C++ skb_copy_expand函数代码示例

PNDIS_PACKET duplicate_pkt_with_TKIP_MIC(
    IN	PRTMP_ADAPTER	pAd,
    IN	PNDIS_PACKET	pPacket)
{
    struct sk_buff	*skb, *newskb;


    skb = RTPKT_TO_OSPKT(pPacket);
    if (skb_tailroom(skb) < TKIP_TX_MIC_SIZE)
    {
        // alloc a new skb and copy the packet
        newskb = skb_copy_expand(skb, skb_headroom(skb), TKIP_TX_MIC_SIZE, GFP_ATOMIC);
        dev_kfree_skb_any(skb);
        if (newskb == NULL)
        {
            DBGPRINT(RT_DEBUG_ERROR, ("Extend Tx.MIC for packet failed!, dropping packet!\n"));
            return NULL;
        }
        skb = newskb;
    }

    return OSPKT_TO_RTPKT(skb);

#if 0
    if ((data = skb_put(skb, TKIP_TX_MIC_SIZE)) != NULL)
    {   // If we can extend it, well, copy it first.
        NdisMoveMemory(data, pAd->PrivateInfo.Tx.MIC, TKIP_TX_MIC_SIZE);
    }
    else
    {
        // Otherwise, copy the packet.
        newskb = skb_copy_expand(skb, skb_headroom(skb), TKIP_TX_MIC_SIZE, GFP_ATOMIC);
        dev_kfree_skb_any(skb);
        if (newskb == NULL)
        {
            DBGPRINT(RT_DEBUG_ERROR, ("Extend Tx.MIC to packet failed!, dropping packet\n"));
            return NULL;
        }
        skb = newskb;

        NdisMoveMemory(skb->tail, pAd->PrivateInfo.Tx.MIC, TKIP_TX_MIC_SIZE);
        skb_put(skb, TKIP_TX_MIC_SIZE);
    }

    return OSPKT_TO_RTPKT(skb);
#endif

}

/*
 * We need to grow the skb to accommodate the expanssion of the ipcomp packet.
 *
 * The following comment comes from the skb_decompress() which does the
 * same...
 *
 * We have no way of knowing the exact length of the resulting
 * decompressed output before we have actually done the decompression.
 * For now, we guess that the packet will not be bigger than the
 * attached ipsec device's mtu or 16260, whichever is biggest.
 * This may be wrong, since the sender's mtu may be bigger yet.
 * XXX This must be dealt with later XXX
 */
static int ipsec_ocf_ipcomp_copy_expand(struct ipsec_rcv_state *irs)
{
	struct sk_buff *nskb;
	unsigned grow_to, grow_by;
	ptrdiff_t ptr_delta;

	if (!irs->skb)
		return IPSEC_RCV_IPCOMPFAILED;

	if (irs->skb->dev) {
		grow_to = irs->skb->dev->mtu <
			  16260 ? 16260 : irs->skb->dev->mtu;
	} else {
		int tot_len;
		if (lsw_ip_hdr_version(irs) == 6)
			tot_len = ntohs(lsw_ip6_hdr(irs)->payload_len) +
				  sizeof(struct ipv6hdr);
		else
			tot_len = ntohs(lsw_ip4_hdr(irs)->tot_len);
		grow_to = 65520 - tot_len;
	}
	grow_by = grow_to - irs->skb->len;
	grow_by -= skb_headroom(irs->skb);
	grow_by -= skb_tailroom(irs->skb);

	/* it's big enough */
	if (!grow_by)
		return IPSEC_RCV_OK;

	nskb = skb_copy_expand(irs->skb, skb_headroom(irs->skb),
			       skb_tailroom(irs->skb) + grow_by, GFP_ATOMIC);
	if (!nskb)
		return IPSEC_RCV_ERRMEMALLOC;

	memcpy(nskb->head, irs->skb->head, skb_headroom(irs->skb));

	skb_set_network_header(nskb,
			       ipsec_skb_offset(irs->skb,
						skb_network_header(irs->skb)));
	skb_set_transport_header(nskb,
				 ipsec_skb_offset(irs->skb,
						  skb_transport_header(
							  irs->skb)));

	/* update all irs pointers */
	ptr_delta = nskb->data - irs->skb->data;
	irs->authenticator = (void*)((char*)irs->authenticator + ptr_delta);
	irs->iph           = (void*)((char*)irs->iph           + ptr_delta);

	/* flip in the large one */
	irs->pre_ipcomp_skb = irs->skb;
	irs->skb = nskb;

	/* move the tail up to the end to let OCF know how big the buffer is */
	if (grow_by > (irs->skb->end - irs->skb->tail))
		grow_by = irs->skb->end - irs->skb->tail;
	skb_put(irs->skb, grow_by);

	return IPSEC_RCV_OK;
}

static int ipq_mangle_ipv4(ipq_verdict_msg_t *v, ipq_queue_element_t *e)
{
	int diff;
	struct iphdr *user_iph = (struct iphdr *)v->payload;

	if (v->data_len < sizeof(*user_iph))
		return 0;
	diff = v->data_len - e->skb->len;
	if (diff < 0)
		skb_trim(e->skb, v->data_len);
	else if (diff > 0) {
		if (v->data_len > 0xFFFF)
			return -EINVAL;
		if (diff > skb_tailroom(e->skb)) {
			struct sk_buff *newskb;
			
			newskb = skb_copy_expand(e->skb,
			                         skb_headroom(e->skb),
			                         diff,
			                         GFP_ATOMIC);
			if (newskb == NULL) {
				printk(KERN_WARNING "ip_queue: OOM "
				      "in mangle, dropping packet\n");
				return -ENOMEM;
			}
			kfree_skb(e->skb);
			e->skb = newskb;
		}
		skb_put(e->skb, diff);
	}
	memcpy(e->skb->data, v->payload, v->data_len);
	e->skb->nfcache |= NFC_ALTERED;
	return 0;
}

static struct sk_buff *
net1080_tx_fixup(struct usbnet *dev, struct sk_buff *skb, gfp_t flags)
{
	struct sk_buff		*skb2;
	struct nc_header	*header = NULL;
	struct nc_trailer	*trailer = NULL;
	int			padlen = sizeof (struct nc_trailer);
	int			len = skb->len;

	if (!((len + padlen + sizeof (struct nc_header)) & 0x01))
		padlen++;
	if (!skb_cloned(skb)) {
		int	headroom = skb_headroom(skb);
		int	tailroom = skb_tailroom(skb);

		if (padlen <= tailroom &&
		    sizeof(struct nc_header) <= headroom)
			/* There's enough head and tail room */
			goto encapsulate;

		if ((sizeof (struct nc_header) + padlen) <
				(headroom + tailroom)) {
			/* There's enough total room, so just readjust */
			skb->data = memmove(skb->head
						+ sizeof (struct nc_header),
					    skb->data, skb->len);
			skb_set_tail_pointer(skb, len);
			goto encapsulate;
		}
	}

	/* Create a new skb to use with the correct size */
	skb2 = skb_copy_expand(skb,
				sizeof (struct nc_header),
				padlen,
				flags);
	dev_kfree_skb_any(skb);
	if (!skb2)
		return skb2;
	skb = skb2;

encapsulate:
	/* header first */
	header = (struct nc_header *) skb_push(skb, sizeof *header);
	header->hdr_len = cpu_to_le16(sizeof (*header));
	header->packet_len = cpu_to_le16(len);
	header->packet_id = cpu_to_le16((u16)dev->xid++);

	/* maybe pad; then trailer */
	if (!((skb->len + sizeof *trailer) & 0x01))
		*skb_put(skb, 1) = PAD_BYTE;
	trailer = (struct nc_trailer *) skb_put(skb, sizeof *trailer);
	put_unaligned(header->packet_id, &trailer->packet_id);
#if 0
	netdev_dbg(dev->net, "frame >tx h %d p %d id %d\n",
		   header->hdr_len, header->packet_len,
		   header->packet_id);
#endif
	return skb;
}

static struct sk_buff *int51x1_tx_fixup(struct usbnet *dev,
		struct sk_buff *skb, gfp_t flags)
{
	int pack_len = skb->len;
	int pack_with_header_len = pack_len + INT51X1_HEADER_SIZE;
	int headroom = skb_headroom(skb);
	int tailroom = skb_tailroom(skb);
	int need_tail = 0;
	__le16 *len;

	/*                                                              */
	if ((pack_with_header_len) < dev->maxpacket)
		need_tail = dev->maxpacket - pack_with_header_len + 1;
	/*
                                                                    
                                                                     
                                 
  */
	else if (!(pack_with_header_len % dev->maxpacket))
		need_tail = 1;

	if (!skb_cloned(skb) &&
			(headroom + tailroom >= need_tail + INT51X1_HEADER_SIZE)) {
		if (headroom < INT51X1_HEADER_SIZE || tailroom < need_tail) {
			skb->data = memmove(skb->head + INT51X1_HEADER_SIZE,
					skb->data, skb->len);
			skb_set_tail_pointer(skb, skb->len);
		}
	} else {
		struct sk_buff *skb2;

		skb2 = skb_copy_expand(skb,
				INT51X1_HEADER_SIZE,
				need_tail,
				flags);
		dev_kfree_skb_any(skb);
		if (!skb2)
			return NULL;
		skb = skb2;
	}

	pack_len += need_tail;
	pack_len &= 0x07ff;

	len = (__le16 *) __skb_push(skb, INT51X1_HEADER_SIZE);
	*len = cpu_to_le16(pack_len);

	if(need_tail)
		memset(__skb_put(skb, need_tail), 0, need_tail);

	return skb;
}

/* Create and initialize an SCTP_REMOTE_ERROR notification.
 *
 * Note: This assumes that the chunk->skb->data already points to the
 * operation error payload.
 *
 * Socket Extensions for SCTP - draft-01
 * 5.3.1.3 SCTP_REMOTE_ERROR
 *
 * A remote peer may send an Operational Error message to its peer.
 * This message indicates a variety of error conditions on an
 * association. The entire error TLV as it appears on the wire is
 * included in a SCTP_REMOTE_ERROR event.  Please refer to the SCTP
 * specification [SCTP] and any extensions for a list of possible
 * error formats.
 */
struct sctp_ulpevent *
sctp_ulpevent_make_remote_error(const struct sctp_association *asoc,
				struct sctp_chunk *chunk, __u16 flags,
				gfp_t gfp)
{
	struct sctp_ulpevent *event;
	struct sctp_remote_error *sre;
	struct sk_buff *skb;
	sctp_errhdr_t *ch;
	__be16 cause;
	int elen;

	ch = (sctp_errhdr_t *)(chunk->skb->data);
	cause = ch->cause;
	elen = SCTP_PAD4(ntohs(ch->length)) - sizeof(sctp_errhdr_t);

	/* Pull off the ERROR header.  */
	skb_pull(chunk->skb, sizeof(sctp_errhdr_t));

	/* Copy the skb to a new skb with room for us to prepend
	 * notification with.
	 */
	skb = skb_copy_expand(chunk->skb, sizeof(*sre), 0, gfp);

	/* Pull off the rest of the cause TLV from the chunk.  */
	skb_pull(chunk->skb, elen);
	if (!skb)
		goto fail;

	/* Embed the event fields inside the cloned skb.  */
	event = sctp_skb2event(skb);
	sctp_ulpevent_init(event, MSG_NOTIFICATION, skb->truesize);

	sre = (struct sctp_remote_error *) skb_push(skb, sizeof(*sre));

	/* Trim the buffer to the right length.  */
	skb_trim(skb, sizeof(*sre) + elen);

	/* RFC6458, Section 6.1.3. SCTP_REMOTE_ERROR */
	memset(sre, 0, sizeof(*sre));
	sre->sre_type = SCTP_REMOTE_ERROR;
	sre->sre_flags = 0;
	sre->sre_length = skb->len;
	sre->sre_error = cause;
	sctp_ulpevent_set_owner(event, asoc);
	sre->sre_assoc_id = sctp_assoc2id(asoc);

	return event;
fail:
	return NULL;
}

static unsigned int ipt_mirror_target(struct sk_buff **pskb,
				      unsigned int hooknum,
				      const struct net_device *in,
				      const struct net_device *out,
				      const void *targinfo,
				      void *userinfo)
{
	struct rtable *rt;
	struct sk_buff *nskb;
	unsigned int hh_len;

	/* If we are not at FORWARD hook (INPUT/PREROUTING),
	 * the TTL isn't decreased by the IP stack */
	if (hooknum != NF_IP_FORWARD) {
		struct iphdr *iph = (*pskb)->nh.iph;
		if (iph->ttl <= 1) {
			/* this will traverse normal stack, and 
			 * thus call conntrack on the icmp packet */
			icmp_send(*pskb, ICMP_TIME_EXCEEDED, 
				  ICMP_EXC_TTL, 0);
			return NF_DROP;
		}
		ip_decrease_ttl(iph);
	}

	if ((rt = route_mirror(*pskb, hooknum == NF_IP_LOCAL_IN)) == NULL)
		return NF_DROP;

	hh_len = (rt->u.dst.dev->hard_header_len + 15) & ~15;

	/* Copy skb (even if skb is about to be dropped, we can't just
	 * clone it because there may be other things, such as tcpdump,
	 * interested in it). We also need to expand headroom in case
	 * hh_len of incoming interface < hh_len of outgoing interface */
	nskb = skb_copy_expand(*pskb, hh_len, skb_tailroom(*pskb), GFP_ATOMIC);
	if (nskb == NULL) {
		dst_release(&rt->u.dst);
		return NF_DROP;
	}

	dst_release(nskb->dst);
	nskb->dst = &rt->u.dst;

	ip_rewrite(nskb);
	/* Don't let conntrack code see this packet:
           it will think we are starting a new
           connection! --RR */
	ip_direct_send(nskb);

	return NF_DROP;
}

int goose_trans_skb(struct net_device *dev, unsigned char *daddr,
					struct sk_buff *__skb, int reliablity)
{
	struct sk_buff *skb = __skb;
	unsigned int skb_pull_len = NLMSG_LENGTH(0) + sizeof(struct nl_data_header);

	if (unlikely((dev == NULL) || (!tran_active)))
		goto goose_trans_skb_fail;
	
	/* We use existing skb to form a new one:
	 *
	 * skb:
	 * old skb->data                      new skb->data
	 *   |                                  |
	 * -----------------------------------------------------------
	 *   | NLMSG_LENGTH(0) | nl_data_header | goose header | APDU
	 * -----------------------------------------------------------
	 *   | <==      skb_pull_len        ==> |
	 * 
	 */		
	skb_pull(skb, skb_pull_len);
	skb_reset_network_header(skb);

	/* But after pulling, if we have still no enough space for link-layer header,
	   we have to reconstruct a new skb */
	if ((skb->head - skb->network_header) < LL_RESERVED_SPACE(dev)) {
		skb = skb_copy_expand(__skb, LL_RESERVED_SPACE(dev), 16, GFP_ATOMIC);
		kfree_skb(__skb);
	}

	/* Specify protocol type and frame information */
	skb->dev = dev;
	skb->protocol = ETH_P_GOOSE;
	skb->pkt_type = PACKET_OUTGOING;
	skb->csum = 0;
	skb->ip_summed = 0;

	/* Set the highest priority */
	skb->priority = 0;
	
	if (unlikely(dev_hard_header(skb, dev, ETH_P_GOOSE, daddr, dev->dev_addr, skb->len) < 0))
		goto goose_trans_skb_fail;

	/* If the message should be transmitted by GOOSE Enhanced Retransmission Mechanism,
	   call goose_enhan_retrans, otherwise transmit it directly.*/
	return reliablity ? goose_enhan_retrans(skb):dev_queue_xmit(skb);
	
goose_trans_skb_fail:
	kfree_skb(skb);
	return -1;
}

static int ipq_mangle_ipv4(ipq_verdict_msg_t *v, ipq_queue_element_t *e)
{
	int diff;
	struct iphdr *user_iph = (struct iphdr *)v->payload;

	if (v->data_len < sizeof(*user_iph))
		return 0;
	diff = v->data_len - e->skb->len;
	if (diff < 0)
		skb_trim(e->skb, v->data_len);
	else if (diff > 0) {
		if (v->data_len > 0xFFFF)
			return -EINVAL;
		if (diff > skb_tailroom(e->skb)) {
			struct sk_buff *newskb;
			
			newskb = skb_copy_expand(e->skb,
			                         skb_headroom(e->skb),
			                         diff,
			                         GFP_ATOMIC);
			if (newskb == NULL) {
				printk(KERN_WARNING "ip_queue: OOM "
				      "in mangle, dropping packet\n");
				return -ENOMEM;
			}
			if (e->skb->sk)
				skb_set_owner_w(newskb, e->skb->sk);
			kfree_skb(e->skb);
			e->skb = newskb;
		}
		skb_put(e->skb, diff);
	}
	memcpy(e->skb->data, v->payload, v->data_len);
	e->skb->nfcache |= NFC_ALTERED;

	/*
	 * Extra routing may needed on local out, as the QUEUE target never
	 * returns control to the table.
	 */
	if (e->info->hook == NF_IP_LOCAL_OUT) {
		struct iphdr *iph = e->skb->nh.iph;

		if (!(iph->tos == e->rt_info.tos
		      && iph->daddr == e->rt_info.daddr
		      && iph->saddr == e->rt_info.saddr))
			return route_me_harder(e->skb);
	}
	return 0;
}

static struct sk_buff *
rndis_tx_fixup(struct usbnet *dev, struct sk_buff *skb, gfp_t flags)
{
	struct rndis_data_hdr	*hdr;
	struct sk_buff		*skb2;
	unsigned		len = skb->len;

	if (likely(!skb_cloned(skb))) {
		int	room = skb_headroom(skb);

		/* enough head room as-is? */
		if (unlikely((sizeof *hdr) <= room))
			goto fill;

		/* enough room, but needs to be readjusted? */
		room += skb_tailroom(skb);
		if (likely((sizeof *hdr) <= room)) {
			skb->data = memmove(skb->head + sizeof *hdr,
					    skb->data, len);
			skb_set_tail_pointer(skb, len);
			goto fill;
		}
	}

	/* create a new skb, with the correct size (and tailpad) */
	skb2 = skb_copy_expand(skb, sizeof *hdr, 1, flags);
	dev_kfree_skb_any(skb);
	if (unlikely(!skb2))
		return skb2;
	skb = skb2;

	/* fill out the RNDIS header.  we won't bother trying to batch
	 * packets; Linux minimizes wasted bandwidth through tx queues.
	 */
fill:
	hdr = (void *) __skb_push(skb, sizeof *hdr);
	memset(hdr, 0, sizeof *hdr);
	hdr->msg_type = RNDIS_MSG_PACKET;
	hdr->msg_len = cpu_to_le32(skb->len);
	hdr->data_offset = ccpu2(sizeof(*hdr) - 8);
	hdr->data_len = cpu_to_le32(len);

	/* FIXME make the last packet always be short ... */
	return skb;
}

/* Unusual, but possible case. */
static int enlarge_skb(struct sk_buff **pskb, unsigned int extra)
{
	struct sk_buff *nskb;

	if ((*pskb)->len + extra > 65535)
		return 0;

	nskb = skb_copy_expand(*pskb, skb_headroom(*pskb), extra, GFP_ATOMIC);
	if (!nskb)
		return 0;

	/* Transfer socket to new skb. */
	if ((*pskb)->sk)
		skb_set_owner_w(nskb, (*pskb)->sk);
	kfree_skb(*pskb);
	*pskb = nskb;
	return 1;
}

static struct sk_buff *
genelink_tx_fixup(struct usbnet *dev, struct sk_buff *skb, gfp_t flags)
{
	int 	padlen;
	int	length = skb->len;
	int	headroom = skb_headroom(skb);
	int	tailroom = skb_tailroom(skb);
	__le32	*packet_count;
	__le32	*packet_len;

	// FIXME:  magic numbers, bleech
	padlen = ((skb->len + (4 + 4*1)) % 64) ? 0 : 1;

	if ((!skb_cloned(skb))
			&& ((headroom + tailroom) >= (padlen + (4 + 4*1)))) {
		if ((headroom < (4 + 4*1)) || (tailroom < padlen)) {
			skb->data = memmove(skb->head + (4 + 4*1),
					     skb->data, skb->len);
			skb_set_tail_pointer(skb, skb->len);
		}
	} else {
		struct sk_buff	*skb2;
		skb2 = skb_copy_expand(skb, (4 + 4*1) , padlen, flags);
		dev_kfree_skb_any(skb);
		skb = skb2;
		if (!skb)
			return NULL;
	}

	// attach the packet count to the header
	packet_count = (__le32 *) skb_push(skb, (4 + 4*1));
	packet_len = packet_count + 1;

	*packet_count = cpu_to_le32(1);
	*packet_len = cpu_to_le32(length);

	// add padding byte
	if ((skb->len % dev->maxpacket) == 0)
		skb_put(skb, 1);

	return skb;
}

/*
 * Prototype    : oamkernel_add_pkt_head
 * Description  : recv data from driver
 * Input        : char main_type
                  char sub_type
                  struct sk_buff *skb
                  void *param
 * Return Value : int32
 * Calls        :
 * Called By    :
 *
 *   History        :
 *   1.Date         : 2013/6/20
 *     Author       : 
 *     Modification : Created function
 */
int32 oamkernel_add_pkt_head( OS_SK_BUFF_STRU *pst_skb, uint8 type, uint8 PrimID)
{
    struct  sk_buff *skb = NULL;
    int32   l_ret = 0;
    if (NULL == pst_skb)
    {
        OAM_ERROR("para fail\n");
        return -EFAIL;
    }
	
    l_ret = pst_skb->len;
    OAM_INFO("entry:len=%d\n", l_ret);

    skb = NULL;
    skb = skb_copy_expand(pst_skb, sizeof(struct oam_header),
                    sizeof(struct oam_end), GFP_ATOMIC);
    if (NULL == skb)
    {
        OAM_ERROR("can't allocate mem for new skb");
        return -EINVAL;
    }
	
    skb_push(skb,sizeof(struct oam_header));
    skb_put(skb,sizeof(struct oam_end));

    OAM_INFO("skb->len=%d\n", skb->len);

    wifi_tx_add_head(skb->data, type, PrimID, skb->len);

    /* push curr skb to skb queue */
    skb_queue_tail(&gst_kerenlglobal.rx_wifi_dbg_seq, skb);

    if (gst_kerenlglobal.rx_wifi_dbg_seq.qlen > RX_WIFI_QUE_MAX_NUM)
    {   /* if rx sdio log queue is too large */
        skb = skb_dequeue(&gst_kerenlglobal.rx_wifi_dbg_seq);
        kfree_skb(skb);
        OAM_ERROR("wifi log queue is too large");
    }
	hwifi_free_skb(pst_skb);
    queue_work(gst_kerenlglobal.oam_rx_workqueue, &gst_kerenlglobal.rx_wifi_work);
    return l_ret;
}

static void mac80211_hwsim_monitor_rx(struct ieee80211_hw *hw,
				      struct sk_buff *tx_skb)
{
	struct mac80211_hwsim_data *data = hw->priv;
	struct sk_buff *skb;
	struct hwsim_radiotap_hdr *hdr;
	u16 flags;
	struct ieee80211_tx_info *info = IEEE80211_SKB_CB(tx_skb);
	struct ieee80211_rate *txrate = ieee80211_get_tx_rate(hw, info);

	if (!netif_running(hwsim_mon))
		return;

	skb = skb_copy_expand(tx_skb, sizeof(*hdr), 0, GFP_ATOMIC);
	if (skb == NULL)
		return;

	hdr = (struct hwsim_radiotap_hdr *) skb_push(skb, sizeof(*hdr));
	hdr->hdr.it_version = PKTHDR_RADIOTAP_VERSION;
	hdr->hdr.it_pad = 0;
	hdr->hdr.it_len = cpu_to_le16(sizeof(*hdr));
	hdr->hdr.it_present = cpu_to_le32((1 << IEEE80211_RADIOTAP_FLAGS) |
					  (1 << IEEE80211_RADIOTAP_RATE) |
					  (1 << IEEE80211_RADIOTAP_CHANNEL));
	hdr->rt_flags = 0;
	hdr->rt_rate = txrate->bitrate / 5;
	hdr->rt_channel = cpu_to_le16(data->channel->center_freq);
	flags = IEEE80211_CHAN_2GHZ;
	if (txrate->flags & IEEE80211_RATE_ERP_G)
		flags |= IEEE80211_CHAN_OFDM;
	else
		flags |= IEEE80211_CHAN_CCK;
	hdr->rt_chbitmask = cpu_to_le16(flags);

	skb->dev = hwsim_mon;
	skb_set_mac_header(skb, 0);
	skb->ip_summed = CHECKSUM_UNNECESSARY;
	skb->pkt_type = PACKET_OTHERHOST;
	skb->protocol = htons(ETH_P_802_2);
	memset(skb->cb, 0, sizeof(skb->cb));
	netif_rx(skb);
}

/** Make enough room in an skb for extra header and trailer.
 *
 * @param pskb return parameter for expanded skb
 * @param skb skb
 * @param head_n required headroom
 * @param tail_n required tailroom
 * @return 0 on success, error code otherwise
 */
int skb_make_room(struct sk_buff **pskb, struct sk_buff *skb, int head_n, int tail_n){
    int err = 0;
    int has_headroom = (head_n <= skb_headroom(skb));
    int has_tailroom = (tail_n <= skb_tailroom(skb));
    int writeable = !skb_cloned(skb) && !skb_shared(skb);

    dprintf("> skb=%p headroom=%d head_n=%d tailroom=%d tail_n=%d\n",
            skb,
            skb_headroom(skb), head_n,
            skb_tailroom(skb), tail_n);
    if(writeable && has_headroom && has_tailroom){
        // There's room! Reuse it.
        *pskb = skb;
    } else if(writeable && has_tailroom){
        // Tailroom, no headroom. Expand header the way GRE does.
        struct sk_buff *new_skb = skb_realloc_headroom(skb, head_n + 16);
        if(!new_skb){
            err = -ENOMEM;
            goto exit;
        }
        kfree_skb(skb);
        *pskb = new_skb;
    } else {
        // No room. Expand. There may be more efficient ways to do
        // this, but this is simple and correct.
        struct sk_buff *new_skb = skb_copy_expand(skb, head_n + 16, tail_n, GFP_ATOMIC);
        if(!new_skb){
            err = -ENOMEM;
            goto exit;
        }
        kfree_skb(skb);
        *pskb = new_skb;
    }
    dprintf("> skb=%p headroom=%d head_n=%d tailroom=%d tail_n=%d\n",
            *pskb,
            skb_headroom(*pskb), head_n,
            skb_tailroom(*pskb), tail_n);
  exit:
    dprintf("< err=%d\n", err);
    return err;
}