Commit d50ecc46 authored by Toke Høiland-Jørgensen's avatar Toke Høiland-Jørgensen Committed by Alexei Starovoitov
Browse files

samples/bpf: Attach XDP programs in driver mode by default 



When attaching XDP programs, userspace can set flags to request the attach
mode (generic/SKB mode, driver mode or hw offloaded mode). If no such flags
are requested, the kernel will attempt to attach in driver mode, and then
silently fall back to SKB mode if this fails.

The silent fallback is a major source of user confusion, as users will try
to load a program on a device without XDP support, and instead of an error
they will get the silent fallback behaviour, not notice, and then wonder
why performance is not what they were expecting.

In an attempt to combat this, let's switch all the samples to default to
explicitly requesting driver-mode attach. As part of this, ensure that all
the userspace utilities have a switch to enable SKB mode. For those that
have a switch to request driver mode, keep it but turn it into a no-op.

Signed-off-by: default avatarToke Høiland-Jørgensen <toke@redhat.com>
Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
Acked-by: default avatarJesper Dangaard Brouer <brouer@redhat.com>
Acked-by: default avatarDavid Ahern <dsahern@gmail.com>
Link: https://lore.kernel.org/bpf/20191216110742.364456-1-toke@redhat.com
parent 45027897

samples/bpf/xdp1_user.c

+4 −1
Original line number Diff line number Diff line
@@ -98,7 +98,7 @@ int main(int argc, char **argv) 
			xdp_flags |= XDP_FLAGS_SKB_MODE;

			break;

		case 'N':

			xdp_flags |= XDP_FLAGS_DRV_MODE;

			/* default, set below */

			break;

		case 'F':

			xdp_flags &= ~XDP_FLAGS_UPDATE_IF_NOEXIST;
@@ -109,6 +109,9 @@ int main(int argc, char **argv) 
		}

	}



	if (!(xdp_flags & XDP_FLAGS_SKB_MODE))

		xdp_flags |= XDP_FLAGS_DRV_MODE;



	if (optind == argc) {

		usage(basename(argv[0]));

		return 1;

samples/bpf/xdp_adjust_tail_user.c

+4 −1
Original line number Diff line number Diff line
@@ -120,7 +120,7 @@ int main(int argc, char **argv) 
			xdp_flags |= XDP_FLAGS_SKB_MODE;

			break;

		case 'N':

			xdp_flags |= XDP_FLAGS_DRV_MODE;

			/* default, set below */

			break;

		case 'F':

			xdp_flags &= ~XDP_FLAGS_UPDATE_IF_NOEXIST;
@@ -132,6 +132,9 @@ int main(int argc, char **argv) 
		opt_flags[opt] = 0;

	}



	if (!(xdp_flags & XDP_FLAGS_SKB_MODE))

		xdp_flags |= XDP_FLAGS_DRV_MODE;



	for (i = 0; i < strlen(optstr); i++) {

		if (opt_flags[(unsigned int)optstr[i]]) {

			fprintf(stderr, "Missing argument -%c\n", optstr[i]);

samples/bpf/xdp_fwd_user.c

+14 −3
Original line number Diff line number Diff line
@@ -27,11 +27,13 @@ 
#include "libbpf.h"

#include <bpf/bpf.h>



static __u32 xdp_flags = XDP_FLAGS_UPDATE_IF_NOEXIST;



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

{

	int err;



	err = bpf_set_link_xdp_fd(idx, prog_fd, 0);

	err = bpf_set_link_xdp_fd(idx, prog_fd, xdp_flags);

	if (err < 0) {

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

		return err;
@@ -49,7 +51,7 @@ static int do_detach(int idx, const char *name) 
{

	int err;



	err = bpf_set_link_xdp_fd(idx, -1, 0);

	err = bpf_set_link_xdp_fd(idx, -1, xdp_flags);

	if (err < 0)

		printf("ERROR: failed to detach program from %s\n", name);
@@ -83,11 +85,17 @@ int main(int argc, char **argv) 
	int attach = 1;

	int ret = 0;



	while ((opt = getopt(argc, argv, ":dD")) != -1) {

	while ((opt = getopt(argc, argv, ":dDSF")) != -1) {

		switch (opt) {

		case 'd':

			attach = 0;

			break;

		case 'S':

			xdp_flags |= XDP_FLAGS_SKB_MODE;

			break;

		case 'F':

			xdp_flags &= ~XDP_FLAGS_UPDATE_IF_NOEXIST;

			break;

		case 'D':

			prog_name = "xdp_fwd_direct";

			break;
@@ -97,6 +105,9 @@ int main(int argc, char **argv) 
		}

	}



	if (!(xdp_flags & XDP_FLAGS_SKB_MODE))

		xdp_flags |= XDP_FLAGS_DRV_MODE;



	if (optind == argc) {

		usage(basename(argv[0]));

		return 1;

samples/bpf/xdp_redirect_cpu_user.c

+4 −0
Original line number Diff line number Diff line
@@ -728,6 +728,10 @@ int main(int argc, char **argv) 
			return EXIT_FAIL_OPTION;

		}

	}



	if (!(xdp_flags & XDP_FLAGS_SKB_MODE))

		xdp_flags |= XDP_FLAGS_DRV_MODE;



	/* Required option */

	if (ifindex == -1) {

		fprintf(stderr, "ERR: required option --dev missing\n");

samples/bpf/xdp_redirect_map_user.c

+4 −1
Original line number Diff line number Diff line
@@ -116,7 +116,7 @@ int main(int argc, char **argv) 
			xdp_flags |= XDP_FLAGS_SKB_MODE;

			break;

		case 'N':

			xdp_flags |= XDP_FLAGS_DRV_MODE;

			/* default, set below */

			break;

		case 'F':

			xdp_flags &= ~XDP_FLAGS_UPDATE_IF_NOEXIST;
@@ -127,6 +127,9 @@ int main(int argc, char **argv) 
		}

	}



	if (!(xdp_flags & XDP_FLAGS_SKB_MODE))

		xdp_flags |= XDP_FLAGS_DRV_MODE;



	if (optind == argc) {

		printf("usage: %s <IFNAME|IFINDEX>_IN <IFNAME|IFINDEX>_OUT\n", argv[0]);

		return 1;

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