Subject: Re: [PATCH bpf-next 12/15] selftests/xsk: add test when some packets are XDP_DROPed

From: Maciej Fijalkowski <[email-masked]>
Date: Mon, 12 Dec 2022 16:13:38 +0100

On Tue, Dec 06, 2022 at 10:08:23AM +0100, Magnus Karlsson wrote:
> From: Magnus Karlsson <[email-masked]>
> 
> Add a new test where some of the packets are not passed to the AF_XDP
> socket and instead get a XDP_DROP verdict. This is important as it
> tests the recycling mechanism of the buffer pool. If a packet is not
> sent to the AF_XDP socket, the buffer the packet resides in is instead
> recycled so it can be used again without the round-trip to user
> space. The test introduces a new XDP program that drops every other
> packet.
> 
> Signed-off-by: Magnus Karlsson <[email-masked]>
> ---
>  tools/testing/selftests/bpf/Makefile          |  2 +-
>  .../selftests/bpf/progs/xsk_xdp_drop.c        | 25 ++++++++++
>  tools/testing/selftests/bpf/xskxceiver.c      | 48 +++++++++++++++++--
>  tools/testing/selftests/bpf/xskxceiver.h      |  3 ++
>  4 files changed, 72 insertions(+), 6 deletions(-)
>  create mode 100644 tools/testing/selftests/bpf/progs/xsk_xdp_drop.c
> 
> diff --git a/tools/testing/selftests/bpf/Makefile b/tools/testing/selftests/bpf/Makefile
> index 42e15b5a34a7..77ef8a8e6db4 100644
> --- a/tools/testing/selftests/bpf/Makefile
> +++ b/tools/testing/selftests/bpf/Makefile
> @@ -240,7 +240,7 @@ $(OUTPUT)/flow_dissector_load: $(TESTING_HELPERS)
>  $(OUTPUT)/test_maps: $(TESTING_HELPERS)
>  $(OUTPUT)/test_verifier: $(TESTING_HELPERS) $(CAP_HELPERS)
>  $(OUTPUT)/xsk.o: $(BPFOBJ)
> -$(OUTPUT)/xskxceiver: $(OUTPUT)/xsk.o $(OUTPUT)/xsk_def_prog.skel.h
> +$(OUTPUT)/xskxceiver: $(OUTPUT)/xsk.o $(OUTPUT)/xsk_def_prog.skel.h $(OUTPUT)/xsk_xdp_drop.skel.h
>  
>  BPFTOOL ?= $(DEFAULT_BPFTOOL)
>  $(DEFAULT_BPFTOOL): $(wildcard $(BPFTOOLDIR)/*.[ch] $(BPFTOOLDIR)/Makefile)    \
> diff --git a/tools/testing/selftests/bpf/progs/xsk_xdp_drop.c b/tools/testing/selftests/bpf/progs/xsk_xdp_drop.c
> new file mode 100644
> index 000000000000..12a12b0d9fc1
> --- /dev/null
> +++ b/tools/testing/selftests/bpf/progs/xsk_xdp_drop.c
> @@ -0,0 +1,25 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/* Copyright (c) 2022 Intel */
> +
> +#include <linux/bpf.h>
> +#include <bpf/bpf_helpers.h>
> +
> +struct {
> +	__uint(type, BPF_MAP_TYPE_XSKMAP);
> +	__uint(max_entries, 1);
> +	__uint(key_size, sizeof(int));
> +	__uint(value_size, sizeof(int));
> +} xsk SEC(".maps");
> +
> +static unsigned int idx;
> +
> +SEC("xdp") int xsk_xdp_drop(struct xdp_md *xdp)
> +{
> +	/* Drop every other packet */
> +	if (idx++ % 2)
> +		return XDP_DROP;
> +
> +	return bpf_redirect_map(&xsk, 0, XDP_DROP);
> +}
> +
> +char _license[] SEC("license") = "GPL";
> diff --git a/tools/testing/selftests/bpf/xskxceiver.c b/tools/testing/selftests/bpf/xskxceiver.c
> index 0cda4e3f1871..522dc1d69c17 100644
> --- a/tools/testing/selftests/bpf/xskxceiver.c
> +++ b/tools/testing/selftests/bpf/xskxceiver.c
> @@ -1654,18 +1654,53 @@ static void testapp_invalid_desc(struct test_spec *test)
>  	pkt_stream_restore_default(test);
>  }
>  
> -static int xsk_load_xdp_program(struct ifobject *ifobj)
> +static void testapp_xdp_drop(struct test_spec *test)
> +{
> +	struct ifobject *ifobj = test->ifobj_rx;
> +	int err;
> +
> +	test_spec_set_name(test, "XDP_CONSUMES_SOME_PACKETS");

XDP_DROP_ODD_PACKETS ?

> +	xsk_detach_xdp_program(ifobj->ifindex, ifobj->xdp_flags);
> +	err = xsk_attach_xdp_program(ifobj->xdp_drop->progs.xsk_xdp_drop, ifobj->ifindex,
> +				     ifobj->xdp_flags);
> +	if (err) {
> +		printf("Error attaching XDP_DROP program\n");
> +		test->fail = true;
> +		return;
> +	}
> +	ifobj->xskmap = ifobj->xdp_drop->maps.xsk;
> +
> +	pkt_stream_receive_half(test);
> +	testapp_validate_traffic(test);
> +
> +	pkt_stream_restore_default(test);
> +	xsk_detach_xdp_program(ifobj->ifindex, ifobj->xdp_flags);
> +	err = xsk_attach_xdp_program(ifobj->def_prog->progs.xsk_def_prog, ifobj->ifindex,
> +				     ifobj->xdp_flags);
> +	if (err) {
> +		printf("Error restoring default XDP program\n");
> +		exit_with_error(-err);
> +	}
> +	ifobj->xskmap = ifobj->def_prog->maps.xsk;
> +}
> +
> +static int xsk_load_xdp_programs(struct ifobject *ifobj)
>  {
>  	ifobj->def_prog = xsk_def_prog__open_and_load();
>  	if (libbpf_get_error(ifobj->def_prog))
>  		return libbpf_get_error(ifobj->def_prog);
>  
> +	ifobj->xdp_drop = xsk_xdp_drop__open_and_load();
> +	if (libbpf_get_error(ifobj->xdp_drop))
> +		return libbpf_get_error(ifobj->xdp_drop);
> +
>  	return 0;
>  }
>  
> -static void xsk_unload_xdp_program(struct ifobject *ifobj)
> +static void xsk_unload_xdp_programs(struct ifobject *ifobj)
>  {
>  	xsk_def_prog__destroy(ifobj->def_prog);
> +	xsk_xdp_drop__destroy(ifobj->xdp_drop);
>  }
>  
>  static void init_iface(struct ifobject *ifobj, const char *dst_mac, const char *src_mac,
> @@ -1692,7 +1727,7 @@ static void init_iface(struct ifobject *ifobj, const char *dst_mac, const char *
>  	if (!load_xdp)
>  		return;
>  
> -	err = xsk_load_xdp_program(ifobj);
> +	err = xsk_load_xdp_programs(ifobj);
>  	if (err) {
>  		printf("Error loading XDP program\n");
>  		exit_with_error(err);
> @@ -1804,6 +1839,9 @@ static void run_pkt_test(struct test_spec *test, enum test_mode mode, enum test_
>  	case TEST_TYPE_HEADROOM:
>  		testapp_headroom(test);
>  		break;
> +	case TEST_TYPE_XDP_CONSUMES_PACKETS:
> +		testapp_xdp_drop(test);
> +		break;
>  	default:
>  		break;
>  	}
> @@ -1971,8 +2009,8 @@ int main(int argc, char **argv)
>  
>  	pkt_stream_delete(tx_pkt_stream_default);
>  	pkt_stream_delete(rx_pkt_stream_default);
> -	xsk_unload_xdp_program(ifobj_tx);
> -	xsk_unload_xdp_program(ifobj_rx);
> +	xsk_unload_xdp_programs(ifobj_tx);
> +	xsk_unload_xdp_programs(ifobj_rx);
>  	ifobject_delete(ifobj_tx);
>  	ifobject_delete(ifobj_rx);
>  
> diff --git a/tools/testing/selftests/bpf/xskxceiver.h b/tools/testing/selftests/bpf/xskxceiver.h
> index eb6355bcc143..3483ac240b2e 100644
> --- a/tools/testing/selftests/bpf/xskxceiver.h
> +++ b/tools/testing/selftests/bpf/xskxceiver.h
> @@ -6,6 +6,7 @@
>  #define XSKXCEIVER_H_
>  
>  #include "xsk_def_prog.skel.h"
> +#include "xsk_xdp_drop.skel.h"
>  
>  #ifndef SOL_XDP
>  #define SOL_XDP 283
> @@ -87,6 +88,7 @@ enum test_type {
>  	TEST_TYPE_STATS_RX_FULL,
>  	TEST_TYPE_STATS_FILL_EMPTY,
>  	TEST_TYPE_BPF_RES,
> +	TEST_TYPE_XDP_CONSUMES_PACKETS,
>  	TEST_TYPE_MAX
>  };
>  
> @@ -141,6 +143,7 @@ struct ifobject {
>  	validation_func_t validation_func;
>  	struct pkt_stream *pkt_stream;
>  	struct xsk_def_prog *def_prog;
> +	struct xsk_xdp_drop *xdp_drop;

Is this going to scale if we add plenty of XDP progs for testing?

>  	struct bpf_map *xskmap;
>  	int ifindex;
>  	u32 dst_ip;
> -- 
> 2.34.1