[IPv4/IPv6]: UFO Scatter-gather approach

Attached is kernel patch for UDP Fragmentation Offload (UFO) feature.

1. This patch incorporate the review comments by Jeff Garzik.
2. Renamed USO as UFO (UDP Fragmentation Offload)
3. udp sendfile support with UFO

This patches uses scatter-gather feature of skb to generate large UDP
datagram. Below is a "how-to" on changes required in network device
driver to use the UFO interface.

UDP Fragmentation Offload (UFO) Interface:
-------------------------------------------
UFO is a feature wherein the Linux kernel network stack will offload the
IP fragmentation functionality of large UDP datagram to hardware. This
will reduce the overhead of stack in fragmenting the large UDP datagram to
MTU sized packets

1) Drivers indicate their capability of UFO using
dev->features |= NETIF_F_UFO | NETIF_F_HW_CSUM | NETIF_F_SG

NETIF_F_HW_CSUM is required for UFO over ipv6.

2) UFO packet will be submitted for transmission using driver xmit routine.
UFO packet will have a non-zero value for

"skb_shinfo(skb)->ufo_size"

skb_shinfo(skb)->ufo_size will indicate the length of data part in each IP
fragment going out of the adapter after IP fragmentation by hardware.

skb->data will contain MAC/IP/UDP header and skb_shinfo(skb)->frags[]
contains the data payload. The skb->ip_summed will be set to CHECKSUM_HW
indicating that hardware has to do checksum calculation. Hardware should
compute the UDP checksum of complete datagram and also ip header checksum of
each fragmented IP packet.

For IPV6 the UFO provides the fragment identification-id in
skb_shinfo(skb)->ip6_frag_id. The adapter should use this ID for generating
IPv6 fragments.

Signed-off-by: Ananda Raju <ananda.raju@neterion.com>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au> (forwarded)
Signed-off-by: Arnaldo Carvalho de Melo <acme@mandriva.com>

1 files changed, 75 insertions, 0 deletions

diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index ef9d46b91eb..95501e40100 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -176,6 +176,8 @@ struct sk_buff *__alloc_skb(unsigned int size, gfp_t gfp_mask,
 	skb_shinfo(skb)->tso_size = 0;
 	skb_shinfo(skb)->tso_segs = 0;
 	skb_shinfo(skb)->frag_list = NULL;
+	skb_shinfo(skb)->ufo_size = 0;
+	skb_shinfo(skb)->ip6_frag_id = 0;
 out:
 	return skb;
 nodata:
@@ -1696,6 +1698,78 @@ unsigned int skb_find_text(struct sk_buff *skb, unsigned int from,
 	return textsearch_find(config, state);
 }
 
+/**
+ * skb_append_datato_frags: - append the user data to a skb
+ * @sk: sock  structure
+ * @skb: skb structure to be appened with user data.
+ * @getfrag: call back function to be used for getting the user data
+ * @from: pointer to user message iov
+ * @length: length of the iov message
+ *
+ * Description: This procedure append the user data in the fragment part
+ * of the skb if any page alloc fails user this procedure returns  -ENOMEM
+ */
+int skb_append_datato_frags(struct sock *sk, struct sk_buff *skb,
+			int getfrag(void *from, char *to, int offset,
+					int len, int odd, struct sk_buff *skb),
+			void *from, int length)
+{
+	int frg_cnt = 0;
+	skb_frag_t *frag = NULL;
+	struct page *page = NULL;
+	int copy, left;
+	int offset = 0;
+	int ret;
+
+	do {
+		/* Return error if we don't have space for new frag */
+		frg_cnt = skb_shinfo(skb)->nr_frags;
+		if (frg_cnt >= MAX_SKB_FRAGS)
+			return -EFAULT;
+
+		/* allocate a new page for next frag */
+		page = alloc_pages(sk->sk_allocation, 0);
+
+		/* If alloc_page fails just return failure and caller will
+		 * free previous allocated pages by doing kfree_skb()
+		 */
+		if (page == NULL)
+			return -ENOMEM;
+
+		/* initialize the next frag */
+		sk->sk_sndmsg_page = page;
+		sk->sk_sndmsg_off = 0;
+		skb_fill_page_desc(skb, frg_cnt, page, 0, 0);
+		skb->truesize += PAGE_SIZE;
+		atomic_add(PAGE_SIZE, &sk->sk_wmem_alloc);
+
+		/* get the new initialized frag */
+		frg_cnt = skb_shinfo(skb)->nr_frags;
+		frag = &skb_shinfo(skb)->frags[frg_cnt - 1];
+
+		/* copy the user data to page */
+		left = PAGE_SIZE - frag->page_offset;
+		copy = (length > left)? left : length;
+
+		ret = getfrag(from, (page_address(frag->page) +
+			    frag->page_offset + frag->size),
+			    offset, copy, 0, skb);
+		if (ret < 0)
+			return -EFAULT;
+
+		/* copy was successful so update the size parameters */
+		sk->sk_sndmsg_off += copy;
+		frag->size += copy;
+		skb->len += copy;
+		skb->data_len += copy;
+		offset += copy;
+		length -= copy;
+
+	} while (length > 0);
+
+	return 0;
+}
+
 void __init skb_init(void)
 {
 	skbuff_head_cache = kmem_cache_create("skbuff_head_cache",
@@ -1747,3 +1821,4 @@ EXPORT_SYMBOL(skb_prepare_seq_read);
 EXPORT_SYMBOL(skb_seq_read);
 EXPORT_SYMBOL(skb_abort_seq_read);
 EXPORT_SYMBOL(skb_find_text);
+EXPORT_SYMBOL(skb_append_datato_frags);