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.



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