Commit 8fdf5b78 authored by Daniel T. Lee's avatar Daniel T. Lee Committed by Alexei Starovoitov
Browse files

samples: bpf: Add max_pckt_size option at xdp_adjust_tail 



Currently, at xdp_adjust_tail_kern.c, MAX_PCKT_SIZE is limited
to 600. To make this size flexible, static global variable
'max_pcktsz' is added.

By updating new packet size from the user space, xdp_adjust_tail_kern.o
will use this value as a new max packet size.

This static global variable can be accesible from .data section with
bpf_object__find_map* from user space, since it is considered as
internal map (accessible with .bss/.data/.rodata suffix).

If no '-P <MAX_PCKT_SIZE>' option is used, the size of maximum packet
will be 600 as a default.

For clarity, change the helper to fetch map from 'bpf_map__next'
to 'bpf_object__find_map_fd_by_name'. Also, changed the way to
test prog_fd, map_fd from '!= 0' to '< 0', since fd could be 0
when stdin is closed.

Signed-off-by: default avatarDaniel T. Lee <danieltimlee@gmail.com>
Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
Acked-by: default avatarAndrii Nakryiko <andriin@fb.com>
Link: https://lore.kernel.org/bpf/20191007172117.3916-1-danieltimlee@gmail.com
parent 72ccd920

samples/bpf/xdp_adjust_tail_kern.c

+5 −2
Original line number Diff line number Diff line
@@ -25,6 +25,9 @@ 
#define ICMP_TOOBIG_SIZE 98

#define ICMP_TOOBIG_PAYLOAD_SIZE 92



/* volatile to prevent compiler optimizations */

static volatile __u32 max_pcktsz = MAX_PCKT_SIZE;



struct bpf_map_def SEC("maps") icmpcnt = {

	.type = BPF_MAP_TYPE_ARRAY,

	.key_size = sizeof(__u32),
@@ -92,7 +95,7 @@ static __always_inline int send_icmp4_too_big(struct xdp_md *xdp) 
	orig_iph = data + off;

	icmp_hdr->type = ICMP_DEST_UNREACH;

	icmp_hdr->code = ICMP_FRAG_NEEDED;

	icmp_hdr->un.frag.mtu = htons(MAX_PCKT_SIZE-sizeof(struct ethhdr));

	icmp_hdr->un.frag.mtu = htons(max_pcktsz - sizeof(struct ethhdr));

	icmp_hdr->checksum = 0;

	ipv4_csum(icmp_hdr, ICMP_TOOBIG_PAYLOAD_SIZE, &csum);

	icmp_hdr->checksum = csum;
@@ -121,7 +124,7 @@ static __always_inline int handle_ipv4(struct xdp_md *xdp) 
	int pckt_size = data_end - data;

	int offset;



	if (pckt_size > MAX_PCKT_SIZE) {

	if (pckt_size > max(max_pcktsz, ICMP_TOOBIG_SIZE)) {

		offset = pckt_size - ICMP_TOOBIG_SIZE;

		if (bpf_xdp_adjust_tail(xdp, 0 - offset))

			return XDP_PASS;

samples/bpf/xdp_adjust_tail_user.c

+20 −9
Original line number Diff line number Diff line
@@ -23,6 +23,7 @@ 
#include "libbpf.h"



#define STATS_INTERVAL_S 2U

#define MAX_PCKT_SIZE 600



static int ifindex = -1;

static __u32 xdp_flags = XDP_FLAGS_UPDATE_IF_NOEXIST;
@@ -72,6 +73,7 @@ static void usage(const char *cmd) 
	printf("Usage: %s [...]\n", cmd);

	printf("    -i <ifname|ifindex> Interface\n");

	printf("    -T <stop-after-X-seconds> Default: 0 (forever)\n");

	printf("    -P <MAX_PCKT_SIZE> Default: %u\n", MAX_PCKT_SIZE);

	printf("    -S use skb-mode\n");

	printf("    -N enforce native mode\n");

	printf("    -F force loading prog\n");
@@ -85,13 +87,14 @@ int main(int argc, char **argv) 
		.prog_type	= BPF_PROG_TYPE_XDP,

	};

	unsigned char opt_flags[256] = {};

	const char *optstr = "i:T:SNFh";

	const char *optstr = "i:T:P:SNFh";

	struct bpf_prog_info info = {};

	__u32 info_len = sizeof(info);

	unsigned int kill_after_s = 0;

	int i, prog_fd, map_fd, opt;

	struct bpf_object *obj;

	struct bpf_map *map;

	__u32 max_pckt_size = 0;

	__u32 key = 0;

	char filename[256];

	int err;
@@ -110,6 +113,9 @@ int main(int argc, char **argv) 
		case 'T':

			kill_after_s = atoi(optarg);

			break;

		case 'P':

			max_pckt_size = atoi(optarg);

			break;

		case 'S':

			xdp_flags |= XDP_FLAGS_SKB_MODE;

			break;
@@ -150,15 +156,20 @@ int main(int argc, char **argv) 
	if (bpf_prog_load_xattr(&prog_load_attr, &obj, &prog_fd))

		return 1;



	map = bpf_map__next(NULL, obj);

	if (!map) {

		printf("finding a map in obj file failed\n");

	/* static global var 'max_pcktsz' is accessible from .data section */

	if (max_pckt_size) {

		map_fd = bpf_object__find_map_fd_by_name(obj, "xdp_adju.data");

		if (map_fd < 0) {

			printf("finding a max_pcktsz map in obj file failed\n");

			return 1;

		}

	map_fd = bpf_map__fd(map);

		bpf_map_update_elem(map_fd, &key, &max_pckt_size, BPF_ANY);

	}



	if (!prog_fd) {

		printf("load_bpf_file: %s\n", strerror(errno));

	/* fetch icmpcnt map */

	map_fd = bpf_object__find_map_fd_by_name(obj, "icmpcnt");

	if (map_fd < 0) {

		printf("finding a icmpcnt map in obj file failed\n");

		return 1;

	}

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