Re: [PATCH v7 4/7] selftests: ksft_exit_fail_perror: support printf style arguments

[Chunyu Hu <chuhu@redhat.com>]

On Mon, Mar 30, 2026 at 11:15:00PM +0800, Chunyu Hu wrote:
> The ksft_exit_fail_perror function previously only accepted a single string
> argument, which limited its flexibility for providing specific context to
> failure messages.
> 
> This change updates ksft_exit_fail_perror to support variable arguments,
> similar to ksft_exit_fail_msg.  Adding the __printf(1, 2) attribute enables
> compile-time checking for format string correctness.
> 
> Signed-off-by: Chunyu Hu <chuhu@redhat.com>
> ---
> Changes in v7:
>   - new patch to convert ksft_exit_fail_perror support variable arguments
> ---
>  tools/testing/selftests/kselftest.h | 21 ++++++++++++++++++---
>  1 file changed, 18 insertions(+), 3 deletions(-)
> 
> diff --git a/tools/testing/selftests/kselftest.h b/tools/testing/selftests/kselftest.h
> index afbcf8412ae5..11cabdabb3f6 100644
> --- a/tools/testing/selftests/kselftest.h
> +++ b/tools/testing/selftests/kselftest.h
> @@ -43,7 +43,7 @@
>   * the program is aborting before finishing all tests):
>   *
>   *    ksft_exit_fail_msg(fmt, ...);
> - *    ksft_exit_fail_perror(msg);
> + *    ksft_exit_fail_perror(fmt, ...);
>   *
>   */
>  #ifndef __KSELFTEST_H
> @@ -417,9 +417,24 @@ static inline __noreturn __printf(1, 2) void ksft_exit_fail_msg(const char *msg,
>  	exit(KSFT_FAIL);
>  }
>  
> -static inline __noreturn void ksft_exit_fail_perror(const char *msg)
> +static inline __noreturn __printf(1, 2) void ksft_exit_fail_perror(const char *msg, ...)
>  {
> -	ksft_exit_fail_msg("%s: %s (%d)\n", msg, strerror(errno), errno);
> +	va_list args;
> +	char *buf = NULL;
> +	int saved_errno = errno;
> +
> +	va_start(args, msg);
> +	if (vasprintf(&buf, msg, args) == -1) {

kernel test robot reported compile error on this, as the vasprintf
required _GNU_SOURCE. Looks like it's not appropriate to be used
in the common header. Looks like it can be replaced with a buf and
vsnprintf instead.

    char buf[512];
	va_start(args, msg);
	vsnprintf(buf, sizeof(buf), msg, args);

```
   In file included from za-fork.c:12:
   ../../kselftest.h: In function 'ksft_exit_fail_perror':
>> ../../kselftest.h:427:13: error: implicit declaration of function 'vasprintf'; did you mean 'vsprintf'? [-Wimplicit-function-declaration]
     427 |         if (vasprintf(&buf, msg, args) == -1) {
         |             ^~~~~~~~~
         |             vsprintf
--
   In file included from basic-gcs.c:16:
   tools/testing/selftests/kselftest.h: In function 'ksft_exit_fail_perror':
>> tools/testing/selftests/kselftest.h:427:13: error: implicit declaration of function 'vasprintf'; did you mean 'vsprintf'? [-Wimplicit-function-declaration]
     427 |         if (vasprintf(&buf, msg, args) == -1) {
         |             ^~~~~~~~~
         |             vsprintf
```



> +		va_end(args);
> +		ksft_exit_fail_msg("vasprintf failed: %s (%d)\n", strerror(saved_errno),
> +				saved_errno);
> +	}
> +	va_end(args);
> +
> +	errno = saved_errno;
> +	ksft_exit_fail_msg("%s: %s (%d)\n", buf, strerror(errno), errno);
> +
> +	free(buf);
>  }
>  
>  static inline __noreturn void ksft_exit_xfail(void)
> -- 
> 2.53.0
>