How can I print the current time in the kernel?

Question

I'm a beginner at Linux. I should print the current time and do something through system call in Linux. I did the other task, but failed to print the current time. I wrote:

#include<linux/kernel.h> #include<linux/time.h> ... asmlinkage long sys_printtime(void) { ... struct timeval time; struct tm tm1; ... do_gettimeofday(&time); local_time=(u32)(time.tv_sec -(sys_tz.tz_minuteswest * 60)); time_to_tm(local_time,(3600*9),&tm1); printk(KERN_DEBUG "time @(%04d-%02d-%02d %02d:%02d:%02d)\n", tm1.tm_year+1900,tm1.tm_mon+1,tm1.tm_mday,tm1.tm_hour,tm1.tm_min,tm1.tm_sec); ... return 0; }

but it doesn't work.

The error says, I can't use do_gettimeofday. I found out that I can't use it anymore, because kernel version 5 doesn't support it. I searched on google and Stackoverflow, but I don't know how to print the current time in kernel version 5.

Can anybody help me?

bornfree · Accepted Answer · 2019-04-11 06:29:49Z

Yes, do_gettimeofday has been removed because of y2038 problem. Instead the kernel provides time interfaces which you can use as per your need. Check the documentation https://www.kernel.org/doc/html/latest/core-api/timekeeping.html.

For example, you have ktime_get_ts64(struct timespec64 *ts) which will provide you time in seconds and nanoseconds.

struct timespec64 { time64_t tv_sec; /* seconds */ long tv_nsec; /* nanoseconds */ };

If you only want in nanoseconds, you can use u64 ktime_get_ns(void). Please check the documentation above for what suits your purpose. Also you can check timekeeping.h and ktime.h for further information.

If you want to find an example just search the function name in the kernel source either using grep -rni <func name> or use cscope. You can also search it online here

Thank you so much! I already solved it using __ktime_get_real_seconds() :) I'll try again using ktime_get_ts64 as you told. thanks again x)

Hirbod Behnam · Accepted Answer · 2022-10-28 14:36:17Z

There is also a one liner to get the rtc time like this:

#include <linux/ktime.h> #include <linux/rtc.h> struct rtc_time t = rtc_ktime_to_tm(ktime_get_real()); printk(KERN_INFO "%ptRs", &t);

Document of ktime_get_real can be found here. I didn't find any documentation for rtc_ktime_to_tm even in the code but it gets the time as Unix epoch in nano seconds as input and outputs struct rtc_time. How to print struct rtc_time can be found here.

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