// 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");
