Re: [PATCH v3 15/16] kunit: uapi: Introduce preinit executable

[David Gow <davidgow@google.com>]

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On Wed, 11 Jun 2025 at 15:38, Thomas Weißschuh
<thomas.weissschuh@linutronix.de> wrote:
>
> UAPI selftests may expect a "normal" userspace environment.
> For example the normal kernel API pseudo-filesystems should be mounted.
> This could be done from kernel code but it is non-idiomatic.
>
> Add a preinit userspace executable which performs these setup steps
> before running the final test executable.
> This preinit executable is only ever run from the kernel.
> Give it access to autoconf.h and kconfig.h to adapt itself to the
> tested kernel.
>
> Signed-off-by: Thomas Weißschuh <thomas.weissschuh@linutronix.de>
> ---

Looks good and works here.

Reviewed-by: David Gow <davidgow@google.com>

(Although, personally, _I wish_ it were more idiomatic to mount things
from kernelspace.)

Cheers,
-- David


>  lib/kunit/Makefile       |  9 ++++++-
>  lib/kunit/uapi-preinit.c | 63 ++++++++++++++++++++++++++++++++++++++++++++++++
>  lib/kunit/uapi.c         | 11 +++++++--
>  3 files changed, 80 insertions(+), 3 deletions(-)
>
> diff --git a/lib/kunit/Makefile b/lib/kunit/Makefile
> index e406a31df1df834a87961663de0b7921b59481c2..19493ec320c61e2ccbb58e8b2e943e9a4ec447e2 100644
> --- a/lib/kunit/Makefile
> +++ b/lib/kunit/Makefile
> @@ -12,7 +12,14 @@ kunit-objs +=                                test.o \
>                                         device.o \
>                                         platform.o
>
> -kunit-$(CONFIG_KUNIT_UAPI) +=          uapi.o
> +userprogs +=                           uapi-preinit
> +uapi-preinit-nolibc :=                 $(CONFIG_ARCH_HAS_NOLIBC)
> +uapi-preinit-userccflags +=            -static \
> +                                       -include include/generated/autoconf.h \
> +                                       -include $(srctree)/tools/include/linux/kconfig.h
> +blobs +=                               uapi-preinit.blob.o
> +uapi-preinit.blob-symbol :=            kunit_uapi_preinit
> +kunit-$(CONFIG_KUNIT_UAPI) +=          uapi.o uapi-preinit.blob.o
>
>  ifeq ($(CONFIG_KUNIT_DEBUGFS),y)
>  kunit-objs +=                          debugfs.o
> diff --git a/lib/kunit/uapi-preinit.c b/lib/kunit/uapi-preinit.c
> new file mode 100644
> index 0000000000000000000000000000000000000000..81182039965a8c93aebb2d5d76f4113bfef277a6
> --- /dev/null
> +++ b/lib/kunit/uapi-preinit.c
> @@ -0,0 +1,63 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * KUnit Userspace environment setup.
> + *
> + * Copyright (C) 2025, Linutronix GmbH.
> + * Author: Thomas Weißschuh <thomas.weissschuh@linutronix.de>
> + *
> + * This is *userspace* code.
> + */
> +
> +#include <sys/mount.h>
> +#include <sys/stat.h>
> +
> +#include "../../tools/testing/selftests/kselftest.h"
> +
> +static int setup_api_mount(const char *target, const char *fstype)
> +{
> +       int ret;
> +
> +       ret = mkdir(target, 0755);
> +       if (ret && errno != EEXIST)
> +               return -errno;
> +
> +       ret = mount("none", target, fstype, 0, NULL);
> +       if (ret && errno != EBUSY)
> +               return -errno;
> +
> +       return 0;
> +}
> +
> +static void exit_failure(const char *stage, int err)
> +{
> +       /* If preinit fails synthesize a failed test report. */
> +       ksft_print_header();
> +       ksft_set_plan(1);
> +       ksft_test_result_fail("Failed during test setup: %s: %s\n", stage, strerror(-err));
> +       ksft_finished();
> +}
> +
> +int main(int argc, char **argv, char **envp)
> +{
> +       int ret;
> +
> +       ret = setup_api_mount("/proc", "proc");
> +       if (ret)
> +               exit_failure("mount /proc", ret);
> +
> +       ret = setup_api_mount("/sys", "sysfs");
> +       if (ret)
> +               exit_failure("mount /sys", ret);
> +
> +       if (IS_ENABLED(CONFIG_DEVTMPFS)) {
> +               ret = setup_api_mount("/dev", "devtmpfs");
> +               if (ret)
> +                       exit_failure("mount /dev", ret);
> +       }
> +
> +       ret = execve(argv[0], argv, envp);
> +       if (ret)
> +               exit_failure("execve", ret);
> +
> +       return 0;
> +}
> diff --git a/lib/kunit/uapi.c b/lib/kunit/uapi.c
> index 121146dda533b3f90aca37c20bd0e7a1d20cb3b5..bccc081a6538507724c1ef340203cfd147170dc4 100644
> --- a/lib/kunit/uapi.c
> +++ b/lib/kunit/uapi.c
> @@ -139,7 +139,7 @@ static int kunit_uapi_user_mode_thread_init(void *data)
>         kernel_sigaction(SIGABRT, SIG_DFL);
>
>         complete(&ctx->setup_done);
> -       ctx->exec_err = kernel_execve(ctx->executable, argv, NULL);
> +       ctx->exec_err = kernel_execve(kbasename(BLOB(kunit_uapi_preinit)->path), argv, NULL);
>         if (!ctx->exec_err)
>                 return 0;
>         do_exit(0);
> @@ -239,6 +239,7 @@ static int kunit_uapi_run_executable_in_mount(struct kunit *test, const char *ex
>
>  static int kunit_uapi_run_executable(struct kunit *test, const struct blob *executable)
>  {
> +       const struct blob *preinit = BLOB(kunit_uapi_preinit);
>         const char *exe_name = kbasename(executable->path);
>         struct vfsmount *mnt;
>         int err;
> @@ -247,7 +248,13 @@ static int kunit_uapi_run_executable(struct kunit *test, const struct blob *exec
>         if (IS_ERR(mnt))
>                 return PTR_ERR(mnt);
>
> -       err = kunit_uapi_write_file(mnt, exe_name, 0755, executable->data, blob_size(executable));
> +       err = kunit_uapi_write_file(mnt, kbasename(preinit->path), 0755,
> +                                   preinit->data,
> +                                   blob_size(preinit));
> +
> +       if (!err)
> +               err = kunit_uapi_write_file(mnt, exe_name, 0755,
> +                                           executable->data, blob_size(executable));
>
>         if (!err)
>                 err = kunit_uapi_run_executable_in_mount(test, exe_name, mnt);
>
> --
> 2.49.0
>

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