/*
   * net/sched/ife.c	Inter-FE action based on ForCES WG InterFE LFB
   *
   *		Refer to:
   *		draft-ietf-forces-interfelfb-03
   *		and
   *		netdev01 paper:
   *		"Distributing Linux Traffic Control Classifier-Action
   *		Subsystem"
   *		Authors: Jamal Hadi Salim and Damascene M. Joachimpillai
   *
   *		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.
   *
   * copyright Jamal Hadi Salim (2015)
   *
  */
  
  #include <linux/types.h>
  #include <linux/kernel.h>
  #include <linux/string.h>
  #include <linux/errno.h>
  #include <linux/skbuff.h>
  #include <linux/rtnetlink.h>
  #include <linux/module.h>
  #include <linux/init.h>
  #include <net/net_namespace.h>
  #include <net/netlink.h>
  #include <net/pkt_sched.h>
  #include <uapi/linux/tc_act/tc_ife.h>
  #include <net/tc_act/tc_ife.h>
  #include <linux/etherdevice.h>
  
  #define IFE_TAB_MASK 15
  
  static int ife_net_id;
  static int max_metacnt = IFE_META_MAX + 1;

  static struct tc_action_ops act_ife_ops;

  
  static const struct nla_policy ife_policy[TCA_IFE_MAX + 1] = {
  	[TCA_IFE_PARMS] = { .len = sizeof(struct tc_ife)},
  	[TCA_IFE_DMAC] = { .len = ETH_ALEN},
  	[TCA_IFE_SMAC] = { .len = ETH_ALEN},
  	[TCA_IFE_TYPE] = { .type = NLA_U16},
  };
  
  /* Caller takes care of presenting data in network order
  */
  int ife_tlv_meta_encode(void *skbdata, u16 attrtype, u16 dlen, const void *dval)
  {
  	u32 *tlv = (u32 *)(skbdata);
  	u16 totlen = nla_total_size(dlen);	/*alignment + hdr */
  	char *dptr = (char *)tlv + NLA_HDRLEN;

  	u32 htlv = attrtype << 16 | (dlen + NLA_HDRLEN);

  
  	*tlv = htonl(htlv);
  	memset(dptr, 0, totlen - NLA_HDRLEN);
  	memcpy(dptr, dval, dlen);
  
  	return totlen;
  }
  EXPORT_SYMBOL_GPL(ife_tlv_meta_encode);

  int ife_encode_meta_u16(u16 metaval, void *skbdata, struct tcf_meta_info *mi)
  {
  	u16 edata = 0;
  
  	if (mi->metaval)
  		edata = *(u16 *)mi->metaval;
  	else if (metaval)
  		edata = metaval;
  
  	if (!edata) /* will not encode */
  		return 0;
  
  	edata = htons(edata);
  	return ife_tlv_meta_encode(skbdata, mi->metaid, 2, &edata);
  }
  EXPORT_SYMBOL_GPL(ife_encode_meta_u16);

  int ife_get_meta_u32(struct sk_buff *skb, struct tcf_meta_info *mi)
  {
  	if (mi->metaval)
  		return nla_put_u32(skb, mi->metaid, *(u32 *)mi->metaval);
  	else
  		return nla_put(skb, mi->metaid, 0, NULL);
  }
  EXPORT_SYMBOL_GPL(ife_get_meta_u32);
  
  int ife_check_meta_u32(u32 metaval, struct tcf_meta_info *mi)
  {
  	if (metaval || mi->metaval)
  		return 8; /* T+L+V == 2+2+4 */
  
  	return 0;
  }
  EXPORT_SYMBOL_GPL(ife_check_meta_u32);

  int ife_check_meta_u16(u16 metaval, struct tcf_meta_info *mi)
  {
  	if (metaval || mi->metaval)
  		return 8; /* T+L+(V) == 2+2+(2+2bytepad) */
  
  	return 0;
  }
  EXPORT_SYMBOL_GPL(ife_check_meta_u16);

  int ife_encode_meta_u32(u32 metaval, void *skbdata, struct tcf_meta_info *mi)
  {
  	u32 edata = metaval;
  
  	if (mi->metaval)
  		edata = *(u32 *)mi->metaval;
  	else if (metaval)
  		edata = metaval;
  
  	if (!edata) /* will not encode */
  		return 0;
  
  	edata = htonl(edata);
  	return ife_tlv_meta_encode(skbdata, mi->metaid, 4, &edata);
  }
  EXPORT_SYMBOL_GPL(ife_encode_meta_u32);
  
  int ife_get_meta_u16(struct sk_buff *skb, struct tcf_meta_info *mi)
  {
  	if (mi->metaval)
  		return nla_put_u16(skb, mi->metaid, *(u16 *)mi->metaval);
  	else
  		return nla_put(skb, mi->metaid, 0, NULL);
  }
  EXPORT_SYMBOL_GPL(ife_get_meta_u16);

  int ife_alloc_meta_u32(struct tcf_meta_info *mi, void *metaval, gfp_t gfp)

  {

  	mi->metaval = kmemdup(metaval, sizeof(u32), gfp);

  	if (!mi->metaval)
  		return -ENOMEM;
  
  	return 0;
  }
  EXPORT_SYMBOL_GPL(ife_alloc_meta_u32);

  int ife_alloc_meta_u16(struct tcf_meta_info *mi, void *metaval, gfp_t gfp)

  {

  	mi->metaval = kmemdup(metaval, sizeof(u16), gfp);

  	if (!mi->metaval)
  		return -ENOMEM;
  
  	return 0;
  }
  EXPORT_SYMBOL_GPL(ife_alloc_meta_u16);
  
  void ife_release_meta_gen(struct tcf_meta_info *mi)
  {
  	kfree(mi->metaval);
  }
  EXPORT_SYMBOL_GPL(ife_release_meta_gen);
  
  int ife_validate_meta_u32(void *val, int len)
  {

  	if (len == sizeof(u32))

  		return 0;
  
  	return -EINVAL;
  }
  EXPORT_SYMBOL_GPL(ife_validate_meta_u32);
  
  int ife_validate_meta_u16(void *val, int len)
  {

  	/* length will not include padding */
  	if (len == sizeof(u16))

  		return 0;
  
  	return -EINVAL;
  }
  EXPORT_SYMBOL_GPL(ife_validate_meta_u16);
  
  static LIST_HEAD(ifeoplist);
  static DEFINE_RWLOCK(ife_mod_lock);
  
  static struct tcf_meta_ops *find_ife_oplist(u16 metaid)
  {
  	struct tcf_meta_ops *o;
  
  	read_lock(&ife_mod_lock);
  	list_for_each_entry(o, &ifeoplist, list) {
  		if (o->metaid == metaid) {
  			if (!try_module_get(o->owner))
  				o = NULL;
  			read_unlock(&ife_mod_lock);
  			return o;
  		}
  	}
  	read_unlock(&ife_mod_lock);
  
  	return NULL;
  }
  
  int register_ife_op(struct tcf_meta_ops *mops)
  {
  	struct tcf_meta_ops *m;
  
  	if (!mops->metaid || !mops->metatype || !mops->name ||
  	    !mops->check_presence || !mops->encode || !mops->decode ||
  	    !mops->get || !mops->alloc)
  		return -EINVAL;
  
  	write_lock(&ife_mod_lock);
  
  	list_for_each_entry(m, &ifeoplist, list) {
  		if (m->metaid == mops->metaid ||
  		    (strcmp(mops->name, m->name) == 0)) {
  			write_unlock(&ife_mod_lock);
  			return -EEXIST;
  		}
  	}
  
  	if (!mops->release)
  		mops->release = ife_release_meta_gen;
  
  	list_add_tail(&mops->list, &ifeoplist);
  	write_unlock(&ife_mod_lock);
  	return 0;
  }
  EXPORT_SYMBOL_GPL(unregister_ife_op);
  
  int unregister_ife_op(struct tcf_meta_ops *mops)
  {
  	struct tcf_meta_ops *m;
  	int err = -ENOENT;
  
  	write_lock(&ife_mod_lock);
  	list_for_each_entry(m, &ifeoplist, list) {
  		if (m->metaid == mops->metaid) {
  			list_del(&mops->list);
  			err = 0;
  			break;
  		}
  	}
  	write_unlock(&ife_mod_lock);
  
  	return err;
  }
  EXPORT_SYMBOL_GPL(register_ife_op);
  
  static int ife_validate_metatype(struct tcf_meta_ops *ops, void *val, int len)
  {
  	int ret = 0;
  	/* XXX: unfortunately cant use nla_policy at this point
  	* because a length of 0 is valid in the case of
  	* "allow". "use" semantics do enforce for proper
  	* length and i couldve use nla_policy but it makes it hard
  	* to use it just for that..
  	*/
  	if (ops->validate)
  		return ops->validate(val, len);
  
  	if (ops->metatype == NLA_U32)
  		ret = ife_validate_meta_u32(val, len);
  	else if (ops->metatype == NLA_U16)
  		ret = ife_validate_meta_u16(val, len);
  
  	return ret;
  }
  
  /* called when adding new meta information

   * under ife->tcf_lock for existing action

  */
  static int load_metaops_and_vet(struct tcf_ife_info *ife, u32 metaid,

  				void *val, int len, bool exists)

  {
  	struct tcf_meta_ops *ops = find_ife_oplist(metaid);
  	int ret = 0;
  
  	if (!ops) {
  		ret = -ENOENT;
  #ifdef CONFIG_MODULES

  		if (exists)
  			spin_unlock_bh(&ife->tcf_lock);

  		rtnl_unlock();
  		request_module("ifemeta%u", metaid);
  		rtnl_lock();

  		if (exists)
  			spin_lock_bh(&ife->tcf_lock);

  		ops = find_ife_oplist(metaid);
  #endif
  	}
  
  	if (ops) {
  		ret = 0;
  		if (len)
  			ret = ife_validate_metatype(ops, val, len);
  
  		module_put(ops->owner);
  	}
  
  	return ret;
  }
  
  /* called when adding new meta information

   * under ife->tcf_lock for existing action

  */
  static int add_metainfo(struct tcf_ife_info *ife, u32 metaid, void *metaval,

  			int len, bool atomic)

  {
  	struct tcf_meta_info *mi = NULL;
  	struct tcf_meta_ops *ops = find_ife_oplist(metaid);
  	int ret = 0;
  
  	if (!ops)
  		return -ENOENT;

  	mi = kzalloc(sizeof(*mi), atomic ? GFP_ATOMIC : GFP_KERNEL);

  	if (!mi) {
  		/*put back what find_ife_oplist took */
  		module_put(ops->owner);
  		return -ENOMEM;
  	}
  
  	mi->metaid = metaid;
  	mi->ops = ops;
  	if (len > 0) {

  		ret = ops->alloc(mi, metaval, atomic ? GFP_ATOMIC : GFP_KERNEL);

  		if (ret != 0) {
  			kfree(mi);
  			module_put(ops->owner);
  			return ret;
  		}
  	}
  
  	list_add_tail(&mi->metalist, &ife->metalist);
  
  	return ret;
  }
  
  static int use_all_metadata(struct tcf_ife_info *ife)
  {
  	struct tcf_meta_ops *o;
  	int rc = 0;
  	int installed = 0;

  	read_lock(&ife_mod_lock);

  	list_for_each_entry(o, &ifeoplist, list) {

  		rc = add_metainfo(ife, o->metaid, NULL, 0, true);

  		if (rc == 0)
  			installed += 1;
  	}

  	read_unlock(&ife_mod_lock);

  
  	if (installed)
  		return 0;
  	else
  		return -EINVAL;
  }
  
  static int dump_metalist(struct sk_buff *skb, struct tcf_ife_info *ife)
  {
  	struct tcf_meta_info *e;
  	struct nlattr *nest;
  	unsigned char *b = skb_tail_pointer(skb);
  	int total_encoded = 0;
  
  	/*can only happen on decode */
  	if (list_empty(&ife->metalist))
  		return 0;
  
  	nest = nla_nest_start(skb, TCA_IFE_METALST);
  	if (!nest)
  		goto out_nlmsg_trim;
  
  	list_for_each_entry(e, &ife->metalist, metalist) {
  		if (!e->ops->get(skb, e))
  			total_encoded += 1;
  	}
  
  	if (!total_encoded)
  		goto out_nlmsg_trim;
  
  	nla_nest_end(skb, nest);
  
  	return 0;
  
  out_nlmsg_trim:
  	nlmsg_trim(skb, b);
  	return -1;
  }
  
  /* under ife->tcf_lock */
  static void _tcf_ife_cleanup(struct tc_action *a, int bind)
  {

  	struct tcf_ife_info *ife = to_ife(a);

  	struct tcf_meta_info *e, *n;
  
  	list_for_each_entry_safe(e, n, &ife->metalist, metalist) {
  		module_put(e->ops->owner);
  		list_del(&e->metalist);
  		if (e->metaval) {
  			if (e->ops->release)
  				e->ops->release(e);
  			else
  				kfree(e->metaval);
  		}
  		kfree(e);
  	}
  }
  
  static void tcf_ife_cleanup(struct tc_action *a, int bind)
  {

  	struct tcf_ife_info *ife = to_ife(a);

  
  	spin_lock_bh(&ife->tcf_lock);
  	_tcf_ife_cleanup(a, bind);
  	spin_unlock_bh(&ife->tcf_lock);
  }

  /* under ife->tcf_lock for existing action */
  static int populate_metalist(struct tcf_ife_info *ife, struct nlattr **tb,
  			     bool exists)

  {
  	int len = 0;
  	int rc = 0;
  	int i = 0;
  	void *val;
  
  	for (i = 1; i < max_metacnt; i++) {
  		if (tb[i]) {
  			val = nla_data(tb[i]);
  			len = nla_len(tb[i]);

  			rc = load_metaops_and_vet(ife, i, val, len, exists);

  			if (rc != 0)
  				return rc;

  			rc = add_metainfo(ife, i, val, len, exists);

  			if (rc)
  				return rc;
  		}
  	}
  
  	return rc;
  }
  
  static int tcf_ife_init(struct net *net, struct nlattr *nla,

  			struct nlattr *est, struct tc_action **a,

  			int ovr, int bind)
  {
  	struct tc_action_net *tn = net_generic(net, ife_net_id);
  	struct nlattr *tb[TCA_IFE_MAX + 1];
  	struct nlattr *tb2[IFE_META_MAX + 1];
  	struct tcf_ife_info *ife;
  	struct tc_ife *parm;
  	u16 ife_type = 0;
  	u8 *daddr = NULL;
  	u8 *saddr = NULL;

  	bool exists = false;
  	int ret = 0;

  	int err;
  
  	err = nla_parse_nested(tb, TCA_IFE_MAX, nla, ife_policy);
  	if (err < 0)
  		return err;
  
  	if (!tb[TCA_IFE_PARMS])
  		return -EINVAL;
  
  	parm = nla_data(tb[TCA_IFE_PARMS]);

  	exists = tcf_hash_check(tn, parm->index, a, bind);
  	if (exists && bind)
  		return 0;

  	if (parm->flags & IFE_ENCODE) {
  		/* Until we get issued the ethertype, we cant have
  		 * a default..
  		**/
  		if (!tb[TCA_IFE_TYPE]) {

  			if (exists)

  				tcf_hash_release(*a, bind);

  			pr_info("You MUST pass etherype for encoding
  ");
  			return -EINVAL;
  		}
  	}

  	if (!exists) {

  		ret = tcf_hash_create(tn, parm->index, est, a, &act_ife_ops,

  				      bind, false);
  		if (ret)
  			return ret;
  		ret = ACT_P_CREATED;
  	} else {

  		tcf_hash_release(*a, bind);

  		if (!ovr)
  			return -EEXIST;
  	}

  	ife = to_ife(*a);

  	ife->flags = parm->flags;
  
  	if (parm->flags & IFE_ENCODE) {
  		ife_type = nla_get_u16(tb[TCA_IFE_TYPE]);
  		if (tb[TCA_IFE_DMAC])
  			daddr = nla_data(tb[TCA_IFE_DMAC]);
  		if (tb[TCA_IFE_SMAC])
  			saddr = nla_data(tb[TCA_IFE_SMAC]);
  	}

  	if (exists)
  		spin_lock_bh(&ife->tcf_lock);

  	ife->tcf_action = parm->action;
  
  	if (parm->flags & IFE_ENCODE) {
  		if (daddr)
  			ether_addr_copy(ife->eth_dst, daddr);
  		else
  			eth_zero_addr(ife->eth_dst);
  
  		if (saddr)
  			ether_addr_copy(ife->eth_src, saddr);
  		else
  			eth_zero_addr(ife->eth_src);
  
  		ife->eth_type = ife_type;
  	}
  
  	if (ret == ACT_P_CREATED)
  		INIT_LIST_HEAD(&ife->metalist);
  
  	if (tb[TCA_IFE_METALST]) {
  		err = nla_parse_nested(tb2, IFE_META_MAX, tb[TCA_IFE_METALST],
  				       NULL);
  		if (err) {
  metadata_parse_err:

  			if (exists)

  				tcf_hash_release(*a, bind);

  			if (ret == ACT_P_CREATED)

  				_tcf_ife_cleanup(*a, bind);

  			if (exists)
  				spin_unlock_bh(&ife->tcf_lock);

  			return err;
  		}

  		err = populate_metalist(ife, tb2, exists);

  		if (err)
  			goto metadata_parse_err;
  
  	} else {
  		/* if no passed metadata allow list or passed allow-all
  		 * then here we process by adding as many supported metadatum
  		 * as we can. You better have at least one else we are
  		 * going to bail out
  		 */
  		err = use_all_metadata(ife);
  		if (err) {
  			if (ret == ACT_P_CREATED)

  				_tcf_ife_cleanup(*a, bind);

  			if (exists)
  				spin_unlock_bh(&ife->tcf_lock);

  			return err;
  		}
  	}

  	if (exists)
  		spin_unlock_bh(&ife->tcf_lock);

  
  	if (ret == ACT_P_CREATED)

  		tcf_hash_insert(tn, *a);

  
  	return ret;
  }
  
  static int tcf_ife_dump(struct sk_buff *skb, struct tc_action *a, int bind,
  			int ref)
  {
  	unsigned char *b = skb_tail_pointer(skb);

  	struct tcf_ife_info *ife = to_ife(a);

  	struct tc_ife opt = {
  		.index = ife->tcf_index,
  		.refcnt = ife->tcf_refcnt - ref,
  		.bindcnt = ife->tcf_bindcnt - bind,
  		.action = ife->tcf_action,
  		.flags = ife->flags,
  	};
  	struct tcf_t t;
  
  	if (nla_put(skb, TCA_IFE_PARMS, sizeof(opt), &opt))
  		goto nla_put_failure;

  	tcf_tm_dump(&t, &ife->tcf_tm);

  	if (nla_put_64bit(skb, TCA_IFE_TM, sizeof(t), &t, TCA_IFE_PAD))

  		goto nla_put_failure;
  
  	if (!is_zero_ether_addr(ife->eth_dst)) {
  		if (nla_put(skb, TCA_IFE_DMAC, ETH_ALEN, ife->eth_dst))
  			goto nla_put_failure;
  	}
  
  	if (!is_zero_ether_addr(ife->eth_src)) {
  		if (nla_put(skb, TCA_IFE_SMAC, ETH_ALEN, ife->eth_src))
  			goto nla_put_failure;
  	}
  
  	if (nla_put(skb, TCA_IFE_TYPE, 2, &ife->eth_type))
  		goto nla_put_failure;
  
  	if (dump_metalist(skb, ife)) {
  		/*ignore failure to dump metalist */
  		pr_info("Failed to dump metalist
  ");
  	}
  
  	return skb->len;
  
  nla_put_failure:
  	nlmsg_trim(skb, b);
  	return -1;
  }
  
  int find_decode_metaid(struct sk_buff *skb, struct tcf_ife_info *ife,
  		       u16 metaid, u16 mlen, void *mdata)
  {
  	struct tcf_meta_info *e;
  
  	/* XXX: use hash to speed up */
  	list_for_each_entry(e, &ife->metalist, metalist) {
  		if (metaid == e->metaid) {
  			if (e->ops) {
  				/* We check for decode presence already */
  				return e->ops->decode(skb, mdata, mlen);
  			}
  		}
  	}
  
  	return 0;
  }
  
  struct ifeheadr {
  	__be16 metalen;
  	u8 tlv_data[];
  };
  
  struct meta_tlvhdr {
  	__be16 type;
  	__be16 len;
  };
  
  static int tcf_ife_decode(struct sk_buff *skb, const struct tc_action *a,
  			  struct tcf_result *res)
  {

  	struct tcf_ife_info *ife = to_ife(a);

  	int action = ife->tcf_action;
  	struct ifeheadr *ifehdr = (struct ifeheadr *)skb->data;

  	int ifehdrln = (int)ifehdr->metalen;

  	struct meta_tlvhdr *tlv = (struct meta_tlvhdr *)(ifehdr->tlv_data);
  
  	spin_lock(&ife->tcf_lock);
  	bstats_update(&ife->tcf_bstats, skb);

  	tcf_lastuse_update(&ife->tcf_tm);

  	spin_unlock(&ife->tcf_lock);
  
  	ifehdrln = ntohs(ifehdrln);
  	if (unlikely(!pskb_may_pull(skb, ifehdrln))) {
  		spin_lock(&ife->tcf_lock);
  		ife->tcf_qstats.drops++;
  		spin_unlock(&ife->tcf_lock);
  		return TC_ACT_SHOT;
  	}
  
  	skb_set_mac_header(skb, ifehdrln);
  	__skb_pull(skb, ifehdrln);
  	skb->protocol = eth_type_trans(skb, skb->dev);
  	ifehdrln -= IFE_METAHDRLEN;
  
  	while (ifehdrln > 0) {
  		u8 *tlvdata = (u8 *)tlv;
  		u16 mtype = tlv->type;
  		u16 mlen = tlv->len;

  		u16 alen;

  
  		mtype = ntohs(mtype);
  		mlen = ntohs(mlen);

  		alen = NLA_ALIGN(mlen);

  		if (find_decode_metaid(skb, ife, mtype, (mlen - NLA_HDRLEN),
  				       (void *)(tlvdata + NLA_HDRLEN))) {

  			/* abuse overlimits to count when we receive metadata
  			 * but dont have an ops for it
  			 */
  			pr_info_ratelimited("Unknown metaid %d alnlen %d
  ",
  					    mtype, mlen);
  			ife->tcf_qstats.overlimits++;
  		}

  		tlvdata += alen;
  		ifehdrln -= alen;

  		tlv = (struct meta_tlvhdr *)tlvdata;
  	}
  
  	skb_reset_network_header(skb);
  	return action;
  }
  
  /*XXX: check if we can do this at install time instead of current
   * send data path
  **/
  static int ife_get_sz(struct sk_buff *skb, struct tcf_ife_info *ife)
  {
  	struct tcf_meta_info *e, *n;
  	int tot_run_sz = 0, run_sz = 0;
  
  	list_for_each_entry_safe(e, n, &ife->metalist, metalist) {
  		if (e->ops->check_presence) {
  			run_sz = e->ops->check_presence(skb, e);
  			tot_run_sz += run_sz;
  		}
  	}
  
  	return tot_run_sz;
  }
  
  static int tcf_ife_encode(struct sk_buff *skb, const struct tc_action *a,
  			  struct tcf_result *res)
  {

  	struct tcf_ife_info *ife = to_ife(a);

  	int action = ife->tcf_action;
  	struct ethhdr *oethh;	/* outer ether header */
  	struct ethhdr *iethh;	/* inner eth header */
  	struct tcf_meta_info *e;
  	/*
  	   OUTERHDR:TOTMETALEN:{TLVHDR:Metadatum:TLVHDR..}:ORIGDATA
  	   where ORIGDATA = original ethernet header ...
  	 */
  	u16 metalen = ife_get_sz(skb, ife);
  	int hdrm = metalen + skb->dev->hard_header_len + IFE_METAHDRLEN;
  	unsigned int skboff = skb->dev->hard_header_len;
  	u32 at = G_TC_AT(skb->tc_verd);
  	int new_len = skb->len + hdrm;
  	bool exceed_mtu = false;
  	int err;
  
  	if (at & AT_EGRESS) {
  		if (new_len > skb->dev->mtu)
  			exceed_mtu = true;
  	}
  
  	spin_lock(&ife->tcf_lock);
  	bstats_update(&ife->tcf_bstats, skb);

  	tcf_lastuse_update(&ife->tcf_tm);

  
  	if (!metalen) {		/* no metadata to send */
  		/* abuse overlimits to count when we allow packet
  		 * with no metadata
  		 */
  		ife->tcf_qstats.overlimits++;
  		spin_unlock(&ife->tcf_lock);
  		return action;
  	}
  	/* could be stupid policy setup or mtu config
  	 * so lets be conservative.. */
  	if ((action == TC_ACT_SHOT) || exceed_mtu) {
  		ife->tcf_qstats.drops++;
  		spin_unlock(&ife->tcf_lock);
  		return TC_ACT_SHOT;
  	}

  	err = skb_cow_head(skb, hdrm);
  	if (unlikely(err)) {
  		ife->tcf_qstats.drops++;
  		spin_unlock(&ife->tcf_lock);
  		return TC_ACT_SHOT;
  	}
  
  	if (!(at & AT_EGRESS))
  		skb_push(skb, skb->dev->hard_header_len);

  	iethh = (struct ethhdr *)skb->data;

  	__skb_push(skb, hdrm);
  	memcpy(skb->data, iethh, skb->mac_len);
  	skb_reset_mac_header(skb);
  	oethh = eth_hdr(skb);
  
  	/*total metadata length */
  	metalen += IFE_METAHDRLEN;
  	metalen = htons(metalen);
  	memcpy((skb->data + skboff), &metalen, IFE_METAHDRLEN);
  	skboff += IFE_METAHDRLEN;
  
  	/* XXX: we dont have a clever way of telling encode to
  	 * not repeat some of the computations that are done by
  	 * ops->presence_check...
  	 */
  	list_for_each_entry(e, &ife->metalist, metalist) {
  		if (e->ops->encode) {
  			err = e->ops->encode(skb, (void *)(skb->data + skboff),
  					     e);
  		}
  		if (err < 0) {
  			/* too corrupt to keep around if overwritten */
  			ife->tcf_qstats.drops++;
  			spin_unlock(&ife->tcf_lock);
  			return TC_ACT_SHOT;
  		}
  		skboff += err;
  	}
  
  	if (!is_zero_ether_addr(ife->eth_src))
  		ether_addr_copy(oethh->h_source, ife->eth_src);
  	else
  		ether_addr_copy(oethh->h_source, iethh->h_source);
  	if (!is_zero_ether_addr(ife->eth_dst))
  		ether_addr_copy(oethh->h_dest, ife->eth_dst);
  	else
  		ether_addr_copy(oethh->h_dest, iethh->h_dest);
  	oethh->h_proto = htons(ife->eth_type);
  
  	if (!(at & AT_EGRESS))
  		skb_pull(skb, skb->dev->hard_header_len);
  
  	spin_unlock(&ife->tcf_lock);
  
  	return action;
  }
  
  static int tcf_ife_act(struct sk_buff *skb, const struct tc_action *a,
  		       struct tcf_result *res)
  {

  	struct tcf_ife_info *ife = to_ife(a);

  
  	if (ife->flags & IFE_ENCODE)
  		return tcf_ife_encode(skb, a, res);
  
  	if (!(ife->flags & IFE_ENCODE))
  		return tcf_ife_decode(skb, a, res);
  
  	pr_info_ratelimited("unknown failure(policy neither de/encode
  ");
  	spin_lock(&ife->tcf_lock);
  	bstats_update(&ife->tcf_bstats, skb);

  	tcf_lastuse_update(&ife->tcf_tm);

  	ife->tcf_qstats.drops++;
  	spin_unlock(&ife->tcf_lock);
  
  	return TC_ACT_SHOT;
  }
  
  static int tcf_ife_walker(struct net *net, struct sk_buff *skb,
  			  struct netlink_callback *cb, int type,

  			  const struct tc_action_ops *ops)

  {
  	struct tc_action_net *tn = net_generic(net, ife_net_id);

  	return tcf_generic_walker(tn, skb, cb, type, ops);

  }

  static int tcf_ife_search(struct net *net, struct tc_action **a, u32 index)

  {
  	struct tc_action_net *tn = net_generic(net, ife_net_id);
  
  	return tcf_hash_search(tn, a, index);
  }
  
  static struct tc_action_ops act_ife_ops = {
  	.kind = "ife",
  	.type = TCA_ACT_IFE,
  	.owner = THIS_MODULE,
  	.act = tcf_ife_act,
  	.dump = tcf_ife_dump,
  	.cleanup = tcf_ife_cleanup,
  	.init = tcf_ife_init,
  	.walk = tcf_ife_walker,
  	.lookup = tcf_ife_search,

  	.size =	sizeof(struct tcf_ife_info),

  };
  
  static __net_init int ife_init_net(struct net *net)
  {
  	struct tc_action_net *tn = net_generic(net, ife_net_id);
  
  	return tc_action_net_init(tn, &act_ife_ops, IFE_TAB_MASK);
  }
  
  static void __net_exit ife_exit_net(struct net *net)
  {
  	struct tc_action_net *tn = net_generic(net, ife_net_id);
  
  	tc_action_net_exit(tn);
  }
  
  static struct pernet_operations ife_net_ops = {
  	.init = ife_init_net,
  	.exit = ife_exit_net,
  	.id   = &ife_net_id,
  	.size = sizeof(struct tc_action_net),
  };
  
  static int __init ife_init_module(void)
  {
  	return tcf_register_action(&act_ife_ops, &ife_net_ops);
  }
  
  static void __exit ife_cleanup_module(void)
  {
  	tcf_unregister_action(&act_ife_ops, &ife_net_ops);
  }
  
  module_init(ife_init_module);
  module_exit(ife_cleanup_module);
  
  MODULE_AUTHOR("Jamal Hadi Salim(2015)");
  MODULE_DESCRIPTION("Inter-FE LFB action");
  MODULE_LICENSE("GPL");