CODEWITHSUNDEEP
clinux-kernel
Sathya
Sathya

Reputation: 67

I don't see /sys/module/mymodule/parameters folder getting created after I insert mymodule

I have created a simple kernel module named mymodule.c. After I insert it:

insmod mymodule.ko param_int=0x100

it gets loaded and it prints the correct value in logs. I can also see the folder /sys/module/mymodule/ getting created. But I don't see the parameters folder getting created inside /sys/module/mymodule/

What am I doing wrong?

#include <linux/module.h>
#include <linux/init.h>
static int param_int = 0xBABE;

module_param(param_int, int, 0);
MODULE_PARM_DESC(param_int, "Pass any integer from insmod, it will be printed");

static int __init ch03_lab1_init(void)
{
    pr_info("Chapter 03 Lab1\n");
    pr_info("param_int = 0x%x\n",param_int);
    return 0;
}

static void __exit ch03_lab1_exit(void)
{
    pr_info("Chapter 03 Lab1 Exit\n");
}

module_init(ch03_lab1_init);
module_exit(ch03_lab1_exit);

MODULE_AUTHOR("SATHYA");
MODULE_LICENSE("GPL");
MODULE_DESCRIPTION("WLDD Chapter3 Lab 1 example");
MODULE_VERSION("2.0");

Upvotes: 2

Views: 719

Answers (2)

Jeremy Kerr
Jeremy Kerr

Reputation: 1935

Here's your problem:

module_param(param_int, int, 0);

The last argument to that module_param macro is the permissions for the variable in sysfs. Since you've specified zero there, the parameter isn't exported.

Change this to something like:

module_param(param_int, int, S_IRUGO | S_IWUSR);

And you should have it appear as expected.

Upvotes: 4

Claudio
Claudio

Reputation: 10947

Entries in sys/ must be created explicitly in the module code:

static DEVICE_ATTR(<name>, 0644, show_data, store_data);
static ssize_t store_data (struct device *dev, \
                       struct device_attribute *attr, \
                       const char *buf, size_t len)
{
        struct platform_device *pdev = to_platform_device(dev);
        unsigned int value = simple_strtoul (buf, NULL, 10);
        /* ... */
        return strnlen(buf, PAGE_SIZE);
}

static ssize_t show_data (struct device *dev, \
                      struct device_attribute *attr, \
                      char *buf)
{
        struct platform_device *pdev = to_platform_device(dev);
        unsigned int value = ...;
        return snprintf(buf, PAGE_SIZE, "%u\n", value);
}

Upvotes: 0

Related Questions