Re: [PATCH v2 01/21] lib/vsprintf: Add specifier for printing struct timespec64

[Petr Mladek <pmladek@suse.com>]

On Tue 2025-11-11 13:20:01, Andy Shevchenko wrote:
> A handful drivers want to print a content of the struct timespec64
> in a format of %lld:%09ld. In order to make their lives easier, add
> the respecting specifier directly to the printf() implementation.
> 
> Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
> ---
>  Documentation/core-api/printk-formats.rst | 11 ++++++++--
>  lib/tests/printf_kunit.c                  |  4 ++++
>  lib/vsprintf.c                            | 25 +++++++++++++++++++++++
>  3 files changed, 38 insertions(+), 2 deletions(-)
> 
> diff --git a/Documentation/core-api/printk-formats.rst b/Documentation/core-api/printk-formats.rst
> index 7f2f11b48286..c0b1b6089307 100644
> --- a/Documentation/core-api/printk-formats.rst
> +++ b/Documentation/core-api/printk-formats.rst
> @@ -547,11 +547,13 @@ Time and date
>  	%pt[RT]s		YYYY-mm-dd HH:MM:SS
>  	%pt[RT]d		YYYY-mm-dd
>  	%pt[RT]t		HH:MM:SS
> -	%pt[RT][dt][r][s]
> +	%ptSp			<seconds>.<nanoseconds>

I know that that there was no good choice. But I am curious.
Does the 'p' stands for some particular word, for example, "plain" ?

I do not want to start bike shedding but I think about
using 'n' as "number".

> +	%pt[RST][dt][r][s]
>  
>  For printing date and time as represented by::
>  
> -	R  struct rtc_time structure
> +	R  content of struct rtc_time
> +	S  content of struct timespec64
>  	T  time64_t type
>  
>  in human readable format.
> @@ -563,6 +565,11 @@ The %pt[RT]s (space) will override ISO 8601 separator by using ' ' (space)
>  instead of 'T' (Capital T) between date and time. It won't have any effect
>  when date or time is omitted.
>  
> +The %ptSp is equivalent to %lld.%09ld for the content of the struct timespec64.
> +When the other specifiers are given, it becomes the respective equivalent of
> +%ptT[dt][r][s].%09ld. In other words, the seconds are being printed in
> +the human readable format followed by a dot and nanoseconds.
> +
>  Passed by reference.
>  
>  struct clk
> diff --git a/lib/vsprintf.c b/lib/vsprintf.c
> index 3f99834fd788..fdd06e8957a3 100644
> --- a/lib/vsprintf.c
> +++ b/lib/vsprintf.c
> @@ -2464,6 +2488,7 @@ early_param("no_hash_pointers", no_hash_pointers_enable);
>   * - 'g' For block_device name (gendisk + partition number)
>   * - 't[RT][dt][r][s]' For time and date as represented by:

We should add 'S' here as well:

   * - 't[RST][dt][r][s]' For time and date as represented by:

That said, I am not sure about the optional '[p]'. We could
either do:

   * - 't[RST][p][dt][r][s]' For time and date as represented by:

or

   * - 'tSp'	For time represented by struct timespec64 printed
		as seconds.nanoseconds
   * - 't[RST][dt][r][s]' For time and date as represented by:

>   *      R    struct rtc_time
> + *      S    struct timespec64
>   *      T    time64_t
>   * - 'C' For a clock, it prints the name (Common Clock Framework) or address
>   *       (legacy clock framework) of the clock

Otherwise, it looks good.

Best Regards,
Petr