text: /*
   * sctp_offload - GRO/GSO Offloading for SCTP
   *
   * Copyright (C) 2015, Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>
   *
   * 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.
   *
   * This program is distributed in the hope that it will be useful,
   * but WITHOUT ANY WARRANTY; without even the implied warranty of
   * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   * GNU General Public License for more details.
   */
  
  #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
  
  #include <linux/kernel.h>
  #include <linux/kprobes.h>
  #include <linux/socket.h>
  #include <linux/sctp.h>
  #include <linux/proc_fs.h>
  #include <linux/vmalloc.h>
  #include <linux/module.h>
  #include <linux/kfifo.h>
  #include <linux/time.h>
  #include <net/net_namespace.h>
  
  #include <linux/skbuff.h>
  #include <net/sctp/sctp.h>
  #include <net/sctp/checksum.h>
  #include <net/protocol.h>
  
  static __le32 sctp_gso_make_checksum(struct sk_buff *skb)
  {
  	skb->ip_summed = CHECKSUM_NONE;
  	skb->csum_not_inet = 0;
  	return sctp_compute_cksum(skb, skb_transport_offset(skb));
  }
  
  static struct sk_buff *sctp_gso_segment(struct sk_buff *skb,
  					netdev_features_t features)
  {
  	struct sk_buff *segs = ERR_PTR(-EINVAL);
  	struct sctphdr *sh;
  
  	if (!(skb_shinfo(skb)->gso_type & SKB_GSO_SCTP))
  		goto out;
  
  	sh = sctp_hdr(skb);
  	if (!pskb_may_pull(skb, sizeof(*sh)))
  		goto out;
  
  	__skb_pull(skb, sizeof(*sh));
  
  	if (skb_gso_ok(skb, features | NETIF_F_GSO_ROBUST)) {
  		/* Packet is from an untrusted source, reset gso_segs. */
  		struct skb_shared_info *pinfo = skb_shinfo(skb);
  		struct sk_buff *frag_iter;
  
  		pinfo->gso_segs = 0;
  		if (skb->len != skb->data_len) {
  			/* Means we have chunks in here too */
  			pinfo->gso_segs++;
  		}
  
  		skb_walk_frags(skb, frag_iter)
  			pinfo->gso_segs++;
  
  		segs = NULL;
  		goto out;
  	}
  
  	segs = skb_segment(skb, features | NETIF_F_HW_CSUM | NETIF_F_SG);
  	if (IS_ERR(segs))
  		goto out;
  
  	/* All that is left is update SCTP CRC if necessary */
  	if (!(features & NETIF_F_SCTP_CRC)) {
  		for (skb = segs; skb; skb = skb->next) {
  			if (skb->ip_summed == CHECKSUM_PARTIAL) {
  				sh = sctp_hdr(skb);
  				sh->checksum = sctp_gso_make_checksum(skb);
  			}
  		}
  	}
  
  out:
  	return segs;
  }
  
  static const struct net_offload sctp_offload = {
  	.callbacks = {
  		.gso_segment = sctp_gso_segment,
  	},
  };
  
  static const struct net_offload sctp6_offload = {
  	.callbacks = {
  		.gso_segment = sctp_gso_segment,
  	},
  };
  
  static const struct skb_checksum_ops crc32c_csum_ops = {
  	.update  = sctp_csum_update,
  	.combine = sctp_csum_combine,
  };
  
  int __init sctp_offload_init(void)
  {
  	int ret;
  
  	ret = inet_add_offload(&sctp_offload, IPPROTO_SCTP);
  	if (ret)
  		goto out;
  
  	ret = inet6_add_offload(&sctp6_offload, IPPROTO_SCTP);
  	if (ret)
  		goto ipv4;
  
  	crc32c_csum_stub = &crc32c_csum_ops;
  	return ret;
  
  ipv4:
  	inet_del_offload(&sctp_offload, IPPROTO_SCTP);
  out:
  	return ret;
  }
  