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 Wed, Feb 28, 2024 at 12:29:49PM -0600, David Vernet wrote:
> 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?

I see you already added that in the next patch. Nice!!

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