// SPDX-License-Identifier: GPL-2.0-only

  /*
   * INET		An implementation of the TCP/IP protocol suite for the LINUX
   *		operating system.  INET is implemented using the  BSD Socket
   *		interface as the means of communication with the user level.
   *
   *		The Internet Protocol (IP) output module.
   *

   * Authors:	Ross Biro

   *		Fred N. van Kempen, <waltje@uWalt.NL.Mugnet.ORG>
   *		Donald Becker, <becker@super.org>
   *		Alan Cox, <Alan.Cox@linux.org>
   *		Richard Underwood
   *		Stefan Becker, <stefanb@yello.ping.de>
   *		Jorge Cwik, <jorge@laser.satlink.net>
   *		Arnt Gulbrandsen, <agulbra@nvg.unit.no>
   *		Hirokazu Takahashi, <taka@valinux.co.jp>
   *
   *	See ip_input.c for original log
   *
   *	Fixes:
   *		Alan Cox	:	Missing nonblock feature in ip_build_xmit.
   *		Mike Kilburn	:	htons() missing in ip_build_xmit.

   *		Bradford Johnson:	Fix faulty handling of some frames when

   *					no route is found.
   *		Alexander Demenshin:	Missing sk/skb free in ip_queue_xmit
   *					(in case if packet not accepted by
   *					output firewall rules)
   *		Mike McLagan	:	Routing by source
   *		Alexey Kuznetsov:	use new route cache
   *		Andi Kleen:		Fix broken PMTU recovery and remove
   *					some redundant tests.
   *	Vitaly E. Lavrov	:	Transparent proxy revived after year coma.
   *		Andi Kleen	: 	Replace ip_reply with ip_send_reply.

   *		Andi Kleen	:	Split fast and slow ip_build_xmit path
   *					for decreased register pressure on x86
   *					and more readibility.

   *		Marc Boucher	:	When call_out_firewall returns FW_QUEUE,
   *					silently drop skb instead of failing with -EPERM.
   *		Detlev Wengorz	:	Copy protocol for fragments.
   *		Hirokazu Takahashi:	HW checksumming for outgoing UDP
   *					datagrams.
   *		Hirokazu Takahashi:	sendfile() on UDP works now.
   */

  #include <linux/uaccess.h>

  #include <linux/module.h>
  #include <linux/types.h>
  #include <linux/kernel.h>

  #include <linux/mm.h>
  #include <linux/string.h>
  #include <linux/errno.h>

  #include <linux/highmem.h>

  #include <linux/slab.h>

  
  #include <linux/socket.h>
  #include <linux/sockios.h>
  #include <linux/in.h>
  #include <linux/inet.h>
  #include <linux/netdevice.h>
  #include <linux/etherdevice.h>
  #include <linux/proc_fs.h>
  #include <linux/stat.h>
  #include <linux/init.h>
  
  #include <net/snmp.h>
  #include <net/ip.h>
  #include <net/protocol.h>
  #include <net/route.h>

  #include <net/xfrm.h>

  #include <linux/skbuff.h>
  #include <net/sock.h>
  #include <net/arp.h>
  #include <net/icmp.h>

  #include <net/checksum.h>
  #include <net/inetpeer.h>

  #include <net/inet_ecn.h>

  #include <net/lwtunnel.h>

  #include <linux/bpf-cgroup.h>

  #include <linux/igmp.h>
  #include <linux/netfilter_ipv4.h>
  #include <linux/netfilter_bridge.h>

  #include <linux/netlink.h>

  #include <linux/tcp.h>

  static int
  ip_fragment(struct net *net, struct sock *sk, struct sk_buff *skb,
  	    unsigned int mtu,
  	    int (*output)(struct net *, struct sock *, struct sk_buff *));

  /* Generate a checksum for an outgoing IP datagram. */

  void ip_send_check(struct iphdr *iph)

  {
  	iph->check = 0;
  	iph->check = ip_fast_csum((unsigned char *)iph, iph->ihl);
  }

  EXPORT_SYMBOL(ip_send_check);

  int __ip_local_out(struct net *net, struct sock *sk, struct sk_buff *skb)

  {
  	struct iphdr *iph = ip_hdr(skb);
  
  	iph->tot_len = htons(skb->len);
  	ip_send_check(iph);

  
  	/* if egress device is enslaved to an L3 master device pass the
  	 * skb to its handler for processing
  	 */
  	skb = l3mdev_ip_out(sk, skb);
  	if (unlikely(!skb))
  		return 0;

  	skb->protocol = htons(ETH_P_IP);

  	return nf_hook(NFPROTO_IPV4, NF_INET_LOCAL_OUT,
  		       net, sk, skb, NULL, skb_dst(skb)->dev,

  		       dst_output);

  }

  int ip_local_out(struct net *net, struct sock *sk, struct sk_buff *skb)

  {
  	int err;

  	err = __ip_local_out(net, sk, skb);

  	if (likely(err == 1))

  		err = dst_output(net, sk, skb);

  
  	return err;
  }

  EXPORT_SYMBOL_GPL(ip_local_out);

  static inline int ip_select_ttl(struct inet_sock *inet, struct dst_entry *dst)
  {
  	int ttl = inet->uc_ttl;
  
  	if (ttl < 0)

  		ttl = ip4_dst_hoplimit(dst);

  	return ttl;
  }

  /*

   *		Add an ip header to a skbuff and send it out.
   *
   */

  int ip_build_and_send_pkt(struct sk_buff *skb, const struct sock *sk,

  			  __be32 saddr, __be32 daddr, struct ip_options_rcu *opt,
  			  u8 tos)

  {
  	struct inet_sock *inet = inet_sk(sk);

  	struct rtable *rt = skb_rtable(skb);

  	struct net *net = sock_net(sk);

  	struct iphdr *iph;
  
  	/* Build the IP header. */

  	skb_push(skb, sizeof(struct iphdr) + (opt ? opt->opt.optlen : 0));

  	skb_reset_network_header(skb);

  	iph = ip_hdr(skb);

  	iph->version  = 4;
  	iph->ihl      = 5;

  	iph->tos      = tos;

  	iph->ttl      = ip_select_ttl(inet, &rt->dst);

  	iph->daddr    = (opt && opt->opt.srr ? opt->opt.faddr : daddr);
  	iph->saddr    = saddr;

  	iph->protocol = sk->sk_protocol;

  	if (ip_dont_fragment(sk, &rt->dst)) {
  		iph->frag_off = htons(IP_DF);
  		iph->id = 0;
  	} else {
  		iph->frag_off = 0;

  		__ip_select_ident(net, iph, 1);

  	}

  	if (opt && opt->opt.optlen) {
  		iph->ihl += opt->opt.optlen>>2;
  		ip_options_build(skb, &opt->opt, daddr, rt, 0);

  	}

  
  	skb->priority = sk->sk_priority;

  	if (!skb->mark)
  		skb->mark = sk->sk_mark;

  
  	/* Send it out. */

  	return ip_local_out(net, skb->sk, skb);

  }

  EXPORT_SYMBOL_GPL(ip_build_and_send_pkt);

  static int ip_finish_output2(struct net *net, struct sock *sk, struct sk_buff *skb)

  {

  	struct dst_entry *dst = skb_dst(skb);

  	struct rtable *rt = (struct rtable *)dst;

  	struct net_device *dev = dst->dev;

  	unsigned int hh_len = LL_RESERVED_SPACE(dev);

  	struct neighbour *neigh;

  	bool is_v6gw = false;

  	if (rt->rt_type == RTN_MULTICAST) {

  		IP_UPD_PO_STATS(net, IPSTATS_MIB_OUTMCAST, skb->len);

  	} else if (rt->rt_type == RTN_BROADCAST)

  		IP_UPD_PO_STATS(net, IPSTATS_MIB_OUTBCAST, skb->len);

  	/* Be paranoid, rather than too clever. */

  	if (unlikely(skb_headroom(skb) < hh_len && dev->header_ops)) {

  		struct sk_buff *skb2;
  
  		skb2 = skb_realloc_headroom(skb, LL_RESERVED_SPACE(dev));

  		if (!skb2) {

  			kfree_skb(skb);
  			return -ENOMEM;
  		}
  		if (skb->sk)
  			skb_set_owner_w(skb2, skb->sk);

  		consume_skb(skb);

  		skb = skb2;
  	}

  	if (lwtunnel_xmit_redirect(dst->lwtstate)) {
  		int res = lwtunnel_xmit(skb);
  
  		if (res < 0 || res == LWTUNNEL_XMIT_DONE)
  			return res;
  	}

  	rcu_read_lock_bh();

  	neigh = ip_neigh_for_gw(rt, skb, &is_v6gw);

  	if (!IS_ERR(neigh)) {

  		int res;
  
  		sock_confirm_neigh(skb, neigh);

  		/* if crossing protocols, can not use the cached header */
  		res = neigh_output(neigh, skb, is_v6gw);

  		rcu_read_unlock_bh();

  		return res;
  	}

  	rcu_read_unlock_bh();

  	net_dbg_ratelimited("%s: No header cache and no neighbour!
  ",
  			    __func__);

  	kfree_skb(skb);
  	return -EINVAL;
  }

  static int ip_finish_output_gso(struct net *net, struct sock *sk,
  				struct sk_buff *skb, unsigned int mtu)

  {

  	struct sk_buff *segs, *nskb;

  	netdev_features_t features;

  	int ret = 0;

  	/* common case: seglen is <= mtu

  	 */

  	if (skb_gso_validate_network_len(skb, mtu))

  		return ip_finish_output2(net, sk, skb);

  	/* Slowpath -  GSO segment length exceeds the egress MTU.

  	 *

  	 * This can happen in several cases:
  	 *  - Forwarding of a TCP GRO skb, when DF flag is not set.
  	 *  - Forwarding of an skb that arrived on a virtualization interface
  	 *    (virtio-net/vhost/tap) with TSO/GSO size set by other network
  	 *    stack.
  	 *  - Local GSO skb transmitted on an NETIF_F_TSO tunnel stacked over an
  	 *    interface with a smaller MTU.
  	 *  - Arriving GRO skb (or GSO skb in a virtualized environment) that is
  	 *    bridged to a NETIF_F_TSO tunnel stacked over an interface with an
  	 *    insufficent MTU.

  	 */
  	features = netif_skb_features(skb);

  	BUILD_BUG_ON(sizeof(*IPCB(skb)) > SKB_GSO_CB_OFFSET);

  	segs = skb_gso_segment(skb, features & ~NETIF_F_GSO_MASK);

  	if (IS_ERR_OR_NULL(segs)) {

  		kfree_skb(skb);
  		return -ENOMEM;
  	}
  
  	consume_skb(skb);

  	skb_list_walk_safe(segs, segs, nskb) {

  		int err;

  		skb_mark_not_on_list(segs);

  		err = ip_fragment(net, sk, segs, mtu, ip_finish_output2);

  
  		if (err && ret == 0)
  			ret = err;

  	}

  
  	return ret;
  }

  static int __ip_finish_output(struct net *net, struct sock *sk, struct sk_buff *skb)

  {

  	unsigned int mtu;

  #if defined(CONFIG_NETFILTER) && defined(CONFIG_XFRM)
  	/* Policy lookup after SNAT yielded a new policy */

  	if (skb_dst(skb)->xfrm) {

  		IPCB(skb)->flags |= IPSKB_REROUTED;

  		return dst_output(net, sk, skb);

  	}

  #endif

  	mtu = ip_skb_dst_mtu(sk, skb);

  	if (skb_is_gso(skb))

  		return ip_finish_output_gso(net, sk, skb, mtu);

  	if (skb->len > mtu || IPCB(skb)->frag_max_size)

  		return ip_fragment(net, sk, skb, mtu, ip_finish_output2);

  	return ip_finish_output2(net, sk, skb);

  }

  static int ip_finish_output(struct net *net, struct sock *sk, struct sk_buff *skb)
  {
  	int ret;
  
  	ret = BPF_CGROUP_RUN_PROG_INET_EGRESS(sk, skb);
  	switch (ret) {
  	case NET_XMIT_SUCCESS:
  		return __ip_finish_output(net, sk, skb);
  	case NET_XMIT_CN:
  		return __ip_finish_output(net, sk, skb) ? : ret;
  	default:
  		kfree_skb(skb);
  		return ret;
  	}
  }

  static int ip_mc_finish_output(struct net *net, struct sock *sk,
  			       struct sk_buff *skb)
  {

  	struct rtable *new_rt;

  	bool do_cn = false;
  	int ret, err;

  
  	ret = BPF_CGROUP_RUN_PROG_INET_EGRESS(sk, skb);

  	switch (ret) {

  	case NET_XMIT_CN:

  		do_cn = true;

  		fallthrough;

  	case NET_XMIT_SUCCESS:
  		break;

  	default:

  		kfree_skb(skb);
  		return ret;
  	}

  	/* Reset rt_iif so that inet_iif() will return skb->skb_iif. Setting
  	 * this to non-zero causes ipi_ifindex in in_pktinfo to be overwritten,
  	 * see ipv4_pktinfo_prepare().
  	 */
  	new_rt = rt_dst_clone(net->loopback_dev, skb_rtable(skb));
  	if (new_rt) {
  		new_rt->rt_iif = 0;
  		skb_dst_drop(skb);
  		skb_dst_set(skb, &new_rt->dst);
  	}

  	err = dev_loopback_xmit(net, sk, skb);
  	return (do_cn && err) ? ret : err;

  }

  int ip_mc_output(struct net *net, struct sock *sk, struct sk_buff *skb)

  {

  	struct rtable *rt = skb_rtable(skb);

  	struct net_device *dev = rt->dst.dev;

  
  	/*
  	 *	If the indicated interface is up and running, send the packet.
  	 */

  	IP_UPD_PO_STATS(net, IPSTATS_MIB_OUT, skb->len);

  
  	skb->dev = dev;
  	skb->protocol = htons(ETH_P_IP);
  
  	/*
  	 *	Multicasts are looped back for other local users
  	 */
  
  	if (rt->rt_flags&RTCF_MULTICAST) {

  		if (sk_mc_loop(sk)

  #ifdef CONFIG_IP_MROUTE
  		/* Small optimization: do not loopback not local frames,
  		   which returned after forwarding; they will be  dropped
  		   by ip_mr_input in any case.
  		   Note, that local frames are looped back to be delivered
  		   to local recipients.
  
  		   This check is duplicated in ip_mr_input at the moment.
  		 */

  		    &&
  		    ((rt->rt_flags & RTCF_LOCAL) ||
  		     !(IPCB(skb)->flags & IPSKB_FORWARDED))

  #endif

  		   ) {

  			struct sk_buff *newskb = skb_clone(skb, GFP_ATOMIC);
  			if (newskb)

  				NF_HOOK(NFPROTO_IPV4, NF_INET_POST_ROUTING,

  					net, sk, newskb, NULL, newskb->dev,

  					ip_mc_finish_output);

  		}
  
  		/* Multicasts with ttl 0 must not go beyond the host */

  		if (ip_hdr(skb)->ttl == 0) {

  			kfree_skb(skb);
  			return 0;
  		}
  	}
  
  	if (rt->rt_flags&RTCF_BROADCAST) {
  		struct sk_buff *newskb = skb_clone(skb, GFP_ATOMIC);
  		if (newskb)

  			NF_HOOK(NFPROTO_IPV4, NF_INET_POST_ROUTING,
  				net, sk, newskb, NULL, newskb->dev,

  				ip_mc_finish_output);

  	}

  	return NF_HOOK_COND(NFPROTO_IPV4, NF_INET_POST_ROUTING,
  			    net, sk, skb, NULL, skb->dev,
  			    ip_finish_output,

  			    !(IPCB(skb)->flags & IPSKB_REROUTED));

  }

  int ip_output(struct net *net, struct sock *sk, struct sk_buff *skb)

  {

  	struct net_device *dev = skb_dst(skb)->dev, *indev = skb->dev;

  	IP_UPD_PO_STATS(net, IPSTATS_MIB_OUT, skb->len);

  	skb->dev = dev;
  	skb->protocol = htons(ETH_P_IP);

  	return NF_HOOK_COND(NFPROTO_IPV4, NF_INET_POST_ROUTING,

  			    net, sk, skb, indev, dev,

  			    ip_finish_output,

  			    !(IPCB(skb)->flags & IPSKB_REROUTED));

  }

  /*
   * copy saddr and daddr, possibly using 64bit load/stores
   * Equivalent to :
   *   iph->saddr = fl4->saddr;
   *   iph->daddr = fl4->daddr;
   */
  static void ip_copy_addrs(struct iphdr *iph, const struct flowi4 *fl4)
  {
  	BUILD_BUG_ON(offsetof(typeof(*fl4), daddr) !=
  		     offsetof(typeof(*fl4), saddr) + sizeof(fl4->saddr));
  	memcpy(&iph->saddr, &fl4->saddr,
  	       sizeof(fl4->saddr) + sizeof(fl4->daddr));
  }

  /* Note: skb->sk can be different from sk, in case of tunnels */

  int __ip_queue_xmit(struct sock *sk, struct sk_buff *skb, struct flowi *fl,
  		    __u8 tos)

  {

  	struct inet_sock *inet = inet_sk(sk);

  	struct net *net = sock_net(sk);

  	struct ip_options_rcu *inet_opt;

  	struct flowi4 *fl4;

  	struct rtable *rt;
  	struct iphdr *iph;

  	int res;

  
  	/* Skip all of this if the packet is already routed,
  	 * f.e. by something like SCTP.
  	 */

  	rcu_read_lock();

  	inet_opt = rcu_dereference(inet->inet_opt);

  	fl4 = &fl->u.ip4;

  	rt = skb_rtable(skb);

  	if (rt)

  		goto packet_routed;
  
  	/* Make sure we can route this packet. */
  	rt = (struct rtable *)__sk_dst_check(sk, 0);

  	if (!rt) {

  		__be32 daddr;

  
  		/* Use correct destination address if we have options. */

  		daddr = inet->inet_daddr;

  		if (inet_opt && inet_opt->opt.srr)
  			daddr = inet_opt->opt.faddr;

  		/* If this fails, retransmit mechanism of transport layer will
  		 * keep trying until route appears or the connection times
  		 * itself out.
  		 */

  		rt = ip_route_output_ports(net, fl4, sk,

  					   daddr, inet->inet_saddr,
  					   inet->inet_dport,
  					   inet->inet_sport,
  					   sk->sk_protocol,

  					   RT_CONN_FLAGS_TOS(sk, tos),

  					   sk->sk_bound_dev_if);
  		if (IS_ERR(rt))
  			goto no_route;

  		sk_setup_caps(sk, &rt->dst);

  	}

  	skb_dst_set_noref(skb, &rt->dst);

  
  packet_routed:

  	if (inet_opt && inet_opt->opt.is_strictroute && rt->rt_uses_gateway)

  		goto no_route;
  
  	/* OK, we know where to send it, allocate and build IP header. */

  	skb_push(skb, sizeof(struct iphdr) + (inet_opt ? inet_opt->opt.optlen : 0));

  	skb_reset_network_header(skb);

  	iph = ip_hdr(skb);

  	*((__be16 *)iph) = htons((4 << 12) | (5 << 8) | (tos & 0xff));

  	if (ip_dont_fragment(sk, &rt->dst) && !skb->ignore_df)

  		iph->frag_off = htons(IP_DF);
  	else
  		iph->frag_off = 0;

  	iph->ttl      = ip_select_ttl(inet, &rt->dst);

  	iph->protocol = sk->sk_protocol;

  	ip_copy_addrs(iph, fl4);

  	/* Transport layer set skb->h.foo itself. */

  	if (inet_opt && inet_opt->opt.optlen) {
  		iph->ihl += inet_opt->opt.optlen >> 2;
  		ip_options_build(skb, &inet_opt->opt, inet->inet_daddr, rt, 0);

  	}

  	ip_select_ident_segs(net, skb, sk,

  			     skb_shinfo(skb)->gso_segs ?: 1);

  	/* TODO : should we use skb->sk here instead of sk ? */

  	skb->priority = sk->sk_priority;

  	skb->mark = sk->sk_mark;

  	res = ip_local_out(net, sk, skb);

  	rcu_read_unlock();
  	return res;

  
  no_route:

  	rcu_read_unlock();

  	IP_INC_STATS(net, IPSTATS_MIB_OUTNOROUTES);

  	kfree_skb(skb);
  	return -EHOSTUNREACH;
  }

  EXPORT_SYMBOL(__ip_queue_xmit);

  int ip_queue_xmit(struct sock *sk, struct sk_buff *skb, struct flowi *fl)
  {
  	return __ip_queue_xmit(sk, skb, fl, inet_sk(sk)->tos);
  }
  EXPORT_SYMBOL(ip_queue_xmit);

  static void ip_copy_metadata(struct sk_buff *to, struct sk_buff *from)
  {
  	to->pkt_type = from->pkt_type;
  	to->priority = from->priority;
  	to->protocol = from->protocol;

  	to->skb_iif = from->skb_iif;

  	skb_dst_drop(to);

  	skb_dst_copy(to, from);

  	to->dev = from->dev;

  	to->mark = from->mark;

  	skb_copy_hash(to, from);

  #ifdef CONFIG_NET_SCHED
  	to->tc_index = from->tc_index;
  #endif

  	nf_copy(to, from);

  	skb_ext_copy(to, from);

  #if IS_ENABLED(CONFIG_IP_VS)

  	to->ipvs_property = from->ipvs_property;
  #endif

  	skb_copy_secmark(to, from);

  }

  static int ip_fragment(struct net *net, struct sock *sk, struct sk_buff *skb,

  		       unsigned int mtu,

  		       int (*output)(struct net *, struct sock *, struct sk_buff *))

  {
  	struct iphdr *iph = ip_hdr(skb);

  	if ((iph->frag_off & htons(IP_DF)) == 0)

  		return ip_do_fragment(net, sk, skb, output);

  
  	if (unlikely(!skb->ignore_df ||

  		     (IPCB(skb)->frag_max_size &&
  		      IPCB(skb)->frag_max_size > mtu))) {

  		IP_INC_STATS(net, IPSTATS_MIB_FRAGFAILS);

  		icmp_send(skb, ICMP_DEST_UNREACH, ICMP_FRAG_NEEDED,
  			  htonl(mtu));
  		kfree_skb(skb);
  		return -EMSGSIZE;
  	}

  	return ip_do_fragment(net, sk, skb, output);

  }

  void ip_fraglist_init(struct sk_buff *skb, struct iphdr *iph,
  		      unsigned int hlen, struct ip_fraglist_iter *iter)
  {
  	unsigned int first_len = skb_pagelen(skb);

  	iter->frag = skb_shinfo(skb)->frag_list;

  	skb_frag_list_init(skb);
  
  	iter->offset = 0;
  	iter->iph = iph;
  	iter->hlen = hlen;
  
  	skb->data_len = first_len - skb_headlen(skb);
  	skb->len = first_len;
  	iph->tot_len = htons(first_len);
  	iph->frag_off = htons(IP_MF);
  	ip_send_check(iph);
  }
  EXPORT_SYMBOL(ip_fraglist_init);

  static void ip_fraglist_ipcb_prepare(struct sk_buff *skb,
  				     struct ip_fraglist_iter *iter)
  {
  	struct sk_buff *to = iter->frag;
  
  	/* Copy the flags to each fragment. */
  	IPCB(to)->flags = IPCB(skb)->flags;
  
  	if (iter->offset == 0)
  		ip_options_fragment(to);
  }

  void ip_fraglist_prepare(struct sk_buff *skb, struct ip_fraglist_iter *iter)
  {
  	unsigned int hlen = iter->hlen;
  	struct iphdr *iph = iter->iph;
  	struct sk_buff *frag;
  
  	frag = iter->frag;
  	frag->ip_summed = CHECKSUM_NONE;
  	skb_reset_transport_header(frag);
  	__skb_push(frag, hlen);
  	skb_reset_network_header(frag);
  	memcpy(skb_network_header(frag), iph, hlen);
  	iter->iph = ip_hdr(frag);
  	iph = iter->iph;
  	iph->tot_len = htons(frag->len);
  	ip_copy_metadata(frag, skb);

  	iter->offset += skb->len - hlen;
  	iph->frag_off = htons(iter->offset >> 3);
  	if (frag->next)
  		iph->frag_off |= htons(IP_MF);
  	/* Ready, complete checksum */
  	ip_send_check(iph);
  }
  EXPORT_SYMBOL(ip_fraglist_prepare);

  void ip_frag_init(struct sk_buff *skb, unsigned int hlen,

  		  unsigned int ll_rs, unsigned int mtu, bool DF,

  		  struct ip_frag_state *state)
  {
  	struct iphdr *iph = ip_hdr(skb);

  	state->DF = DF;

  	state->hlen = hlen;
  	state->ll_rs = ll_rs;
  	state->mtu = mtu;
  
  	state->left = skb->len - hlen;	/* Space per frame */
  	state->ptr = hlen;		/* Where to start from */
  
  	state->offset = (ntohs(iph->frag_off) & IP_OFFSET) << 3;
  	state->not_last_frag = iph->frag_off & htons(IP_MF);
  }
  EXPORT_SYMBOL(ip_frag_init);

  static void ip_frag_ipcb(struct sk_buff *from, struct sk_buff *to,
  			 bool first_frag, struct ip_frag_state *state)
  {
  	/* Copy the flags to each fragment. */
  	IPCB(to)->flags = IPCB(from)->flags;

  	/* ANK: dirty, but effective trick. Upgrade options only if
  	 * the segment to be fragmented was THE FIRST (otherwise,
  	 * options are already fixed) and make it ONCE
  	 * on the initial skb, so that all the following fragments
  	 * will inherit fixed options.
  	 */
  	if (first_frag)
  		ip_options_fragment(from);
  }

  struct sk_buff *ip_frag_next(struct sk_buff *skb, struct ip_frag_state *state)
  {
  	unsigned int len = state->left;
  	struct sk_buff *skb2;
  	struct iphdr *iph;
  
  	len = state->left;
  	/* IF: it doesn't fit, use 'mtu' - the data space left */
  	if (len > state->mtu)
  		len = state->mtu;
  	/* IF: we are not sending up to and including the packet end
  	   then align the next start on an eight byte boundary */
  	if (len < state->left)	{
  		len &= ~7;
  	}
  
  	/* Allocate buffer */
  	skb2 = alloc_skb(len + state->hlen + state->ll_rs, GFP_ATOMIC);
  	if (!skb2)
  		return ERR_PTR(-ENOMEM);
  
  	/*
  	 *	Set up data on packet
  	 */
  
  	ip_copy_metadata(skb2, skb);
  	skb_reserve(skb2, state->ll_rs);
  	skb_put(skb2, len + state->hlen);
  	skb_reset_network_header(skb2);
  	skb2->transport_header = skb2->network_header + state->hlen;
  
  	/*
  	 *	Charge the memory for the fragment to any owner
  	 *	it might possess
  	 */
  
  	if (skb->sk)
  		skb_set_owner_w(skb2, skb->sk);
  
  	/*
  	 *	Copy the packet header into the new buffer.
  	 */
  
  	skb_copy_from_linear_data(skb, skb_network_header(skb2), state->hlen);
  
  	/*
  	 *	Copy a block of the IP datagram.
  	 */
  	if (skb_copy_bits(skb, state->ptr, skb_transport_header(skb2), len))
  		BUG();
  	state->left -= len;
  
  	/*
  	 *	Fill in the new header fields.
  	 */
  	iph = ip_hdr(skb2);
  	iph->frag_off = htons((state->offset >> 3));

  	if (state->DF)
  		iph->frag_off |= htons(IP_DF);

  	/*
  	 *	Added AC : If we are fragmenting a fragment that's not the
  	 *		   last fragment then keep MF on each bit
  	 */
  	if (state->left > 0 || state->not_last_frag)
  		iph->frag_off |= htons(IP_MF);
  	state->ptr += len;
  	state->offset += len;
  
  	iph->tot_len = htons(len + state->hlen);
  
  	ip_send_check(iph);
  
  	return skb2;
  }
  EXPORT_SYMBOL(ip_frag_next);

  /*
   *	This IP datagram is too large to be sent in one piece.  Break it up into
   *	smaller pieces (each of size equal to IP header plus
   *	a block of the data of the original IP data part) that will yet fit in a
   *	single device frame, and queue such a frame for sending.
   */

  int ip_do_fragment(struct net *net, struct sock *sk, struct sk_buff *skb,
  		   int (*output)(struct net *, struct sock *, struct sk_buff *))

  {
  	struct iphdr *iph;

  	struct sk_buff *skb2;

  	struct rtable *rt = skb_rtable(skb);

  	unsigned int mtu, hlen, ll_rs;

  	struct ip_fraglist_iter iter;

  	ktime_t tstamp = skb->tstamp;

  	struct ip_frag_state state;

  	int err = 0;

  	/* for offloaded checksums cleanup checksum before fragmentation */
  	if (skb->ip_summed == CHECKSUM_PARTIAL &&
  	    (err = skb_checksum_help(skb)))
  		goto fail;

  	/*
  	 *	Point into the IP datagram header.
  	 */

  	iph = ip_hdr(skb);

  	mtu = ip_skb_dst_mtu(sk, skb);

  	if (IPCB(skb)->frag_max_size && IPCB(skb)->frag_max_size < mtu)
  		mtu = IPCB(skb)->frag_max_size;

  
  	/*
  	 *	Setup starting values.
  	 */
  
  	hlen = iph->ihl * 4;

  	mtu = mtu - hlen;	/* Size of data space */

  	IPCB(skb)->flags |= IPSKB_FRAG_COMPLETE;

  	ll_rs = LL_RESERVED_SPACE(rt->dst.dev);

  
  	/* When frag_list is given, use it. First, check its validity:
  	 * some transformers could create wrong frag_list or break existing
  	 * one, it is not prohibited. In this case fall back to copying.
  	 *
  	 * LATER: this step can be merged to real generation of fragments,
  	 * we can switch to copy when see the first bad fragment.
  	 */

  	if (skb_has_frag_list(skb)) {

  		struct sk_buff *frag, *frag2;

  		unsigned int first_len = skb_pagelen(skb);

  
  		if (first_len - hlen > mtu ||
  		    ((first_len - hlen) & 7) ||

  		    ip_is_fragment(iph) ||

  		    skb_cloned(skb) ||
  		    skb_headroom(skb) < ll_rs)

  			goto slow_path;

  		skb_walk_frags(skb, frag) {

  			/* Correct geometry. */
  			if (frag->len > mtu ||
  			    ((frag->len & 7) && frag->next) ||

  			    skb_headroom(frag) < hlen + ll_rs)

  				goto slow_path_clean;

  
  			/* Partially cloned skb? */
  			if (skb_shared(frag))

  				goto slow_path_clean;

  
  			BUG_ON(frag->sk);
  			if (skb->sk) {

  				frag->sk = skb->sk;
  				frag->destructor = sock_wfree;

  			}

  			skb->truesize -= frag->truesize;

  		}
  
  		/* Everything is OK. Generate! */

  		ip_fraglist_init(skb, iph, hlen, &iter);

  
  		for (;;) {
  			/* Prepare header of the next frame,
  			 * before previous one went down. */

  			if (iter.frag) {
  				ip_fraglist_ipcb_prepare(skb, &iter);

  				ip_fraglist_prepare(skb, &iter);

  			}

  			skb->tstamp = tstamp;

  			err = output(net, sk, skb);

  			if (!err)

  				IP_INC_STATS(net, IPSTATS_MIB_FRAGCREATES);

  			if (err || !iter.frag)

  				break;

  			skb = ip_fraglist_next(&iter);

  		}
  
  		if (err == 0) {

  			IP_INC_STATS(net, IPSTATS_MIB_FRAGOKS);

  			return 0;
  		}

  		kfree_skb_list(iter.frag);

  		IP_INC_STATS(net, IPSTATS_MIB_FRAGFAILS);

  		return err;

  
  slow_path_clean:
  		skb_walk_frags(skb, frag2) {
  			if (frag2 == frag)
  				break;
  			frag2->sk = NULL;
  			frag2->destructor = NULL;
  			skb->truesize += frag2->truesize;
  		}

  	}
  
  slow_path:

  	/*
  	 *	Fragment the datagram.
  	 */

  	ip_frag_init(skb, hlen, ll_rs, mtu, IPCB(skb)->flags & IPSKB_FRAG_PMTU,
  		     &state);

  
  	/*
  	 *	Keep copying data until we run out.
  	 */

  	while (state.left > 0) {

  		bool first_frag = (state.offset == 0);

  		skb2 = ip_frag_next(skb, &state);
  		if (IS_ERR(skb2)) {
  			err = PTR_ERR(skb2);

  			goto fail;
  		}

  		ip_frag_ipcb(skb, skb2, first_frag, &state);

  
  		/*

  		 *	Put this fragment into the sending queue.
  		 */

  		skb2->tstamp = tstamp;

  		err = output(net, sk, skb2);

  		if (err)
  			goto fail;

  		IP_INC_STATS(net, IPSTATS_MIB_FRAGCREATES);

  	}

  	consume_skb(skb);

  	IP_INC_STATS(net, IPSTATS_MIB_FRAGOKS);

  	return err;
  
  fail:

  	kfree_skb(skb);

  	IP_INC_STATS(net, IPSTATS_MIB_FRAGFAILS);

  	return err;
  }

  EXPORT_SYMBOL(ip_do_fragment);

  int
  ip_generic_getfrag(void *from, char *to, int offset, int len, int odd, struct sk_buff *skb)
  {

  	struct msghdr *msg = from;

  	if (skb->ip_summed == CHECKSUM_PARTIAL) {

  		if (!copy_from_iter_full(to, len, &msg->msg_iter))

  			return -EFAULT;
  	} else {

  		__wsum csum = 0;

  		if (!csum_and_copy_from_iter_full(to, len, &csum, &msg->msg_iter))

  			return -EFAULT;
  		skb->csum = csum_block_add(skb->csum, csum, odd);
  	}
  	return 0;
  }

  EXPORT_SYMBOL(ip_generic_getfrag);

  static inline __wsum

  csum_page(struct page *page, int offset, int copy)
  {
  	char *kaddr;

  	__wsum csum;

  	kaddr = kmap(page);
  	csum = csum_partial(kaddr + offset, copy, 0);
  	kunmap(page);
  	return csum;
  }

  static int __ip_append_data(struct sock *sk,
  			    struct flowi4 *fl4,
  			    struct sk_buff_head *queue,

  			    struct inet_cork *cork,

  			    struct page_frag *pfrag,

  			    int getfrag(void *from, char *to, int offset,
  					int len, int odd, struct sk_buff *skb),
  			    void *from, int length, int transhdrlen,
  			    unsigned int flags)

  {
  	struct inet_sock *inet = inet_sk(sk);

  	struct ubuf_info *uarg = NULL;

  	struct sk_buff *skb;

  	struct ip_options *opt = cork->opt;

  	int hh_len;
  	int exthdrlen;
  	int mtu;
  	int copy;
  	int err;
  	int offset = 0;

  	unsigned int maxfraglen, fragheaderlen, maxnonfragsize;

  	int csummode = CHECKSUM_NONE;

  	struct rtable *rt = (struct rtable *)cork->dst;

  	unsigned int wmem_alloc_delta = 0;

  	bool paged, extra_uref = false;

  	u32 tskey = 0;

  	skb = skb_peek_tail(queue);
  
  	exthdrlen = !skb ? rt->dst.header_len : 0;

  	mtu = cork->gso_size ? IP_MAX_MTU : cork->fragsize;

  	paged = !!cork->gso_size;

  	if (cork->tx_flags & SKBTX_ANY_SW_TSTAMP &&
  	    sk->sk_tsflags & SOF_TIMESTAMPING_OPT_ID)
  		tskey = sk->sk_tskey++;

  	hh_len = LL_RESERVED_SPACE(rt->dst.dev);

  
  	fragheaderlen = sizeof(struct iphdr) + (opt ? opt->optlen : 0);
  	maxfraglen = ((mtu - fragheaderlen) & ~7) + fragheaderlen;

  	maxnonfragsize = ip_sk_ignore_df(sk) ? IP_MAX_MTU : mtu;

  	if (cork->length + length > maxnonfragsize - fragheaderlen) {

  		ip_local_error(sk, EMSGSIZE, fl4->daddr, inet->inet_dport,

  			       mtu - (opt ? opt->optlen : 0));

  		return -EMSGSIZE;
  	}
  
  	/*
  	 * transhdrlen > 0 means that this is the first fragment and we wish
  	 * it won't be fragmented in the future.
  	 */
  	if (transhdrlen &&
  	    length + fragheaderlen <= mtu &&

  	    rt->dst.dev->features & (NETIF_F_HW_CSUM | NETIF_F_IP_CSUM) &&

  	    (!(flags & MSG_MORE) || cork->gso_size) &&

  	    (!exthdrlen || (rt->dst.dev->features & NETIF_F_HW_ESP_TX_CSUM)))

  		csummode = CHECKSUM_PARTIAL;

  	if (flags & MSG_ZEROCOPY && length && sock_flag(sk, SOCK_ZEROCOPY)) {
  		uarg = sock_zerocopy_realloc(sk, length, skb_zcopy(skb));
  		if (!uarg)
  			return -ENOBUFS;

  		extra_uref = !skb_zcopy(skb);	/* only ref on new uarg */

  		if (rt->dst.dev->features & NETIF_F_SG &&
  		    csummode == CHECKSUM_PARTIAL) {
  			paged = true;
  		} else {
  			uarg->zerocopy = 0;

  			skb_zcopy_set(skb, uarg, &extra_uref);

  		}
  	}

  	cork->length += length;

  
  	/* So, what's going on in the loop below?
  	 *
  	 * We use calculated fragment length to generate chained skb,
  	 * each of segments is IP fragment ready for sending to network after
  	 * adding appropriate IP header.
  	 */

  	if (!skb)

  		goto alloc_new_skb;
  
  	while (length > 0) {
  		/* Check if the remaining data fits into current packet. */
  		copy = mtu - skb->len;
  		if (copy < length)
  			copy = maxfraglen - skb->len;
  		if (copy <= 0) {
  			char *data;
  			unsigned int datalen;
  			unsigned int fraglen;
  			unsigned int fraggap;
  			unsigned int alloclen;

  			unsigned int pagedlen;

  			struct sk_buff *skb_prev;
  alloc_new_skb:
  			skb_prev = skb;
  			if (skb_prev)
  				fraggap = skb_prev->len - maxfraglen;
  			else
  				fraggap = 0;
  
  			/*
  			 * If remaining data exceeds the mtu,
  			 * we know we need more fragment(s).
  			 */
  			datalen = length + fraggap;
  			if (datalen > mtu - fragheaderlen)
  				datalen = maxfraglen - fragheaderlen;
  			fraglen = datalen + fragheaderlen;

  			pagedlen = 0;

  			if ((flags & MSG_MORE) &&

  			    !(rt->dst.dev->features&NETIF_F_SG))

  				alloclen = mtu;

  			else if (!paged)

  				alloclen = fraglen;

  			else {
  				alloclen = min_t(int, fraglen, MAX_HEADER);
  				pagedlen = fraglen - alloclen;
  			}

  			alloclen += exthdrlen;

  			/* The last fragment gets additional space at tail.
  			 * Note, with MSG_MORE we overallocate on fragments,
  			 * because we have no idea what fragment will be
  			 * the last.
  			 */

  			if (datalen == length + fraggap)

  				alloclen += rt->dst.trailer_len;

  			if (transhdrlen) {

  				skb = sock_alloc_send_skb(sk,

  						alloclen + hh_len + 15,
  						(flags & MSG_DONTWAIT), &err);
  			} else {
  				skb = NULL;

  				if (refcount_read(&sk->sk_wmem_alloc) + wmem_alloc_delta <=

  				    2 * sk->sk_sndbuf)

  					skb = alloc_skb(alloclen + hh_len + 15,
  							sk->sk_allocation);

  				if (unlikely(!skb))

  					err = -ENOBUFS;
  			}

  			if (!skb)

  				goto error;
  
  			/*
  			 *	Fill in the control structures
  			 */
  			skb->ip_summed = csummode;
  			skb->csum = 0;
  			skb_reserve(skb, hh_len);

  			/*
  			 *	Find where to start putting bytes.
  			 */

  			data = skb_put(skb, fraglen + exthdrlen - pagedlen);

  			skb_set_network_header(skb, exthdrlen);

  			skb->transport_header = (skb->network_header +
  						 fragheaderlen);

  			data += fragheaderlen + exthdrlen;

  
  			if (fraggap) {
  				skb->csum = skb_copy_and_csum_bits(
  					skb_prev, maxfraglen,

  					data + transhdrlen, fraggap);

  				skb_prev->csum = csum_sub(skb_prev->csum,
  							  skb->csum);
  				data += fraggap;

  				pskb_trim_unique(skb_prev, maxfraglen);

  			}

  			copy = datalen - transhdrlen - fraggap - pagedlen;

  			if (copy > 0 && getfrag(from, data + transhdrlen, offset, copy, fraggap, skb) < 0) {
  				err = -EFAULT;
  				kfree_skb(skb);
  				goto error;
  			}
  
  			offset += copy;

  			length -= copy + transhdrlen;

  			transhdrlen = 0;
  			exthdrlen = 0;
  			csummode = CHECKSUM_NONE;

  			/* only the initial fragment is time stamped */
  			skb_shinfo(skb)->tx_flags = cork->tx_flags;
  			cork->tx_flags = 0;
  			skb_shinfo(skb)->tskey = tskey;
  			tskey = 0;
  			skb_zcopy_set(skb, uarg, &extra_uref);

  			if ((flags & MSG_CONFIRM) && !skb_prev)
  				skb_set_dst_pending_confirm(skb, 1);

  			/*
  			 * Put the packet on the pending queue.
  			 */

  			if (!skb->destructor) {
  				skb->destructor = sock_wfree;
  				skb->sk = sk;
  				wmem_alloc_delta += skb->truesize;
  			}

  			__skb_queue_tail(queue, skb);

  			continue;
  		}
  
  		if (copy > length)
  			copy = length;

  		if (!(rt->dst.dev->features&NETIF_F_SG) &&
  		    skb_tailroom(skb) >= copy) {

  			unsigned int off;
  
  			off = skb->len;

  			if (getfrag(from, skb_put(skb, copy),

  					offset, copy, off, skb) < 0) {
  				__skb_trim(skb, off);
  				err = -EFAULT;
  				goto error;
  			}

  		} else if (!uarg || !uarg->zerocopy) {

  			int i = skb_shinfo(skb)->nr_frags;

  			err = -ENOMEM;
  			if (!sk_page_frag_refill(sk, pfrag))

  				goto error;

  
  			if (!skb_can_coalesce(skb, i, pfrag->page,
  					      pfrag->offset)) {
  				err = -EMSGSIZE;
  				if (i == MAX_SKB_FRAGS)
  					goto error;
  
  				__skb_fill_page_desc(skb, i, pfrag->page,
  						     pfrag->offset, 0);
  				skb_shinfo(skb)->nr_frags = ++i;
  				get_page(pfrag->page);

  			}

  			copy = min_t(int, copy, pfrag->size - pfrag->offset);
  			if (getfrag(from,
  				    page_address(pfrag->page) + pfrag->offset,
  				    offset, copy, skb->len, skb) < 0)
  				goto error_efault;
  
  			pfrag->offset += copy;
  			skb_frag_size_add(&skb_shinfo(skb)->frags[i - 1], copy);

  			skb->len += copy;
  			skb->data_len += copy;

  			skb->truesize += copy;

  			wmem_alloc_delta += copy;

  		} else {
  			err = skb_zerocopy_iter_dgram(skb, from, copy);
  			if (err < 0)
  				goto error;

  		}
  		offset += copy;
  		length -= copy;
  	}

  	if (wmem_alloc_delta)
  		refcount_add(wmem_alloc_delta, &sk->sk_wmem_alloc);

  	return 0;

  error_efault:
  	err = -EFAULT;

  error:

  	if (uarg)
  		sock_zerocopy_put_abort(uarg, extra_uref);

  	cork->length -= length;

  	IP_INC_STATS(sock_net(sk), IPSTATS_MIB_OUTDISCARDS);

  	refcount_add(wmem_alloc_delta, &sk->sk_wmem_alloc);

  	return err;

  }

  static int ip_setup_cork(struct sock *sk, struct inet_cork *cork,
  			 struct ipcm_cookie *ipc, struct rtable **rtp)
  {

  	struct ip_options_rcu *opt;

  	struct rtable *rt;

  	rt = *rtp;
  	if (unlikely(!rt))
  		return -EFAULT;

  	/*
  	 * setup for corking.
  	 */
  	opt = ipc->opt;
  	if (opt) {

  		if (!cork->opt) {

  			cork->opt = kmalloc(sizeof(struct ip_options) + 40,
  					    sk->sk_allocation);

  			if (unlikely(!cork->opt))

  				return -ENOBUFS;
  		}

  		memcpy(cork->opt, &opt->opt, sizeof(struct ip_options) + opt->opt.optlen);

  		cork->flags |= IPCORK_OPT;
  		cork->addr = ipc->addr;
  	}

  	cork->fragsize = ip_sk_use_pmtu(sk) ?

  			 dst_mtu(&rt->dst) : READ_ONCE(rt->dst.dev->mtu);
  
  	if (!inetdev_valid_mtu(cork->fragsize))
  		return -ENETUNREACH;

  	cork->gso_size = ipc->gso_size;

  	cork->dst = &rt->dst;

  	/* We stole this route, caller should not release it. */
  	*rtp = NULL;

  	cork->length = 0;

  	cork->ttl = ipc->ttl;
  	cork->tos = ipc->tos;

  	cork->mark = ipc->sockc.mark;

  	cork->priority = ipc->priority;

  	cork->transmit_time = ipc->sockc.transmit_time;

  	cork->tx_flags = 0;
  	sock_tx_timestamp(sk, ipc->sockc.tsflags, &cork->tx_flags);

  
  	return 0;
  }
  
  /*
   *	ip_append_data() and ip_append_page() can make one large IP datagram
   *	from many pieces of data. Each pieces will be holded on the socket
   *	until ip_push_pending_frames() is called. Each piece can be a page
   *	or non-page data.
   *
   *	Not only UDP, other transport protocols - e.g. raw sockets - can use
   *	this interface potentially.
   *
   *	LATER: length must be adjusted by pad at tail, when it is required.
   */

  int ip_append_data(struct sock *sk, struct flowi4 *fl4,

  		   int getfrag(void *from, char *to, int offset, int len,
  			       int odd, struct sk_buff *skb),
  		   void *from, int length, int transhdrlen,
  		   struct ipcm_cookie *ipc, struct rtable **rtp,
  		   unsigned int flags)
  {
  	struct inet_sock *inet = inet_sk(sk);
  	int err;
  
  	if (flags&MSG_PROBE)
  		return 0;
  
  	if (skb_queue_empty(&sk->sk_write_queue)) {

  		err = ip_setup_cork(sk, &inet->cork.base, ipc, rtp);

  		if (err)
  			return err;
  	} else {
  		transhdrlen = 0;
  	}

  	return __ip_append_data(sk, fl4, &sk->sk_write_queue, &inet->cork.base,
  				sk_page_frag(sk), getfrag,

  				from, length, transhdrlen, flags);
  }

  ssize_t	ip_append_page(struct sock *sk, struct flowi4 *fl4, struct page *page,

  		       int offset, size_t size, int flags)
  {
  	struct inet_sock *inet = inet_sk(sk);
  	struct sk_buff *skb;
  	struct rtable *rt;
  	struct ip_options *opt = NULL;

  	struct inet_cork *cork;

  	int hh_len;
  	int mtu;
  	int len;
  	int err;

  	unsigned int maxfraglen, fragheaderlen, fraggap, maxnonfragsize;

  
  	if (inet->hdrincl)
  		return -EPERM;
  
  	if (flags&MSG_PROBE)
  		return 0;
  
  	if (skb_queue_empty(&sk->sk_write_queue))
  		return -EINVAL;

  	cork = &inet->cork.base;
  	rt = (struct rtable *)cork->dst;
  	if (cork->flags & IPCORK_OPT)
  		opt = cork->opt;

  	if (!(rt->dst.dev->features & NETIF_F_SG))

  		return -EOPNOTSUPP;

  	hh_len = LL_RESERVED_SPACE(rt->dst.dev);

  	mtu = cork->gso_size ? IP_MAX_MTU : cork->fragsize;

  
  	fragheaderlen = sizeof(struct iphdr) + (opt ? opt->optlen : 0);
  	maxfraglen = ((mtu - fragheaderlen) & ~7) + fragheaderlen;

  	maxnonfragsize = ip_sk_ignore_df(sk) ? 0xFFFF : mtu;

  	if (cork->length + size > maxnonfragsize - fragheaderlen) {

  		ip_local_error(sk, EMSGSIZE, fl4->daddr, inet->inet_dport,
  			       mtu - (opt ? opt->optlen : 0));

  		return -EMSGSIZE;
  	}

  	skb = skb_peek_tail(&sk->sk_write_queue);
  	if (!skb)

  		return -EINVAL;

  	cork->length += size;

  	while (size > 0) {

  		/* Check if the remaining data fits into current packet. */
  		len = mtu - skb->len;
  		if (len < size)
  			len = maxfraglen - skb->len;

  		if (len <= 0) {
  			struct sk_buff *skb_prev;

  			int alloclen;
  
  			skb_prev = skb;

  			fraggap = skb_prev->len - maxfraglen;

  
  			alloclen = fragheaderlen + hh_len + fraggap + 15;
  			skb = sock_wmalloc(sk, alloclen, 1, sk->sk_allocation);
  			if (unlikely(!skb)) {
  				err = -ENOBUFS;
  				goto error;
  			}
  
  			/*
  			 *	Fill in the control structures
  			 */
  			skb->ip_summed = CHECKSUM_NONE;
  			skb->csum = 0;
  			skb_reserve(skb, hh_len);
  
  			/*
  			 *	Find where to start putting bytes.
  			 */

  			skb_put(skb, fragheaderlen + fraggap);

  			skb_reset_network_header(skb);

  			skb->transport_header = (skb->network_header +
  						 fragheaderlen);

  			if (fraggap) {

  				skb->csum = skb_copy_and_csum_bits(skb_prev,
  								   maxfraglen,

  						    skb_transport_header(skb),

  								   fraggap);

  				skb_prev->csum = csum_sub(skb_prev->csum,
  							  skb->csum);

  				pskb_trim_unique(skb_prev, maxfraglen);

  			}
  
  			/*
  			 * Put the packet on the pending queue.
  			 */
  			__skb_queue_tail(&sk->sk_write_queue, skb);
  			continue;
  		}

  		if (len > size)
  			len = size;

  
  		if (skb_append_pagefrags(skb, page, offset, len)) {

  			err = -EMSGSIZE;
  			goto error;
  		}
  
  		if (skb->ip_summed == CHECKSUM_NONE) {

  			__wsum csum;

  			csum = csum_page(page, offset, len);
  			skb->csum = csum_block_add(skb->csum, csum, skb->len);
  		}
  
  		skb->len += len;
  		skb->data_len += len;

  		skb->truesize += len;

  		refcount_add(len, &sk->sk_wmem_alloc);

  		offset += len;
  		size -= len;
  	}
  	return 0;
  
  error:

  	cork->length -= size;

  	IP_INC_STATS(sock_net(sk), IPSTATS_MIB_OUTDISCARDS);

  	return err;
  }

  static void ip_cork_release(struct inet_cork *cork)

  {

  	cork->flags &= ~IPCORK_OPT;
  	kfree(cork->opt);
  	cork->opt = NULL;
  	dst_release(cork->dst);
  	cork->dst = NULL;

  }

  /*
   *	Combined all pending IP fragments on the socket as one IP datagram
   *	and push them out.
   */

  struct sk_buff *__ip_make_skb(struct sock *sk,

  			      struct flowi4 *fl4,

  			      struct sk_buff_head *queue,
  			      struct inet_cork *cork)

  {
  	struct sk_buff *skb, *tmp_skb;
  	struct sk_buff **tail_skb;
  	struct inet_sock *inet = inet_sk(sk);

  	struct net *net = sock_net(sk);

  	struct ip_options *opt = NULL;

  	struct rtable *rt = (struct rtable *)cork->dst;

  	struct iphdr *iph;

  	__be16 df = 0;

  	__u8 ttl;

  	skb = __skb_dequeue(queue);
  	if (!skb)

  		goto out;
  	tail_skb = &(skb_shinfo(skb)->frag_list);
  
  	/* move skb->data to ip header from ext header */

  	if (skb->data < skb_network_header(skb))

  		__skb_pull(skb, skb_network_offset(skb));

  	while ((tmp_skb = __skb_dequeue(queue)) != NULL) {

  		__skb_pull(tmp_skb, skb_network_header_len(skb));

  		*tail_skb = tmp_skb;
  		tail_skb = &(tmp_skb->next);
  		skb->len += tmp_skb->len;
  		skb->data_len += tmp_skb->len;
  		skb->truesize += tmp_skb->truesize;

  		tmp_skb->destructor = NULL;
  		tmp_skb->sk = NULL;
  	}
  
  	/* Unless user demanded real pmtu discovery (IP_PMTUDISC_DO), we allow
  	 * to fragment the frame generated here. No matter, what transforms
  	 * how transforms change size of the packet, it will come out.
  	 */

  	skb->ignore_df = ip_sk_ignore_df(sk);

  
  	/* DF bit is set when we want to see DF on outgoing frames.

  	 * If ignore_df is set too, we still allow to fragment this frame

  	 * locally. */

  	if (inet->pmtudisc == IP_PMTUDISC_DO ||
  	    inet->pmtudisc == IP_PMTUDISC_PROBE ||

  	    (skb->len <= dst_mtu(&rt->dst) &&
  	     ip_dont_fragment(sk, &rt->dst)))

  		df = htons(IP_DF);

  	if (cork->flags & IPCORK_OPT)
  		opt = cork->opt;

  	if (cork->ttl != 0)
  		ttl = cork->ttl;
  	else if (rt->rt_type == RTN_MULTICAST)

  		ttl = inet->mc_ttl;
  	else

  		ttl = ip_select_ttl(inet, &rt->dst);

  	iph = ip_hdr(skb);

  	iph->version = 4;
  	iph->ihl = 5;

  	iph->tos = (cork->tos != -1) ? cork->tos : inet->tos;

  	iph->frag_off = df;

  	iph->ttl = ttl;
  	iph->protocol = sk->sk_protocol;

  	ip_copy_addrs(iph, fl4);

  	ip_select_ident(net, skb, sk);

  	if (opt) {

  		iph->ihl += opt->optlen >> 2;

  		ip_options_build(skb, opt, cork->addr, rt, 0);
  	}

  	skb->priority = (cork->tos != -1) ? cork->priority: sk->sk_priority;

  	skb->mark = cork->mark;