Re: [PATCH] printk.c: removed unnecessary code

Michal Hocko
2016-11-30T09:14:35Z

[Resending with the full CC list as my email client has clobbered it in
the previous attempt for some reason]

On Tue 29-11-16 16:19:01, Sebastian Duda wrote:
> snprintf((char *) ?, 0, ...); always returns Zero and doesn't change the data.
> Thus the execution of
> snprintf(NULL, 0, "[%5lu.000000] ", (unsigned long)ts);
> has no effect on program.
> The substitution with 0 increases the readability of the code.

Are you sure this is correct. As per vsnprintf documentation:
"
* The return value is the number of characters which would
* be generated for the given input, excluding the trailing
* '\0', as per ISO C99.
"

this should just work as 35dac27cedd1 ("printk: fix incorrect length
from print_time() when seconds > 99999") intended.

I haven't checked the implementation though so I might be wrong here.

>
> Signed-off-by: Sebastian Duda <sebastian.duda@fau.de>
> Signed-off-by: Tobias Baumeister <tobias.baumeister@fau.de>
> ---
> kernel/printk/printk.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
> index 5028f4f..fe3fec1 100644
> --- a/kernel/printk/printk.c
> +++ b/kernel/printk/printk.c
> @@ -1186,7 +1186,7 @@ static size_t print_time(u64 ts, char *buf)
> rem_nsec = do_div(ts, 1000000000);
>
> if (!buf)
> - return snprintf(NULL, 0, "[%5lu.000000] ", (unsigned long)ts);
> + return 0;
>
> return sprintf(buf, "[%5lu.%06lu] ",
> (unsigned long)ts, rem_nsec / 1000);
> --
> 2.7.4

--
Michal Hocko
SUSE Labs