Commit a32a32cb authored by Jesper Dangaard Brouer's avatar Jesper Dangaard Brouer Committed by Daniel Borkmann
Browse files

samples/bpf: make xdp_fwd more practically usable via devmap lookup 



This address the TODO in samples/bpf/xdp_fwd_kern.c, which points out
that the chosen egress index should be checked for existence in the
devmap. This can now be done via taking advantage of Toke's work in
commit 0cdbb4b0 ("devmap: Allow map lookups from eBPF").

This change makes xdp_fwd more practically usable, as this allows for
a mixed environment, where IP-forwarding fallback to network stack, if
the egress device isn't configured to use XDP.

Signed-off-by: default avatarJesper Dangaard Brouer <brouer@redhat.com>
Reviewed-by: default avatarDavid Ahern <dsahern@gmail.com>
Reviewed-by: default avatarToke Høiland-Jørgensen <toke@redhat.com>
Acked-by: default avatarYonghong Song <yhs@fb.com>
Signed-off-by: default avatarDaniel Borkmann <daniel@iogearbox.net>
parent 3783d437

samples/bpf/xdp_fwd_kern.c

+11 −6
Original line number Diff line number Diff line
@@ -104,13 +104,18 @@ static __always_inline int xdp_fwd_flags(struct xdp_md *ctx, u32 flags) 


	rc = bpf_fib_lookup(ctx, &fib_params, sizeof(fib_params), flags);



	/* verify egress index has xdp support

	 * TO-DO bpf_map_lookup_elem(&tx_port, &key) fails with

	if (rc == 0) {

		/* Verify egress index has been configured as TX-port.

		 * (Note: User can still have inserted an egress ifindex that

		 * doesn't support XDP xmit, which will result in packet drops).

		 *

		 * Note: lookup in devmap supported since 0cdbb4b09a0.

		 * If not supported will fail with:

		 *  cannot pass map_type 14 into func bpf_map_lookup_elem#1:

	 * NOTE: without verification that egress index supports XDP

	 *       forwarding packets are dropped.

		 */

	if (rc == 0) {

		if (!bpf_map_lookup_elem(&xdp_tx_ports, &fib_params.ifindex))

			return XDP_PASS;



		if (h_proto == htons(ETH_P_IP))

			ip_decrease_ttl(iph);

		else if (h_proto == htons(ETH_P_IPV6))

samples/bpf/xdp_fwd_user.c

+22 −11
Original line number Diff line number Diff line
@@ -27,14 +27,20 @@ 
#include "libbpf.h"

#include <bpf/bpf.h>





static int do_attach(int idx, int fd, const char *name)

static int do_attach(int idx, int prog_fd, int map_fd, const char *name)

{

	int err;



	err = bpf_set_link_xdp_fd(idx, fd, 0);

	if (err < 0)

	err = bpf_set_link_xdp_fd(idx, prog_fd, 0);

	if (err < 0) {

		printf("ERROR: failed to attach program to %s\n", name);

		return err;

	}



	/* Adding ifindex as a possible egress TX port */

	err = bpf_map_update_elem(map_fd, &idx, &idx, 0);

	if (err)

		printf("ERROR: failed using device %s as TX-port\n", name);



	return err;

}
@@ -47,6 +53,9 @@ static int do_detach(int idx, const char *name) 
	if (err < 0)

		printf("ERROR: failed to detach program from %s\n", name);



	/* TODO: Remember to cleanup map, when adding use of shared map

	 *  bpf_map_delete_elem((map_fd, &idx);

	 */

	return err;

}
@@ -67,10 +76,10 @@ int main(int argc, char **argv) 
	};

	const char *prog_name = "xdp_fwd";

	struct bpf_program *prog;

	int prog_fd, map_fd = -1;

	char filename[PATH_MAX];

	struct bpf_object *obj;

	int opt, i, idx, err;

	int prog_fd, map_fd;

	int attach = 1;

	int ret = 0;
@@ -103,8 +112,14 @@ int main(int argc, char **argv) 
			return 1;

		}



		if (bpf_prog_load_xattr(&prog_load_attr, &obj, &prog_fd))

		err = bpf_prog_load_xattr(&prog_load_attr, &obj, &prog_fd);

		if (err) {

			printf("Does kernel support devmap lookup?\n");

			/* If not, the error message will be:

			 *  "cannot pass map_type 14 into func bpf_map_lookup_elem#1"

			 */

			return 1;

		}



		prog = bpf_object__find_program_by_title(obj, prog_name);

		prog_fd = bpf_program__fd(prog);
@@ -119,10 +134,6 @@ int main(int argc, char **argv) 
			return 1;

		}

	}

	if (attach) {

		for (i = 1; i < 64; ++i)

			bpf_map_update_elem(map_fd, &i, &i, 0);

	}



	for (i = optind; i < argc; ++i) {

		idx = if_nametoindex(argv[i]);
@@ -138,7 +149,7 @@ int main(int argc, char **argv) 
			if (err)

				ret = err;

		} else {

			err = do_attach(idx, prog_fd, argv[i]);

			err = do_attach(idx, prog_fd, map_fd, argv[i]);

			if (err)

				ret = err;

		}

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