s390/qeth: no ETH header for outbound AF_IUCV

With AF_IUCV traffic, the skb passed to hard_start_xmit() has a 14 byte
slot at skb->data, intended for an ETH header. qeth_l3_fill_af_iucv_hdr()
fills this ETH header... and then immediately moves it to the
skb's headroom, where it disappears and is never seen again.

But it's still possible for us to return NETDEV_TX_BUSY after the skb has
been modified. Since we didn't get a private copy of the skb, the next
time the skb is delivered to hard_start_xmit() it no longer has the
expected layout (we moved the ETH header to the headroom, so skb->data
now starts at the IUCV_TRANS header). So when qeth_l3_fill_af_iucv_hdr()
does another round of rebuilding, the resulting qeth header ends up
all wrong. On transmission, the buffer is then rejected by
the HiperSockets device with SBALF15 = x'04'.
When this error is passed back to af_iucv as TX_NOTIFY_UNREACHABLE, it
tears down the offending socket.

As the ETH header for AF_IUCV serves no purpose, just align the code to
what we do for IP traffic on L3 HiperSockets: keep the ETH header at
skb->data, and pass down data_offset = ETH_HLEN to qeth_fill_buffer().
When mapping the payload into the SBAL elements, the ETH header is then
stripped off. This avoids the skb manipulations in
qeth_l3_fill_af_iucv_hdr(), and any buffer re-entering hard_start_xmit()
after NETDEV_TX_BUSY is now processed properly.
Signed-off-by: NJulian Wiedmann <jwi@linux.vnet.ibm.com>
Signed-off-by: NUrsula Braun <ubraun@linux.vnet.ibm.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/s390/net/qeth_l3_main.c

@@ -2609,17 +2609,13 @@ static void qeth_l3_fill_af_iucv_hdr(struct qeth_card *card,
 	char daddr[16];
 	struct af_iucv_trans_hdr *iucv_hdr;
 
-	skb_pull(skb, 14);
-	card->dev->header_ops->create(skb, card->dev, 0,
-				      card->dev->dev_addr, card->dev->dev_addr,
-				      card->dev->addr_len);
-	skb_pull(skb, 14);
-	iucv_hdr = (struct af_iucv_trans_hdr *)skb->data;
 	memset(hdr, 0, sizeof(struct qeth_hdr));
 	hdr->hdr.l3.id = QETH_HEADER_TYPE_LAYER3;
 	hdr->hdr.l3.ext_flags = 0;
-	hdr->hdr.l3.length = skb->len;
+	hdr->hdr.l3.length = skb->len - ETH_HLEN;
 	hdr->hdr.l3.flags = QETH_HDR_IPV6 | QETH_CAST_UNICAST;
+
+	iucv_hdr = (struct af_iucv_trans_hdr *) (skb->data + ETH_HLEN);
 	memset(daddr, 0, sizeof(daddr));
 	daddr[0] = 0xfe;
 	daddr[1] = 0x80;
@@ -2823,10 +2819,7 @@ static int qeth_l3_hard_start_xmit(struct sk_buff *skb, struct net_device *dev)
 	if ((card->info.type == QETH_CARD_TYPE_IQD) &&
 	    !skb_is_nonlinear(skb)) {
 		new_skb = skb;
-		if (new_skb->protocol == ETH_P_AF_IUCV)
-			data_offset = 0;
-		else
-			data_offset = ETH_HLEN;
+		data_offset = ETH_HLEN;
 		hdr = kmem_cache_alloc(qeth_core_header_cache, GFP_ATOMIC);
 		if (!hdr)
 			goto tx_drop;