/*
 * ip_vs_xmit.c: various packet transmitters for IPVS
 *
 * Version:     $Id: ip_vs_xmit.c,v 1.2 2002/11/30 01:50:35 wensong Exp $
 *
 * Authors:     Wensong Zhang <wensong@linuxvirtualserver.org>
 *              Julian Anastasov <ja@ssi.bg>
 *
 *              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.
 *
 * Changes:
 *
 */

#include <linux/kernel.h>
#include <linux/tcp.h>                  /* for tcphdr */
#include <net/ip.h>
#include <net/tcp.h>                    /* for csum_tcpudp_magic */
#include <net/udp.h>
#include <net/icmp.h>                   /* for icmp_send */
#include <net/route.h>                  /* for ip_route_output */
#include <linux/netfilter.h>
#include <linux/netfilter_ipv4.h>

#include <net/ip_vs.h>


/*
 *      Destination cache to speed up outgoing route lookup
 */
static inline void
__ip_vs_dst_set(struct ip_vs_dest *dest, u32 rtos, struct dst_entry *dst)
{
        struct dst_entry *old_dst;

        old_dst = dest->dst_cache;
        dest->dst_cache = dst;
        dest->dst_rtos = rtos;
        dst_release(old_dst);
}

static inline struct dst_entry *
__ip_vs_dst_check(struct ip_vs_dest *dest, u32 rtos, u32 cookie)
{
        struct dst_entry *dst = dest->dst_cache;

        if (!dst)
                return NULL;
        if ((dst->obsolete || rtos != dest->dst_rtos) &&
            dst->ops->check(dst, cookie) == NULL) {
                dest->dst_cache = NULL;
                dst_release(dst);
                return NULL;
        }
        dst_hold(dst);
        return dst;
}

static struct rtable *
__ip_vs_get_out_rt(struct ip_vs_conn *cp, u32 rtos)
{
        struct rtable *rt;                      /* Route to the other host */
        struct ip_vs_dest *dest = cp->dest;

        if (dest) {
                spin_lock(&dest->dst_lock);
                if (!(rt = (struct rtable *)
                      __ip_vs_dst_check(dest, rtos, 0))) {
                        struct flowi fl = {
                                .oif = 0,
                                .nl_u = {
                                        .ip4_u = {
                                                .daddr = dest->addr,
                                                .saddr = 0,
                                                .tos = rtos, } },
                        };

                        if (ip_route_output_key(&init_net, &rt, &fl)) {
                                spin_unlock(&dest->dst_lock);
                                IP_VS_DBG_RL("ip_route_output error, "
                                             "dest: %u.%u.%u.%u\n",
                                             NIPQUAD(dest->addr));
                                return NULL;
                        }
                        __ip_vs_dst_set(dest, rtos, dst_clone(&rt->u.dst));
                        IP_VS_DBG(10, "new dst %u.%u.%u.%u, refcnt=%d, rtos=%X\n",
                                  NIPQUAD(dest->addr),
                                  atomic_read(&rt->u.dst.__refcnt), rtos);
                }
                spin_unlock(&dest->dst_lock);
        } else {
                struct flowi fl = {
                        .oif = 0,
                        .nl_u = {
                                .ip4_u = {
                                        .daddr = cp->daddr,
                                        .saddr = 0,
                                        .tos = rtos, } },
                };

                if (ip_route_output_key(&init_net, &rt, &fl)) {
                        IP_VS_DBG_RL("ip_route_output error, dest: "
                                     "%u.%u.%u.%u\n", NIPQUAD(cp->daddr));
                        return NULL;
                }
        }

        return rt;
}


/*
 *      Release dest->dst_cache before a dest is removed
 */
void
ip_vs_dst_reset(struct ip_vs_dest *dest)
{
        struct dst_entry *old_dst;

        old_dst = dest->dst_cache;
        dest->dst_cache = NULL;
        dst_release(old_dst);
}

#define IP_VS_XMIT(skb, rt)                             \
do {                                                    \
        (skb)->ipvs_property = 1;                       \
        skb_forward_csum(skb);                          \
        NF_HOOK(PF_INET, NF_INET_LOCAL_OUT, (skb), NULL,        \
                (rt)->u.dst.dev, dst_output);           \
} while (0)


/*
 *      NULL transmitter (do nothing except return NF_ACCEPT)
 */
int
ip_vs_null_xmit(struct sk_buff *skb, struct ip_vs_conn *cp,
                struct ip_vs_protocol *pp)
{
        /* we do not touch skb and do not need pskb ptr */
        return NF_ACCEPT;
}


/*
 *      Bypass transmitter
 *      Let packets bypass the destination when the destination is not
 *      available, it may be only used in transparent cache cluster.
 */
int
ip_vs_bypass_xmit(struct sk_buff *skb, struct ip_vs_conn *cp,
                  struct ip_vs_protocol *pp)
{
        struct rtable *rt;                      /* Route to the other host */
        struct iphdr  *iph = ip_hdr(skb);
        u8     tos = iph->tos;
        int    mtu;
        struct flowi fl = {
                .oif = 0,
                .nl_u = {
                        .ip4_u = {
                                .daddr = iph->daddr,
                                .saddr = 0,
                                .tos = RT_TOS(tos), } },
        };

        EnterFunction(10);

        if (ip_route_output_key(&init_net, &rt, &fl)) {
                IP_VS_DBG_RL("ip_vs_bypass_xmit(): ip_route_output error, "
                             "dest: %u.%u.%u.%u\n", NIPQUAD(iph->daddr));
                goto tx_error_icmp;
        }

        /* MTU checking */
        mtu = dst_mtu(&rt->u.dst);
        if ((skb->len > mtu) && (iph->frag_off & htons(IP_DF))) {
                ip_rt_put(rt);
                icmp_send(skb, ICMP_DEST_UNREACH,ICMP_FRAG_NEEDED, htonl(mtu));
                IP_VS_DBG_RL("ip_vs_bypass_xmit(): frag needed\n");
                goto tx_error;
        }

        /*
         * Call ip_send_check because we are not sure it is called
         * after ip_defrag. Is copy-on-write needed?
         */
        if (unlikely((skb = skb_share_check(skb, GFP_ATOMIC)) == NULL)) {
                ip_rt_put(rt);
                return NF_STOLEN;
        }
        ip_send_check(ip_hdr(skb));

        /* drop old route */
        dst_release(skb->dst);
        skb->dst = &rt->u.dst;

        /* Another hack: avoid icmp_send in ip_fragment */
        skb->local_df = 1;

        IP_VS_XMIT(skb, rt);

        LeaveFunction(10);
        return NF_STOLEN;

 tx_error_icmp:
        dst_link_failure(skb);
 tx_error:
        kfree_skb(skb);
        LeaveFunction(10);
        return NF_STOLEN;
}


/*
 *      NAT transmitter (only for outside-to-inside nat forwarding)
 *      Not used for related ICMP
 */
int
ip_vs_nat_xmit(struct sk_buff *skb, struct ip_vs_conn *cp,
               struct ip_vs_protocol *pp)
{
        struct rtable *rt;              /* Route to the other host */
        int mtu;
        struct iphdr *iph = ip_hdr(skb);

        EnterFunction(10);

        /* check if it is a connection of no-client-port */
        if (unlikely(cp->flags & IP_VS_CONN_F_NO_CPORT)) {
                __be16 _pt, *p;
                p = skb_header_pointer(skb, iph->ihl*4, sizeof(_pt), &_pt);
                if (p == NULL)
                        goto tx_error;
                ip_vs_conn_fill_cport(cp, *p);
                IP_VS_DBG(10, "filled cport=%d\n", ntohs(*p));
        }

        if (!(rt = __ip_vs_get_out_rt(cp, RT_TOS(iph->tos))))
                goto tx_error_icmp;

        /* MTU checking */
        mtu = dst_mtu(&rt->u.dst);
        if ((skb->len > mtu) && (iph->frag_off & htons(IP_DF))) {
                ip_rt_put(rt);
                icmp_send(skb, ICMP_DEST_UNREACH,ICMP_FRAG_NEEDED, htonl(mtu));
                IP_VS_DBG_RL_PKT(0, pp, skb, 0, "ip_vs_nat_xmit(): frag needed for");
                goto tx_error;
        }

        /* copy-on-write the packet before mangling it */
        if (!skb_make_writable(skb, sizeof(struct iphdr)))
                goto tx_error_put;

        if (skb_cow(skb, rt->u.dst.dev->hard_header_len))
                goto tx_error_put;

        /* drop old route */
        dst_release(skb->dst);
        skb->dst = &rt->u.dst;

        /* mangle the packet */
        if (pp->dnat_handler && !pp->dnat_handler(skb, pp, cp))
                goto tx_error;
        ip_hdr(skb)->daddr = cp->daddr;
        ip_send_check(ip_hdr(skb));

        IP_VS_DBG_PKT(10, pp, skb, 0, "After DNAT");

        /* FIXME: when application helper enlarges the packet and the length
           is larger than the MTU of outgoing device, there will be still
           MTU problem. */

        /* Another hack: avoid icmp_send in ip_fragment */
        skb->local_df = 1;

        IP_VS_XMIT(skb, rt);

        LeaveFunction(10);
        return NF_STOLEN;

  tx_error_icmp:
        dst_link_failure(skb);
  tx_error:
        LeaveFunction(10);
        kfree_skb(skb);
        return NF_STOLEN;
  tx_error_put:
        ip_rt_put(rt);
        goto tx_error;
}


/*
 *   IP Tunneling transmitter
 *
 *   This function encapsulates the packet in a new IP packet, its
 *   destination will be set to cp->daddr. Most code of this function
 *   is taken from ipip.c.
 *
 *   It is used in VS/TUN cluster. The load balancer selects a real
 *   server from a cluster based on a scheduling algorithm,
 *   encapsulates the request packet and forwards it to the selected
 *   server. For example, all real servers are configured with
 *   "ifconfig tunl0 <Virtual IP Address> up". When the server receives
 *   the encapsulated packet, it will decapsulate the packet, processe
 *   the request and return the response packets directly to the client
 *   without passing the load balancer. This can greatly increase the
 *   scalability of virtual server.
 *
 *   Used for ANY protocol
 */
int
ip_vs_tunnel_xmit(struct sk_buff *skb, struct ip_vs_conn *cp,
                  struct ip_vs_protocol *pp)
{
        struct rtable *rt;                      /* Route to the other host */
        struct net_device *tdev;                /* Device to other host */
        struct iphdr  *old_iph = ip_hdr(skb);
        u8     tos = old_iph->tos;
        __be16 df = old_iph->frag_off;
        sk_buff_data_t old_transport_header = skb->transport_header;
        struct iphdr  *iph;                     /* Our new IP header */
        unsigned int max_headroom;              /* The extra header space needed */
        int    mtu;

        EnterFunction(10);

        if (skb->protocol != htons(ETH_P_IP)) {
                IP_VS_DBG_RL("ip_vs_tunnel_xmit(): protocol error, "
                             "ETH_P_IP: %d, skb protocol: %d\n",
                             htons(ETH_P_IP), skb->protocol);
                goto tx_error;
        }

        if (!(rt = __ip_vs_get_out_rt(cp, RT_TOS(tos))))
                goto tx_error_icmp;

        tdev = rt->u.dst.dev;

        mtu = dst_mtu(&rt->u.dst) - sizeof(struct iphdr);
        if (mtu < 68) {
                ip_rt_put(rt);
                IP_VS_DBG_RL("ip_vs_tunnel_xmit(): mtu less than 68\n");
                goto tx_error;
        }
        if (skb->dst)
                skb->dst->ops->update_pmtu(skb->dst, mtu);

        df |= (old_iph->frag_off & htons(IP_DF));

        if ((old_iph->frag_off & htons(IP_DF))
            && mtu < ntohs(old_iph->tot_len)) {
                icmp_send(skb, ICMP_DEST_UNREACH,ICMP_FRAG_NEEDED, htonl(mtu));
                ip_rt_put(rt);
                IP_VS_DBG_RL("ip_vs_tunnel_xmit(): frag needed\n");
                goto tx_error;
        }

        /*
         * Okay, now see if we can stuff it in the buffer as-is.
         */
        max_headroom = LL_RESERVED_SPACE(tdev) + sizeof(struct iphdr);

        if (skb_headroom(skb) < max_headroom
            || skb_cloned(skb) || skb_shared(skb)) {
                struct sk_buff *new_skb =
                        skb_realloc_headroom(skb, max_headroom);
                if (!new_skb) {
                        ip_rt_put(rt);
                        kfree_skb(skb);
                        IP_VS_ERR_RL("ip_vs_tunnel_xmit(): no memory\n");
                        return NF_STOLEN;
                }
                kfree_skb(skb);
                skb = new_skb;
                old_iph = ip_hdr(skb);
        }

        skb->transport_header = old_transport_header;

        /* fix old IP header checksum */
        ip_send_check(old_iph);

        skb_push(skb, sizeof(struct iphdr));
        skb_reset_network_header(skb);
        memset(&(IPCB(skb)->opt), 0, sizeof(IPCB(skb)->opt));

        /* drop old route */
        dst_release(skb->dst);
        skb->dst = &rt->u.dst;

        /*
         *      Push down and install the IPIP header.
         */
        iph                     =       ip_hdr(skb);
        iph->version            =       4;
        iph->ihl                =       sizeof(struct iphdr)>>2;
        iph->frag_off           =       df;
        iph->protocol           =       IPPROTO_IPIP;
        iph->tos                =       tos;
        iph->daddr              =       rt->rt_dst;
        iph->saddr              =       rt->rt_src;
        iph->ttl                =       old_iph->ttl;
        ip_select_ident(iph, &rt->u.dst, NULL);

        /* Another hack: avoid icmp_send in ip_fragment */
        skb->local_df = 1;

        ip_local_out(skb);

        LeaveFunction(10);

        return NF_STOLEN;

  tx_error_icmp:
        dst_link_failure(skb);
  tx_error:
        kfree_skb(skb);
        LeaveFunction(10);
        return NF_STOLEN;
}


/*
 *      Direct Routing transmitter
 *      Used for ANY protocol
 */
int
ip_vs_dr_xmit(struct sk_buff *skb, struct ip_vs_conn *cp,
              struct ip_vs_protocol *pp)
{
        struct rtable *rt;                      /* Route to the other host */
        struct iphdr  *iph = ip_hdr(skb);
        int    mtu;

        EnterFunction(10);

        if (!(rt = __ip_vs_get_out_rt(cp, RT_TOS(iph->tos))))
                goto tx_error_icmp;

        /* MTU checking */
        mtu = dst_mtu(&rt->u.dst);
        if ((iph->frag_off & htons(IP_DF)) && skb->len > mtu) {
                icmp_send(skb, ICMP_DEST_UNREACH,ICMP_FRAG_NEEDED, htonl(mtu));
                ip_rt_put(rt);
                IP_VS_DBG_RL("ip_vs_dr_xmit(): frag needed\n");
                goto tx_error;
        }

        /*
         * Call ip_send_check because we are not sure it is called
         * after ip_defrag. Is copy-on-write needed?
         */
        if (unlikely((skb = skb_share_check(skb, GFP_ATOMIC)) == NULL)) {
                ip_rt_put(rt);
                return NF_STOLEN;
        }
        ip_send_check(ip_hdr(skb));

        /* drop old route */
        dst_release(skb->dst);
        skb->dst = &rt->u.dst;

        /* Another hack: avoid icmp_send in ip_fragment */
        skb->local_df = 1;

        IP_VS_XMIT(skb, rt);

        LeaveFunction(10);
        return NF_STOLEN;

  tx_error_icmp:
        dst_link_failure(skb);
  tx_error:
        kfree_skb(skb);
        LeaveFunction(10);
        return NF_STOLEN;
}


/*
 *      ICMP packet transmitter
 *      called by the ip_vs_in_icmp
 */
int
ip_vs_icmp_xmit(struct sk_buff *skb, struct ip_vs_conn *cp,
                struct ip_vs_protocol *pp, int offset)
{
        struct rtable   *rt;    /* Route to the other host */
        int mtu;
        int rc;

        EnterFunction(10);

        /* The ICMP packet for VS/TUN, VS/DR and LOCALNODE will be
           forwarded directly here, because there is no need to
           translate address/port back */
        if (IP_VS_FWD_METHOD(cp) != IP_VS_CONN_F_MASQ) {
                if (cp->packet_xmit)
                        rc = cp->packet_xmit(skb, cp, pp);
                else
                        rc = NF_ACCEPT;
                /* do not touch skb anymore */
                atomic_inc(&cp->in_pkts);
                goto out;
        }

        /*
         * mangle and send the packet here (only for VS/NAT)
         */

        if (!(rt = __ip_vs_get_out_rt(cp, RT_TOS(ip_hdr(skb)->tos))))
                goto tx_error_icmp;

        /* MTU checking */
        mtu = dst_mtu(&rt->u.dst);
        if ((skb->len > mtu) && (ip_hdr(skb)->frag_off & htons(IP_DF))) {
                ip_rt_put(rt);
                icmp_send(skb, ICMP_DEST_UNREACH, ICMP_FRAG_NEEDED, htonl(mtu));
                IP_VS_DBG_RL("ip_vs_in_icmp(): frag needed\n");
                goto tx_error;
        }

        /* copy-on-write the packet before mangling it */
        if (!skb_make_writable(skb, offset))
                goto tx_error_put;

        if (skb_cow(skb, rt->u.dst.dev->hard_header_len))
                goto tx_error_put;

        /* drop the old route when skb is not shared */
        dst_release(skb->dst);
        skb->dst = &rt->u.dst;

        ip_vs_nat_icmp(skb, pp, cp, 0);

        /* Another hack: avoid icmp_send in ip_fragment */
        skb->local_df = 1;

        IP_VS_XMIT(skb, rt);

        rc = NF_STOLEN;
        goto out;

  tx_error_icmp:
        dst_link_failure(skb);
  tx_error:
        dev_kfree_skb(skb);
        rc = NF_STOLEN;
  out:
        LeaveFunction(10);
        return rc;
  tx_error_put:
        ip_rt_put(rt);
        goto tx_error;
}