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packet: move helpers which rewrite headers to a separate file
Move helpers which rewrite headers, such as vlan_tag_pop or swap_src_dst_ipv4 to a separate header file so that they can be reused. Signed-off-by: Anton Protopopov <a.s.protopopov@gmail.com>
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2 files changed

Lines changed: 142 additions & 113 deletions

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‎common/rewrite_helpers.h‎

Lines changed: 141 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,141 @@
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/* SPDX-License-Identifier: GPL-2.0 */
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/*
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* This file contains functions that are used in the packetXX XDP programs to
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* manipulate on packets data. The functions are marked as __always_inline, and
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* fully defined in this header file to be included in the BPF program.
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*/
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#ifndef __REWRITE_HELPERS_H
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#define __REWRITE_HELPERS_H
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#include <linux/bpf.h>
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#include <linux/ip.h>
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#include <linux/ipv6.h>
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#include <linux/if_ether.h>
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#include "bpf_helpers.h"
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#include "bpf_endian.h"
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/* Pops the outermost VLAN tag off the packet. Returns the popped VLAN ID on
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* success or negative errno on failure.
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*/
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static __always_inline int vlan_tag_pop(struct xdp_md *ctx, struct ethhdr *eth)
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{
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void *data_end = (void *)(long)ctx->data_end;
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struct ethhdr eth_cpy;
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struct vlan_hdr *vlh;
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__be16 h_proto;
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int vlid;
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if (!proto_is_vlan(eth->h_proto))
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return -1;
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/* Careful with the parenthesis here */
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vlh = (void *)(eth + 1);
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/* Still need to do bounds checking */
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if (vlh + 1 > data_end)
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return -1;
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/* Save vlan ID for returning, h_proto for updating Ethernet header */
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vlid = bpf_ntohs(vlh->h_vlan_TCI);
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h_proto = vlh->h_vlan_encapsulated_proto;
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/* Make a copy of the outer Ethernet header before we cut it off */
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__builtin_memcpy(&eth_cpy, eth, sizeof(eth_cpy));
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/* Actually adjust the head pointer */
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if (bpf_xdp_adjust_head(ctx, (int)sizeof(*vlh)))
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return -1;
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/* Need to re-evaluate data *and* data_end and do new bounds checking
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* after adjusting head
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*/
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eth = (void *)(long)ctx->data;
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data_end = (void *)(long)ctx->data_end;
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if (eth + 1 > data_end)
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return -1;
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/* Copy back the old Ethernet header and update the proto type */
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__builtin_memcpy(eth, &eth_cpy, sizeof(*eth));
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eth->h_proto = h_proto;
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return vlid;
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}
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/* Pushes a new VLAN tag after the Ethernet header. Returns 0 on success,
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* -1 on failure.
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*/
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static __always_inline int vlan_tag_push(struct xdp_md *ctx,
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struct ethhdr *eth, int vlid)
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{
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void *data_end = (void *)(long)ctx->data_end;
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struct ethhdr eth_cpy;
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struct vlan_hdr *vlh;
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/* First copy the original Ethernet header */
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__builtin_memcpy(&eth_cpy, eth, sizeof(eth_cpy));
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/* Then add space in front of the packet */
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if (bpf_xdp_adjust_head(ctx, 0 - (int)sizeof(*vlh)))
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return -1;
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/* Need to re-evaluate data_end and data after head adjustment, and
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* bounds check, even though we know there is enough space (as we
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* increased it).
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*/
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data_end = (void *)(long)ctx->data_end;
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eth = (void *)(long)ctx->data;
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if (eth + 1 > data_end)
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return -1;
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/* Copy back the Ethernet header in the right place, populate the VLAN
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* tag with the ID and proto, and set the outer Ethernet header to VLAN
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* type. */
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__builtin_memcpy(eth, &eth_cpy, sizeof(*eth));
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vlh = (void *)(eth +1);
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if (vlh + 1 > data_end)
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return -1;
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vlh->h_vlan_TCI = bpf_htons(vlid);
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vlh->h_vlan_encapsulated_proto = eth->h_proto;
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eth->h_proto = bpf_htons(ETH_P_8021Q);
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return 0;
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}
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/*
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* Swaps destination and source MAC addresses inside an Ethernet header
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*/
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static __always_inline void swap_src_dst_mac(struct ethhdr *eth)
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{
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__u8 h_tmp[ETH_ALEN];
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__builtin_memcpy(h_tmp, eth->h_source, ETH_ALEN);
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__builtin_memcpy(eth->h_source, eth->h_dest, ETH_ALEN);
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__builtin_memcpy(eth->h_dest, h_tmp, ETH_ALEN);
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}
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/*
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* Swaps destination and source IPv6 addresses inside an IPv6 header
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*/
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static __always_inline void swap_src_dst_ipv6(struct ipv6hdr *ipv6)
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{
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struct in6_addr tmp = ipv6->saddr;
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ipv6->saddr = ipv6->daddr;
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ipv6->daddr = tmp;
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}
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/*
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* Swaps destination and source IPv4 addresses inside an IPv4 header
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*/
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static __always_inline void swap_src_dst_ipv4(struct iphdr *iphdr)
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{
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__be32 tmp = iphdr->saddr;
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iphdr->saddr = iphdr->daddr;
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iphdr->daddr = tmp;
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}
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#endif /* __REWRITE_HELPERS_H */

‎packet-solutions/xdp_prog_kern.c‎

Lines changed: 1 addition & 113 deletions
Original file line numberDiff line numberDiff line change
@@ -6,6 +6,7 @@
66

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// The parsing helper functions from the packet01 lesson have moved here
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#include "../common/parsing_helpers.h"
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#include "../common/rewrite_helpers.h"
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/* Defines xdp_stats_map */
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#include "../common/xdp_stats_kern_user.h"
@@ -29,97 +30,6 @@ struct bpf_map_def SEC("maps") redirect_params = {
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.max_entries = 1,
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};
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/* Pops the outermost VLAN tag off the packet. Returns the popped VLAN ID on
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* success or negative errno on failure.
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*/
35-
static __always_inline int vlan_tag_pop(struct xdp_md *ctx, struct ethhdr *eth)
36-
{
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void *data_end = (void *)(long)ctx->data_end;
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struct ethhdr eth_cpy;
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struct vlan_hdr *vlh;
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__be16 h_proto;
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int vlid;
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if (!proto_is_vlan(eth->h_proto))
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return -1;
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/* Careful with the parenthesis here */
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vlh = (void *)(eth + 1);
48-
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/* Still need to do bounds checking */
50-
if (vlh + 1 > data_end)
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return -1;
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/* Save vlan ID for returning, h_proto for updating Ethernet header */
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vlid = bpf_ntohs(vlh->h_vlan_TCI);
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h_proto = vlh->h_vlan_encapsulated_proto;
56-
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/* Make a copy of the outer Ethernet header before we cut it off */
58-
__builtin_memcpy(&eth_cpy, eth, sizeof(eth_cpy));
59-
60-
/* Actually adjust the head pointer */
61-
if (bpf_xdp_adjust_head(ctx, (int)sizeof(*vlh)))
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return -1;
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64-
/* Need to re-evaluate data *and* data_end and do new bounds checking
65-
* after adjusting head
66-
*/
67-
eth = (void *)(long)ctx->data;
68-
data_end = (void *)(long)ctx->data_end;
69-
if (eth + 1 > data_end)
70-
return -1;
71-
72-
/* Copy back the old Ethernet header and update the proto type */
73-
__builtin_memcpy(eth, &eth_cpy, sizeof(*eth));
74-
eth->h_proto = h_proto;
75-
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return vlid;
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}
78-
79-
/* Pushes a new VLAN tag after the Ethernet header. Returns 0 on success,
80-
* -1 on failure.
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*/
82-
static __always_inline int vlan_tag_push(struct xdp_md *ctx,
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struct ethhdr *eth, int vlid)
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{
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void *data_end = (void *)(long)ctx->data_end;
86-
struct ethhdr eth_cpy;
87-
struct vlan_hdr *vlh;
88-
89-
/* First copy the original Ethernet header */
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__builtin_memcpy(&eth_cpy, eth, sizeof(eth_cpy));
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/* Then add space in front of the packet */
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if (bpf_xdp_adjust_head(ctx, 0 - (int)sizeof(*vlh)))
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return -1;
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/* Need to re-evaluate data_end and data after head adjustment, and
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* bounds check, even though we know there is enough space (as we
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* increased it).
99-
*/
100-
data_end = (void *)(long)ctx->data_end;
101-
eth = (void *)(long)ctx->data;
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103-
if (eth + 1 > data_end)
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return -1;
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/* Copy back the Ethernet header in the right place, populate the VLAN
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* tag with the ID and proto, and set the outer Ethernet header to VLAN
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* type. */
109-
__builtin_memcpy(eth, &eth_cpy, sizeof(*eth));
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vlh = (void *)(eth +1);
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113-
if (vlh + 1 > data_end)
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return -1;
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116-
vlh->h_vlan_TCI = bpf_htons(vlid);
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vlh->h_vlan_encapsulated_proto = eth->h_proto;
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eth->h_proto = bpf_htons(ETH_P_8021Q);
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return 0;
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}
122-
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/* Solution to the assignments in lesson packet02: Will pop outermost VLAN tag
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* if it exists, otherwise push a new one with ID 1
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*/
@@ -147,28 +57,6 @@ int xdp_vlan_swap_func(struct xdp_md *ctx)
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return XDP_PASS;
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}
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150-
static __always_inline void swap_src_dst_mac(struct ethhdr *eth)
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{
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__u8 h_tmp[ETH_ALEN];
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memcpy(h_tmp, eth->h_source, ETH_ALEN);
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memcpy(eth->h_source, eth->h_dest, ETH_ALEN);
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memcpy(eth->h_dest, h_tmp, ETH_ALEN);
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}
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158-
static __always_inline void swap_src_dst_ipv6(struct ipv6hdr *ipv6)
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{
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struct in6_addr tmp = ipv6->saddr;
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ipv6->saddr = ipv6->daddr;
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ipv6->daddr = tmp;
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}
164-
165-
static __always_inline void swap_src_dst_ipv4(struct iphdr *iphdr)
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{
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__be32 tmp = iphdr->saddr;
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iphdr->saddr = iphdr->daddr;
169-
iphdr->daddr = tmp;
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}
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static __always_inline __u16 csum16_add(__u16 csum, __u16 addend)
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{
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csum += addend;

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