/*
 *      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) {
                int delta;

                swap(gso_skb->sk, skb->sk);
                swap(gso_skb->destructor, skb->destructor);
                sum_truesize += skb->truesize;
                delta = sum_truesize - gso_skb->truesize;
                /* In some pathological cases, delta can be negative.
                 * We need to either use refcount_add() or refcount_sub_and_test()
                 */
                if (likely(delta >= 0))
                        refcount_add(delta, &skb->sk->sk_wmem_alloc);
                else
                        WARN_ON_ONCE(refcount_sub_and_test(-delta, &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;
        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);

        /* When we receive our second frame we can made a decision on if we
         * continue this flow as an atomic flow with a fixed ID or if we use
         * an incrementing ID.
         */
        if (NAPI_GRO_CB(p)->flush_id != 1 ||
            NAPI_GRO_CB(p)->count != 1 ||
            !NAPI_GRO_CB(p)->is_atomic)
                flush |= NAPI_GRO_CB(p)->flush_id;
        else
                NAPI_GRO_CB(p)->is_atomic = false;

        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;

        if (NAPI_GRO_CB(skb)->is_atomic)
                skb_shinfo(skb)->gso_type |= SKB_GSO_TCP_FIXEDID;

        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);
}