Introduction to module_param char

The module_param char is a macro in the Linux kernel programming that allows a kernel module parameter to be defined as a character. This macro is part of the module parameter API, which enables passing arguments to kernel modules during module loading.

Usage

The module_param char macro can be used to define a character parameter that can be passed to a kernel module when it is loaded.

The syntax for module_param char is as follows:

module_param(name, type, permissions)

• name: The name of the parameter.
• type: The data type of the parameter (char for character).
• permissions: The permissions for the parameter (read/write permissions).

Example

Here's an example of how to use module_param char to define a character parameter in a kernel module:

#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/moduleparam.h>

MODULE_LICENSE("GPL");

static char* my_char_param = "default value";
module_param(my_char_param, char, S_IRUSR | S_IWUSR);

int init_module(void) {
    printk(KERN_INFO "My character parameter: %s\n", my_char_param);
    return 0;
}

void cleanup_module(void) {
    printk(KERN_INFO "Module unloaded\n");
}

In the example above, a character parameter named my_char_param is defined using module_param, with the default value set to "default value". The permission flags S_IRUSR and S_IWUSR are used to set read/write permissions for the parameter.

When the module is loaded, the init_module function is called, and the value of the character parameter is printed to the kernel log using printk. Similarly, when the module is unloaded, the cleanup_module function is called, and a message is printed to the kernel log.

Notes

• The module_param char macro should be used with caution as it can be a security risk if the parameter is not properly validated.
• There are other variations of the module_param macro, such as module_param_array, which can be used to define arrays of characters as module parameters.

For more information, refer to the Linux kernel documentation.

Please note that the code snippet may not be complete and may require additional code to properly function as a kernel module.