net/dsa/tag_trailer.c

   1 /*
   2  * net/dsa/tag_trailer.c - Trailer tag format handling
   3  * Copyright (c) 2008-2009 Marvell Semiconductor
   4  *
   5  * This program is free software; you can redistribute it and/or modify
   6  * it under the terms of the GNU General Public License as published by
   7  * the Free Software Foundation; either version 2 of the License, or
   8  * (at your option) any later version.
   9  */
  10
  11 #include <linux/etherdevice.h>
  12 #include <linux/list.h>
  13 #include <linux/slab.h>
  14
  15 #include "dsa_priv.h"
  16
  17 static struct sk_buff *trailer_xmit(struct sk_buff *skb, struct net_device *dev)
  18 {
  19         struct dsa_port *dp = dsa_slave_to_port(dev);
  20         struct sk_buff *nskb;
  21         int padlen;
  22         u8 *trailer;
  23
  24         /*
  25          * We have to make sure that the trailer ends up as the very
  26          * last 4 bytes of the packet.  This means that we have to pad
  27          * the packet to the minimum ethernet frame size, if necessary,
  28          * before adding the trailer.
  29          */
  30         padlen = 0;
  31         if (skb->len < 60)
  32                 padlen = 60 - skb->len;
  33
  34         nskb = alloc_skb(NET_IP_ALIGN + skb->len + padlen + 4, GFP_ATOMIC);
  35         if (!nskb)
  36                 return NULL;
  37         skb_reserve(nskb, NET_IP_ALIGN);
  38
  39         skb_reset_mac_header(nskb);
  40         skb_set_network_header(nskb, skb_network_header(skb) - skb->head);
  41         skb_set_transport_header(nskb, skb_transport_header(skb) - skb->head);
  42         skb_copy_and_csum_dev(skb, skb_put(nskb, skb->len));
  43         consume_skb(skb);
  44
  45         if (padlen) {
  46                 skb_put_zero(nskb, padlen);
  47         }
  48
  49         trailer = skb_put(nskb, 4);
  50         trailer[0] = 0x80;
  51         trailer[1] = 1 << dp->index;
  52         trailer[2] = 0x10;
  53         trailer[3] = 0x00;
  54
  55         return nskb;
  56 }
  57
  58 static struct sk_buff *trailer_rcv(struct sk_buff *skb, struct net_device *dev,
  59                                    struct packet_type *pt)
  60 {
  61         u8 *trailer;
  62         int source_port;
  63
  64         if (skb_linearize(skb))
  65                 return NULL;
  66
  67         trailer = skb_tail_pointer(skb) - 4;
  68         if (trailer[0] != 0x80 || (trailer[1] & 0xf8) != 0x00 ||
  69             (trailer[2] & 0xef) != 0x00 || trailer[3] != 0x00)
  70                 return NULL;
  71
  72         source_port = trailer[1] & 7;
  73
  74         skb->dev = dsa_master_find_slave(dev, 0, source_port);
  75         if (!skb->dev)
  76                 return NULL;
  77
  78         pskb_trim_rcsum(skb, skb->len - 4);
  79
  80         return skb;
  81 }
  82
  83 const struct dsa_device_ops trailer_netdev_ops = {
  84         .xmit   = trailer_xmit,
  85         .rcv    = trailer_rcv,
  86 };