Re: [PATCH 1/6] selftests/liveupdate: add framework for memfd tests

[Mike Rapoport <rppt@kernel.org>]

On Mon, Mar 09, 2026 at 11:54:34AM +0000, Pratyush Yadav wrote:
> From: "Pratyush Yadav (Google)" <pratyush@kernel.org>
> 
> Currently memfd preservation using LUO is only tested indirectly via the
> luo_multi_session or luo_kexec_simple tests. Their main purpose is to
> test other live update functionality.
> 
> Add a framework for writing memfd tests. The framework hooks into the
> kselftest harness, but adds some things on top to make it suitable for
> live update.
> 
> The LUO FD (/dev/liveupdate) can only be opened by one process at a
> time. Each test runs in its own process. This means the LUO FD must be
> owned by the main process and shared to children. main() opens the LUO
> FD and shares it to child runners using a global variable.
> 
> Live update tests run in two stages. One before kexec and one after.
> Detect the stage using a special state session. If the session is
> present, it means the test is in post-kexec state.
> 
> Additionally, take in an optional --stage argument that lets callers
> specify expected stage. This is useful as a safety net to catch LUO core
> failures. If LUO core fails to preserve the state session properly, this
> option can help detect this and fail early. Since the option is not
> recognized by the kselftest harness, remove it from argv before calling
> test_harness_run().
> 
> Signed-off-by: Pratyush Yadav (Google) <pratyush@kernel.org>

Reviewed-by: Mike Rapoport (Microsoft) <rppt@kernel.org>

with a few nits below.

> ---
>  tools/testing/selftests/liveupdate/Makefile   |  1 +
>  .../testing/selftests/liveupdate/luo_memfd.c  | 77 +++++++++++++++++++
>  2 files changed, 78 insertions(+)
>  create mode 100644 tools/testing/selftests/liveupdate/luo_memfd.c
> 
> diff --git a/tools/testing/selftests/liveupdate/Makefile b/tools/testing/selftests/liveupdate/Makefile
> index 080754787ede..051daae55eec 100644
> --- a/tools/testing/selftests/liveupdate/Makefile
> +++ b/tools/testing/selftests/liveupdate/Makefile
> @@ -6,6 +6,7 @@ TEST_GEN_PROGS += liveupdate
>  
>  TEST_GEN_PROGS_EXTENDED += luo_kexec_simple
>  TEST_GEN_PROGS_EXTENDED += luo_multi_session
> +TEST_GEN_PROGS_EXTENDED += luo_memfd
>  
>  TEST_FILES += do_kexec.sh
>  
> diff --git a/tools/testing/selftests/liveupdate/luo_memfd.c b/tools/testing/selftests/liveupdate/luo_memfd.c
> new file mode 100644
> index 000000000000..b779eee18387
> --- /dev/null
> +++ b/tools/testing/selftests/liveupdate/luo_memfd.c
> @@ -0,0 +1,77 @@
> +// SPDX-License-Identifier: GPL-2.0
> +
> +/*
> + * Copyright (c) 2026, Google LLC.
> + * Pratyush Yadav (Google) <pratyush@kernel.org>
> + */
> +
> +/*
> + * Selftests for memfd preservation via LUO.
> + */
> +
> +#include <errno.h>
> +#include <fcntl.h>
> +#include <string.h>
> +#include <sys/ioctl.h>
> +#include <unistd.h>
> +
> +#include <linux/liveupdate.h>
> +
> +#include "../kselftest.h"
> +#include "../kselftest_harness.h"
> +
> +#include "luo_test_utils.h"
> +
> +#define STATE_SESSION_NAME "luo-state"
> +#define STATE_MEMFD_TOKEN 1
> +
> +#define LIVEUPDATE_DEV "/dev/liveupdate"
> +static int luo_fd = -1, stage;

Nit: declaring stage on a separate line is a bit clearer.

> +
> +int main(int argc, char *argv[])
> +{
> +	int session, expected_stage = 0;

Ditto.

> +
> +	/*
> +	 * The test takes an optional --stage argument. This lets callers
> +	 * provide the expected stage, and if that doesn't match the test errors
> +	 * out.
> +	 *
> +	 * Look for the stage. Since test_harness_run() doesn't recognize it,
> +	 * once found, remove it from argv.
> +	 */
> +	for (int i = 1; i < argc; i++) {
> +		if (strcmp(argv[i], "--stage") == 0) {
> +			if (i + 1 < argc) {
> +				expected_stage = atoi(argv[i + 1]);
> +				memmove(&argv[i], &argv[i + 2], (argc - i - 1) * sizeof(char *));
> +				argc -= 2;
> +				i--;
> +			} else {
> +				ksft_exit_fail_msg("Option --stage requires an argument\n");
> +			}
> +		}
> +	}
> +
> +	luo_fd = luo_open_device();
> +	if (luo_fd < 0)
> +		ksft_exit_skip("Failed to open %s (%s). Is the luo module loaded?\n",

LUO can't be a module :) Maybe

"Is LUO enabled in the kernel?"


> +			       strerror(errno), LUO_DEVICE);
> +
> +	session = luo_retrieve_session(luo_fd, STATE_SESSION_NAME);
> +	if (session == -ENOENT)
> +		stage = 1;
> +	else if (session >= 0)
> +		stage = 2;
> +	else
> +		fail_exit("Failed to check for state session");

There is ksft_exit_fail_perror(), would be more consistent with other exit
paths.

> +
> +	if (expected_stage && expected_stage != stage)
> +		ksft_exit_fail_msg("Stage mismatch: expected %d, got %d\n",
> +				   expected_stage, stage);
> +
> +	if (stage == 1)
> +		create_state_file(luo_fd, STATE_SESSION_NAME, STATE_MEMFD_TOKEN, 2);
> +
> +	test_harness_run(argc, argv);
> +}
> -- 
> 2.53.0.473.g4a7958ca14-goog
> 

-- 
Sincerely yours,
Mike.