// SPDX-License-Identifier: GPL-2.0-or-later
/*
 *      MPLS GSO Support
 *
 *      Authors: Simon Horman (horms@verge.net.au)
 *
 *      Based on: GSO portions of net/ipv4/gre.c
 */

#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

#include <linux/err.h>
#include <linux/module.h>
#include <linux/netdev_features.h>
#include <linux/netdevice.h>
#include <linux/skbuff.h>
#include <net/gso.h>
#include <net/mpls.h>

static struct sk_buff *mpls_gso_segment(struct sk_buff *skb,
                                       netdev_features_t features)
{
        struct sk_buff *segs = ERR_PTR(-EINVAL);
        u16 mac_offset = skb->mac_header;
        netdev_features_t mpls_features;
        u16 mac_len = skb->mac_len;
        __be16 mpls_protocol;
        unsigned int mpls_hlen;

        if (!skb_inner_network_header_was_set(skb))
                goto out;

        skb_reset_network_header(skb);
        mpls_hlen = skb_inner_network_header(skb) - skb_network_header(skb);
        if (unlikely(!mpls_hlen || mpls_hlen % MPLS_HLEN))
                goto out;
        if (unlikely(!pskb_may_pull(skb, mpls_hlen)))
                goto out;

        /* Setup inner SKB. */
        mpls_protocol = skb->protocol;
        skb->protocol = skb->inner_protocol;

        __skb_pull(skb, mpls_hlen);

        skb->mac_len = 0;
        skb_reset_mac_header(skb);

        /* Segment inner packet. */
        mpls_features = skb->dev->mpls_features & features;
        segs = skb_mac_gso_segment(skb, mpls_features);
        if (IS_ERR_OR_NULL(segs)) {
                skb_gso_error_unwind(skb, mpls_protocol, mpls_hlen, mac_offset,
                                     mac_len);
                goto out;
        }
        skb = segs;

        mpls_hlen += mac_len;
        do {
                skb->mac_len = mac_len;
                skb->protocol = mpls_protocol;

                skb_reset_inner_network_header(skb);

                __skb_push(skb, mpls_hlen);

                skb_reset_mac_header(skb);
                skb_set_network_header(skb, mac_len);
        } while ((skb = skb->next));

out:
        return segs;
}

static struct packet_offload mpls_mc_offload __read_mostly = {
        .type = cpu_to_be16(ETH_P_MPLS_MC),
        .priority = 15,
        .callbacks = {
                .gso_segment    =       mpls_gso_segment,
        },
};

static struct packet_offload mpls_uc_offload __read_mostly = {
        .type = cpu_to_be16(ETH_P_MPLS_UC),
        .priority = 15,
        .callbacks = {
                .gso_segment    =       mpls_gso_segment,
        },
};

static int __init mpls_gso_init(void)
{
        pr_info("MPLS GSO support\n");

        dev_add_offload(&mpls_uc_offload);
        dev_add_offload(&mpls_mc_offload);

        return 0;
}

static void __exit mpls_gso_exit(void)
{
        dev_remove_offload(&mpls_uc_offload);
        dev_remove_offload(&mpls_mc_offload);
}

module_init(mpls_gso_init);
module_exit(mpls_gso_exit);

MODULE_DESCRIPTION("MPLS GSO support");
MODULE_AUTHOR("Simon Horman <horms@verge.net.au>");
MODULE_LICENSE("GPL");