[PATCH 3/5] [net/9p] Add support for placing page addresses directly on the sg list.

["Venkateswararao Jujjuri (JV)" <jvrao@linux.vnet.ibm.com>]

This patch adds necessary infrastructure for placing page addresses
directly on the sg list for the server to consume.

The newly added routine pack_sg_list_p() is just like pack_sg_list()
except that it takes page array as an input and directly places them on
the sg list after taking care of the first page offset.

Signed-off-by: Venkateswararao Jujjuri <jvrao@linux.vnet.ibm.com>
Signed-off-by: Badari Pulavarty <pbadari@us.ibm.com>
---
 include/net/9p/9p.h   |    6 ++++-
 net/9p/client.c       |    4 +++
 net/9p/trans_virtio.c |   59 ++++++++++++++++++++++++++++++++++++++++++++++--
 3 files changed, 65 insertions(+), 4 deletions(-)

diff --git a/include/net/9p/9p.h b/include/net/9p/9p.h
index a8de812..382ef22 100644
--- a/include/net/9p/9p.h
+++ b/include/net/9p/9p.h
@@ -651,7 +651,11 @@ struct p9_fcall {
 
 	size_t offset;
 	size_t capacity;
-
+	struct page **pdata;
+	uint32_t pdata_mapped_pages;
+	uint32_t pdata_off;
+	uint32_t pdata_write_len;
+	uint32_t pdata_read_len;
 	uint8_t *sdata;
 };
 
diff --git a/net/9p/client.c b/net/9p/client.c
index 29bbbbd..5487896 100644
--- a/net/9p/client.c
+++ b/net/9p/client.c
@@ -244,8 +244,12 @@ static struct p9_req_t *p9_tag_alloc(struct p9_client *c, u16 tag)
 		}
 		req->tc->sdata = (char *) req->tc + sizeof(struct p9_fcall);
 		req->tc->capacity = c->msize;
+		req->tc->pdata_write_len = 0;
+		req->tc->pdata_read_len = 0;
 		req->rc->sdata = (char *) req->rc + sizeof(struct p9_fcall);
 		req->rc->capacity = c->msize;
+		req->rc->pdata_write_len = 0;
+		req->rc->pdata_read_len = 0;
 	}
 
 	p9pdu_reset(req->tc);
diff --git a/net/9p/trans_virtio.c b/net/9p/trans_virtio.c
index 762c19f..8f86cb5 100644
--- a/net/9p/trans_virtio.c
+++ b/net/9p/trans_virtio.c
@@ -180,6 +180,44 @@ pack_sg_list(struct scatterlist *sg, int start, int limit, char *data,
 	return index-start;
 }
 
+/**
+ * pack_sg_list_p - Pack a scatter gather list from an array of pages.
+ * @sg: scatter/gather list to pack into
+ * @start: which segment of the sg_list to start at
+ * @limit: maximum segment to pack data to
+ * @pdu: pdu prepared to put on the wire.
+ * @count: amount of data to pack into the scatter/gather list
+ *
+ * This is just like pack_sg_list() except that it takes page array
+ * as an input and directly places them on the sg list after taking
+ * care of the first page offset.
+ */
+
+static int
+pack_sg_list_p(struct scatterlist *sg, int start, int limit,
+		struct p9_fcall *pdu, int count)
+{
+	int s;
+	int i = 0;
+	int index = start;
+
+	if (pdu->pdata_off) {
+		s = min((int)(PAGE_SIZE - pdu->pdata_off), count);
+		sg_set_page(&sg[index++], pdu->pdata[i++], s, pdu->pdata_off);
+		count -= s;
+	}
+
+	while (count) {
+		BUG_ON(index > limit);
+		s = min((int)PAGE_SIZE, count);
+		sg_set_page(&sg[index++], pdu->pdata[i++], s, 0);
+		count -= s;
+	}
+
+	return index-start;
+}
+
+
 /* We don't currently allow canceling of virtio requests */
 static int p9_virtio_cancel(struct p9_client *client, struct p9_req_t *req)
 {
@@ -196,16 +234,31 @@ 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, outp, inp;
 	struct virtio_chan *chan = client->trans;
 	char *rdata = (char *)req->rc+sizeof(struct p9_fcall);
 
 	P9_DPRINTK(P9_DEBUG_TRANS, "9p debug: virtio request\n");
 
 	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,
+			req->tc->size);
+
+	BUG_ON(req->tc->pdata_write_len && req->tc->pdata_read_len);
+
+	if (req->tc->pdata_write_len) {
+		outp = pack_sg_list_p(chan->sg, out, VIRTQUEUE_NUM,
+					req->tc, req->tc->pdata_write_len);
+		out += outp;
+	}
+	if (req->tc->pdata_read_len) {
+		inp = pack_sg_list(chan->sg, out, VIRTQUEUE_NUM, rdata, 11);
+		in = pack_sg_list_p(chan->sg, out+inp, VIRTQUEUE_NUM,
+					req->tc, req->tc->pdata_read_len);
+		in += inp;
+	} else {
+		in = pack_sg_list(chan->sg, out, VIRTQUEUE_NUM, rdata,
 								client->msize);
+	}
 
 	req->status = REQ_STATUS_SENT;
 
-- 
1.6.5.2