Device Driver 관련 예제를 분석중입니다

간단하게 가상 메모리를 동적으로 할당하고
거기에 읽고 쓰는 메모리 Device Driver를 분석하고 있습니다.
간단히 쏘스는 아래와 같습니다.

#include <linux/kernel.h>
#include <linux/module.h>

#include <linux/fs.h>
#include <linux/kdev_t.h>
#include <asm/uaccess.h>

#define DEVICE_NAME "minibuf"
#define BUFFER_LEN 1024

// Global variables
static int s_nMajor = 0;
static int s_bDeviceOpen = 0;
static char s_strBuf[BUFFER_LEN];
static int s_nBufPos = 0, s_nBufEnd = 0;

// Function Prototypes
static int device_open(struct inode *inode, struct file *flip);
static int device_release(struct inode *inode, struct file *flip);
static ssize_t device_read(struct file *flip, char *buffer, size_t length,loff_t *offset);
static ssize_t device_write(struct file *flip, char *buffer, size_t length, loff_t *offset);
static int is_buffer_empty(void);
static int is_buffer_full(void);
static int read_buffer_char(char *buffer);
static int write_buffer_char(char *buffer);

static struct file_operations device_fops =
{
	read:device_read,     /* read */
	write:device_write,    /* write */
	open:device_open,     /* open */
	release:device_release   /* release */
};

int init_module()
{
	printk("RAM Buffer Module loading...\n");
	if( ( s_nMajor = register_chrdev(0, DEVICE_NAME, &device_fops) )<0 )
	{
		printk(DEVICE_NAME" : Device Registration Failed ~! (%d) \n",s_nMajor);
		return s_nMajor;
	}
	printk(DEVICE_NAME" : Device Registration with Major Number = %d\n",s_nMajor);
	strcpy(s_strBuf,"안녕하세요 세상들이셔~!\n");
	s_nBufEnd = strlen(s_strBuf) + 1;
	return 0;
}

void cleanup_module(void)
{
	int nRetCode;
	printk("Unloading RAM Buffer Module\n");
	if( (nRetCode = unregister_chrdev(s_nMajor, DEVICE_NAME))<0 )
	{
		printk(DEVICE_NAME" : Device unregisteration failed (%d)\n",nRetCode);
	}
}

int device_open(struct inode *inode, struct file *flip)
{
	printk(DEVICE_NAME" : Device open (%d, %d)\n",MAJOR(inode->i_rdev), MINOR(inode->i_rdev) );
	if(s_bDeviceOpen)
	{
		printk(DEVICE_NAME" : Device already open\n");
		return -EBUSY;
	}
	++s_bDeviceOpen;
	MOD_INC_USE_COUNT;
	return 0;
}

int device_release(struct inode *inode, struct file *flip)
{
	printk(DEVICE_NAME" : Device Release (%d, %d)\n",MAJOR(inode->i_rdev), MINOR(inode->i_rdev) );
	if(!s_bDeviceOpen)
	{
		printk(DEVICE_NAME" : Device has not opened\n");
		return -EINVAL;
	}
	--s_bDeviceOpen;
	MOD_DEC_USE_COUNT;
	return 0;									
}

ssize_t device_read(struct file *filp, char *buffer, size_t length, loff_t *offset)
{
	int count = 0;
	if (is_buffer_empty()) {
		printk(DEVICE_NAME " : Read return EOF\n");
		return 0;
	} // end if
	while (!is_buffer_empty() && length > 1) {
		read_buffer_char(buffer);
		++buffer;
		--length;
		++count;
	} // end while
	put_user(0, buffer);
	++count;
	printk(DEVICE_NAME " : read %d bytes\n", count);
	return count;
} // end func

ssize_t device_write(struct file *filp, char *buffer, size_t length, loff_t *offset)
{
	return -ENOSYS;
} // end func

// Buffer Management
int is_buffer_empty() {
	return (s_nBufPos == s_nBufEnd) ? 1 : 0;
} // end func

int is_buffer_full() {
	int pos = s_nBufEnd + 1;
	if (pos == BUFFER_LEN) pos = 0;
	return (pos == s_nBufPos) ? 1 : 0;
} // end func

int read_buffer_char(char *buffer) {
	if (is_buffer_empty()) return -1;
	put_user(s_strBuf[s_nBufPos], buffer);
	if (++s_nBufPos == BUFFER_LEN) s_nBufPos = 0;
	return 0;
} // end func

int write_buffer_char(char *buffer) {
	if (is_buffer_full()) return -1;
	get_user(s_strBuf[s_nBufEnd], buffer);
	if (++s_nBufEnd == BUFFER_LEN) s_nBufEnd = 0;
	return 0;
} // end func

다름이 아니라 여기에 나온 put_user와 get_user부분에 관련된
manual을 알고 싶은데 man put_user로 해서도 찾을 수 없었습니다.
관련된 부분을 어떻게 찾을 수 있을지요?

그리고 아마 여기서 가장 중요한
함수인듯한데, 간단히라도 좋으니 put_user와
get_user의 기능을 알려주신다면 감사하겠습니다.