Re: [PATCH bpf-next v4 5/6] selftests/bpf: Test bpf_xdp_pull_data

[Maciej Fijalkowski <maciej.fijalkowski@intel.com>]

On Wed, Sep 17, 2025 at 03:55:12PM -0700, Amery Hung wrote:
> Test bpf_xdp_pull_data() with xdp packets with different layouts. The
> xdp bpf program first checks if the layout is as expected. Then, it
> calls bpf_xdp_pull_data(). Finally, it checks the 0xbb marker at offset
> 1024 using directly packet access.
> 
> Signed-off-by: Amery Hung <ameryhung@gmail.com>
> ---
>  .../selftests/bpf/prog_tests/xdp_pull_data.c  | 176 ++++++++++++++++++
>  .../selftests/bpf/progs/test_xdp_pull_data.c  |  48 +++++
>  2 files changed, 224 insertions(+)
>  create mode 100644 tools/testing/selftests/bpf/prog_tests/xdp_pull_data.c
>  create mode 100644 tools/testing/selftests/bpf/progs/test_xdp_pull_data.c
> 
> diff --git a/tools/testing/selftests/bpf/prog_tests/xdp_pull_data.c b/tools/testing/selftests/bpf/prog_tests/xdp_pull_data.c
> new file mode 100644
> index 000000000000..c16801b73fed
> --- /dev/null
> +++ b/tools/testing/selftests/bpf/prog_tests/xdp_pull_data.c
> @@ -0,0 +1,176 @@
> +// SPDX-License-Identifier: GPL-2.0
> +
> +#include <test_progs.h>
> +#include <network_helpers.h>
> +#include "test_xdp_pull_data.skel.h"
> +
> +#define PULL_MAX	(1 << 31)
> +#define PULL_PLUS_ONE	(1 << 30)
> +
> +#define XDP_PACKET_HEADROOM 256
> +
> +/* Find sizes of struct skb_shared_info and struct xdp_frame so that
> + * we can calculate the maximum pull lengths for test cases

do you really need this hack? Wouldn't it be possible to find these sizes
via BTF?

> + */
> +static int find_xdp_sizes(struct test_xdp_pull_data *skel, int frame_sz)
> +{
> +	LIBBPF_OPTS(bpf_test_run_opts, topts);
> +	struct xdp_md ctx = {};
> +	int prog_fd, err;
> +	__u8 *buf;
> +
> +	buf = calloc(frame_sz, sizeof(__u8));
> +	if (!ASSERT_OK_PTR(buf, "calloc buf"))
> +		return -ENOMEM;
> +
> +	topts.data_in = buf;
> +	topts.data_out = buf;
> +	topts.data_size_in = frame_sz;
> +	topts.data_size_out = frame_sz;
> +	/* Pass a data_end larger than the linear space available to make sure
> +	 * bpf_prog_test_run_xdp() will fill the linear data area so that
> +	 * xdp_find_data_hard_end can infer the size of struct skb_shared_info

what is xdp_find_data_hard_end ?

> +	 */
> +	ctx.data_end = frame_sz;
> +	topts.ctx_in = &ctx;
> +	topts.ctx_out = &ctx;
> +	topts.ctx_size_in = sizeof(ctx);
> +	topts.ctx_size_out = sizeof(ctx);
> +
> +	prog_fd = bpf_program__fd(skel->progs.xdp_find_sizes);
> +	err = bpf_prog_test_run_opts(prog_fd, &topts);
> +	ASSERT_OK(err, "bpf_prog_test_run_opts");
> +
> +	free(buf);
> +
> +	return err;
> +}
> +
> +/* xdp_pull_data_prog will directly read a marker 0xbb stored at buf[1024]
> + * so caller expecting XDP_PASS should always pass pull_len no less than 1024
> + */
> +static void run_test(struct test_xdp_pull_data *skel, int retval,
> +		     int frame_sz, int buff_len, int meta_len, int data_len,
> +		     int pull_len)
> +{
> +	LIBBPF_OPTS(bpf_test_run_opts, topts);
> +	struct xdp_md ctx = {};
> +	int prog_fd, err;
> +	__u8 *buf;
> +
> +	buf = calloc(buff_len, sizeof(__u8));
> +	if (!ASSERT_OK_PTR(buf, "calloc buf"))
> +		return;
> +
> +	buf[meta_len + 1023] = 0xaa;
> +	buf[meta_len + 1024] = 0xbb;
> +	buf[meta_len + 1025] = 0xcc;
> +
> +	topts.data_in = buf;
> +	topts.data_out = buf;
> +	topts.data_size_in = buff_len;
> +	topts.data_size_out = buff_len;
> +	ctx.data = meta_len;
> +	ctx.data_end = meta_len + data_len;
> +	topts.ctx_in = &ctx;
> +	topts.ctx_out = &ctx;
> +	topts.ctx_size_in = sizeof(ctx);
> +	topts.ctx_size_out = sizeof(ctx);
> +
> +	skel->bss->data_len = data_len;
> +	if (pull_len & PULL_MAX) {
> +		int headroom = XDP_PACKET_HEADROOM - meta_len - skel->bss->xdpf_sz;
> +		int tailroom = frame_sz - XDP_PACKET_HEADROOM -
> +			       data_len - skel->bss->sinfo_sz;
> +
> +		pull_len = pull_len & PULL_PLUS_ONE ? 1 : 0;

nit: pull_len = !!(pull_len & PULL_PLUS_ONE);

> +		pull_len += headroom + tailroom + data_len;
> +	}
> +	skel->bss->pull_len = pull_len;
> +
> +	prog_fd = bpf_program__fd(skel->progs.xdp_pull_data_prog);
> +	err = bpf_prog_test_run_opts(prog_fd, &topts);
> +	ASSERT_OK(err, "bpf_prog_test_run_opts");
> +	ASSERT_EQ(topts.retval, retval, "xdp_pull_data_prog retval");
> +
> +	if (retval == XDP_DROP)
> +		goto out;
> +
> +	ASSERT_EQ(ctx.data_end, meta_len + pull_len, "linear data size");
> +	ASSERT_EQ(topts.data_size_out, buff_len, "linear + non-linear data size");
> +	/* Make sure data around xdp->data_end was not messed up by
> +	 * bpf_xdp_pull_data()
> +	 */
> +	ASSERT_EQ(buf[meta_len + 1023], 0xaa, "data[1023]");
> +	ASSERT_EQ(buf[meta_len + 1024], 0xbb, "data[1024]");
> +	ASSERT_EQ(buf[meta_len + 1025], 0xcc, "data[1025]");
> +out:
> +	free(buf);
> +}
> +
> +static void test_xdp_pull_data_basic(void)
> +{
> +	u32 pg_sz, max_meta_len, max_data_len;
> +	struct test_xdp_pull_data *skel;
> +
> +	skel = test_xdp_pull_data__open_and_load();
> +	if (!ASSERT_OK_PTR(skel, "test_xdp_pull_data__open_and_load"))
> +		return;
> +
> +	pg_sz = sysconf(_SC_PAGE_SIZE);
> +
> +	if (find_xdp_sizes(skel, pg_sz))
> +		goto out;
> +
> +	max_meta_len = XDP_PACKET_HEADROOM - skel->bss->xdpf_sz;
> +	max_data_len = pg_sz - XDP_PACKET_HEADROOM - skel->bss->sinfo_sz;
> +
> +	/* linear xdp pkt, pull 0 byte */
> +	run_test(skel, XDP_PASS, pg_sz, 2048, 0, 2048, 2048);

you're passing pg_sz to avoid repeated syscalls I assume? Is it worth to pass
prog_fd as well?

> +
> +	/* multi-buf pkt, pull results in linear xdp pkt */
> +	run_test(skel, XDP_PASS, pg_sz, 2048, 0, 1024, 2048);
> +
> +	/* multi-buf pkt, pull 1 byte to linear data area */
> +	run_test(skel, XDP_PASS, pg_sz, 9000, 0, 1024, 1025);
> +
> +	/* multi-buf pkt, pull 0 byte to linear data area */
> +	run_test(skel, XDP_PASS, pg_sz, 9000, 0, 1025, 1025);
> +
> +	/* multi-buf pkt, empty linear data area, pull requires memmove */
> +	run_test(skel, XDP_PASS, pg_sz, 9000, 0, 0, PULL_MAX);
> +
> +	/* multi-buf pkt, no headroom */
> +	run_test(skel, XDP_PASS, pg_sz, 9000, max_meta_len, 1024, PULL_MAX);
> +
> +	/* multi-buf pkt, no tailroom, pull requires memmove */
> +	run_test(skel, XDP_PASS, pg_sz, 9000, 0, max_data_len, PULL_MAX);
> +

nit: double empty line

> +
> +	/* linear xdp pkt, pull more than total data len */
> +	run_test(skel, XDP_DROP, pg_sz, 2048, 0, 2048, 2049);
> +
> +	/* multi-buf pkt with no space left in linear data area */
> +	run_test(skel, XDP_DROP, pg_sz, 9000, max_meta_len, max_data_len,
> +		 PULL_MAX | PULL_PLUS_ONE);
> +
> +	/* multi-buf pkt, empty linear data area */
> +	run_test(skel, XDP_DROP, pg_sz, 9000, 0, 0, PULL_MAX | PULL_PLUS_ONE);
> +
> +	/* multi-buf pkt, no headroom */
> +	run_test(skel, XDP_DROP, pg_sz, 9000, max_meta_len, 1024,
> +		 PULL_MAX | PULL_PLUS_ONE);
> +
> +	/* multi-buf pkt, no tailroom */
> +	run_test(skel, XDP_DROP, pg_sz, 9000, 0, max_data_len,
> +		 PULL_MAX | PULL_PLUS_ONE);
> +
> +out:
> +	test_xdp_pull_data__destroy(skel);
> +}
> +
> +void test_xdp_pull_data(void)
> +{
> +	if (test__start_subtest("xdp_pull_data"))
> +		test_xdp_pull_data_basic();
> +}
> diff --git a/tools/testing/selftests/bpf/progs/test_xdp_pull_data.c b/tools/testing/selftests/bpf/progs/test_xdp_pull_data.c
> new file mode 100644
> index 000000000000..dd901bb109b6
> --- /dev/null
> +++ b/tools/testing/selftests/bpf/progs/test_xdp_pull_data.c
> @@ -0,0 +1,48 @@
> +// SPDX-License-Identifier: GPL-2.0
> +
> +#include  "vmlinux.h"
> +#include <bpf/bpf_helpers.h>
> +
> +int xdpf_sz;
> +int sinfo_sz;
> +int data_len;
> +int pull_len;
> +
> +#define XDP_PACKET_HEADROOM 256
> +
> +SEC("xdp.frags")
> +int xdp_find_sizes(struct xdp_md *ctx)
> +{
> +	xdpf_sz = sizeof(struct xdp_frame);
> +	sinfo_sz = __PAGE_SIZE - XDP_PACKET_HEADROOM -
> +		   (ctx->data_end - ctx->data);
> +
> +	return XDP_PASS;
> +}
> +
> +SEC("xdp.frags")
> +int xdp_pull_data_prog(struct xdp_md *ctx)
> +{
> +	__u8 *data_end = (void *)(long)ctx->data_end;
> +	__u8 *data = (void *)(long)ctx->data;
> +	__u8 *val_p;
> +	int err;
> +
> +	if (data_len != data_end - data)
> +		return XDP_DROP;
> +
> +	err = bpf_xdp_pull_data(ctx, pull_len);
> +	if (err)
> +		return XDP_DROP;
> +
> +	val_p = (void *)(long)ctx->data + 1024;
> +	if (val_p + 1 > (void *)(long)ctx->data_end)
> +		return XDP_DROP;
> +
> +	if (*val_p != 0xbb)
> +		return XDP_DROP;
> +
> +	return XDP_PASS;
> +}
> +
> +char _license[] SEC("license") = "GPL";
> -- 
> 2.47.3
>