text: /*
   *	IPV4 GSO/GRO offload support
   *	Linux INET implementation
   *
   *	This program is free software; you can redistribute it and/or
   *	modify it under the terms of the GNU General Public License
   *	as published by the Free Software Foundation; either version
   *	2 of the License, or (at your option) any later version.
   *
   *	TCPv4 GSO/GRO support
   */
  
  #include <linux/skbuff.h>
  #include <net/tcp.h>
  #include <net/protocol.h>
  
  static void tcp_gso_tstamp(struct sk_buff *skb, unsigned int ts_seq,
  			   unsigned int seq, unsigned int mss)
  {
  	while (skb) {
  		if (before(ts_seq, seq + mss)) {
  			skb_shinfo(skb)->tx_flags |= SKBTX_SW_TSTAMP;
  			skb_shinfo(skb)->tskey = ts_seq;
  			return;
  		}
  
  		skb = skb->next;
  		seq += mss;
  	}
  }
  
  static struct sk_buff *tcp4_gso_segment(struct sk_buff *skb,
  					netdev_features_t features)
  {
  	if (!(skb_shinfo(skb)->gso_type & SKB_GSO_TCPV4))
  		return ERR_PTR(-EINVAL);
  
  	if (!pskb_may_pull(skb, sizeof(struct tcphdr)))
  		return ERR_PTR(-EINVAL);
  
  	if (unlikely(skb->ip_summed != CHECKSUM_PARTIAL)) {
  		const struct iphdr *iph = ip_hdr(skb);
  		struct tcphdr *th = tcp_hdr(skb);
  
  		/* Set up checksum pseudo header, usually expect stack to
  		 * have done this already.
  		 */
  
  		th->check = 0;
  		skb->ip_summed = CHECKSUM_PARTIAL;
  		__tcp_v4_send_check(skb, iph->saddr, iph->daddr);
  	}
  
  	return tcp_gso_segment(skb, features);
  }
  
  struct sk_buff *tcp_gso_segment(struct sk_buff *skb,
  				netdev_features_t features)
  {
  	struct sk_buff *segs = ERR_PTR(-EINVAL);
  	unsigned int sum_truesize = 0;
  	struct tcphdr *th;
  	unsigned int thlen;
  	unsigned int seq;
  	__be32 delta;
  	unsigned int oldlen;
  	unsigned int mss;
  	struct sk_buff *gso_skb = skb;
  	__sum16 newcheck;
  	bool ooo_okay, copy_destructor;
  
  	th = tcp_hdr(skb);
  	thlen = th->doff * 4;
  	if (thlen < sizeof(*th))
  		goto out;
  
  	if (!pskb_may_pull(skb, thlen))
  		goto out;
  
  	oldlen = (u16)~skb->len;
  	__skb_pull(skb, thlen);
  
  	mss = skb_shinfo(skb)->gso_size;
  	if (unlikely(skb->len <= mss))
  		goto out;
  
  	if (skb_gso_ok(skb, features | NETIF_F_GSO_ROBUST)) {
  		/* Packet is from an untrusted source, reset gso_segs. */
  
  		skb_shinfo(skb)->gso_segs = DIV_ROUND_UP(skb->len, mss);
  
  		segs = NULL;
  		goto out;
  	}
  
  	copy_destructor = gso_skb->destructor == tcp_wfree;
  	ooo_okay = gso_skb->ooo_okay;
  	/* All segments but the first should have ooo_okay cleared */
  	skb->ooo_okay = 0;
  
  	segs = skb_segment(skb, features);
  	if (IS_ERR(segs))
  		goto out;
  
  	/* Only first segment might have ooo_okay set */
  	segs->ooo_okay = ooo_okay;
  
  	/* GSO partial and frag_list segmentation only requires splitting
  	 * the frame into an MSS multiple and possibly a remainder, both
  	 * cases return a GSO skb. So update the mss now.
  	 */
  	if (skb_is_gso(segs))
  		mss *= skb_shinfo(segs)->gso_segs;
  
  	delta = htonl(oldlen + (thlen + mss));
  
  	skb = segs;
  	th = tcp_hdr(skb);
  	seq = ntohl(th->seq);
  
  	if (unlikely(skb_shinfo(gso_skb)->tx_flags & SKBTX_SW_TSTAMP))
  		tcp_gso_tstamp(segs, skb_shinfo(gso_skb)->tskey, seq, mss);
  
  	newcheck = ~csum_fold((__force __wsum)((__force u32)th->check +
  					       (__force u32)delta));
  
  	while (skb->next) {
  		th->fin = th->psh = 0;
  		th->check = newcheck;
  
  		if (skb->ip_summed == CHECKSUM_PARTIAL)
  			gso_reset_checksum(skb, ~th->check);
  		else
  			th->check = gso_make_checksum(skb, ~th->check);
  
  		seq += mss;
  		if (copy_destructor) {
  			skb->destructor = gso_skb->destructor;
  			skb->sk = gso_skb->sk;
  			sum_truesize += skb->truesize;
  		}
  		skb = skb->next;
  		th = tcp_hdr(skb);
  
  		th->seq = htonl(seq);
  		th->cwr = 0;
  	}
  
  	/* Following permits TCP Small Queues to work well with GSO :
  	 * The callback to TCP stack will be called at the time last frag
  	 * is freed at TX completion, and not right now when gso_skb
  	 * is freed by GSO engine
  	 */
  	if (copy_destructor) {
  		swap(gso_skb->sk, skb->sk);
  		swap(gso_skb->destructor, skb->destructor);
  		sum_truesize += skb->truesize;
  		atomic_add(sum_truesize - gso_skb->truesize,
  			   &skb->sk->sk_wmem_alloc);
  	}
  
  	delta = htonl(oldlen + (skb_tail_pointer(skb) -
  				skb_transport_header(skb)) +
  		      skb->data_len);
  	th->check = ~csum_fold((__force __wsum)((__force u32)th->check +
  				(__force u32)delta));
  	if (skb->ip_summed == CHECKSUM_PARTIAL)
  		gso_reset_checksum(skb, ~th->check);
  	else
  		th->check = gso_make_checksum(skb, ~th->check);
  out:
  	return segs;
  }
  
  struct sk_buff **tcp_gro_receive(struct sk_buff **head, struct sk_buff *skb)
  {
  	struct sk_buff **pp = NULL;
  	struct sk_buff *p;
  	struct tcphdr *th;
  	struct tcphdr *th2;
  	unsigned int len;
  	unsigned int thlen;
  	__be32 flags;
  	unsigned int mss = 1;
  	unsigned int hlen;
  	unsigned int off;
  	int flush = 1;
  	int i;
  
  	off = skb_gro_offset(skb);
  	hlen = off + sizeof(*th);
  	th = skb_gro_header_fast(skb, off);
  	if (skb_gro_header_hard(skb, hlen)) {
  		th = skb_gro_header_slow(skb, hlen, off);
  		if (unlikely(!th))
  			goto out;
  	}
  
  	thlen = th->doff * 4;
  	if (thlen < sizeof(*th))
  		goto out;
  
  	hlen = off + thlen;
  	if (skb_gro_header_hard(skb, hlen)) {
  		th = skb_gro_header_slow(skb, hlen, off);
  		if (unlikely(!th))
  			goto out;
  	}
  
  	skb_gro_pull(skb, thlen);
  
  	len = skb_gro_len(skb);
  	flags = tcp_flag_word(th);
  
  	for (; (p = *head); head = &p->next) {
  		if (!NAPI_GRO_CB(p)->same_flow)
  			continue;
  
  		th2 = tcp_hdr(p);
  
  		if (*(u32 *)&th->source ^ *(u32 *)&th2->source) {
  			NAPI_GRO_CB(p)->same_flow = 0;
  			continue;
  		}
  
  		goto found;
  	}
  
  	goto out_check_final;
  
  found:
  	/* Include the IP ID check below from the inner most IP hdr */
  	flush = NAPI_GRO_CB(p)->flush | NAPI_GRO_CB(p)->flush_id;
  	flush |= (__force int)(flags & TCP_FLAG_CWR);
  	flush |= (__force int)((flags ^ tcp_flag_word(th2)) &
  		  ~(TCP_FLAG_CWR | TCP_FLAG_FIN | TCP_FLAG_PSH));
  	flush |= (__force int)(th->ack_seq ^ th2->ack_seq);
  	for (i = sizeof(*th); i < thlen; i += 4)
  		flush |= *(u32 *)((u8 *)th + i) ^
  			 *(u32 *)((u8 *)th2 + i);
  
  	mss = skb_shinfo(p)->gso_size;
  
  	flush |= (len - 1) >= mss;
  	flush |= (ntohl(th2->seq) + skb_gro_len(p)) ^ ntohl(th->seq);
  
  	if (flush || skb_gro_receive(head, skb)) {
  		mss = 1;
  		goto out_check_final;
  	}
  
  	p = *head;
  	th2 = tcp_hdr(p);
  	tcp_flag_word(th2) |= flags & (TCP_FLAG_FIN | TCP_FLAG_PSH);
  
  out_check_final:
  	flush = len < mss;
  	flush |= (__force int)(flags & (TCP_FLAG_URG | TCP_FLAG_PSH |
  					TCP_FLAG_RST | TCP_FLAG_SYN |
  					TCP_FLAG_FIN));
  
  	if (p && (!NAPI_GRO_CB(skb)->same_flow || flush))
  		pp = head;
  
  out:
  	NAPI_GRO_CB(skb)->flush |= (flush != 0);
  
  	return pp;
  }
  
  int tcp_gro_complete(struct sk_buff *skb)
  {
  	struct tcphdr *th = tcp_hdr(skb);
  
  	skb->csum_start = (unsigned char *)th - skb->head;
  	skb->csum_offset = offsetof(struct tcphdr, check);
  	skb->ip_summed = CHECKSUM_PARTIAL;
  
  	skb_shinfo(skb)->gso_segs = NAPI_GRO_CB(skb)->count;
  
  	if (th->cwr)
  		skb_shinfo(skb)->gso_type |= SKB_GSO_TCP_ECN;
  
  	return 0;
  }
  EXPORT_SYMBOL(tcp_gro_complete);
  
  static struct sk_buff **tcp4_gro_receive(struct sk_buff **head, struct sk_buff *skb)
  {
  	/* Don't bother verifying checksum if we're going to flush anyway. */
  	if (!NAPI_GRO_CB(skb)->flush &&
  	    skb_gro_checksum_validate(skb, IPPROTO_TCP,
  				      inet_gro_compute_pseudo)) {
  		NAPI_GRO_CB(skb)->flush = 1;
  		return NULL;
  	}
  
  	return tcp_gro_receive(head, skb);
  }
  
  static int tcp4_gro_complete(struct sk_buff *skb, int thoff)
  {
  	const struct iphdr *iph = ip_hdr(skb);
  	struct tcphdr *th = tcp_hdr(skb);
  
  	th->check = ~tcp_v4_check(skb->len - thoff, iph->saddr,
  				  iph->daddr, 0);
  	skb_shinfo(skb)->gso_type |= SKB_GSO_TCPV4;
  
  	return tcp_gro_complete(skb);
  }
  
  static const struct net_offload tcpv4_offload = {
  	.callbacks = {
  		.gso_segment	=	tcp4_gso_segment,
  		.gro_receive	=	tcp4_gro_receive,
  		.gro_complete	=	tcp4_gro_complete,
  	},
  };
  
  int __init tcpv4_offload_init(void)
  {
  	return inet_add_offload(&tcpv4_offload, IPPROTO_TCP);
  }
  