Example of using getnstimeofday in linux kernel

The linux kernel provides a number of interfaces to manage time. getnstimeofday is one of them, which gives the time in seconds and nanoseconds . The function is implemented in "timekeeping32.h" and returns a structure of the type timespec which has two members.

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

To print the time, we only need to print the values of tv_sec and tv_nsec which gets filled by the call to the function getnstimeofday.

In the following example code, we have created a proc entry called gettime, which prints out the values of seconds and nanoseconds when read.

	#include <linux/module.h>
	#include <linux/kernel.h>
	#include <linux/proc_fs.h>
	#include<linux/slab.h>
	int len;
	char *msg;
	ssize_t size;
	struct timespec ts;
	ssize_t read_proc(struct file *filp,char *buf,size_t count,loff_t *offp )
	{
	struct timespec ts;
	char *temp;
	temp=kmalloc(50*sizeof(char),GFP_KERNEL);
	getnstimeofday(&ts);
	sprintf(temp,"%ld seconds \n%ld nanoseconds\n",ts.tv_sec, ts.tv_nsec);
	len=strlen(temp);
	size=sizeof(char)*len;
	return simple_read_from_buffer(buf,count,offp,temp,size);
	}
	struct file_operations proc_fops = {
	read: read_proc
	};
	void create_new_proc_entry(void)
	{
	proc_create("gettime",0,NULL,&proc_fops);
	}
	int proc_init (void) {
	create_new_proc_entry();
	return 0;
	}
	void proc_cleanup(void) {
	remove_proc_entry("gettime",NULL);
	}
	MODULE_LICENSE("GPL");
	module_init(proc_init);
	module_exit(proc_cleanup);

view raw proc_read_gettimeofday.c hosted with ❤ by GitHub

Save the above code as proc_read_gettimeofday.c and compile the code using the following makefile.

ifneq ($(KERNELRELEASE),) obj-m := proc_read_gettimeofday.o else KERNELDIR ?= /lib/modules/$(shell uname -r)/build PWD := $(shell pwd) default: $(MAKE) -C $(KERNELDIR) M=$(PWD) modules clean: $(MAKE) -C $(KERNELDIR) M=$(PWD) clean endif

Compile and insert the module using

$ make $ sudo insmod proc_read_getnstimeofday.ko

To see the output, just read the proc entry gettime, using the cat command.

cat /proc/gettime 1584690328 seconds 290430470 nanoseconds