> +		s = min((int)(PAGE_SIZE - pdata_off), count);
> +		sg_set_page(&sg[index++], pdata[i++], s, pdata_off);
> +		count -= s;
> +	}
> +
> +	while (count) {
> +		BUG_ON(index > limit);
> +		s = min((int)PAGE_SIZE, count);
> +		sg_set_page(&sg[index++], pdata[i++], s, 0);
> +		count -= s;
> +	}
> +
> +	return index-start;
> +}
> +
>  /**
>   * p9_virtio_request - issue a request
>   * @client: client instance issuing the request
> @@ -212,22 +245,82 @@ static int p9_virtio_cancel(struct p9_client *client, struct p9_req_t *req)
>  static int
>  p9_virtio_request(struct p9_client *client, struct p9_req_t *req)
>  {
> -	int in, out;
> +	int in, out, inp, outp;
>  	struct virtio_chan *chan = client->trans;
>  	char *rdata = (char *)req->rc+sizeof(struct p9_fcall);
>  	unsigned long flags;
> -	int err;
> +	size_t pdata_off = 0;
> +	struct trans_rpage_info *rpinfo = NULL;
> +	int err, pdata_len = 0;
> 
>  	P9_DPRINTK(P9_DEBUG_TRANS, "9p debug: virtio request\n");
> 
>  req_retry:
>  	req->status = REQ_STATUS_SENT;
> 
> +	if (req->tc->pbuf_size &&
> +			(req->tc->pubuf && !segment_eq(get_fs(), KERNEL_DS))) {
> +		int nr_pages = p9_nr_pages(req);
> +		int rpinfo_size = sizeof(struct trans_rpage_info) +
> +			sizeof(struct page *) * nr_pages;
> +
> +		if (rpinfo_size <= (req->tc->capacity - req->tc->size)) {
> +			/* We can use sdata */
> +			req->tc->private = req->tc->sdata + req->tc->size;
> +			rpinfo = (struct trans_rpage_info *)req->tc->private;
> +			rpinfo->rp_alloc = 0;
> +		} else {
> +			req->tc->private = kmalloc(rpinfo_size, GFP_KERNEL);
> +			rpinfo = (struct trans_rpage_info *)req->tc->private;
> +			rpinfo->rp_alloc = 1;
> +		}
> +
> +		err = p9_payload_gup(req, &pdata_off, &pdata_len, nr_pages,
> +				req->tc->id == P9_TREAD ? 1 : 0);
> +		if (err < 0) {
> +			if (rpinfo->rp_alloc)
> +				kfree(rpinfo);
> +			return err;
> +		}
> +	}
> +
>  	spin_lock_irqsave(&chan->lock, flags);
> -	out = pack_sg_list(chan->sg, 0, VIRTQUEUE_NUM, req->tc->sdata,
> -								req->tc->size);
> -	in = pack_sg_list(chan->sg, out, VIRTQUEUE_NUM-out, rdata,
> -								client->msize);
> +
> +	/* Handle out VirtIO ring buffers */
> +	if (req->tc->pbuf_size && (req->tc->id == P9_TWRITE)) {
> +		/* We have additional write payload buffer to take care */
> +		out = pack_sg_list(chan->sg, 0, VIRTQUEUE_NUM, req->tc->sdata,
> +				req->tc->size);
> +		outp = pack_sg_list_p(chan->sg, out, VIRTQUEUE_NUM,
> +				pdata_off, rpinfo->rp_data, pdata_len);
> +		out += outp;
> +	} else {
> +		out = pack_sg_list(chan->sg, 0, VIRTQUEUE_NUM, req->tc->sdata,
> +				req->tc->size);
> +	}

How about  ?

  out = pack_sg_list(chan->sg, 0, VIRTQUEUE_NUM, req->tc->sdata, req->tc->size);
  /*
   * We have additional write payload buffer to take care
   * in case of zero copy and the request is TWRITE
   */
   if (req->tc->pbuf_size && (req->tc->id == P9_TWRITE)) {
          outp = pack_sg_list_p(chan->sg, out, VIRTQUEUE_NUM,
				pdata_off, rpinfo->rp_data, pdata_len);
	  out += outp;
   }


> +
> +	/* Handle in VirtIO ring buffers */
> +	if (req->tc->pbuf_size && (req->tc->id == P9_TREAD)) {
> +		/* We have additional Read payload buffer to take care */
> +		inp = pack_sg_list(chan->sg, out, VIRTQUEUE_NUM, rdata, 11);
> +		/*
> +		 * Running executables in the filesystem may result in
> +		 * a read request with kernel buffer as opposed to user buffer.
> +		 */
> +		if (req->tc->pubuf && !segment_eq(get_fs(), KERNEL_DS)) {
> +			in = pack_sg_list_p(chan->sg, out+inp, VIRTQUEUE_NUM,
> +					pdata_off, rpinfo->rp_data, pdata_len);
> +		} else {
> +			char *pbuf = req->tc->pubuf ? req->tc->pubuf :
> +								req->tc->pkbuf;
> +			in = pack_sg_list(chan->sg, out, VIRTQUEUE_NUM,
> +					pbuf, req->tc->pbuf_size);
> +		}
> +		in += inp;
> +	} else {
> +		in = pack_sg_list(chan->sg, out, VIRTQUEUE_NUM, rdata,
> +				client->msize);
> +	}
> 
>  	err = virtqueue_add_buf(chan->vq, chan->sg, out, in, req->tc);
>  	if (err < 0) {
> @@ -246,6 +339,8 @@ req_retry:
>  			P9_DPRINTK(P9_DEBUG_TRANS,
>  					"9p debug: "
>  					"virtio rpc add_buf returned failure");
> +			if (rpinfo && rpinfo->rp_alloc)
> +				kfree(rpinfo);
>  			return -EIO;
>  		}
>  	}

-aneesh