Re: [PATCH bpf-next v1 6/8] selftests/bpf: test autocreate behavior for struct_ops maps

[David Vernet <void@manifault.com>]

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On Tue, Feb 27, 2024 at 10:45:54PM +0200, Eduard Zingerman wrote:
> Check that bpf_map__set_autocreate() can be used to disable automatic
> creation for struct_ops maps.
> 
> Signed-off-by: Eduard Zingerman <eddyz87@gmail.com>
> ---
>  .../bpf/prog_tests/struct_ops_autocreate.c    | 79 +++++++++++++++++++
>  .../bpf/progs/struct_ops_autocreate.c         | 42 ++++++++++
>  2 files changed, 121 insertions(+)
>  create mode 100644 tools/testing/selftests/bpf/prog_tests/struct_ops_autocreate.c
>  create mode 100644 tools/testing/selftests/bpf/progs/struct_ops_autocreate.c
> 
> diff --git a/tools/testing/selftests/bpf/prog_tests/struct_ops_autocreate.c b/tools/testing/selftests/bpf/prog_tests/struct_ops_autocreate.c
> new file mode 100644
> index 000000000000..b21b10f94fc2
> --- /dev/null
> +++ b/tools/testing/selftests/bpf/prog_tests/struct_ops_autocreate.c
> @@ -0,0 +1,79 @@
> +// SPDX-License-Identifier: GPL-2.0
> +
> +#include <test_progs.h>
> +#include "struct_ops_autocreate.skel.h"
> +
> +#define EXPECTED_MSG "libbpf: struct_ops init_kern"
> +
> +static libbpf_print_fn_t old_print_cb;
> +static bool msg_found;
> +
> +static int print_cb(enum libbpf_print_level level, const char *fmt, va_list args)
> +{
> +	old_print_cb(level, fmt, args);
> +	if (level == LIBBPF_WARN && strncmp(fmt, EXPECTED_MSG, strlen(EXPECTED_MSG)) == 0)
> +		msg_found = true;
> +
> +	return 0;
> +}
> +
> +static void cant_load_full_object(void)
> +{
> +	struct struct_ops_autocreate *skel;
> +	int err;
> +
> +	old_print_cb = libbpf_set_print(print_cb);
> +	skel = struct_ops_autocreate__open_and_load();

Optional suggestion: It might be useful to add a comment here explaining
exactly why we expect this to fail? Something like:

	/* The testmod_2 map BTF type (struct bpf_testmod_ops___v2) doesn't
	 * match the BTF of the actual struct bpf_testmod_ops defined in the
	 * kernel, so we should fail to load it if we don't disable autocreate
	 * for the map.
	 */

Feel free to ignore -- I recognize that some might just consider that
unnecessary noise.

> +	err = errno;
> +	libbpf_set_print(old_print_cb);
> +	if (!ASSERT_NULL(skel, "struct_ops_autocreate__open_and_load"))
> +		return;
> +
> +	ASSERT_EQ(err, ENOTSUP, "errno should be ENOTSUP");
> +	ASSERT_TRUE(msg_found, "expected message");
> +
> +	struct_ops_autocreate__destroy(skel);
> +}
> +
> +static void can_load_partial_object(void)
> +{
> +	DECLARE_LIBBPF_OPTS(bpf_object_open_opts, opts);
> +	struct struct_ops_autocreate *skel;
> +	struct bpf_link *link = NULL;
> +	int err;
> +
> +	skel = struct_ops_autocreate__open_opts(&opts);
> +	if (!ASSERT_OK_PTR(skel, "struct_ops_autocreate__open_opts"))
> +		return;
> +
> +	err = bpf_program__set_autoload(skel->progs.test_2, false);
> +	if (!ASSERT_OK(err, "bpf_program__set_autoload"))
> +		goto cleanup;

It feels a bit awkward to have to specify that a struct_ops prog isn't
autoloaded if it's not associated with an autoloaded / autocreated struct_ops
map. Would it be possible to teach libbpf to not autoload such progs by
default?

> +	err = bpf_map__set_autocreate(skel->maps.testmod_2, false);
> +	if (!ASSERT_OK(err, "bpf_map__set_autocreate"))
> +		goto cleanup;
> +
> +	err = struct_ops_autocreate__load(skel);
> +	if (ASSERT_OK(err, "struct_ops_autocreate__load"))
> +		goto cleanup;
> +
> +	link = bpf_map__attach_struct_ops(skel->maps.testmod_1);
> +	if (!ASSERT_OK_PTR(link, "bpf_map__attach_struct_ops"))
> +		goto cleanup;
> +
> +	/* test_1() would be called from bpf_dummy_reg2() in bpf_testmod.c */
> +	ASSERT_EQ(skel->bss->test_1_result, 42, "test_1_result");
> +
> +cleanup:
> +	bpf_link__destroy(link);
> +	struct_ops_autocreate__destroy(skel);
> +}
> +
> +void serial_test_struct_ops_autocreate(void)
> +{
> +	if (test__start_subtest("cant_load_full_object"))
> +		cant_load_full_object();
> +	if (test__start_subtest("can_load_partial_object"))
> +		can_load_partial_object();
> +}
> diff --git a/tools/testing/selftests/bpf/progs/struct_ops_autocreate.c b/tools/testing/selftests/bpf/progs/struct_ops_autocreate.c
> new file mode 100644
> index 000000000000..294d48bb8e3c
> --- /dev/null
> +++ b/tools/testing/selftests/bpf/progs/struct_ops_autocreate.c
> @@ -0,0 +1,42 @@
> +// SPDX-License-Identifier: GPL-2.0
> +
> +#include <vmlinux.h>
> +#include <bpf/bpf_helpers.h>
> +#include <bpf/bpf_tracing.h>
> +
> +char _license[] SEC("license") = "GPL";
> +
> +int test_1_result = 0;
> +
> +SEC("struct_ops/test_1")
> +int BPF_PROG(test_1)
> +{
> +	test_1_result = 42;
> +	return 0;
> +}
> +
> +SEC("struct_ops/test_1")
> +int BPF_PROG(test_2)
> +{
> +	return 0;
> +}
> +
> +struct bpf_testmod_ops___v1 {
> +	int (*test_1)(void);
> +};
> +
> +struct bpf_testmod_ops___v2 {
> +	int (*test_1)(void);
> +	int (*does_not_exist)(void);
> +};
> +
> +SEC(".struct_ops.link")
> +struct bpf_testmod_ops___v1 testmod_1 = {
> +	.test_1 = (void *)test_1
> +};
> +
> +SEC(".struct_ops.link")
> +struct bpf_testmod_ops___v2 testmod_2 = {
> +	.test_1 = (void *)test_1,
> +	.does_not_exist = (void *)test_2
> +};
> -- 
> 2.43.0
> 

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