[PATCH v2 09/13] vu_common: Pass iov_tail to vu_set_vnethdr()

[Laurent Vivier <lvivier@redhat.com>]

Refactor vu_set_vnethdr() to take an iov_tail pointer instead of a
direct pointer to the virtio_net_hdr_mrg_rxbuf structure.
This makes the function use IOV_PEEK_HEADER() and IOV_PUT_HEADER()
to read and write the virtio-net header through the iov_tail abstraction.

Signed-off-by: Laurent Vivier <lvivier@redhat.com>
---
 tcp_vu.c    |  8 +++++---
 udp_vu.c    |  3 +--
 vu_common.c | 21 +++++++++++++++------
 vu_common.h |  2 +-
 4 files changed, 22 insertions(+), 12 deletions(-)

diff --git a/tcp_vu.c b/tcp_vu.c
index 8da2dcfe78d0..688f48905d46 100644
--- a/tcp_vu.c
+++ b/tcp_vu.c
@@ -94,10 +94,11 @@ int tcp_vu_send_flag(const struct ctx *c, struct tcp_tap_conn *conn, int flags)
 	if (elem_cnt != 1)
 		return -1;
 
-	ASSERT(flags_elem[0].in_sg[0].iov_len >=
+	payload = IOV_TAIL(&flags_elem[0].in_sg[0], elem_cnt, 0);
+	ASSERT(iov_tail_size(&payload) >=
 	       MAX(hdrlen + sizeof(*opts), ETH_ZLEN + VNET_HLEN));
 
-	vu_set_vnethdr(flags_elem[0].in_sg[0].iov_base, 1);
+	vu_set_vnethdr(&payload, 1);
 
 	eh = vu_eth(flags_elem[0].in_sg[0].iov_base);
 
@@ -454,6 +455,7 @@ int tcp_vu_data_from_sock(const struct ctx *c, struct tcp_tap_conn *conn)
 	for (i = 0, previous_dlen = -1, check = NULL; i < head_cnt; i++) {
 		struct iovec *iov = &elem[head[i]].in_sg[0];
 		int buf_cnt = head[i + 1] - head[i];
+		struct iov_tail data = IOV_TAIL(iov, buf_cnt, 0);
 		size_t frame_size = iov_size(iov, buf_cnt);
 		bool push = i == head_cnt - 1;
 		ssize_t dlen;
@@ -461,7 +463,7 @@ int tcp_vu_data_from_sock(const struct ctx *c, struct tcp_tap_conn *conn)
 		ASSERT(frame_size >= hdrlen);
 
 		dlen = frame_size - hdrlen;
-		vu_set_vnethdr(iov->iov_base, buf_cnt);
+		vu_set_vnethdr(&data, buf_cnt);
 
 		/* The IPv4 header checksum varies only with dlen */
 		if (previous_dlen != dlen)
diff --git a/udp_vu.c b/udp_vu.c
index a21a03dbf23e..414750ff742a 100644
--- a/udp_vu.c
+++ b/udp_vu.c
@@ -233,8 +233,7 @@ void udp_vu_sock_to_tap(const struct ctx *c, int s, int n, flow_sidx_t tosidx)
 		vu_queue_rewind(vq, elem_cnt - elem_used);
 		if (iov_cnt > 0) {
 			struct iov_tail data = IOV_TAIL(iov_vu, iov_cnt, 0);
-			vu_set_vnethdr(iov_vu[0].iov_base, elem_used);
-			iov_drop_header(&data, VNET_HLEN);
+			vu_set_vnethdr(&data, elem_used);
 			udp_vu_prepare(c, &data, toside);
 			if (*c->pcap) {
 				udp_vu_csum(toside, &data);
diff --git a/vu_common.c b/vu_common.c
index 8afa5199908f..3538e59581b7 100644
--- a/vu_common.c
+++ b/vu_common.c
@@ -120,17 +120,24 @@ int vu_collect(const struct vu_dev *vdev, struct vu_virtq *vq,
 }
 
 /**
- * vu_set_vnethdr() - set virtio-net headers
- * @vnethdr:		Address of the header to set
+ * vu_set_vnethdr() - set virtio-net header
+ * @data:		IOV tail to write header to, updated to
+ * 			point after the virtio-net header
  * @num_buffers:	Number of guest buffers of the frame
  */
-void vu_set_vnethdr(struct virtio_net_hdr_mrg_rxbuf *vnethdr, int num_buffers)
+void vu_set_vnethdr(struct iov_tail *data, int num_buffers)
 {
+	struct virtio_net_hdr_mrg_rxbuf vnethdr_storage, *vnethdr;
+
+	vnethdr = IOV_PEEK_HEADER(data, vnethdr_storage);
+
 	vnethdr->hdr = VU_HEADER;
 	/* Note: if VIRTIO_NET_F_MRG_RXBUF is not negotiated,
 	 * num_buffers must be 1
 	 */
 	vnethdr->num_buffers = htole16(num_buffers);
+
+	IOV_PUT_HEADER(data, vnethdr);
 }
 
 /**
@@ -267,6 +274,7 @@ int vu_send_single(const struct ctx *c, const void *buf, size_t size)
 	struct vu_virtq *vq = &vdev->vq[VHOST_USER_RX_QUEUE];
 	struct vu_virtq_element elem[VIRTQUEUE_MAX_SIZE];
 	struct iovec in_sg[VIRTQUEUE_MAX_SIZE];
+	struct iov_tail data;
 	size_t total;
 	int elem_cnt;
 	int i;
@@ -295,15 +303,16 @@ int vu_send_single(const struct ctx *c, const void *buf, size_t size)
 	}
 	elem_cnt = iov_truncate(in_sg, elem_cnt, size);
 
-	vu_set_vnethdr(in_sg[0].iov_base, elem_cnt);
+	data = IOV_TAIL(&in_sg[0], elem_cnt, 0);
+	vu_set_vnethdr(&data, elem_cnt);
 
 	size -= VNET_HLEN;
 
 	/* copy data from the buffer to the iovec */
-	iov_from_buf(in_sg, elem_cnt, VNET_HLEN, buf, size);
+	iov_from_buf(in_sg, elem_cnt, data.off, buf, size);
 
 	if (*c->pcap)
-		pcap_iov(in_sg, elem_cnt, VNET_HLEN);
+		pcap_iov(data.iov, data.cnt, data.off);
 
 	vu_flush(vdev, vq, elem, elem_cnt);
 
diff --git a/vu_common.h b/vu_common.h
index 5de0c987b936..d068c61695f8 100644
--- a/vu_common.h
+++ b/vu_common.h
@@ -55,7 +55,7 @@ void vu_init_elem(struct vu_virtq_element *elem, struct iovec *iov,
 int vu_collect(const struct vu_dev *vdev, struct vu_virtq *vq,
 	       struct vu_virtq_element *elem, int max_elem, size_t size,
 	       size_t *collected);
-void vu_set_vnethdr(struct virtio_net_hdr_mrg_rxbuf *vnethdr, int num_buffers);
+void vu_set_vnethdr(struct iov_tail *data, int num_buffers);
 void vu_flush(const struct vu_dev *vdev, struct vu_virtq *vq,
 	      struct vu_virtq_element *elem, int elem_cnt);
 void vu_kick_cb(struct vu_dev *vdev, union epoll_ref ref,
-- 
2.53.0