/*
   * Copyright (c) 2007-2013 Nicira, Inc.
   *
   * This program is free software; you can redistribute it and/or
   * modify it under the terms of version 2 of the GNU General Public
   * License as published by the Free Software Foundation.
   *
   * This program is distributed in the hope that it will be useful, but
   * WITHOUT ANY WARRANTY; without even the implied warranty of
   * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
   * General Public License for more details.
   *
   * You should have received a copy of the GNU General Public License
   * along with this program; if not, write to the Free Software
   * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
   * 02110-1301, USA
   */

  #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
  
  #include <linux/if.h>
  #include <linux/skbuff.h>
  #include <linux/ip.h>
  #include <linux/if_tunnel.h>
  #include <linux/if_vlan.h>
  #include <linux/in.h>

  #include <linux/in_route.h>
  #include <linux/inetdevice.h>
  #include <linux/jhash.h>
  #include <linux/list.h>
  #include <linux/kernel.h>
  #include <linux/workqueue.h>
  #include <linux/rculist.h>
  #include <net/route.h>
  #include <net/xfrm.h>
  
  #include <net/icmp.h>
  #include <net/ip.h>
  #include <net/ip_tunnels.h>
  #include <net/gre.h>
  #include <net/net_namespace.h>
  #include <net/netns/generic.h>
  #include <net/protocol.h>
  
  #include "datapath.h"
  #include "vport.h"
  
  /* Returns the least-significant 32 bits of a __be64. */
  static __be32 be64_get_low32(__be64 x)
  {
  #ifdef __BIG_ENDIAN
  	return (__force __be32)x;
  #else
  	return (__force __be32)((__force u64)x >> 32);
  #endif
  }
  
  static __be16 filter_tnl_flags(__be16 flags)
  {
  	return flags & (TUNNEL_CSUM | TUNNEL_KEY);
  }
  
  static struct sk_buff *__build_header(struct sk_buff *skb,
  				      int tunnel_hlen)
  {
  	const struct ovs_key_ipv4_tunnel *tun_key = OVS_CB(skb)->tun_key;
  	struct tnl_ptk_info tpi;
  
  	skb = gre_handle_offloads(skb, !!(tun_key->tun_flags & TUNNEL_CSUM));
  	if (IS_ERR(skb))
  		return NULL;
  
  	tpi.flags = filter_tnl_flags(tun_key->tun_flags);
  	tpi.proto = htons(ETH_P_TEB);
  	tpi.key = be64_get_low32(tun_key->tun_id);
  	tpi.seq = 0;
  	gre_build_header(skb, &tpi, tunnel_hlen);
  
  	return skb;
  }
  
  static __be64 key_to_tunnel_id(__be32 key, __be32 seq)
  {
  #ifdef __BIG_ENDIAN
  	return (__force __be64)((__force u64)seq << 32 | (__force u32)key);
  #else
  	return (__force __be64)((__force u64)key << 32 | (__force u32)seq);
  #endif
  }
  
  /* Called with rcu_read_lock and BH disabled. */
  static int gre_rcv(struct sk_buff *skb,
  		   const struct tnl_ptk_info *tpi)
  {
  	struct ovs_key_ipv4_tunnel tun_key;
  	struct ovs_net *ovs_net;
  	struct vport *vport;
  	__be64 key;
  
  	ovs_net = net_generic(dev_net(skb->dev), ovs_net_id);
  	vport = rcu_dereference(ovs_net->vport_net.gre_vport);
  	if (unlikely(!vport))
  		return PACKET_REJECT;
  
  	key = key_to_tunnel_id(tpi->key, tpi->seq);
  	ovs_flow_tun_key_init(&tun_key, ip_hdr(skb), key,
  			      filter_tnl_flags(tpi->flags));
  
  	ovs_vport_receive(vport, skb, &tun_key);
  	return PACKET_RCVD;
  }
  
  static int gre_tnl_send(struct vport *vport, struct sk_buff *skb)
  {
  	struct net *net = ovs_dp_get_net(vport->dp);
  	struct flowi4 fl;
  	struct rtable *rt;
  	int min_headroom;
  	int tunnel_hlen;
  	__be16 df;
  	int err;
  
  	if (unlikely(!OVS_CB(skb)->tun_key)) {
  		err = -EINVAL;
  		goto error;
  	}
  
  	/* Route lookup */
  	memset(&fl, 0, sizeof(fl));
  	fl.daddr = OVS_CB(skb)->tun_key->ipv4_dst;
  	fl.saddr = OVS_CB(skb)->tun_key->ipv4_src;
  	fl.flowi4_tos = RT_TOS(OVS_CB(skb)->tun_key->ipv4_tos);
  	fl.flowi4_mark = skb->mark;
  	fl.flowi4_proto = IPPROTO_GRE;
  
  	rt = ip_route_output_key(net, &fl);
  	if (IS_ERR(rt))
  		return PTR_ERR(rt);
  
  	tunnel_hlen = ip_gre_calc_hlen(OVS_CB(skb)->tun_key->tun_flags);
  
  	min_headroom = LL_RESERVED_SPACE(rt->dst.dev) + rt->dst.header_len
  			+ tunnel_hlen + sizeof(struct iphdr)
  			+ (vlan_tx_tag_present(skb) ? VLAN_HLEN : 0);
  	if (skb_headroom(skb) < min_headroom || skb_header_cloned(skb)) {
  		int head_delta = SKB_DATA_ALIGN(min_headroom -
  						skb_headroom(skb) +
  						16);
  		err = pskb_expand_head(skb, max_t(int, head_delta, 0),
  					0, GFP_ATOMIC);
  		if (unlikely(err))
  			goto err_free_rt;
  	}
  
  	if (vlan_tx_tag_present(skb)) {
  		if (unlikely(!__vlan_put_tag(skb,
  					     skb->vlan_proto,
  					     vlan_tx_tag_get(skb)))) {
  			err = -ENOMEM;
  			goto err_free_rt;
  		}
  		skb->vlan_tci = 0;
  	}
  
  	/* Push Tunnel header. */
  	skb = __build_header(skb, tunnel_hlen);
  	if (unlikely(!skb)) {
  		err = 0;
  		goto err_free_rt;
  	}
  
  	df = OVS_CB(skb)->tun_key->tun_flags & TUNNEL_DONT_FRAGMENT ?
  		htons(IP_DF) : 0;

  	skb->ignore_df = 1;

  	return iptunnel_xmit(skb->sk, rt, skb, fl.saddr,

  			     OVS_CB(skb)->tun_key->ipv4_dst, IPPROTO_GRE,
  			     OVS_CB(skb)->tun_key->ipv4_tos,

  			     OVS_CB(skb)->tun_key->ipv4_ttl, df, false);

  err_free_rt:
  	ip_rt_put(rt);
  error:
  	return err;
  }
  
  static struct gre_cisco_protocol gre_protocol = {
  	.handler        = gre_rcv,
  	.priority       = 1,
  };
  
  static int gre_ports;
  static int gre_init(void)
  {
  	int err;
  
  	gre_ports++;
  	if (gre_ports > 1)
  		return 0;
  
  	err = gre_cisco_register(&gre_protocol);
  	if (err)
  		pr_warn("cannot register gre protocol handler
  ");
  
  	return err;
  }
  
  static void gre_exit(void)
  {
  	gre_ports--;
  	if (gre_ports > 0)
  		return;
  
  	gre_cisco_unregister(&gre_protocol);
  }
  
  static const char *gre_get_name(const struct vport *vport)
  {
  	return vport_priv(vport);
  }
  
  static struct vport *gre_create(const struct vport_parms *parms)
  {
  	struct net *net = ovs_dp_get_net(parms->dp);
  	struct ovs_net *ovs_net;
  	struct vport *vport;
  	int err;
  
  	err = gre_init();
  	if (err)
  		return ERR_PTR(err);
  
  	ovs_net = net_generic(net, ovs_net_id);
  	if (ovsl_dereference(ovs_net->vport_net.gre_vport)) {
  		vport = ERR_PTR(-EEXIST);
  		goto error;
  	}
  
  	vport = ovs_vport_alloc(IFNAMSIZ, &ovs_gre_vport_ops, parms);
  	if (IS_ERR(vport))
  		goto error;
  
  	strncpy(vport_priv(vport), parms->name, IFNAMSIZ);
  	rcu_assign_pointer(ovs_net->vport_net.gre_vport, vport);
  	return vport;
  
  error:
  	gre_exit();
  	return vport;
  }
  
  static void gre_tnl_destroy(struct vport *vport)
  {
  	struct net *net = ovs_dp_get_net(vport->dp);
  	struct ovs_net *ovs_net;
  
  	ovs_net = net_generic(net, ovs_net_id);

  	RCU_INIT_POINTER(ovs_net->vport_net.gre_vport, NULL);

  	ovs_vport_deferred_free(vport);
  	gre_exit();
  }
  
  const struct vport_ops ovs_gre_vport_ops = {
  	.type		= OVS_VPORT_TYPE_GRE,
  	.create		= gre_create,
  	.destroy	= gre_tnl_destroy,
  	.get_name	= gre_get_name,
  	.send		= gre_tnl_send,
  };