Re: [PATCH v3 2/3] fs/proc: apply the time namespace offset to /proc/stat btime

[Andrei Vagin <avagin@gmail.com>]

On Sun, Oct 11, 2020 at 04:59:23PM +0200, Michael Weiß wrote:
> @@ -79,6 +80,20 @@ static u64 get_iowait_time(struct kernel_cpustat *kcs, int cpu)
>  
>  #endif
>  
> +static void get_boottime(struct timespec64 *ts)
> +{

> +	ktime_t boottime;
> +
> +	/* get kernel internal system boot timestamp */
> +	getboottime64(ts);
> +
> +	/* shift boot timestamp according to the timens offset */
> +	boottime = timespec64_to_ktime(*ts);
> +	boottime = timens_ktime_to_host(CLOCK_BOOTTIME, boottime);

timens_ktime_to_host is used to convert timens' time to host's time.
Here it looks like we are using it in the opposite direction. I spent
some time to figure out what is going on here. I think it worth to add a
comment here.

> +
> +	*ts = ktime_to_timespec64(boottime);

I don't like all these conversions back and forth. Maybe something like
this will look better:

#ifdef CONFIG_TIME_NS
	if (current->nsproxy->time_ns != init_time_ns) {
		struct timens_offsets *ns_offsets;
		ns_offsets = &current->nsproxy->time_ns->offsets;
		ts = timespec64_sub(ts, timens_offsets->boottime);
	}
#endif


Thanks,
Andrei