Kernel Pt.6 - FCM#93

#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/fs.h>
#include <linux/init.h>
#include <linux/proc_fs.h>
#include <linux/seq_file.h>
#include "internal.h"       // contains struct proc_dir_entry
#include <asm/uaccess.h>    // contains copy_from_user
#include <linux/utsname.h>

static struct proc_dir_entry *hostname_entry = NULL;
#define MAX_BUFFER_SIZE 100

static ssize_t hostname_proc_write(struct file *file, const char __user *user_data, size_t len, loff_t *offset)
{
    int buffer_size = 0;
    int i;
    char buffer[MAX_BUFFER_SIZE];
    printk(KERN_INFO "hostname_proc_write, len=%ld\n", len);
    buffer_size = len > MAX_BUFFER_SIZE ? MAX_BUFFER_SIZE : len;
    i = 0;
    buffer[0] = '\0';
    while ((i < buffer_size) && (user_data[i] > ' ')) {
        buffer[i] = user_data[i];
        i++;
    }
    buffer[i] = '\0';
    buffer_size = i+1;

    printk(KERN_INFO "wrote %d bytes\n", buffer_size);
    printk(KERN_INFO "hostname=%s\n", buffer);

    if (buffer_size <= __NEW_UTS_LEN)
        for (i = 0; i < buffer_size; i++)
            utsname()->nodename[i] = buffer[i];

    return len;
}

static int hostname_proc_show(struct seq_file *m, void *v)
{
    seq_printf(m, "system hostname is currently: %s\n", utsname()->nodename);
    seq_printf(m, "write new name to this file to change hostname\n\n");
    return 0;
}

static int hostname_proc_open(struct inode *inode, struct file *file)
{
    return single_open(file, hostname_proc_show, NULL);
}

static int hostname_proc_permission(struct inode *inode, int op)
{
    // allow access to everybody, for read (4) and write(2),
    // but not execute (1)
    return ((op == 4) || (op == 2));
}

static const struct inode_operations hostname_proc_iops = {
    .permission = hostname_proc_permission,
};

static const struct file_operations hostname_proc_fops = {
    .open       = hostname_proc_open,
    .read       = seq_read,
    .write      = hostname_proc_write,
    .llseek     = seq_lseek,
    .release    = single_release,
};

static int __init hostname_proc_init(void)
{
    printk(KERN_INFO "hostname loading\n");
    hostname_entry = proc_create("hostname", 0666, NULL, &hostname_proc_fops);

    if (hostname_entry == NULL)
        printk(KERN_INFO "hostname could not create /proc entry\n");
    else {
        hostname_entry->proc_iops = &hostname_proc_iops;
        printk(KERN_INFO "hostname /proc entry created\n");
    }

    return 0;
}

static void __exit hostname_proc_exit(void)
{
    printk(KERN_INFO "hostname unloading\n");

    if (hostname_entry == NULL)
        printk(KERN_INFO "hostname /proc entry does not exist, not removing\n");
    else {
        proc_remove(hostname_entry);
        printk(KERN_INFO "hostname /proc entry removed\n");
    }
}

module_init(hostname_iproc_nit);
module_exit(hostname_proc_exit);

MODULE_AUTHOR("Alan Ward");
MODULE_LICENSE("GPL v2");
MODULE_DESCRIPTION("hostname module for Full Circle Magazine");