net/dsa/tag_trailer.c

/*
 * net/dsa/tag_trailer.c - Trailer tag format handling
 * Copyright (c) 2008-2009 Marvell Semiconductor
 *
 * 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.
 */

#include <linux/etherdevice.h>
#include <linux/list.h>
#include <linux/slab.h>

#include "dsa_priv.h"

static struct sk_buff *trailer_xmit(struct sk_buff *skb, struct net_device *dev)
{
	struct dsa_slave_priv *p = netdev_priv(dev);
	struct sk_buff *nskb;
	int padlen;
	u8 *trailer;

	/*
	 * We have to make sure that the trailer ends up as the very
	 * last 4 bytes of the packet.  This means that we have to pad
	 * the packet to the minimum ethernet frame size, if necessary,
	 * before adding the trailer.
	 */
	padlen = 0;
	if (skb->len < 60)
		padlen = 60 - skb->len;

	nskb = alloc_skb(NET_IP_ALIGN + skb->len + padlen + 4, GFP_ATOMIC);
	if (!nskb)
		return NULL;
	skb_reserve(nskb, NET_IP_ALIGN);

	skb_reset_mac_header(nskb);
	skb_set_network_header(nskb, skb_network_header(skb) - skb->head);
	skb_set_transport_header(nskb, skb_transport_header(skb) - skb->head);
	skb_copy_and_csum_dev(skb, skb_put(nskb, skb->len));
	kfree_skb(skb);

	if (padlen) {
		skb_put_zero(nskb, padlen);
	}

	trailer = skb_put(nskb, 4);
	trailer[0] = 0x80;
	trailer[1] = 1 << p->dp->index;
	trailer[2] = 0x10;
	trailer[3] = 0x00;

	return nskb;
}

static struct sk_buff *trailer_rcv(struct sk_buff *skb, struct net_device *dev,
				   struct packet_type *pt,
				   struct net_device *orig_dev)
{
	struct dsa_switch_tree *dst = dev->dsa_ptr;
	struct dsa_port *cpu_dp = dsa_get_cpu_port(dst);
	struct dsa_switch *ds = cpu_dp->ds;
	u8 *trailer;
	int source_port;

	if (skb_linearize(skb))
		return NULL;

	trailer = skb_tail_pointer(skb) - 4;
	if (trailer[0] != 0x80 || (trailer[1] & 0xf8) != 0x00 ||
	    (trailer[2] & 0xef) != 0x00 || trailer[3] != 0x00)
		return NULL;

	source_port = trailer[1] & 7;
	if (source_port >= ds->num_ports || !ds->ports[source_port].netdev)
		return NULL;

	pskb_trim_rcsum(skb, skb->len - 4);

	skb->dev = ds->ports[source_port].netdev;

	return skb;
}

const struct dsa_device_ops trailer_netdev_ops = {
	.xmit	= trailer_xmit,
	.rcv	= trailer_rcv,
};