Invalid parameter while insert kernel module

Question

I wrote a simple kernel module and declared 3 parameters:

#include<linux/module.h>

int date = 1, month = 1, year = 2000;
module_param(date, int, 0);
MODULE_PARM_DESC(date, "date of time");
module_param(month, int, 0);
MODULE_PARM_DESC(month, "month of time");
module_param(year, int, 0);
MODULE_PARM_DESC(year, "year of time");

int init_module(void) {
    printk(KERN_INFO "Today is %d/%d/%d.\n", year, month, date);  // write to dmesg file
    return 0;
}

When I execute this command:

sudo insmod hello.ko year=`date +%Y` month=`date +%m` date=`date +%d`

The terminal shows:

insmod: ERROR: could not insert module hello.ko: Invalid parameters

So I check the dmesg log:

[ 4283.774215] hello: `09' invalid for parameter `date'

But when I chang the command to:

sudo insmod hello.ko year=`date +%Y` month=`date +%m` date=9

It worked!

[ 4373.679843] Today is 2023/7/9.

Why date +%d can't work but the others work?

Answer 1

You should rewrite your command on this way to avoid leading zeros in date command:

sudo insmod hello.ko year=`date +%Y` month=`date +%-m` date=`date +%-d`

(the - tell date not to add leading zero)