How to read /write files within a Linux kernel module

Reading or writing files in Linux kernel modules is not a common operation because kernel modules are typically designed to manage hardware devices, file systems, networks, or other system resources rather than directly interacting with files. However, if it is necessary to operate on files within a kernel module, you can use functions provided by the kernel to achieve this.

Reading Files

1. Open the file: Use the filp_open() function to open the file. This function accepts the file path and flags (e.g., read-only or write-only), returning a pointer to a struct file for subsequent operations.

c
struct file *filp = filp_open("/path/to/file", O_RDONLY, 0);
if (IS_ERR(filp)) {
    printk(KERN_ERR "filp_open error %ld\n", PTR_ERR(filp));
    return;
}

1. Read data: Use the kernel_read() function to read data from the opened file. This function requires a file pointer, a buffer, the number of bytes to read, and an offset.

c
char buf[100];
loff_t pos = 0;
ssize_t bytes = kernel_read(filp, buf, sizeof(buf), &pos);

1. Close the file: Use the filp_close() function to close the file.

c
filp_close(filp, NULL);

Writing Files

1. Open the file: Use filp_open() with write-related flags such as O_WRONLY or O_APPEND.

2. Write data: Use the kernel_write() function to write data to the file.

c
ssize_t bytes_written = kernel_write(filp, buf, bytes_to_write, &pos);

1. Close the file: Use filp_close().

Important Considerations

• Exercise extreme caution when operating on files in kernel space, as incorrect operations can cause data corruption or system instability.
• This operation is generally not recommended for production kernel modules. Instead, handle file data in user-space applications and communicate with the kernel module via system calls or other mechanisms.
• Implement proper error handling and permission checks to prevent security vulnerabilities.

The above outlines the basic methods and steps for reading and writing files in Linux kernel modules. In actual development, prioritize system security and stability.