/* SPDX-License-Identifier: GPL-2.0-or-later */

#ifndef _NET_GSO_H
#define _NET_GSO_H

#include <linux/skbuff.h>

/* Keeps track of mac header offset relative to skb->head.
 * It is useful for TSO of Tunneling protocol. e.g. GRE.
 * For non-tunnel skb it points to skb_mac_header() and for
 * tunnel skb it points to outer mac header.
 * Keeps track of level of encapsulation of network headers.
 */
struct skb_gso_cb {
    union {
        int    mac_offset;
        int    data_offset;
    };
    int    encap_level;
    __wsum    csum;
    __u16    csum_start;
};
#define SKB_GSO_CB_OFFSET    32
#define SKB_GSO_CB(skb) ((struct skb_gso_cb *)((skb)->cb + SKB_GSO_CB_OFFSET))

static inline int skb_tnl_header_len(const struct sk_buff *inner_skb)
{
    return (skb_mac_header(inner_skb) - inner_skb->head) -
        SKB_GSO_CB(inner_skb)->mac_offset;
}

static inline int gso_pskb_expand_head(struct sk_buff *skb, int extra)
{
    int new_headroom, headroom;
    int ret;

    headroom = skb_headroom(skb);
    ret = pskb_expand_head(skb, extra, 0, GFP_ATOMIC);
    if (ret)
        return ret;

    new_headroom = skb_headroom(skb);
    SKB_GSO_CB(skb)->mac_offset += (new_headroom - headroom);
    return 0;
}

static inline void gso_reset_checksum(struct sk_buff *skb, __wsum res)
{
    /* Do not update partial checksums if remote checksum is enabled. */
    if (skb->remcsum_offload)
        return;

    SKB_GSO_CB(skb)->csum = res;
    SKB_GSO_CB(skb)->csum_start = skb_checksum_start(skb) - skb->head;
}

/* Compute the checksum for a gso segment. First compute the checksum value
 * from the start of transport header to SKB_GSO_CB(skb)->csum_start, and
 * then add in skb->csum (checksum from csum_start to end of packet).
 * skb->csum and csum_start are then updated to reflect the checksum of the
 * resultant packet starting from the transport header-- the resultant checksum
 * is in the res argument (i.e. normally zero or ~ of checksum of a pseudo
 * header.
 */
static inline __sum16 gso_make_checksum(struct sk_buff *skb, __wsum res)
{
    unsigned char *csum_start = skb_transport_header(skb);
    int plen = (skb->head + SKB_GSO_CB(skb)->csum_start) - csum_start;
    __wsum partial = SKB_GSO_CB(skb)->csum;

    SKB_GSO_CB(skb)->csum = res;
    SKB_GSO_CB(skb)->csum_start = csum_start - skb->head;

    return csum_fold(csum_partial(csum_start, plen, partial));
}

struct sk_buff *__skb_gso_segment(struct sk_buff *skb,
                  netdev_features_t features, bool tx_path);

static inline struct sk_buff *skb_gso_segment(struct sk_buff *skb,
                          netdev_features_t features)
{
    return __skb_gso_segment(skb, features, true);
}

struct sk_buff *skb_eth_gso_segment(struct sk_buff *skb,
                    netdev_features_t features, __be16 type);

struct sk_buff *skb_mac_gso_segment(struct sk_buff *skb,
                    netdev_features_t features);

bool skb_gso_validate_network_len(const struct sk_buff *skb, unsigned int mtu);

bool skb_gso_validate_mac_len(const struct sk_buff *skb, unsigned int len);

static inline void skb_gso_error_unwind(struct sk_buff *skb, __be16 protocol,
                    int pulled_hlen, u16 mac_offset,
                    int mac_len)
{
    skb->protocol = protocol;
    skb->encapsulation = 1;
    skb_push(skb, pulled_hlen);
    skb_reset_transport_header(skb);
    skb->mac_header = mac_offset;
    skb->network_header = skb->mac_header + mac_len;
    skb->mac_len = mac_len;
}

#endif /* _NET_GSO_H */