Re: [PATCH v3 1/3] selftests/landlock: Add filesystem access benchmark

["Mickaël Salaün" <mic@digikod.net>]

On Fri, Feb 06, 2026 at 04:11:53PM +0100, Günther Noack wrote:
> fs_bench benchmarks the performance of Landlock's path walk
> by exercising it in a scenario that amplifies Landlock's overhead:
> 
> * Create a large number of nested directories
> * Enforce a Landlock policy in which a rule is associated with each of
>   these subdirectories
> * Benchmark openat() applied to the deepest directory,
>   forcing Landlock to walk the entire path.
> 
> Signed-off-by: Günther Noack <gnoack3000@gmail.com>
> ---
>  tools/testing/selftests/landlock/.gitignore |   1 +
>  tools/testing/selftests/landlock/Makefile   |   1 +
>  tools/testing/selftests/landlock/fs_bench.c | 214 ++++++++++++++++++++
>  3 files changed, 216 insertions(+)
>  create mode 100644 tools/testing/selftests/landlock/fs_bench.c
> 
> diff --git a/tools/testing/selftests/landlock/.gitignore b/tools/testing/selftests/landlock/.gitignore
> index a820329cae0d..1974e17a2611 100644
> --- a/tools/testing/selftests/landlock/.gitignore
> +++ b/tools/testing/selftests/landlock/.gitignore
> @@ -1,4 +1,5 @@
>  /*_test
> +/fs_bench
>  /sandbox-and-launch
>  /true
>  /wait-pipe
> diff --git a/tools/testing/selftests/landlock/Makefile b/tools/testing/selftests/landlock/Makefile
> index 044b83bde16e..fc43225d319a 100644
> --- a/tools/testing/selftests/landlock/Makefile
> +++ b/tools/testing/selftests/landlock/Makefile

> +int main(int argc, char *argv[])
> +{
> +	bool use_landlock = true;
> +	size_t num_iterations = 100000;
> +	size_t num_subdirs = 10000;
> +	int c, curr, fd;
> +	struct tms start_time, end_time;
> +
> +	setbuf(stdout, NULL);
> +	while ((c = getopt(argc, argv, "hLd:n:")) != -1) {
> +		switch (c) {
> +		case 'h':
> +			usage(argv[0]);
> +			return EXIT_SUCCESS;
> +		case 'L':
> +			use_landlock = false;
> +			break;
> +		case 'd':
> +			num_subdirs = atoi(optarg);
> +			break;
> +		case 'n':
> +			num_iterations = atoi(optarg);
> +			break;
> +		default:
> +			usage(argv[0]);
> +			return EXIT_FAILURE;
> +		}
> +	}
> +
> +	printf("*** Benchmark ***\n");
> +	printf("%zu dirs, %zu iterations, %s landlock\n", num_subdirs,
> +	       num_iterations, use_landlock ? "with" : "without");
> +
> +	if (times(&start_time) == -1)
> +		err(1, "times");
> +
> +	curr = build_directory(num_subdirs, use_landlock);
> +
> +	for (int i = 0; i < num_iterations; i++) {
> +		fd = openat(curr, "file.txt", O_CREAT | O_TRUNC | O_WRONLY);

Some build environments complain that O_CREAT requires the fourth
openat argument to be set.  I set the mode to 0600.

> +		if (use_landlock) {
> +			if (fd == 0)
> +				errx(1, "openat succeeded, expected EACCES");
> +			if (errno != EACCES)
> +				err(1, "openat expected EACCES, but got");
> +		}
> +		if (fd != -1)
> +			close(fd);
> +	}
> +
> +	if (times(&end_time) == -1)
> +		err(1, "times");
> +
> +	printf("*** Benchmark concluded ***\n");
> +	printf("System: %ld clocks\n",
> +	       end_time.tms_stime - start_time.tms_stime);
> +	printf("User  : %ld clocks\n",
> +	       end_time.tms_utime - start_time.tms_utime);
> +	printf("Clocks per second: %ld\n", CLOCKS_PER_SEC);
> +
> +	close(curr);
> +
> +	remove_recursively(num_subdirs);
> +}
> -- 
> 2.52.0
> 
>