C++ skb_cow_head函数代码示例

/* Transmit a fully formatted Geneve frame.
 *
 * When calling this function. The skb->data should point
 * to the geneve header which is fully formed.
 *
 * This function will add other UDP tunnel headers.
 */
int geneve_xmit_skb(struct geneve_sock *gs, struct rtable *rt,
		    struct sk_buff *skb, __be32 src, __be32 dst, __u8 tos,
		    __u8 ttl, __be16 df, __be16 src_port, __be16 dst_port,
		    __be16 tun_flags, u8 vni[3], u8 opt_len, u8 *opt,
		    bool xnet)
{
	struct genevehdr *gnvh;
	int min_headroom;
	int err;

	skb = udp_tunnel_handle_offloads(skb, !gs->sock->sk->sk_no_check_tx);

	min_headroom = LL_RESERVED_SPACE(rt->dst.dev) + rt->dst.header_len
			+ GENEVE_BASE_HLEN + opt_len + sizeof(struct iphdr)
			+ (vlan_tx_tag_present(skb) ? VLAN_HLEN : 0);

	err = skb_cow_head(skb, min_headroom);
	if (unlikely(err))
		return err;

	skb = vlan_hwaccel_push_inside(skb);
	if (unlikely(!skb))
		return -ENOMEM;

	gnvh = (struct genevehdr *)__skb_push(skb, sizeof(*gnvh) + opt_len);
	geneve_build_header(gnvh, tun_flags, vni, opt_len, opt);

	skb_set_inner_protocol(skb, htons(ETH_P_TEB));

	return udp_tunnel_xmit_skb(gs->sock, rt, skb, src, dst,
				   tos, ttl, df, src_port, dst_port, xnet);
}

static netdev_tx_t gre_tap_xmit(struct sk_buff *skb,
				struct net_device *dev)
{
	struct ip_tunnel *tunnel = netdev_priv(dev);

	if (OVTYPE_IS_GRETAP (skb)) {
		gretap_gre_tap_xmit_in (skb) = rdtsc ();
	}

	skb = gre_handle_offloads(skb, !!(tunnel->parms.o_flags&TUNNEL_CSUM));
	if (IS_ERR(skb))
		goto out;

	if (skb_cow_head(skb, dev->needed_headroom))
		goto free_skb;

	__gre_xmit(skb, dev, &tunnel->parms.iph, htons(ETH_P_TEB));

	return NETDEV_TX_OK;

free_skb:
	kfree_skb(skb);
out:
	dev->stats.tx_dropped++;
	return NETDEV_TX_OK;
}

/*
 * Transmit a packet to the base station on behalf of the network stack
 *
 *
 * Returns: NETDEV_TX_OK (always, even in case of error)
 *
 * In case of error, we just drop it. Reasons:
 *
 *  - we add a hw header to each skb, and if the network stack
 *    retries, we have no way to know if that skb has it or not.
 *
 *  - network protocols have their own drop-recovery mechanisms
 *
 *  - there is not much else we can do
 *
 * If the device is idle, we need to wake it up; that is an operation
 * that will sleep. See i2400m_net_wake_tx() for details.
 */
static
netdev_tx_t i2400m_hard_start_xmit(struct sk_buff *skb,
					 struct net_device *net_dev)
{
	struct i2400m *i2400m = net_dev_to_i2400m(net_dev);
	struct device *dev = i2400m_dev(i2400m);
	int result = -1;

	d_fnstart(3, dev, "(skb %p net_dev %p)\n", skb, net_dev);

	if (skb_cow_head(skb, 0))
		goto drop;

	if (i2400m->state == I2400M_SS_IDLE)
		result = i2400m_net_wake_tx(i2400m, net_dev, skb);
	else
		result = i2400m_net_tx(i2400m, net_dev, skb);
	if (result <  0) {
drop:
		net_dev->stats.tx_dropped++;
	} else {
		net_dev->stats.tx_packets++;
		net_dev->stats.tx_bytes += skb->len;
	}
	dev_kfree_skb(skb);
	d_fnend(3, dev, "(skb %p net_dev %p) = %d\n", skb, net_dev, result);
	return NETDEV_TX_OK;
}

static int xlgmac_prep_tso(struct sk_buff *skb,
			   struct xlgmac_pkt_info *pkt_info)
{
	int ret;

	if (!XLGMAC_GET_REG_BITS(pkt_info->attributes,
				 TX_PACKET_ATTRIBUTES_TSO_ENABLE_POS,
				 TX_PACKET_ATTRIBUTES_TSO_ENABLE_LEN))
		return 0;

	ret = skb_cow_head(skb, 0);
	if (ret)
		return ret;

	pkt_info->header_len = skb_transport_offset(skb) + tcp_hdrlen(skb);
	pkt_info->tcp_header_len = tcp_hdrlen(skb);
	pkt_info->tcp_payload_len = skb->len - pkt_info->header_len;
	pkt_info->mss = skb_shinfo(skb)->gso_size;

	XLGMAC_PR("header_len=%u\n", pkt_info->header_len);
	XLGMAC_PR("tcp_header_len=%u, tcp_payload_len=%u\n",
		  pkt_info->tcp_header_len, pkt_info->tcp_payload_len);
	XLGMAC_PR("mss=%u\n", pkt_info->mss);

	/* Update the number of packets that will ultimately be transmitted
	 * along with the extra bytes for each extra packet
	 */
	pkt_info->tx_packets = skb_shinfo(skb)->gso_segs;
	pkt_info->tx_bytes += (pkt_info->tx_packets - 1) * pkt_info->header_len;

	return 0;
}

static int push_eth(struct sk_buff *skb, struct sw_flow_key *key,
		    const struct ovs_action_push_eth *ethh)
{
	struct ethhdr *hdr;

	/* Add the new Ethernet header */
	if (skb_cow_head(skb, ETH_HLEN) < 0)
		return -ENOMEM;

	skb_push(skb, ETH_HLEN);
	skb_reset_mac_header(skb);
	skb_reset_mac_len(skb);

	hdr = eth_hdr(skb);
	ether_addr_copy(hdr->h_source, ethh->addresses.eth_src);
	ether_addr_copy(hdr->h_dest, ethh->addresses.eth_dst);
	hdr->h_proto = skb->protocol;

	skb_postpush_rcsum(skb, hdr, ETH_HLEN);

	/* safe right before invalidate_flow_key */
	key->mac_proto = MAC_PROTO_ETHERNET;
	invalidate_flow_key(key);
	return 0;
}

static int push_mpls(struct sk_buff *skb, struct sw_flow_key *key,
		     const struct ovs_action_push_mpls *mpls)
{
	struct mpls_shim_hdr *new_mpls_lse;

	/* Networking stack do not allow simultaneous Tunnel and MPLS GSO. */
	if (skb->encapsulation)
		return -ENOTSUPP;

	if (skb_cow_head(skb, MPLS_HLEN) < 0)
		return -ENOMEM;

	if (!skb->inner_protocol) {
		skb_set_inner_network_header(skb, skb->mac_len);
		skb_set_inner_protocol(skb, skb->protocol);
	}

	skb_push(skb, MPLS_HLEN);
	memmove(skb_mac_header(skb) - MPLS_HLEN, skb_mac_header(skb),
		skb->mac_len);
	skb_reset_mac_header(skb);
	skb_set_network_header(skb, skb->mac_len);

	new_mpls_lse = mpls_hdr(skb);
	new_mpls_lse->label_stack_entry = mpls->mpls_lse;

	skb_postpush_rcsum(skb, new_mpls_lse, MPLS_HLEN);

	if (ovs_key_mac_proto(key) == MAC_PROTO_ETHERNET)
		update_ethertype(skb, eth_hdr(skb), mpls->mpls_ethertype);
	skb->protocol = mpls->mpls_ethertype;

	invalidate_flow_key(key);
	return 0;
}

static int xfrm6_beet_input(struct xfrm_state *x, struct sk_buff *skb)
{
	struct ipv6hdr *ip6h;
	const unsigned char *old_mac;
	int size = sizeof(struct ipv6hdr);
	int err;

	err = skb_cow_head(skb, size + skb->mac_len);
	if (err)
		goto out;

	__skb_push(skb, size);
	skb_reset_network_header(skb);

	old_mac = skb_mac_header(skb);
	skb_set_mac_header(skb, -skb->mac_len);
	memmove(skb_mac_header(skb), old_mac, skb->mac_len);

	xfrm6_beet_make_header(skb);

	ip6h = ipv6_hdr(skb);
	ip6h->payload_len = htons(skb->len - size);
	ipv6_addr_copy(&ip6h->daddr, (struct in6_addr *) &x->sel.daddr.a6);
	ipv6_addr_copy(&ip6h->saddr, (struct in6_addr *) &x->sel.saddr.a6);
	err = 0;
out:
	return err;
}

static struct sk_buff *lan9303_xmit(struct sk_buff *skb, struct net_device *dev)
{
	struct dsa_port *dp = dsa_slave_to_port(dev);
	u16 *lan9303_tag;

	/* insert a special VLAN tag between the MAC addresses
	 * and the current ethertype field.
	 */
	if (skb_cow_head(skb, LAN9303_TAG_LEN) < 0) {
		dev_dbg(&dev->dev,
			"Cannot make room for the special tag. Dropping packet\n");
		return NULL;
	}

	/* provide 'LAN9303_TAG_LEN' bytes additional space */
	skb_push(skb, LAN9303_TAG_LEN);

	/* make room between MACs and Ether-Type */
	memmove(skb->data, skb->data + LAN9303_TAG_LEN, 2 * ETH_ALEN);

	lan9303_tag = (u16 *)(skb->data + 2 * ETH_ALEN);
	lan9303_tag[0] = htons(ETH_P_8021Q);
	lan9303_tag[1] = lan9303_xmit_use_arl(dp, skb->data) ?
				LAN9303_TAG_TX_USE_ALR :
				dp->index | LAN9303_TAG_TX_STP_OVERRIDE;
	lan9303_tag[1] = htons(lan9303_tag[1]);

	return skb;
}

static int push_mpls(struct sk_buff *skb, struct sw_flow_key *key,
		     const struct ovs_action_push_mpls *mpls)
{
	__be32 *new_mpls_lse;

	/* Networking stack do not allow simultaneous Tunnel and MPLS GSO. */
	if (skb->encapsulation)
		return -ENOTSUPP;

	if (skb_cow_head(skb, MPLS_HLEN) < 0)
		return -ENOMEM;

	skb_push(skb, MPLS_HLEN);
	memmove(skb_mac_header(skb) - MPLS_HLEN, skb_mac_header(skb),
		skb->mac_len);
	skb_reset_mac_header(skb);

	new_mpls_lse = (__be32 *)skb_mpls_header(skb);
	*new_mpls_lse = mpls->mpls_lse;

	skb_postpush_rcsum(skb, new_mpls_lse, MPLS_HLEN);

	update_ethertype(skb, eth_hdr(skb), mpls->mpls_ethertype);
	if (!skb->inner_protocol)
		skb_set_inner_protocol(skb, skb->protocol);
	skb->protocol = mpls->mpls_ethertype;

	invalidate_flow_key(key);
	return 0;
}

static int push_mpls(struct sk_buff *skb,
		     const struct ovs_action_push_mpls *mpls)
{
	__be32 *new_mpls_lse;
	struct ethhdr *hdr;

	if (skb_cow_head(skb, MPLS_HLEN) < 0)
		return -ENOMEM;

	skb_push(skb, MPLS_HLEN);
	memmove(skb_mac_header(skb) - MPLS_HLEN, skb_mac_header(skb),
		skb->mac_len);
	skb_reset_mac_header(skb);

	new_mpls_lse = (__be32 *)mac_header_end(skb);
	*new_mpls_lse = mpls->mpls_lse;

	if (skb->ip_summed == CHECKSUM_COMPLETE)
		skb->csum = csum_add(skb->csum, csum_partial(new_mpls_lse,
							     MPLS_HLEN, 0));

	hdr = eth_hdr(skb);
	hdr->h_proto = mpls->mpls_ethertype;
	if (!ovs_skb_get_inner_protocol(skb))
		ovs_skb_set_inner_protocol(skb, skb->protocol);
	skb->protocol = mpls->mpls_ethertype;
	return 0;
}

static int push_mpls(struct sk_buff *skb, struct sw_flow_key *key,
		     const struct ovs_action_push_mpls *mpls)
{
	__be32 *new_mpls_lse;
	struct ethhdr *hdr;

	/* Networking stack do not allow simultaneous Tunnel and MPLS GSO. */
	if (skb->encapsulation)
		return -ENOTSUPP;

	if (skb_cow_head(skb, MPLS_HLEN) < 0)
		return -ENOMEM;

	skb_push(skb, MPLS_HLEN);
	memmove(skb_mac_header(skb) - MPLS_HLEN, skb_mac_header(skb),
		skb->mac_len);
	skb_reset_mac_header(skb);

	new_mpls_lse = (__be32 *)skb_mpls_header(skb);
	*new_mpls_lse = mpls->mpls_lse;

	if (skb->ip_summed == CHECKSUM_COMPLETE)
		skb->csum = csum_add(skb->csum, csum_partial(new_mpls_lse,
							     MPLS_HLEN, 0));

	hdr = eth_hdr(skb);
	hdr->h_proto = mpls->mpls_ethertype;

	if (!skb->inner_protocol)
		skb_set_inner_protocol(skb, skb->protocol);
	skb->protocol = mpls->mpls_ethertype;

	invalidate_flow_key(key);
	return 0;
}

static netdev_tx_t ipgre_xmit(struct sk_buff *skb,
			      struct net_device *dev)
{
	struct ip_tunnel *tunnel = netdev_priv(dev);
	const struct iphdr *tnl_params;

	if (OVTYPE_IS_GRE (skb)) {
		gre_ipgre_xmit_in (skb) = rdtsc ();
	}

	if (dev->header_ops) {
		/* Need space for new headers */
		if (skb_cow_head(skb, dev->needed_headroom -
				      (tunnel->hlen + sizeof(struct iphdr))))
			goto free_skb;

		tnl_params = (const struct iphdr *)skb->data;

		/* Pull skb since ip_tunnel_xmit() needs skb->data pointing
		 * to gre header.
		 */
		skb_pull(skb, tunnel->hlen + sizeof(struct iphdr));
		skb_reset_mac_header(skb);
	} else {
		if (skb_cow_head(skb, dev->needed_headroom))
			goto free_skb;

		tnl_params = &tunnel->parms.iph;
	}

	skb = gre_handle_offloads(skb, !!(tunnel->parms.o_flags&TUNNEL_CSUM));
	if (IS_ERR(skb))
		goto out;

	__gre_xmit(skb, dev, tnl_params, skb->protocol);

	return NETDEV_TX_OK;

free_skb:
	kfree_skb(skb);
out:
	dev->stats.tx_dropped++;
	return NETDEV_TX_OK;
}

static int rawsock_add_header(struct sk_buff *skb)
{

	if (skb_cow_head(skb, 1))
		return -ENOMEM;

	*skb_push(skb, 1) = 0;

	return 0;
}

static void nci_add_rx_data_frag(struct nci_dev *ndev,
				 struct sk_buff *skb,
				 __u8 pbf, __u8 conn_id, __u8 status)
{
	int reassembly_len;
	int err = 0;

	if (status) {
		err = status;
		goto exit;
	}

	if (ndev->rx_data_reassembly) {
		reassembly_len = ndev->rx_data_reassembly->len;

		/* first, make enough room for the already accumulated data */
		if (skb_cow_head(skb, reassembly_len)) {
			pr_err("error adding room for accumulated rx data\n");

			kfree_skb(skb);
			skb = NULL;

			kfree_skb(ndev->rx_data_reassembly);
			ndev->rx_data_reassembly = NULL;

			err = -ENOMEM;
			goto exit;
		}

		/* second, combine the two fragments */
		memcpy(skb_push(skb, reassembly_len),
		       ndev->rx_data_reassembly->data,
		       reassembly_len);

		/* third, free old reassembly */
		kfree_skb(ndev->rx_data_reassembly);
		ndev->rx_data_reassembly = NULL;
	}

	if (pbf == NCI_PBF_CONT) {
		/* need to wait for next fragment, store skb and exit */
		ndev->rx_data_reassembly = skb;
		return;
	}

exit:
	if (ndev->nfc_dev->rf_mode == NFC_RF_TARGET) {
		/* Data received in Target mode, forward to nfc core */
		err = nfc_tm_data_received(ndev->nfc_dev, skb);
		if (err)
			pr_err("unable to handle received data\n");
	} else {
		nci_data_exchange_complete(ndev, skb, conn_id, err);
	}
}

int vxlan_xmit_skb(struct vxlan_sock *vs,
		   struct rtable *rt, struct sk_buff *skb,
		   __be32 src, __be32 dst, __u8 tos, __u8 ttl, __be16 df,
		   __be16 src_port, __be16 dst_port, __be32 vni)
{
	struct vxlanhdr *vxh;
	struct udphdr *uh;
	int min_headroom;
	int err;

	min_headroom = LL_RESERVED_SPACE(rt_dst(rt).dev) + rt_dst(rt).header_len
			+ VXLAN_HLEN + sizeof(struct iphdr)
			+ (vlan_tx_tag_present(skb) ? VLAN_HLEN : 0);

	/* Need space for new headers (invalidates iph ptr) */
	err = skb_cow_head(skb, min_headroom);
	if (unlikely(err)) {
		kfree_skb(skb);
		return err;
	}

	if (vlan_tx_tag_present(skb)) {
		if (unlikely(!vlan_insert_tag_set_proto(skb,
							skb->vlan_proto,
							vlan_tx_tag_get(skb))))
			return -ENOMEM;

		vlan_set_tci(skb, 0);
	}

	skb_reset_inner_headers(skb);

	vxh = (struct vxlanhdr *) __skb_push(skb, sizeof(*vxh));
	vxh->vx_flags = htonl(VXLAN_FLAGS);
	vxh->vx_vni = vni;

	__skb_push(skb, sizeof(*uh));
	skb_reset_transport_header(skb);
	uh = udp_hdr(skb);

	uh->dest = dst_port;
	uh->source = src_port;

	uh->len = htons(skb->len);
	uh->check = 0;

	vxlan_set_owner(vs->sock->sk, skb);

	skb = handle_offloads(skb);
	if (IS_ERR(skb))
		return PTR_ERR(skb);

	return iptunnel_xmit(vs->sock->sk, rt, skb, src, dst, IPPROTO_UDP,
			     tos, ttl, df, false);
}