net/af_iucv: locate IUCV header via skb_network_header()

This patch attempts to untangle the TX and RX code in qeth from
af_iucv's respective HiperTransport path:
On the TX side, pointing skb_network_header() at the IUCV header
means that qeth_l3_fill_af_iucv_hdr() no longer needs a magical offset
to access the header.
On the RX side, qeth pulls the (fake) L2 header off the skb like any
normal ethernet driver would. This makes working with the IUCV header
in af_iucv easier, since we no longer have to assume a fixed skb layout.

While at it, replace the open-coded length checks in af_iucv's RX path
with pskb_may_pull().

Signed-off-by: Julian Wiedmann <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

drivers/s390/net/qeth_l3_main.c

···
 static int qeth_l3_process_inbound_buffer(struct qeth_card *card,
 				int budget, int *done)
 {
+	struct net_device *dev = card->dev;
 	int work_done = 0;
 	struct sk_buff *skb;
 	struct qeth_hdr *hdr;
···
 			magic = *(__u16 *)skb->data;
 			if ((card->info.type == QETH_CARD_TYPE_IQD) &&
 			    (magic == ETH_P_AF_IUCV)) {
-				skb->protocol = cpu_to_be16(ETH_P_AF_IUCV);
 				len = skb->len;
-				card->dev->header_ops->create(skb, card->dev, 0,
-					card->dev->dev_addr, "FAKELL", len);
-				skb_reset_mac_header(skb);
+				dev_hard_header(skb, dev, ETH_P_AF_IUCV,
+						dev->dev_addr, "FAKELL", len);
+				skb->protocol = eth_type_trans(skb, dev);
 				netif_receive_skb(skb);
 			} else {
 				qeth_l3_rebuild_skb(card, skb, hdr);
···
 				     unsigned int data_len)
 {
 	char daddr[16];
-	struct af_iucv_trans_hdr *iucv_hdr;
 
 	hdr->hdr.l3.id = QETH_HEADER_TYPE_LAYER3;
 	hdr->hdr.l3.length = data_len;
 	hdr->hdr.l3.flags = QETH_HDR_IPV6 | QETH_CAST_UNICAST;
 
-	iucv_hdr = (struct af_iucv_trans_hdr *)(skb_mac_header(skb) + ETH_HLEN);
 	memset(daddr, 0, sizeof(daddr));
 	daddr[0] = 0xfe;
 	daddr[1] = 0x80;
-	memcpy(&daddr[8], iucv_hdr->destUserID, 8);
+	memcpy(&daddr[8], iucv_trans_hdr(skb)->destUserID, 8);
 	memcpy(hdr->hdr.l3.next_hop.ipv6_addr, daddr, 16);
 }
 

include/net/iucv/af_iucv.h

···
 	u8 pad;                          /* total 104 bytes */
 } __packed;
 
+static inline struct af_iucv_trans_hdr *iucv_trans_hdr(struct sk_buff *skb)
+{
+	return (struct af_iucv_trans_hdr *)skb_network_header(skb);
+}
+
 enum iucv_tx_notify {
 	/* transmission of skb is completed and was successful */
 	TX_NOTIFY_OK = 0,

net/iucv/af_iucv.c

···
 	struct sk_buff *nskb;
 	int err, confirm_recv = 0;
 
-	memset(skb->head, 0, ETH_HLEN);
-	phs_hdr = skb_push(skb, sizeof(struct af_iucv_trans_hdr));
-	skb_reset_mac_header(skb);
+	phs_hdr = skb_push(skb, sizeof(*phs_hdr));
+	memset(phs_hdr, 0, sizeof(*phs_hdr));
 	skb_reset_network_header(skb);
-	skb_push(skb, ETH_HLEN);
-	skb_reset_mac_header(skb);
-	memset(phs_hdr, 0, sizeof(struct af_iucv_trans_hdr));
 
 	phs_hdr->magic = ETH_P_AF_IUCV;
 	phs_hdr->version = 1;
···
 	ASCEBC(phs_hdr->srcAppName, sizeof(phs_hdr->srcAppName));
 	if (imsg)
 		memcpy(&phs_hdr->iucv_hdr, imsg, sizeof(struct iucv_message));
+
+	skb_push(skb, ETH_HLEN);
+	memset(skb->data, 0, ETH_HLEN);
 
 	skb->dev = iucv->hs_dev;
 	if (!skb->dev) {
···
 /***************** HiperSockets transport callbacks ********************/
 static void afiucv_swap_src_dest(struct sk_buff *skb)
 {
-	struct af_iucv_trans_hdr *trans_hdr =
-				(struct af_iucv_trans_hdr *)skb->data;
+	struct af_iucv_trans_hdr *trans_hdr = iucv_trans_hdr(skb);
 	char tmpID[8];
 	char tmpName[8];
 
···
  **/
 static int afiucv_hs_callback_syn(struct sock *sk, struct sk_buff *skb)
 {
+	struct af_iucv_trans_hdr *trans_hdr = iucv_trans_hdr(skb);
 	struct sock *nsk;
 	struct iucv_sock *iucv, *niucv;
-	struct af_iucv_trans_hdr *trans_hdr;
 	int err;
 
 	iucv = iucv_sk(sk);
-	trans_hdr = (struct af_iucv_trans_hdr *)skb->data;
 	if (!iucv) {
 		/* no sock - connection refused */
 		afiucv_swap_src_dest(skb);
···
 static int afiucv_hs_callback_synack(struct sock *sk, struct sk_buff *skb)
 {
 	struct iucv_sock *iucv = iucv_sk(sk);
-	struct af_iucv_trans_hdr *trans_hdr =
-					(struct af_iucv_trans_hdr *)skb->data;
 
 	if (!iucv)
 		goto out;
 	if (sk->sk_state != IUCV_BOUND)
 		goto out;
 	bh_lock_sock(sk);
-	iucv->msglimit_peer = trans_hdr->window;
+	iucv->msglimit_peer = iucv_trans_hdr(skb)->window;
 	sk->sk_state = IUCV_CONNECTED;
 	sk->sk_state_change(sk);
 	bh_unlock_sock(sk);
···
 static int afiucv_hs_callback_win(struct sock *sk, struct sk_buff *skb)
 {
 	struct iucv_sock *iucv = iucv_sk(sk);
-	struct af_iucv_trans_hdr *trans_hdr =
-					(struct af_iucv_trans_hdr *)skb->data;
 
 	if (!iucv)
 		return NET_RX_SUCCESS;
···
 	if (sk->sk_state != IUCV_CONNECTED)
 		return NET_RX_SUCCESS;
 
-	atomic_sub(trans_hdr->window, &iucv->msg_sent);
+	atomic_sub(iucv_trans_hdr(skb)->window, &iucv->msg_sent);
 	iucv_sock_wake_msglim(sk);
 	return NET_RX_SUCCESS;
 }
···
 	int err = NET_RX_SUCCESS;
 	char nullstring[8];
 
-	if (skb->len < (ETH_HLEN + sizeof(struct af_iucv_trans_hdr))) {
-		WARN_ONCE(1, "AF_IUCV too short skb, len=%d, min=%d",
-			  (int)skb->len,
-			  (int)(ETH_HLEN + sizeof(struct af_iucv_trans_hdr)));
+	if (!pskb_may_pull(skb, sizeof(*trans_hdr))) {
+		WARN_ONCE(1, "AF_IUCV failed to receive skb, len=%u", skb->len);
 		kfree_skb(skb);
 		return NET_RX_SUCCESS;
 	}
-	if (skb_headlen(skb) < (ETH_HLEN + sizeof(struct af_iucv_trans_hdr)))
-		if (skb_linearize(skb)) {
-			WARN_ONCE(1, "AF_IUCV skb_linearize failed, len=%d",
-				  (int)skb->len);
-			kfree_skb(skb);
-			return NET_RX_SUCCESS;
-		}
-	skb_pull(skb, ETH_HLEN);
-	trans_hdr = (struct af_iucv_trans_hdr *)skb->data;
+
+	trans_hdr = iucv_trans_hdr(skb);
 	EBCASC(trans_hdr->destAppName, sizeof(trans_hdr->destAppName));
 	EBCASC(trans_hdr->destUserID, sizeof(trans_hdr->destUserID));
 	EBCASC(trans_hdr->srcAppName, sizeof(trans_hdr->srcAppName));