Re: [PATCH net-next v2 2/6] 6lowpan: fix fragmentation on sending side

From: Alexander Aring <alex.aring@gmail.com>
Date: Fri, 21 Feb 2014 19:58:58 +0100

+	err = lowpan_fragment_xmit(skb, head, header_length,
+				   frag_plen + lowpan_size, 0,
+				   LOWPAN_DISPATCH_FRAG1);
 	if (err) {
 		pr_debug("%s unable to send FRAG1 packet (tag: %d)",
 			 __func__, tag);
 		goto exit;
 	}
 
-	offset = LOWPAN_FRAG_SIZE;
+	offset = lowpan_size + frag_plen;
+	dgram_offset = mac_cb(skb)->frag_info.d_offset + frag_plen;

This isn't going to work.

Once you call dev_queue_xmit(), the skb control block can be reused by
other layers.  In particular the device qdisc layer is going to
scramble the control block on you.

Once a packet travels from one layer to another, SKB control block
is likewise transferred.