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Linux/net/dsa/tag_trailer.c

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  1 // SPDX-License-Identifier: GPL-2.0+
  2 /*
  3  * net/dsa/tag_trailer.c - Trailer tag format handling
  4  * Copyright (c) 2008-2009 Marvell Semiconductor
  5  */
  6 
  7 #include <linux/etherdevice.h>
  8 #include <linux/list.h>
  9 #include <linux/slab.h>
 10 
 11 #include "dsa_priv.h"
 12 
 13 static struct sk_buff *trailer_xmit(struct sk_buff *skb, struct net_device *dev)
 14 {
 15         struct dsa_port *dp = dsa_slave_to_port(dev);
 16         struct sk_buff *nskb;
 17         int padlen;
 18         u8 *trailer;
 19 
 20         /*
 21          * We have to make sure that the trailer ends up as the very
 22          * last 4 bytes of the packet.  This means that we have to pad
 23          * the packet to the minimum ethernet frame size, if necessary,
 24          * before adding the trailer.
 25          */
 26         padlen = 0;
 27         if (skb->len < 60)
 28                 padlen = 60 - skb->len;
 29 
 30         nskb = alloc_skb(NET_IP_ALIGN + skb->len + padlen + 4, GFP_ATOMIC);
 31         if (!nskb)
 32                 return NULL;
 33         skb_reserve(nskb, NET_IP_ALIGN);
 34 
 35         skb_reset_mac_header(nskb);
 36         skb_set_network_header(nskb, skb_network_header(skb) - skb->head);
 37         skb_set_transport_header(nskb, skb_transport_header(skb) - skb->head);
 38         skb_copy_and_csum_dev(skb, skb_put(nskb, skb->len));
 39         consume_skb(skb);
 40 
 41         if (padlen) {
 42                 skb_put_zero(nskb, padlen);
 43         }
 44 
 45         trailer = skb_put(nskb, 4);
 46         trailer[0] = 0x80;
 47         trailer[1] = 1 << dp->index;
 48         trailer[2] = 0x10;
 49         trailer[3] = 0x00;
 50 
 51         return nskb;
 52 }
 53 
 54 static struct sk_buff *trailer_rcv(struct sk_buff *skb, struct net_device *dev,
 55                                    struct packet_type *pt)
 56 {
 57         u8 *trailer;
 58         int source_port;
 59 
 60         if (skb_linearize(skb))
 61                 return NULL;
 62 
 63         trailer = skb_tail_pointer(skb) - 4;
 64         if (trailer[0] != 0x80 || (trailer[1] & 0xf8) != 0x00 ||
 65             (trailer[2] & 0xef) != 0x00 || trailer[3] != 0x00)
 66                 return NULL;
 67 
 68         source_port = trailer[1] & 7;
 69 
 70         skb->dev = dsa_master_find_slave(dev, 0, source_port);
 71         if (!skb->dev)
 72                 return NULL;
 73 
 74         if (pskb_trim_rcsum(skb, skb->len - 4))
 75                 return NULL;
 76 
 77         return skb;
 78 }
 79 
 80 static const struct dsa_device_ops trailer_netdev_ops = {
 81         .name   = "trailer",
 82         .proto  = DSA_TAG_PROTO_TRAILER,
 83         .xmit   = trailer_xmit,
 84         .rcv    = trailer_rcv,
 85         .overhead = 4,
 86 };
 87 
 88 MODULE_LICENSE("GPL");
 89 MODULE_ALIAS_DSA_TAG_DRIVER(DSA_TAG_PROTO_TRAILER);
 90 
 91 module_dsa_tag_driver(trailer_netdev_ops);
 92 

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