Hi,

i am trying experimentally to program a kernel module that checks a file on the system, namely in /etc.

If I compile the module dynamically, the code works. But if I compile it statically it doesn't work, it doesn't find the file in /etc

the code goes something like this:

#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/init.h>
#include <linux/fs.h>
#include <linux/uaccess.h>

MODULE_AUTHOR("my name");
MODULE_DESCRIPTION("file check");
MODULE_LICENSE("GPL");

static int isRegistered(void) {
    struct file *file;
    char buffer[16];
    int registered = 0;

    // Apre il file di configurazione
    file = filp_open("/etc/testfile", O_RDONLY, 0);
    if (IS_ERR(file)) {
        // open error
        return registered;
    }

    // Reads the contents of the file
    if (file->f_op->read(file, buffer, sizeof(buffer), &file->f_pos) > 0) {
        if (strncmp(buffer, "registered", 10) == 0) {
            registered = 1;
        }
    }

    // Closes the file
    filp_close(file, NULL);

    return registered;
}

int check_registration(void) {
    if (!isRegistered()) {
        printk(KERN_ALERT "Not check.\n");
        return -1;
    }

    printk(KERN_INFO "check.\n");
    return 0;
}
EXPORT_SYMBOL_GPL(check_registration);

static int __init registration_check_init(void) {
    /* Does not execute control logic here */
    return 0;
}

static void __exit registration_check_exit(void) {
    printk(KERN_INFO "Registration control form terminated.\n");
}

module_init(registration_check_init);
module_exit(registration_check_exit);

/* Performs control logic */
late_initcall(check_registration);