Linux操作系统内核和设备文件对话

ex chardev.c 

/* chardev.c 
* 
* Create an input/output character device 
*/ 

/* Copyright (C) 1998-99 by Ori Pomerantz */ 

/* The necessary header files */ 

/* Standard in kernel modules */ 
#include /* Were doing kernel work */ 
#include /* Specifically, a module */ 

/* Deal with CONFIG_MODVERSIONS */ 
#if CONFIG_MODVERSIONS==1 
#define MODVERSIONS 
#include 
#endif 

/* For character devices */ 

/* The character device definitions are here */ 
#include 

/* A wrapper which does next to nothing at 
* at present, but may help for compatibility 
* with future versions of Linux */ 
#include 

/* Our own ioctl numbers */ 
#include "chardev.h" 

/* In 2.2.3 /usr/include/linux/version.h includes a 
* macro for this, but 2.0.35 doesnt - so I add it 
* here if necessary. */ 
#ifndef KERNEL_VERSION 
#define KERNEL_VERSION(a,b,c) ((a)*65536+(b)*256+(c)) 
#endif 

#if LINUX_VERSION_CODE >= KERNEL_VERSION(2,2,0) 
#include /* for get_user and put_user */ 
#endif 

#define SUCCESS 0 

/* Device Declarations ******************************** */ 

/* The name for our device, as it will appear in 
* /proc/devices */ 
#define DEVICE_NAME "char_dev" 

/* The maximum length of the message for the device */ 
#define BUF_LEN 80 

/* Is the device open right now? Used to prevent 
* concurent access into the same device */ 
static int Device_Open = 0; 

/* The message the device will give when asked */ 
static char Message[BUF_LEN]; 

/* How far did the process reading the message get? 
* Useful if the message is larger than the size of the 
* buffer we get to fill in device_read. */ 
static char *Message_Ptr; 

/* This function is called whenever a process attempts 
* to open the device file */ 
static int device_open(struct inode *inode, 
struct file *file) 
{ 
#ifdef DEBUG 
printk ("device_open(%p)\n", file); 
#endif 

/* We dont want to talk to two processes at the 
* same time */ 
if (Device_Open) 
return -EBUSY; 

/* If this was a process, we would have had to be 
* more careful here, because one process might have 
* checked Device_Open right before the other one 
* tried to increment it. However, were in the 
* kernel, so were protected against context switches. 
* 
* This is NOT the right attitude to take, because we 
* might be running on an SMP box, but well deal with 
* SMP in a later chapter. 
*/ 

Device_Open++; 

/* Initialize the message */ 
Message_Ptr = Message; 

MOD_INC_USE_COUNT; 

return SUCCESS; 
} 

/* This function is called when a process closes the 
* device file. It doesnt have a return value because 
* it cannot fail. Regardless of what else happens, you 
* should always be able to close a device (in 2.0, a 2.2 
* device file could be impossible to close). */ 
#if LINUX_VERSION_CODE >= KERNEL_VERSION(2,2,0) 
static int device_release(struct inode *inode, 
struct file *file) 
#else 
static void device_release(struct inode *inode, 
struct file *file) 
#endif 
{ 
#ifdef DEBUG 
printk ("device_release(%p,%p)\n", inode, file); 
#endif 

/* Were now ready for our next caller */ 
Device_Open --; 

MOD_DEC_USE_COUNT; 

#if LINUX_VERSION_CODE >= KERNEL_VERSION(2,2,0) 
return 0; 
#endif 
}

/* This function is called whenever a process which 
* has already opened the device file attempts to 
* read from it. */ 
#if LINUX_VERSION_CODE >= KERNEL_VERSION(2,2,0) 
static ssize_t device_read( 
struct file *file, 
char *buffer, /* The buffer to fill with the data */ 
size_t length, /* The length of the buffer */ 
loff_t *offset) /* offset to the file */ 
#else 
static int device_read( 
struct inode *inode, 
struct file *file, 
char *buffer, /* The buffer to fill with the data */ 
int length) /* The length of the buffer 
* (mustnt write beyond that!) */ 
#endif 
{ 
/* Number of bytes actually written to the buffer */ 
int bytes_read = 0; 

#ifdef DEBUG 
printk("device_read(%p,%p,%d)\n", 
file, buffer, length); 
#endif 

/* If were at the end of the message, return 0 
* (which signifies end of file) */ 
if (*Message_Ptr == 0) 
return 0; 

/* Actually put the data into the buffer */ 
while (length && *Message_Ptr) { 

/* Because the buffer is in the user data segment, 
* not the kernel data segment, assignment wouldnt 
* work. Instead, we have to use put_user which 
* copies data from the kernel data segment to the 
* user data segment. */ 
put_user(*(Message_Ptr++), buffer++); 
length --; 
bytes_read ++; 
} 

#ifdef DEBUG 
printk ("Read %d bytes, %d left\n", 
bytes_read, length); 
#endif 

/* Read functions are supposed to return the number 
* of bytes actually inserted into the buffer */ 
return bytes_read; 
}

/* This function is called when somebody tries to 
* write into our device file. */ 
#if LINUX_VERSION_CODE >= KERNEL_VERSION(2,2,0) 
static ssize_t device_write(struct file *file, 
const char *buffer, 
size_t length, 
loff_t *offset) 
#else 
static int device_write(struct inode *inode, 
struct file *file, 
const char *buffer, 
int length) 
#endif 
{ 
int i; 

#ifdef DEBUG 
printk ("device_write(%p,%s,%d)", 
file, buffer, length); 
#endif 

for(i=0; i 
#if LINUX_VERSION_CODE >= KERNEL_VERSION(2,2,0) 
get_user(Message, buffer+i); 
#else 
Message = get_user(buffer+i); 
#endif 

Message_Ptr = Message; 

/* Again, return the number of input characters used */ 
return i; 
}

/* This function is called whenever a process tries to 
* do an ioctl on our device file. We get two extra 
* parameters (additional to the inode and file 
* structures, which all device functions get): the number 
* of the ioctl called and the parameter given to the 
* ioctl function. 
* 
* If the ioctl is write or read/write (meaning output 
* is returned to the calling process), the ioctl call 
* returns the output of this function. 
*/ 
int device_ioctl( 
struct inode *inode, 
struct file *file, 
unsigned int ioctl_num,/* The number of the ioctl */ 
unsigned long ioctl_param) /* The parameter to it */ 
{ 
int i; 
char *temp; 
#if LINUX_VERSION_CODE >= KERNEL_VERSION(2,2,0) 
char ch; 
#endif 

/* Switch according to the ioctl called */ 
switch (ioctl_num) { 
case IOCTL_SET_MSG: 
/* Receive a pointer to a message (in user space) 
* and set that to be the devices message. */ 

/* Get the parameter given to ioctl by the process */ 
temp = (char *) ioctl_param; 

/* Find the length of the message */ 
#if LINUX_VERSION_CODE >= KERNEL_VERSION(2,2,0) 
get_user(ch, temp); 
for (i=0; ch && ibr temp++) i++,> get_user(ch, temp); 
#else 
for (i=0; get_user(temp) && ibr temp++) i++,> ; 
#endif 

/* Dont reinvent the wheel - call device_write */ 
#if LINUX_VERSION_CODE >= KERNEL_VERSION(2,2,0) 
device_write(file, (char *) ioctl_param, i, 0); 
#else 
device_write(inode, file, (char *) ioctl_param, i); 
#endif 
break; 

case IOCTL_GET_MSG: 
/* Give the current message to the calling 
* process - the parameter we got is a pointer, 
* fill it. */ 
#if LINUX_VERSION_CODE >= KERNEL_VERSION(2,2,0) 
i = device_read(file, (char *) ioctl_param, 99, 0); 
#else 
i = device_read(inode, file, (char *) ioctl_param, 
99); 
#endif 
/* Warning - we assume here the buffer length is 
* 100. If its less than that we might overflow 
* the buffer, causing the process to core dump. 
* 
* The reason we only allow up to 99 characters is 
* that the NULL which terminates the string also 
* needs room. */ 

/* Put a zero at the end of the buffer, so it 
* will be properly terminated */ 
put_user(\, (char *) ioctl_param+i); 
break; 

case IOCTL_GET_NTH_BYTE: 
/* This ioctl is both input (ioctl_param) and 
* output (the return value of this function) */ 
return Message[ioctl_param]; 
break; 
} 

return SUCCESS; 
}

/* Module Declarations *************************** */ 
/* This structure will hold the functions to be called 
* when a process does something to the device we 
* created. Since a pointer to this structure is kept in 
* the devices table, it cant be local to 
* init_module. NULL is for unimplemented functions. */ 
struct file_operations Fops = { 
NULL, /* seek */ 
device_read, 
device_write, 
NULL, /* readdir */ 
NULL, /* select */ 
device_ioctl, /* ioctl */ 
NULL, /* mmap */ 
device_open, 
#if LINUX_VERSION_CODE >= KERNEL_VERSION(2,2,0) 
NULL, /* flush */ 
#endif 
device_release /* a.k.a. close */ 
}; 

/* Initialize the module - Register the character device */ 
int init_module() 
{ 
int ret_val; 

/* Register the character device (atleast try) */ 
ret_val = module_register_chrdev(MAJOR_NUM, 
DEVICE_NAME, 
&Fops); 

/* Negative values signify an error */ 
if (ret_val < 0) { 
printk ("%s failed with %d\n", 
"Sorry, registering the character device ", 
ret_val); 
return ret_val; 
} 

printk ("%s The major device number is %d.\n", 
"Registeration is a success", 
MAJOR_NUM); 
printk ("If you want to talk to the device driver,\n"); 
printk ("youll have to create a device file. \n"); 
printk ("We suggest you use:\n"); 
printk ("mknod %s c %d 0\n", DEVICE_FILE_NAME, 
MAJOR_NUM); 
printk ("The device file name is important, because\n"); 
printk ("the ioctl program assumes thats the\n"); 
printk ("file youll use.\n"); 

return 0; 
} 

/* Cleanup - unregister the appropriate file from /proc */ 
void cleanup_module() 
{ 
int ret; 

/* Unregister the device */ 
ret = module_unregister_chrdev(MAJOR_NUM, DEVICE_NAME); 

/* If theres an error, report it */ 
if (ret < 0) 
printk("Error in module_unregister_chrdev: %d\n", ret); 
} 
ex chardev.h 

/* chardev.h - the header file with the ioctl definitions. 
* 
* The declarations here have to be in a header file, 
* because they need to be known both to the kernel 
* module (in chardev.c) and the process calling ioctl 
* (ioctl.c) 
*/ 

#ifndef CHARDEV_H 
#define CHARDEV_H 

#include 

/* The major device number. We cant rely on dynamic 
* registration any more, because ioctls need to know 
* it. */ 
#define MAJOR_NUM 100 

/* Set the message of the device driver */ 
#define IOCTL_SET_MSG _IOR(MAJOR_NUM, 0, char *) 
/* _IOR means that were creating an ioctl command 
* number for passing information from a user process 
* to the kernel module. 
* 
* The first arguments, MAJOR_NUM, is the major device 
* number were using. 
* 
* The second argument is the number of the command 
* (there could be several with different meanings). 
* 
* The third argument is the type we want to get from 
* the process to the kernel. 
*/ 

/* Get the message of the device driver */ 
#define IOCTL_GET_MSG _IOR(MAJOR_NUM, 1, char *) 
/* This IOCTL is used for output, to get the message 
* of the device driver. However, we still need the 
* buffer to place the message in to be input, 
* as it is allocated by the process. 
*/ 

/* Get the nth byte of the message */ 
#define IOCTL_GET_NTH_BYTE _IOWR(MAJOR_NUM, 2, int) 
/* The IOCTL is used for both input and output. It 
* receives from the user a number, n, and returns 
* Message[n]. */ 

/* The name of the device file */ 
#define DEVICE_FILE_NAME "char_dev" 

#endif 

ex ioctl.c 

/* ioctl.c - the process to use ioctls to control the 
* kernel module 
* 
* Until now we could have used cat for input and 
* output. But now we need to do ioctls, which require 
* writing our own process. 
*/ 

/* Copyright (C) 1998 by Ori Pomerantz */ 

/* device specifics, such as ioctl numbers and the 
* major device file. */ 
#include "chardev.h" 

#include /* open */ 
#include /* exit */ 
#include /* ioctl */ 

/* Functions for the ioctl calls */ 

ioctl_set_msg(int file_desc, char *message) 
{ 
int ret_val; 

ret_val = ioctl(file_desc, IOCTL_SET_MSG, message); 

if (ret_val < 0) { 
printf ("ioctl_set_msg failed:%d\n", ret_val); 
exit(-1); 
} 
} 

ioctl_get_msg(int file_desc) 
{ 
int ret_val; 
char message[100]; 

/* Warning - this is dangerous because we dont tell 
* the kernel how far its allowed to write, so it 
* might overflow the buffer. In a real production 
* program, we would have used two ioctls - one to tell 
* the kernel the buffer length and another to give 
* it the buffer to fill 
*/ 
ret_val = ioctl(file_desc, IOCTL_GET_MSG, message); 

if (ret_val < 0) { 
printf ("ioctl_get_msg failed:%d\n", ret_val); 
exit(-1); 
} 

printf("get_msg message:%s\n", message); 
} 

ioctl_get_nth_byte(int file_desc) 
{ 
int i; 
char c; 

printf("get_nth_byte message:"); 

i = 0; 
while (c != 0) { 
c = ioctl(file_desc, IOCTL_GET_NTH_BYTE, i++); 

if (c < 0) { 
printf( 
"ioctl_get_nth_byte failed at the %dth byte:\n", i); 
exit(-1); 
} 

putchar(c); 
} 
putchar(\n); 
} 

/* Main - Call the ioctl functions */ 
main() 
{ 
int file_desc, ret_val; 
char *msg = "Message passed by ioctl\n"; 

file_desc = open(DEVICE_FILE_NAME, 0); 
if (file_desc < 0) { 
printf ("Cant open device file: %s\n", 
DEVICE_FILE_NAME); 
exit(-1); 
} 

ioctl_get_nth_byte(file_desc); 
ioctl_get_msg(file_desc); 
ioctl_set_msg(file_desc, msg); 

close(file_desc); 
}