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samples/bpf: Attach XDP programs in driver mode by default
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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: Toke Høiland-Jørgensen <toke@redhat.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Jesper Dangaard Brouer <brouer@redhat.com>
Acked-by: David Ahern <dsahern@gmail.com>
Link: https://lore.kernel.org/bpf/20191216110742.364456-1-toke@redhat.com
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Toke Høiland-Jørgensen authored and Alexei Starovoitov committed Dec 16, 2019
1 parent 4502789 commit d50ecc4
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Showing 11 changed files with 58 additions and 12 deletions.
5 changes: 4 additions & 1 deletion samples/bpf/xdp1_user.c
Original file line number Diff line number Diff line change
Expand Up @@ -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;
Expand All @@ -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;
Expand Down
5 changes: 4 additions & 1 deletion samples/bpf/xdp_adjust_tail_user.c
Original file line number Diff line number Diff line change
Expand Up @@ -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;
Expand All @@ -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]);
Expand Down
17 changes: 14 additions & 3 deletions samples/bpf/xdp_fwd_user.c
Original file line number Diff line number Diff line change
Expand Up @@ -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;
Expand All @@ -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);

Expand Down Expand Up @@ -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;
Expand All @@ -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;
Expand Down
4 changes: 4 additions & 0 deletions samples/bpf/xdp_redirect_cpu_user.c
Original file line number Diff line number Diff line change
Expand Up @@ -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");
Expand Down
5 changes: 4 additions & 1 deletion samples/bpf/xdp_redirect_map_user.c
Original file line number Diff line number Diff line change
Expand Up @@ -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;
Expand All @@ -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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5 changes: 4 additions & 1 deletion samples/bpf/xdp_redirect_user.c
Original file line number Diff line number Diff line change
Expand Up @@ -117,7 +117,7 @@ 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;
Expand All @@ -128,6 +128,9 @@ 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;
Expand Down
3 changes: 3 additions & 0 deletions samples/bpf/xdp_router_ipv4_user.c
Original file line number Diff line number Diff line change
Expand Up @@ -662,6 +662,9 @@ int main(int ac, char **argv)
}
}

if (!(flags & XDP_FLAGS_SKB_MODE))
flags |= XDP_FLAGS_DRV_MODE;

if (optind == ac) {
usage(basename(argv[0]));
return 1;
Expand Down
4 changes: 4 additions & 0 deletions samples/bpf/xdp_rxq_info_user.c
Original file line number Diff line number Diff line change
Expand Up @@ -551,6 +551,10 @@ 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");
Expand Down
12 changes: 9 additions & 3 deletions samples/bpf/xdp_sample_pkts_user.c
Original file line number Diff line number Diff line change
Expand Up @@ -52,13 +52,13 @@ static int do_detach(int idx, const char *name)
__u32 curr_prog_id = 0;
int err = 0;

err = bpf_get_link_xdp_id(idx, &curr_prog_id, 0);
err = bpf_get_link_xdp_id(idx, &curr_prog_id, xdp_flags);
if (err) {
printf("bpf_get_link_xdp_id failed\n");
return err;
}
if (prog_id == curr_prog_id) {
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 prog from %s\n", name);
} else if (!curr_prog_id) {
Expand Down Expand Up @@ -115,7 +115,7 @@ int main(int argc, char **argv)
.prog_type = BPF_PROG_TYPE_XDP,
};
struct perf_buffer_opts pb_opts = {};
const char *optstr = "F";
const char *optstr = "FS";
int prog_fd, map_fd, opt;
struct bpf_object *obj;
struct bpf_map *map;
Expand All @@ -127,12 +127,18 @@ int main(int argc, char **argv)
case 'F':
xdp_flags &= ~XDP_FLAGS_UPDATE_IF_NOEXIST;
break;
case 'S':
xdp_flags |= XDP_FLAGS_SKB_MODE;
break;
default:
usage(basename(argv[0]));
return 1;
}
}

if (!(xdp_flags & XDP_FLAGS_SKB_MODE))
xdp_flags |= XDP_FLAGS_DRV_MODE;

if (optind == argc) {
usage(basename(argv[0]));
return 1;
Expand Down
5 changes: 4 additions & 1 deletion samples/bpf/xdp_tx_iptunnel_user.c
Original file line number Diff line number Diff line change
Expand Up @@ -231,7 +231,7 @@ 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;
Expand All @@ -243,6 +243,9 @@ 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]);
Expand Down
5 changes: 4 additions & 1 deletion samples/bpf/xdpsock_user.c
Original file line number Diff line number Diff line change
Expand Up @@ -440,7 +440,7 @@ static void parse_command_line(int argc, char **argv)
opt_xdp_bind_flags |= XDP_COPY;
break;
case 'N':
opt_xdp_flags |= XDP_FLAGS_DRV_MODE;
/* default, set below */
break;
case 'n':
opt_interval = atoi(optarg);
Expand Down Expand Up @@ -474,6 +474,9 @@ static void parse_command_line(int argc, char **argv)
}
}

if (!(opt_xdp_flags & XDP_FLAGS_SKB_MODE))
opt_xdp_flags |= XDP_FLAGS_DRV_MODE;

opt_ifindex = if_nametoindex(opt_if);
if (!opt_ifindex) {
fprintf(stderr, "ERROR: interface \"%s\" does not exist\n",
Expand Down

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