batman-adv: Fragment and send skbs larger than mtu

Non-broadcast packets larger than MTU are fragmented and sent with
an encapsulating header. Up to 16 fragments are supported, which are
sent in reverse order on the wire to allow minimal memory copying when
creating fragments.

Signed-off-by: Martin Hundebøll <martin@hundeboll.net>
Signed-off-by: Marek Lindner <lindner_marek@yahoo.de>
Signed-off-by: Antonio Quartulli <antonio@meshcoding.com>

1 files changed, 121 insertions, 0 deletions

diff --git a/net/batman-adv/fragmentation.c b/net/batman-adv/fragmentation.c
index c829d3cee89c..271d321b3a04 100644
--- a/net/batman-adv/fragmentation.c
+++ b/net/batman-adv/fragmentation.c
@@ -368,3 +368,124 @@ out:
 		batadv_neigh_node_free_ref(neigh_node);
 	return ret;
 }
+
+/**
+ * batadv_frag_create - create a fragment from skb
+ * @skb: skb to create fragment from
+ * @frag_head: header to use in new fragment
+ * @mtu: size of new fragment
+ *
+ * Split the passed skb into two fragments: A new one with size matching the
+ * passed mtu and the old one with the rest. The new skb contains data from the
+ * tail of the old skb.
+ *
+ * Returns the new fragment, NULL on error.
+ */
+static struct sk_buff *batadv_frag_create(struct sk_buff *skb,
+					  struct batadv_frag_packet *frag_head,
+					  unsigned int mtu)
+{
+	struct sk_buff *skb_fragment;
+	unsigned header_size = sizeof(*frag_head);
+	unsigned fragment_size = mtu - header_size;
+
+	skb_fragment = netdev_alloc_skb(NULL, mtu + ETH_HLEN);
+	if (!skb_fragment)
+		goto err;
+
+	skb->priority = TC_PRIO_CONTROL;
+
+	/* Eat the last mtu-bytes of the skb */
+	skb_reserve(skb_fragment, header_size + ETH_HLEN);
+	skb_split(skb, skb_fragment, skb->len - fragment_size);
+
+	/* Add the header */
+	skb_push(skb_fragment, header_size);
+	memcpy(skb_fragment->data, frag_head, header_size);
+
+err:
+	return skb_fragment;
+}
+
+/**
+ * batadv_frag_send_packet - create up to 16 fragments from the passed skb
+ * @skb: skb to create fragments from
+ * @orig_node: final destination of the created fragments
+ * @neigh_node: next-hop of the created fragments
+ *
+ * Returns true on success, false otherwise.
+ */
+bool batadv_frag_send_packet(struct sk_buff *skb,
+			     struct batadv_orig_node *orig_node,
+			     struct batadv_neigh_node *neigh_node)
+{
+	struct batadv_priv *bat_priv;
+	struct batadv_hard_iface *primary_if;
+	struct batadv_frag_packet frag_header;
+	struct sk_buff *skb_fragment;
+	unsigned mtu = neigh_node->if_incoming->net_dev->mtu;
+	unsigned header_size = sizeof(frag_header);
+	unsigned max_fragment_size, max_packet_size;
+
+	/* To avoid merge and refragmentation at next-hops we never send
+	 * fragments larger than BATADV_FRAG_MAX_FRAG_SIZE
+	 */
+	mtu = min_t(unsigned, mtu, BATADV_FRAG_MAX_FRAG_SIZE);
+	max_fragment_size = (mtu - header_size - ETH_HLEN);
+	max_packet_size = max_fragment_size * BATADV_FRAG_MAX_FRAGMENTS;
+
+	/* Don't even try to fragment, if we need more than 16 fragments */
+	if (skb->len > max_packet_size)
+		goto out_err;
+
+	bat_priv = orig_node->bat_priv;
+	primary_if = batadv_primary_if_get_selected(bat_priv);
+	if (!primary_if)
+		goto out_err;
+
+	/* Create one header to be copied to all fragments */
+	frag_header.header.packet_type = BATADV_UNICAST_FRAG;
+	frag_header.header.version = BATADV_COMPAT_VERSION;
+	frag_header.header.ttl = BATADV_TTL;
+	frag_header.seqno = htons(atomic_inc_return(&bat_priv->frag_seqno));
+	frag_header.reserved = 0;
+	frag_header.no = 0;
+	frag_header.total_size = htons(skb->len);
+	memcpy(frag_header.orig, primary_if->net_dev->dev_addr, ETH_ALEN);
+	memcpy(frag_header.dest, orig_node->orig, ETH_ALEN);
+
+	/* Eat and send fragments from the tail of skb */
+	while (skb->len > max_fragment_size) {
+		skb_fragment = batadv_frag_create(skb, &frag_header, mtu);
+		if (!skb_fragment)
+			goto out_err;
+
+		batadv_inc_counter(bat_priv, BATADV_CNT_FRAG_TX);
+		batadv_add_counter(bat_priv, BATADV_CNT_FRAG_TX_BYTES,
+				   skb_fragment->len + ETH_HLEN);
+		batadv_send_skb_packet(skb_fragment, neigh_node->if_incoming,
+				       neigh_node->addr);
+		frag_header.no++;
+
+		/* The initial check in this function should cover this case */
+		if (frag_header.no == BATADV_FRAG_MAX_FRAGMENTS - 1)
+			goto out_err;
+	}
+
+	/* Make room for the fragment header. */
+	if (batadv_skb_head_push(skb, header_size) < 0 ||
+	    pskb_expand_head(skb, header_size + ETH_HLEN, 0, GFP_ATOMIC) < 0)
+		goto out_err;
+
+	memcpy(skb->data, &frag_header, header_size);
+
+	/* Send the last fragment */
+	batadv_inc_counter(bat_priv, BATADV_CNT_FRAG_TX);
+	batadv_add_counter(bat_priv, BATADV_CNT_FRAG_TX_BYTES,
+			   skb->len + ETH_HLEN);
+	batadv_send_skb_packet(skb, neigh_node->if_incoming, neigh_node->addr);
+
+	return true;
+out_err:
+	return false;
+}