Re: [PATCH v3 16/16] kunit: uapi: Validate usability of /proc

[David Gow <davidgow@google.com>]

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On Wed, 11 Jun 2025 at 15:38, Thomas Weißschuh
<thomas.weissschuh@linutronix.de> wrote:
>
> Show that the selftests are executed from a fairly "normal"
> userspace context.
>
> Signed-off-by: Thomas Weißschuh <thomas.weissschuh@linutronix.de>
> ---

This is good. I'm not 100% sure the example test is the best place for
it, though.

Would it make more sense to either have this:
- in the main kunit test (since it's really _verifying_ the KUnit
environment, rather than documenting it)
- in a separate kunit-uapi test (if we want to keep some separation
between the UAPI and entirely in-kernel tests)
- in a separate procfs test (since it tests procfs functionality as
much as it's testing the KUnit environment)

Personally, my gut feeling is the main kunit-test is the best place
for this, even if it means spinning up a separate file is best here.

As for the actual implementation, though, that looks fine to me. A few
small comments below, but nothing particularly important.

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

Cheers,
-- David

>  lib/kunit/kunit-example-uapi.c | 34 +++++++++++++++++++++++++++++++++-
>  1 file changed, 33 insertions(+), 1 deletion(-)
>
> diff --git a/lib/kunit/kunit-example-uapi.c b/lib/kunit/kunit-example-uapi.c
> index 4ce657050dd4a576632a41ca0309c4cb5134ce14..5e7a0f3b68f182c42b03e667567e66f02d8c2b86 100644
> --- a/lib/kunit/kunit-example-uapi.c
> +++ b/lib/kunit/kunit-example-uapi.c
> @@ -8,13 +8,45 @@
>   * This is *userspace* code.
>   */
>
> +#include <fcntl.h>
> +#include <unistd.h>
> +#include <string.h>
> +
>  #include "../../tools/testing/selftests/kselftest.h"
>
> +static void test_procfs(void)
> +{
> +       char buf[256];
> +       ssize_t r;
> +       int fd;
> +
> +       fd = open("/proc/self/comm", O_RDONLY);
> +       if (fd == -1) {
> +               ksft_test_result_fail("procfs: open() failed: %s\n", strerror(errno));
> +               return;
> +       }
> +
> +       r = read(fd, buf, sizeof(buf));
> +       close(fd);
> +
> +       if (r == -1) {
> +               ksft_test_result_fail("procfs: read() failed: %s\n", strerror(errno));
> +               return;
> +       }
> +

Do we want to use TASK_COMM_LEN rather than hardcoding 16 below?

(And, if so, do we need something more complicated in case it's not 16?)


> +       if (r != 16 || strncmp("kunit-example-u\n", buf, 16) != 0) {
> +               ksft_test_result_fail("procfs: incorrect comm\n");
> +               return;
> +       }
> +
> +       ksft_test_result_pass("procfs\n");
> +}
> +
>  int main(void)
>  {
>         ksft_print_header();
>         ksft_set_plan(4);
> -       ksft_test_result_pass("userspace test 1\n");
> +       test_procfs();
>         ksft_test_result_pass("userspace test 2\n");
>         ksft_test_result_skip("userspace test 3: some reason\n");
>         ksft_test_result_pass("userspace test 4\n");
>
> --
> 2.49.0
>

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