ieee802154: change needed headroom/tailroom

This patch cleanups needed_headroom, needed_tailroom and hard_header_len
fields for wpan and lowpan interfaces.

For wpan interfaces the worst case mac header len should be part of
needed_headroom, currently this is set as hard_header_len, but
hard_header_len should be set to the minimum header length which xmit
call assumes and this is the minimum frame length of 802.15.4.
The hard_header_len value will check inside send callbacl of AF_PACKET
raw sockets.

For lowpan interfaces, if fragmentation isn't needed the skb will
call dev_hard_header for 802154 layer and queue it afterwards. This
happens without new skb allocation, so we need the same headroom and
tailroom lengths like 802154 inside 802154 6lowpan layer. At least we
assume as minimum header length an ipv6 header size.

Signed-off-by: Alexander Aring <alex.aring@gmail.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>

2 files changed, 21 insertions, 5 deletions

diff --git a/net/ieee802154/6lowpan/core.c b/net/ieee802154/6lowpan/core.c
index 9f0cfa598e3a..44420ed95574 100644
--- a/net/ieee802154/6lowpan/core.c
+++ b/net/ieee802154/6lowpan/core.c
@@ -104,9 +104,8 @@ static void lowpan_setup(struct net_device *ldev)
 	ldev->addr_len		= IEEE802154_ADDR_LEN;
 	memset(ldev->broadcast, 0xff, IEEE802154_ADDR_LEN);
 	ldev->type		= ARPHRD_6LOWPAN;
-	/* Frame Control + Sequence Number + Address fields + Security Header */
-	ldev->hard_header_len	= 2 + 1 + 20 + 14;
-	ldev->needed_tailroom	= 2; /* FCS */
+	/* We need an ipv6hdr as minimum len when calling xmit */
+	ldev->hard_header_len	= sizeof(struct ipv6hdr);
 	ldev->mtu		= IPV6_MIN_MTU;
 	ldev->priv_flags	|= IFF_NO_QUEUE;
 	ldev->flags		= IFF_BROADCAST | IFF_MULTICAST;
@@ -156,6 +155,15 @@ static int lowpan_newlink(struct net *src_net, struct net_device *ldev,
 	lowpan_dev_info(ldev)->wdev = wdev;
 	/* Set the lowpan hardware address to the wpan hardware address. */
 	memcpy(ldev->dev_addr, wdev->dev_addr, IEEE802154_ADDR_LEN);
+	/* We need headroom for possible wpan_dev_hard_header call and tailroom
+	 * for encryption/fcs handling. The lowpan interface will replace
+	 * the IPv6 header with 6LoWPAN header. At worst case the 6LoWPAN
+	 * header has LOWPAN_IPHC_MAX_HEADER_LEN more bytes than the IPv6
+	 * header.
+	 */
+	ldev->needed_headroom = LOWPAN_IPHC_MAX_HEADER_LEN +
+				wdev->needed_headroom;
+	ldev->needed_tailroom = wdev->needed_tailroom;
 
 	lowpan_netdev_setup(ldev, LOWPAN_LLTYPE_IEEE802154);
 
diff --git a/net/ieee802154/6lowpan/tx.c b/net/ieee802154/6lowpan/tx.c
index 6067e064a3fe..7e0563eaea98 100644
--- a/net/ieee802154/6lowpan/tx.c
+++ b/net/ieee802154/6lowpan/tx.c
@@ -10,6 +10,7 @@
 
 #include <net/6lowpan.h>
 #include <net/ieee802154_netdev.h>
+#include <net/mac802154.h>
 
 #include "6lowpan_i.h"
 
@@ -36,6 +37,13 @@ lowpan_addr_info *lowpan_skb_priv(const struct sk_buff *skb)
 			sizeof(struct lowpan_addr_info));
 }
 
+/* This callback will be called from AF_PACKET and IPv6 stack, the AF_PACKET
+ * sockets gives an 8 byte array for addresses only!
+ *
+ * TODO I think AF_PACKET DGRAM (sending/receiving) RAW (sending) makes no
+ * sense here. We should disable it, the right use-case would be AF_INET6
+ * RAW/DGRAM sockets.
+ */
 int lowpan_header_create(struct sk_buff *skb, struct net_device *ldev,
 			 unsigned short type, const void *_daddr,
 			 const void *_saddr, unsigned int len)
@@ -77,13 +85,13 @@ lowpan_alloc_frag(struct sk_buff *skb, int size,
 	struct sk_buff *frag;
 	int rc;
 
-	frag = alloc_skb(wdev->hard_header_len + wdev->needed_tailroom + size,
+	frag = alloc_skb(wdev->needed_headroom + wdev->needed_tailroom + size,
 			 GFP_ATOMIC);
 
 	if (likely(frag)) {
 		frag->dev = wdev;
 		frag->priority = skb->priority;
-		skb_reserve(frag, wdev->hard_header_len);
+		skb_reserve(frag, wdev->needed_headroom);
 		skb_reset_network_header(frag);
 		*mac_cb(frag) = *mac_cb(skb);