#include <linux/init.h>  
#include <linux/version.h>  
#include <linux/module.h>  
#include <linux/sched.h>  
#include <linux/uaccess.h>  
#include <linux/proc_fs.h>  
#include <linux/fs.h>  
#include <linux/seq_file.h>   

#include <asm/uaccess.h>  
 
#define STRING_LEN 1024  
 
char global_buffer[STRING_LEN] = {0};

static int my_proc_show(struct seq_file *seq, void *v)
{
    printk("my_proc_show called\n");
    seq_printf(seq, "current kernel time is %ld\n", jiffies);  
    seq_printf(seq, "global_buffer: %s", global_buffer);

    return 0;        
}

static int my_proc_open(struct inode *inode, struct file *file)
{
    return single_open(file, my_proc_show, inode->i_private);
} 

static ssize_t my_proc_write(struct file *file, const char __user *buffer, size_t count, loff_t *pos)
{
    if (count > 0) {
        printk("my_proc_write called\n");
        copy_from_user(global_buffer, buffer, count);  
    }

    return count;
} 

struct file_operations proc_fops =
{
    .open  = my_proc_open,
    .read  = seq_read,
    .write  = my_proc_write,
    .llseek  = seq_lseek,
    .release = single_release,
};

static struct proc_dir_entry *proc_dir = NULL;
static struct proc_dir_entry *proc_file = NULL; 

static int __init proc_test_init(void) 
{  
    proc_dir = proc_mkdir("my_proc", NULL);
    if (!proc_dir) {
         printk(KERN_DEBUG"proc_mkdir failed");
         return 0;
    }
    
    proc_file = proc_create("buffer", 0666, proc_dir, &proc_fops);
    if (!proc_file) {
         printk(KERN_DEBUG"proc_create failed");
         return 0;
    }

    strcpy(global_buffer, "hello"); 
    return 0;  
}  
 
static void __exit proc_test_exit(void) 
{  
    remove_proc_entry("buffer", proc_dir);  
    remove_proc_entry("my_proc", NULL);  
}  
 
module_init(proc_test_init);  
module_exit(proc_test_exit);
MODULE_AUTHOR("derek.yi");  
MODULE_LICENSE("GPL");  


/*
echo "Hello from kernel" > /proc/my_proc/buffer
cat /proc/my_proc/buffer
*/

derek@ubox:~/share/ldd5$ cat /proc/my_proc/buffer
current kernel time is 4295327951
global_buffer: hello
derek@ubox:~/share/ldd5$ echo "Hello from kernel" > /proc/my_proc/buffer
derek@ubox:~/share/ldd5$ cat /proc/my_proc/buffer                       
current kernel time is 4295330282
global_buffer: Hello from kernel