[PATCH 1/1] xdp: Sample xdp program implementing ip forward
Jacob, Christina
Christina.Jacob at cavium.com
Mon Oct 9 19:24:39 PDT 2017
Sorry for the late reply. I will include the suggested changes in the next revision of the patch.
Please see inline for clarifications and questions.
Thanks,
Christina
________________________________
From: Daniel Borkmann <daniel at iogearbox.net>
Sent: Tuesday, October 3, 2017 9:24 PM
To: Jacob, Christina; netdev at vger.kernel.org
Cc: linux-kernel at vger.kernel.org; linux-arm-kernel at lists.infradead.org; alexei.starovoitov at gmail.com
Subject: Re: [PATCH 1/1] xdp: Sample xdp program implementing ip forward
>On 10/03/2017 09:37 AM, cjacob wrote:
>> Implements port to port forwarding with route table and arp table
>> lookup for ipv4 packets using bpf_redirect helper function and
>> lpm_trie map.
>>
>> Signed-off-by: cjacob <Christina.Jacob at cavium.com>
>
>Thanks for the patch, just few minor comments below!
>
>Note, should be full name, e.g.:
>
> Signed-off-by: Christina Jacob <Christina.Jacob at cavium.com>
>
>Also you From: only shows 'cjacob' as can be seen from the cover letter
>as well, so perhaps check your git settings to make that full name:
>
> cjacob (1):
> xdp: Sample xdp program implementing ip forward
>
>If there's one single patch, then cover letter is not needed, only
>for >1 sets.
>
>[...]
>> +#define KBUILD_MODNAME "foo"
>> +#include <uapi/linux/bpf.h>
>> +#include <linux/in.h>
>> +#include <linux/if_ether.h>
>> +#include <linux/if_packet.h>
>> +#include <linux/if_vlan.h>
>> +#include <linux/ip.h>
>> +#include <linux/ipv6.h>
>> +#include "bpf_helpers.h"
>> +#include <linux/slab.h>
>> +#include <net/ip_fib.h>
>> +
>> +struct trie_value {
>> + __u8 prefix[4];
>> + long value;
>> + int gw;
>> + int ifindex;
>> + int metric;
>> +};
>> +
>> +union key_4 {
>> + u32 b32[2];
>> + u8 b8[8];
>> +};
>> +
>> +struct arp_entry {
>> + int dst;
>> + long mac;
>> +};
>> +
>> +struct direct_map {
>> + long mac;
>> + int ifindex;
>> + struct arp_entry arp;
>> +};
>> +
>> +/* Map for trie implementation*/
>> +struct bpf_map_def SEC("maps") lpm_map = {
>> + .type = BPF_MAP_TYPE_LPM_TRIE,
>> + .key_size = 8,
>> + .value_size =
>> + sizeof(struct trie_value),
>
>(Nit: there are couple of such breaks throughout the patch, can we
> just use single line for such cases where reasonable?)
>
>> + .max_entries = 50,
>> + .map_flags = BPF_F_NO_PREALLOC,
>> +};
>> +
>> +/* Map for counter*/
>> +struct bpf_map_def SEC("maps") rxcnt = {
>> + .type = BPF_MAP_TYPE_PERCPU_ARRAY,
>> + .key_size = sizeof(u32),
>> + .value_size = sizeof(long),
>> + .max_entries = 256,
>> +};
>> +
>> +/* Map for ARP table*/
>> +struct bpf_map_def SEC("maps") arp_table = {
>> + .type = BPF_MAP_TYPE_HASH,
>> + .key_size = sizeof(int),
>> + .value_size = sizeof(long),
>
>Perhaps these should be proper structs here, such that it
>becomes easier to read/handle later on lookup.
>
I am not clear about this. I am defining a ebpf map.
I did not understand what structure you are refering to
Am I missing something here?.
>> + .max_entries = 50,
>> +};
>> +
>> +/* Map to keep the exact match entries in the route table*/
>> +struct bpf_map_def SEC("maps") exact_match = {
>> + .type = BPF_MAP_TYPE_HASH,
>> + .key_size = sizeof(int),
>> + .value_size = sizeof(struct direct_map),
>> + .max_entries = 50,
>> +};
>> +
>> +/**
>> + * Function to set source and destination mac of the packet
>> + */
>> +static inline void set_src_dst_mac(void *data, void *src, void *dst)
>> +{
>> + unsigned short *p = data;
>> + unsigned short *dest = dst;
>> + unsigned short *source = src;
>> +
>> + p[3] = source[0];
>> + p[4] = source[1];
>> + p[5] = source[2];
>> + p[0] = dest[0];
>> + p[1] = dest[1];
>> + p[2] = dest[2];
>
>You could just use __builtin_memcpy() given length is
>constant anyway, so LLVM will do the inlining.
>
>> +}
>> +
>> +/**
>> + * Parse IPV4 packet to get SRC, DST IP and protocol
>> + */
>> +static inline int parse_ipv4(void *data, u64 nh_off, void *data_end,
>> + unsigned int *src, unsigned int *dest)
>> +{
>> + struct iphdr *iph = data + nh_off;
>> +
>> + if (iph + 1 > data_end)
>> + return 0;
>> + *src = (unsigned int)iph->saddr;
>> + *dest = (unsigned int)iph->daddr;
>
>Why not stay with __be32 types?
>
>> + return iph->protocol;
>> +}
>> +
>> +SEC("xdp3")
>> +int xdp_prog3(struct xdp_md *ctx)
>> +{
>> + void *data_end = (void *)(long)ctx->data_end;
>> + void *data = (void *)(long)ctx->data;
>> + struct ethhdr *eth = data;
>> + int rc = XDP_DROP, forward_to;
>> + long *value;
>> + struct trie_value *prefix_value;
>> + long *dest_mac = NULL, *src_mac = NULL;
>> + u16 h_proto;
>> + u64 nh_off;
>> + u32 ipproto;
>> + union key_4 key4;
>> +
>> + nh_off = sizeof(*eth);
>> + if (data + nh_off > data_end)
>> + return rc;
>> +
>> + h_proto = eth->h_proto;
>> +
>> + if (h_proto == htons(ETH_P_8021Q) || h_proto == htons(ETH_P_8021AD)) {
>> + struct vlan_hdr *vhdr;
>> +
>> + vhdr = data + nh_off;
>> + nh_off += sizeof(struct vlan_hdr);
>> + if (data + nh_off > data_end)
>> + return rc;
>> + h_proto = vhdr->h_vlan_encapsulated_proto;
>> + }
>> + if (h_proto == htons(ETH_P_ARP)) {
>> + return XDP_PASS;
>> + } else if (h_proto == htons(ETH_P_IP)) {
>> + int src_ip = 0, dest_ip = 0;
>> + struct direct_map *direct_entry;
>> +
>> + ipproto = parse_ipv4(data, nh_off, data_end, &src_ip, &dest_ip);
>> + direct_entry = (struct direct_map *)bpf_map_lookup_elem
>> + (&exact_match, &dest_ip);
>> + /*check for exact match, this would give a faster lookup*/
>> + if (direct_entry && direct_entry->mac &&
>> + direct_entry->arp.mac) {
>> + src_mac = &direct_entry->mac;
>> + dest_mac = &direct_entry->arp.mac;
>> + forward_to = direct_entry->ifindex;
>> + } else {
>> + /*Look up in the trie for lpm*/
>> + // Key for trie
>
>Nit: please check style throughout the patch.
>
>> + key4.b32[0] = 32;
>> + key4.b8[4] = dest_ip % 0x100;
>> + key4.b8[5] = (dest_ip >> 8) % 0x100;
>> + key4.b8[6] = (dest_ip >> 16) % 0x100;
>> + key4.b8[7] = (dest_ip >> 24) % 0x100;
>> + prefix_value =
>> + ((struct trie_value *)bpf_map_lookup_elem
>> + (&lpm_map, &key4));
>
>For key, please use proper struct bpf_lpm_trie_key, see also
>usage example in tools/testing/selftests/bpf/test_lpm_map.c
>for LPM handling.
>
I am following the way how it is done in the kernel program of other sample programs.
Can we do dynamic memory allocation in ebpf kernel program. I am getting invalid instruction errors in runtime.
>> + if (!prefix_value) {
>> + return XDP_DROP;
>> + } else {
>> + src_mac = &prefix_value->value;
>> + if (src_mac) {
>> + dest_mac = (long *)bpf_map_lookup_elem
>> + (&arp_table, &dest_ip);
>> + if (!dest_mac) {
>> + if (prefix_value->gw) {
>> + dest_ip = *(unsigned int *)(&(prefix_value->gw));
>> + dest_mac = (long *)bpf_map_lookup_elem
>> + (&arp_table, &dest_ip);
>> + } else {
>> + return XDP_DROP;
>> + }
>> + }
>> + forward_to = prefix_value->ifindex;
>> + } else {
>> + return XDP_DROP;
>> + }
>> + }
>> + }
>> + } else {
>> + ipproto = 0;
>> + }
>> + if (src_mac && dest_mac) {
>> + set_src_dst_mac(data, src_mac,
>> + dest_mac);
>> + value = bpf_map_lookup_elem
>> + (&rxcnt, &ipproto);
>> + if (value)
>> + *value += 1;
>> + return bpf_redirect(
>> + forward_to,
>> + 0);
>> + }
>> + return rc;
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