NFC: Reserve tx head and tail room

We can have the NFC core layer allocating the tx head and tail
room for the drivers and avoid 1 or more SKBs copy on write on
the Tx path.

Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

drivers/nfc/pn533.c

@@ -1246,7 +1246,6 @@ static int pn533_data_exchange_tx_frame(struct pn533 *dev, struct sk_buff *skb)
 {
 	int payload_len = skb->len;
 	struct pn533_frame *out_frame;
-	struct sk_buff *discarded;
 	u8 tg;
 
 	nfc_dev_dbg(&dev->interface->dev, "%s - Sending %d bytes", __func__,
@@ -1260,18 +1259,6 @@ static int pn533_data_exchange_tx_frame(struct pn533 *dev, struct sk_buff *skb)
 		return -ENOSYS;
 	}
 
-	/* Reserving header space */
-	if (skb_cow_head(skb, PN533_CMD_DATAEXCH_HEAD_LEN)) {
-		nfc_dev_err(&dev->interface->dev, "Error to add header data");
-		return -ENOMEM;
-	}
-
-	/* Reserving tail space, see pn533_tx_frame_finish */
-	if (skb_cow_data(skb, PN533_FRAME_TAIL_SIZE, &discarded) < 0) {
-		nfc_dev_err(&dev->interface->dev, "Error to add tail data");
-		return -ENOMEM;
-	}
-
 	skb_push(skb, PN533_CMD_DATAEXCH_HEAD_LEN);
 	out_frame = (struct pn533_frame *) skb->data;
 
@@ -1536,7 +1523,9 @@ static int pn533_probe(struct usb_interface *interface,
 			| NFC_PROTO_ISO14443_MASK
 			| NFC_PROTO_NFC_DEP_MASK;
 
-	dev->nfc_dev = nfc_allocate_device(&pn533_nfc_ops, protocols);
+	dev->nfc_dev = nfc_allocate_device(&pn533_nfc_ops, protocols,
+					   PN533_CMD_DATAEXCH_HEAD_LEN,
+					   PN533_FRAME_TAIL_SIZE);
 	if (!dev->nfc_dev)
 		goto kill_tasklet;
 

include/linux/nfc.h

@@ -123,4 +123,6 @@ struct sockaddr_nfc {
 #define NFC_SOCKPROTO_RAW	0
 #define NFC_SOCKPROTO_MAX	1
 
+#define NFC_HEADER_SIZE 1
+
 #endif /*__LINUX_NFC_H */

include/net/nfc.h

@@ -82,6 +82,9 @@ struct nfc_dev {
 	struct nfc_genl_data genl_data;
 	u32 supported_protocols;
 
+	int tx_headroom;
+	int tx_tailroom;
+
 	struct nfc_ops *ops;
 };
 #define to_nfc_dev(_dev) container_of(_dev, struct nfc_dev, dev)
@@ -89,7 +92,9 @@ struct nfc_dev {
 extern struct class nfc_class;
 
 struct nfc_dev *nfc_allocate_device(struct nfc_ops *ops,
-					u32 supported_protocols);
+					u32 supported_protocols,
+					int tx_headroom,
+					int tx_tailroom);
 
 /**
  * nfc_free_device - free nfc device

net/nfc/core.c

@@ -322,7 +322,9 @@ struct nfc_dev *nfc_get_device(unsigned idx)
  * @supported_protocols: NFC protocols supported by the device
  */
 struct nfc_dev *nfc_allocate_device(struct nfc_ops *ops,
-					u32 supported_protocols)
+					u32 supported_protocols,
+					int tx_headroom,
+					int tx_tailroom)
 {
 	static atomic_t dev_no = ATOMIC_INIT(0);
 	struct nfc_dev *dev;
@@ -345,6 +347,8 @@ struct nfc_dev *nfc_allocate_device(struct nfc_ops *ops,
 
 	dev->ops = ops;
 	dev->supported_protocols = supported_protocols;
+	dev->tx_headroom = tx_headroom;
+	dev->tx_tailroom = tx_tailroom;
 
 	spin_lock_init(&dev->targets_lock);
 	nfc_genl_data_init(&dev->genl_data);

net/nfc/rawsock.c

@@ -123,11 +123,7 @@ error:
 
 static int rawsock_add_header(struct sk_buff *skb)
 {
-
-	if (skb_cow_head(skb, 1))
-		return -ENOMEM;
-
-	*skb_push(skb, 1) = 0;
+	*skb_push(skb, NFC_HEADER_SIZE) = 0;
 
 	return 0;
 }
@@ -197,6 +193,7 @@ static int rawsock_sendmsg(struct kiocb *iocb, struct socket *sock,
 					struct msghdr *msg, size_t len)
 {
 	struct sock *sk = sock->sk;
+	struct nfc_dev *dev = nfc_rawsock(sk)->dev;
 	struct sk_buff *skb;
 	int rc;
 
@@ -208,11 +205,13 @@ static int rawsock_sendmsg(struct kiocb *iocb, struct socket *sock,
 	if (sock->state != SS_CONNECTED)
 		return -ENOTCONN;
 
-	skb = sock_alloc_send_skb(sk, len, msg->msg_flags & MSG_DONTWAIT,
-									&rc);
+	skb = sock_alloc_send_skb(sk, len + dev->tx_headroom + dev->tx_tailroom + NFC_HEADER_SIZE,
+					msg->msg_flags & MSG_DONTWAIT, &rc);
 	if (!skb)
 		return rc;
 
+	skb_reserve(skb, dev->tx_headroom + NFC_HEADER_SIZE);
+
 	rc = memcpy_fromiovec(skb_put(skb, len), msg->msg_iov, len);
 	if (rc < 0) {
 		kfree_skb(skb);