[RFC PATCH v2 01/15] vsock/virtio: prepare for non-linear skb support

[Arseniy Krasnov]

This is preparation patch for non-linear skbuff handling. It does two
things:
1) Handles freeing of non-linear skbuffs.
2) Adds copying from non-linear skbuffs to user's buffer.

Signed-off-by: Arseniy Krasnov <AVKrasnov@xxxxxxxxxxxxxx>
---
 include/linux/virtio_vsock.h            |  7 +++
 net/vmw_vsock/virtio_transport_common.c | 84 +++++++++++++++++++++++--
 2 files changed, 87 insertions(+), 4 deletions(-)

diff --git a/include/linux/virtio_vsock.h b/include/linux/virtio_vsock.h
index c58453699ee9..848ec255e665 100644
--- a/include/linux/virtio_vsock.h
+++ b/include/linux/virtio_vsock.h
@@ -12,6 +12,10 @@
 struct virtio_vsock_skb_cb {
 	bool reply;
 	bool tap_delivered;
+	/* Current fragment in 'frags' of skb. */
+	u32 curr_frag;
+	/* Offset from 0 in current fragment. */
+	u32 frag_off;
 };
 
 #define VIRTIO_VSOCK_SKB_CB(skb) ((struct virtio_vsock_skb_cb *)((skb)->cb))
@@ -246,4 +250,7 @@ void virtio_transport_put_credit(struct virtio_vsock_sock *vvs, u32 credit);
 void virtio_transport_deliver_tap_pkt(struct sk_buff *skb);
 int virtio_transport_purge_skbs(void *vsk, struct sk_buff_head *list);
 int virtio_transport_read_skb(struct vsock_sock *vsk, skb_read_actor_t read_actor);
+int virtio_transport_nl_skb_to_iov(struct sk_buff *skb,
+				   struct iov_iter *iov_iter, size_t len,
+				   bool peek);
 #endif /* _LINUX_VIRTIO_VSOCK_H */
diff --git a/net/vmw_vsock/virtio_transport_common.c b/net/vmw_vsock/virtio_transport_common.c
index dde3c870bddd..b901017b9f92 100644
--- a/net/vmw_vsock/virtio_transport_common.c
+++ b/net/vmw_vsock/virtio_transport_common.c
@@ -337,6 +337,60 @@ static int virtio_transport_send_credit_update(struct vsock_sock *vsk)
 	return virtio_transport_send_pkt_info(vsk, &info);
 }
 
+int virtio_transport_nl_skb_to_iov(struct sk_buff *skb,
+				   struct iov_iter *iov_iter,
+				   size_t len,
+				   bool peek)
+{
+	unsigned int skb_len;
+	size_t rest_len = len;
+	int curr_frag;
+	int curr_offs;
+	int err = 0;
+
+	skb_len = skb->len;
+	curr_frag = VIRTIO_VSOCK_SKB_CB(skb)->curr_frag;
+	curr_offs = VIRTIO_VSOCK_SKB_CB(skb)->frag_off;
+
+	while (rest_len && skb->len) {
+		struct bio_vec *curr_vec;
+		size_t curr_vec_end;
+		size_t to_copy;
+		void *data;
+
+		curr_vec = &skb_shinfo(skb)->frags[curr_frag];
+		curr_vec_end = curr_vec->bv_offset + curr_vec->bv_len;
+		to_copy = min(rest_len, (size_t)(curr_vec_end - curr_offs));
+		data = kmap_local_page(curr_vec->bv_page);
+
+		if (copy_to_iter(data + curr_offs, to_copy, iov_iter) != to_copy)
+			err = -EFAULT;
+
+		kunmap_local(data);
+
+		if (err)
+			break;
+
+		rest_len -= to_copy;
+		skb_len -= to_copy;
+		curr_offs += to_copy;
+
+		if (curr_offs == (curr_vec_end)) {
+			curr_frag++;
+			curr_offs = 0;
+		}
+	}
+
+	if (!peek) {
+		skb->len = skb_len;
+		VIRTIO_VSOCK_SKB_CB(skb)->curr_frag = curr_frag;
+		VIRTIO_VSOCK_SKB_CB(skb)->frag_off = curr_offs;
+	}
+
+	return err;
+}
+EXPORT_SYMBOL_GPL(virtio_transport_nl_skb_to_iov);
+
 static ssize_t
 virtio_transport_stream_do_peek(struct vsock_sock *vsk,
 				struct msghdr *msg,
@@ -365,7 +419,14 @@ virtio_transport_stream_do_peek(struct vsock_sock *vsk,
 			 */
 			spin_unlock_bh(&vvs->rx_lock);
 
-			err = memcpy_to_msg(msg, skb->data + off, bytes);
+			if (skb_is_nonlinear(skb)) {
+				err = virtio_transport_nl_skb_to_iov(skb,
+								     &msg->msg_iter,
+								     bytes,
+								     true);
+			} else {
+				err = memcpy_to_msg(msg, skb->data + off, bytes);
+			}
 			if (err)
 				goto out;
 
@@ -417,14 +478,22 @@ virtio_transport_stream_do_dequeue(struct vsock_sock *vsk,
 		 */
 		spin_unlock_bh(&vvs->rx_lock);
 
-		err = memcpy_to_msg(msg, skb->data, bytes);
+		if (skb_is_nonlinear(skb)) {
+			err = virtio_transport_nl_skb_to_iov(skb, &msg->msg_iter,
+							     bytes, false);
+		} else {
+			err = memcpy_to_msg(msg, skb->data, bytes);
+		}
+
 		if (err)
 			goto out;
 
 		spin_lock_bh(&vvs->rx_lock);
 
 		total += bytes;
-		skb_pull(skb, bytes);
+
+		if (!skb_is_nonlinear(skb))
+			skb_pull(skb, bytes);
 
 		if (skb->len == 0) {
 			u32 pkt_len = le32_to_cpu(virtio_vsock_hdr(skb)->len);
@@ -498,7 +567,14 @@ static int virtio_transport_seqpacket_do_dequeue(struct vsock_sock *vsk,
 				 */
 				spin_unlock_bh(&vvs->rx_lock);
 
-				err = memcpy_to_msg(msg, skb->data, bytes_to_copy);
+				if (skb_is_nonlinear(skb)) {
+					err = virtio_transport_nl_skb_to_iov(skb,
+									     &msg->msg_iter,
+									     bytes_to_copy,
+									     false);
+				} else {
+					err = memcpy_to_msg(msg, skb->data, bytes_to_copy);
+				}
 				if (err) {
 					/* Copy of message failed. Rest of
 					 * fragments will be freed without copy.
-- 
2.25.1