function::kernel_string_n - Linux

Overview

kernel_string_n is a function used in Linux kernel programming to retrieve a string from the kernel’s memory. It is primarily used for accessing string data stored in various kernel structures.

Syntax

char *kernel_string_n(const void *ptr, int n);

| Argument | Description |
|—|—|
| ptr | Pointer to the kernel memory location |
| n | Maximum number of characters to copy |

Options/Flags

None

Examples

Simple usage: Retrieve a string from the kernel memory at 0x12345678:

char *str = kernel_string_n((void *)0x12345678, 100);

Example from kernel source: This example retrieves the name of the current kernel module:

char *modname = kernel_string_n(module->name, strlen(module->name));

Common Issues

  • NULL pointer: Make sure the provided pointer points to a valid memory location in the kernel. Otherwise, the function will return NULL.
  • Invalid n value: The n argument should be a positive integer representing the maximum number of characters to copy. A non-positive value will result in undefined behavior.

Integration

kernel_string_n is commonly used with other functions that provide pointers to kernel memory, such as get_user(), copy_from_user(), and vmalloc_to_phys().

Related Commands

  • kmalloc(): Allocates memory in the kernel.
  • kfree(): Frees memory allocated by kmalloc().
  • phys_to_virt(): Converts a physical address to a virtual address.