net: Add Generic Receive Offload infrastructure

This patch adds the top-level GRO (Generic Receive Offload) infrastructure.
This is pretty similar to LRO except that this is protocol-independent.
Instead of holding packets in an lro_mgr structure, they're now held in
napi_struct.

For drivers that intend to use this, they can set the NETIF_F_GRO bit and
call napi_gro_receive instead of netif_receive_skb or just call netif_rx.
The latter will call napi_receive_skb automatically.  When napi_gro_receive
is used, the driver must either call napi_complete/napi_rx_complete, or
call napi_gro_flush in softirq context if the driver uses the primitives
__napi_complete/__napi_rx_complete.

Protocols will set the gro_receive and gro_complete function pointers in
order to participate in this scheme.

In addition to the packet, gro_receive will get a list of currently held
packets.  Each packet in the list has a same_flow field which is non-zero
if it is a potential match for the new packet.  For each packet that may
match, they also have a flush field which is non-zero if the held packet
must not be merged with the new packet.

Once gro_receive has determined that the new skb matches a held packet,
the held packet may be processed immediately if the new skb cannot be
merged with it.  In this case gro_receive should return the pointer to
the existing skb in gro_list.  Otherwise the new skb should be merged into
the existing packet and NULL should be returned, unless the new skb makes
it impossible for any further merges to be made (e.g., FIN packet) where
the merged skb should be returned.

Whenever the skb is merged into an existing entry, the gro_receive
function should set NAPI_GRO_CB(skb)->same_flow.  Note that if an skb
merely matches an existing entry but can't be merged with it, then
this shouldn't be set.

If gro_receive finds it pointless to hold the new skb for future merging,
it should set NAPI_GRO_CB(skb)->flush.

Held packets will be flushed by napi_gro_flush which is called by
napi_complete and napi_rx_complete.

Currently held packets are stored in a singly liked list just like LRO.
The list is limited to a maximum of 8 entries.  In future, this may be
expanded to use a hash table to allow more flows to be held for merging.

Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 191 insertions, 2 deletions

diff --git a/net/core/dev.c b/net/core/dev.c
index e415f0b..d8d7d1f 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -129,6 +129,9 @@
 
 #include "net-sysfs.h"
 
+/* Instead of increasing this, you should create a hash table. */
+#define MAX_GRO_SKBS 8
+
 /*
  *	The list of packet types we will receive (as opposed to discard)
  *	and the routines to invoke.
@@ -2335,6 +2338,122 @@ static void flush_backlog(void *arg)
 		}
 }
 
+static int napi_gro_complete(struct sk_buff *skb)
+{
+	struct packet_type *ptype;
+	__be16 type = skb->protocol;
+	struct list_head *head = &ptype_base[ntohs(type) & PTYPE_HASH_MASK];
+	int err = -ENOENT;
+
+	if (!skb_shinfo(skb)->frag_list)
+		goto out;
+
+	rcu_read_lock();
+	list_for_each_entry_rcu(ptype, head, list) {
+		if (ptype->type != type || ptype->dev || !ptype->gro_complete)
+			continue;
+
+		err = ptype->gro_complete(skb);
+		break;
+	}
+	rcu_read_unlock();
+
+	if (err) {
+		WARN_ON(&ptype->list == head);
+		kfree_skb(skb);
+		return NET_RX_SUCCESS;
+	}
+
+out:
+	__skb_push(skb, -skb_network_offset(skb));
+	return netif_receive_skb(skb);
+}
+
+void napi_gro_flush(struct napi_struct *napi)
+{
+	struct sk_buff *skb, *next;
+
+	for (skb = napi->gro_list; skb; skb = next) {
+		next = skb->next;
+		skb->next = NULL;
+		napi_gro_complete(skb);
+	}
+
+	napi->gro_list = NULL;
+}
+EXPORT_SYMBOL(napi_gro_flush);
+
+int napi_gro_receive(struct napi_struct *napi, struct sk_buff *skb)
+{
+	struct sk_buff **pp = NULL;
+	struct packet_type *ptype;
+	__be16 type = skb->protocol;
+	struct list_head *head = &ptype_base[ntohs(type) & PTYPE_HASH_MASK];
+	int count = 0;
+	int mac_len;
+
+	if (!(skb->dev->features & NETIF_F_GRO))
+		goto normal;
+
+	rcu_read_lock();
+	list_for_each_entry_rcu(ptype, head, list) {
+		struct sk_buff *p;
+
+		if (ptype->type != type || ptype->dev || !ptype->gro_receive)
+			continue;
+
+		skb_reset_network_header(skb);
+		mac_len = skb->network_header - skb->mac_header;
+		skb->mac_len = mac_len;
+		NAPI_GRO_CB(skb)->same_flow = 0;
+		NAPI_GRO_CB(skb)->flush = 0;
+
+		for (p = napi->gro_list; p; p = p->next) {
+			count++;
+			NAPI_GRO_CB(p)->same_flow =
+				p->mac_len == mac_len &&
+				!memcmp(skb_mac_header(p), skb_mac_header(skb),
+					mac_len);
+			NAPI_GRO_CB(p)->flush = 0;
+		}
+
+		pp = ptype->gro_receive(&napi->gro_list, skb);
+		break;
+	}
+	rcu_read_unlock();
+
+	if (&ptype->list == head)
+		goto normal;
+
+	if (pp) {
+		struct sk_buff *nskb = *pp;
+
+		*pp = nskb->next;
+		nskb->next = NULL;
+		napi_gro_complete(nskb);
+		count--;
+	}
+
+	if (NAPI_GRO_CB(skb)->same_flow)
+		goto ok;
+
+	if (NAPI_GRO_CB(skb)->flush || count >= MAX_GRO_SKBS) {
+		__skb_push(skb, -skb_network_offset(skb));
+		goto normal;
+	}
+
+	NAPI_GRO_CB(skb)->count = 1;
+	skb->next = napi->gro_list;
+	napi->gro_list = skb;
+
+ok:
+	return NET_RX_SUCCESS;
+
+normal:
+	return netif_receive_skb(skb);
+}
+EXPORT_SYMBOL(napi_gro_receive);
+
 static int process_backlog(struct napi_struct *napi, int quota)
 {
 	int work = 0;
@@ -2354,9 +2473,11 @@ static int process_backlog(struct napi_struct *napi, int quota)
 		}
 		local_irq_enable();
 
-		netif_receive_skb(skb);
+		napi_gro_receive(napi, skb);
 	} while (++work < quota && jiffies == start_time);
 
+	napi_gro_flush(napi);
+
 	return work;
 }
 
@@ -2377,6 +2498,68 @@ void __napi_schedule(struct napi_struct *n)
 }
 EXPORT_SYMBOL(__napi_schedule);
 
+void __napi_complete(struct napi_struct *n)
+{
+	BUG_ON(!test_bit(NAPI_STATE_SCHED, &n->state));
+	BUG_ON(n->gro_list);
+
+	list_del(&n->poll_list);
+	smp_mb__before_clear_bit();
+	clear_bit(NAPI_STATE_SCHED, &n->state);
+}
+EXPORT_SYMBOL(__napi_complete);
+
+void napi_complete(struct napi_struct *n)
+{
+	unsigned long flags;
+
+	/*
+	 * don't let napi dequeue from the cpu poll list
+	 * just in case its running on a different cpu
+	 */
+	if (unlikely(test_bit(NAPI_STATE_NPSVC, &n->state)))
+		return;
+
+	napi_gro_flush(n);
+	local_irq_save(flags);
+	__napi_complete(n);
+	local_irq_restore(flags);
+}
+EXPORT_SYMBOL(napi_complete);
+
+void netif_napi_add(struct net_device *dev, struct napi_struct *napi,
+		    int (*poll)(struct napi_struct *, int), int weight)
+{
+	INIT_LIST_HEAD(&napi->poll_list);
+	napi->gro_list = NULL;
+	napi->poll = poll;
+	napi->weight = weight;
+	list_add(&napi->dev_list, &dev->napi_list);
+#ifdef CONFIG_NETPOLL
+	napi->dev = dev;
+	spin_lock_init(&napi->poll_lock);
+	napi->poll_owner = -1;
+#endif
+	set_bit(NAPI_STATE_SCHED, &napi->state);
+}
+EXPORT_SYMBOL(netif_napi_add);
+
+void netif_napi_del(struct napi_struct *napi)
+{
+	struct sk_buff *skb, *next;
+
+	list_del(&napi->dev_list);
+
+	for (skb = napi->gro_list; skb; skb = next) {
+		next = skb->next;
+		skb->next = NULL;
+		kfree_skb(skb);
+	}
+
+	napi->gro_list = NULL;
+}
+EXPORT_SYMBOL(netif_napi_del);
+
 
 static void net_rx_action(struct softirq_action *h)
 {
@@ -4380,7 +4563,7 @@ struct net_device *alloc_netdev_mq(int sizeof_priv, const char *name,
 
 	netdev_init_queues(dev);
 
-	netpoll_netdev_init(dev);
+	INIT_LIST_HEAD(&dev->napi_list);
 	setup(dev);
 	strcpy(dev->name, name);
 	return dev;
@@ -4397,10 +4580,15 @@ EXPORT_SYMBOL(alloc_netdev_mq);
  */
 void free_netdev(struct net_device *dev)
 {
+	struct napi_struct *p, *n;
+
 	release_net(dev_net(dev));
 
 	kfree(dev->_tx);
 
+	list_for_each_entry_safe(p, n, &dev->napi_list, dev_list)
+		netif_napi_del(p);
+
 	/*  Compatibility with error handling in drivers */
 	if (dev->reg_state == NETREG_UNINITIALIZED) {
 		kfree((char *)dev - dev->padded);
@@ -4949,6 +5137,7 @@ static int __init net_dev_init(void)
 
 		queue->backlog.poll = process_backlog;
 		queue->backlog.weight = weight_p;
+		queue->backlog.gro_list = NULL;
 	}
 
 	dev_boot_phase = 0;