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struct file_operations {
struct module *owner;
loff_t (*llseek) (struct file *, loff_t, int);
ssize_t (*read) (struct file *, char __user *, size_t, loff_t *);
ssize_t (*write) (struct file *, const char __user *, size_t, loff_t *);
ssize_t (*read_iter) (struct kiocb *, struct iov_iter *);
ssize_t (*write_iter) (struct kiocb *, struct iov_iter *);
int (*iterate) (struct file *, struct dir_context *);
int (*iterate_shared) (struct file *, struct dir_context *);
__poll_t (*poll) (struct file *, struct poll_table_struct *);
long (*unlocked_ioctl) (struct file *, unsigned int, unsigned long);
long (*compat_ioctl) (struct file *, unsigned int, unsigned long);
int (*mmap) (struct file *, struct vm_area_struct *);
unsigned long mmap_supported_flags;
int (*open) (struct inode *, struct file *);
int (*flush) (struct file *, fl_owner_t id);
int (*release) (struct inode *, struct file *);
int (*fsync) (struct file *, loff_t, loff_t, int datasync);
int (*fasync) (int, struct file *, int);
int (*lock) (struct file *, int, struct file_lock *);
ssize_t (*sendpage) (struct file *, struct page *, int, size_t, loff_t *, int);
unsigned long (*get_unmapped_area)(struct file *, unsigned long, unsigned long, unsigned long, unsigned long);
int (*check_flags)(int);
int (*setfl)(struct file *, unsigned long);
int (*flock) (struct file *, int, struct file_lock *);
ssize_t (*splice_write)(struct pipe_inode_info *, struct file *, loff_t *, size_t, unsigned int);
ssize_t (*splice_read)(struct file *, loff_t *, struct pipe_inode_info *, size_t, unsigned int);
int (*setlease)(struct file *, long, struct file_lock **, void **);
long (*fallocate)(struct file *file, int mode, loff_t offset,loff_t len);
void (*show_fdinfo)(struct seq_file *m, struct file *f);
#ifndef CONFIG_MMU
unsigned (*mmap_capabilities)(struct file *);
#endif
ssize_t (*copy_file_range)(struct file *, loff_t, struct file *, loff_t, size_t, unsigned int);
int (*clone_file_range)(struct file *, loff_t, struct file *, loff_t, u64);
ssize_t (*dedupe_file_range)(struct file *, u64, u64, struct file *, u64);
} __randomize_layout; |
작성한 함수의 명은 "struct file_operations" 형태로 선언된 구조체의 ".open" 필드에 함수의 주소(chardev_open)를 저장합니다.
static int chardev_open(struct inode *inode, struct file *file)
{
printk("chardev_open");
return 0;
}
struct file_operations chardev_fops = {
.open = chardev_open,
}; |
lazenca0x0@ubuntu:~$ uname -a Linux ubuntu 4.18.0-11-generic #12-Ubuntu SMP Tue Oct 23 19:22:37 UTC 2018 x86_64 x86_64 x86_64 GNU/Linux lazenca0x0@ubuntu:~$ gcc --version gcc (Ubuntu 8.2.0-7ubuntu1) 8.2.0 Copyright (C) 2018 Free Software Foundation, Inc. This is free software; see the source for copying conditions. There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. lazenca0x0@ubuntu:~$ |
User space에서 디바이스가 open할때 chardev_open()함수가 호출됩니다.
#include <linux/init.h>
#include <linux/module.h>
#include <linux/types.h>
#include <linux/kernel.h>
#include <linux/fs.h>
#include <linux/cdev.h>
#include <linux/sched.h>
#include <linux/device.h>
#include <linux/slab.h>
#include <asm/current.h>
#include <linux/uaccess.h>
#define DEVICE_NAME "chardev"
#define DEVICE_FILE_NAME "chardev"
#define MAJOR_NUM 100
static int chardev_open(struct inode *inode, struct file *file)
{
printk("chardev_open");
return 0;
}
struct file_operations chardev_fops = {
.open = chardev_open,
};
static int chardev_init(void)
{
int ret_val;
ret_val = register_chrdev(MAJOR_NUM, DEVICE_NAME, &chardev_fops);
if (ret_val < 0) {
printk(KERN_ALERT "%s failed with %d\n",
"Sorry, registering the character device ", ret_val);
return ret_val;
}
printk(KERN_INFO "%s The major device number is %d.\n",
"Registeration is a success", MAJOR_NUM);
printk(KERN_INFO "If you want to talk to the device driver,\n");
printk(KERN_INFO "you'll have to create a device file. \n");
printk(KERN_INFO "We suggest you use:\n");
printk(KERN_INFO "mknod %s c %d 0\n", DEVICE_FILE_NAME, MAJOR_NUM);
printk(KERN_INFO "The device file name is important, because\n");
printk(KERN_INFO "the ioctl program assumes that's the\n");
printk(KERN_INFO "file you'll use.\n");
return 0;
}
static void chardev_exit(void)
{
unregister_chrdev(MAJOR_NUM, DEVICE_NAME);
}
module_init(chardev_init);
module_exit(chardev_exit); |
obj-m := chardev.o all: make -C /lib/modules/$(shell uname -r)/build M=$(shell pwd) modules clean: make -C /lib/modules/$(shell uname -r)/build M=$(shell pwd) clean |
lazenca0x0@ubuntu:~/Kernel/Module/chardev$ make make -C /lib/modules/4.18.0-11-generic/build M=/home/lazenca0x0/Kernel/Module/chardev modules make[1]: Entering directory '/usr/src/linux-headers-4.18.0-11-generic' Makefile:982: "Cannot use CONFIG_STACK_VALIDATION=y, please install libelf-dev, libelf-devel or elfutils-libelf-devel" CC [M] /home/lazenca0x0/Kernel/Module/chardev/chardev.o Building modules, stage 2. MODPOST 1 modules WARNING: modpost: missing MODULE_LICENSE() in /home/lazenca0x0/Kernel/Module/chardev/chardev.o see include/linux/module.h for more information CC /home/lazenca0x0/Kernel/Module/chardev/chardev.mod.o LD [M] /home/lazenca0x0/Kernel/Module/chardev/chardev.ko make[1]: Leaving directory '/usr/src/linux-headers-4.18.0-11-generic' |
lazenca0x0@ubuntu:~/Kernel/Module/chardev$ sudo insmod chardev.ko lazenca0x0@ubuntu:~/Kernel/Module/chardev$ dmesg |tail [14735.412269] chardev_open [14886.237136] chardev_open [15136.839556] Registeration is a success The major device number is 100. [15136.839557] If you want to talk to the device driver, [15136.839558] you'll have to create a device file. [15136.839582] We suggest you use: [15136.839583] mknod chardev c 100 0 [15136.839583] The device file name is important, because [15136.839584] the ioctl program assumes that's the [15136.839584] file you'll use. lazenca0x0@ubuntu:~/Kernel/Module/chardev$ sudo mknod chardev c 100 0 lazenca0x0@ubuntu:~/Kernel/Module/chardev$ sudo chmod 666 chardev lazenca0x0@ubuntu:~/Kernel/Module/chardev$ echo 'A' > chardev -bash: echo: write error: Invalid argument lazenca0x0@ubuntu:~/Kernel/Module/chardev$ dmesg |tail [14886.237136] chardev_open [15136.839556] Registeration is a success The major device number is 100. [15136.839557] If you want to talk to the device driver, [15136.839558] you'll have to create a device file. [15136.839582] We suggest you use: [15136.839583] mknod chardev c 100 0 [15136.839583] The device file name is important, because [15136.839584] the ioctl program assumes that's the [15136.839584] file you'll use. [15231.493826] chardev_open lazenca0x0@ubuntu:~/Kernel/Module/chardev$ |
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해당 모듈이 커널에 등록될 때 chardev_init() 함수에서 다음 기능을 처리합니다.
class_destroy() 함수를 이용하여 class_create() 함수에 의해 생성된 디바이스 클래스를 소멸시킵니다.
unregister_chrdev_region() 함수를 이용하여 alloc_chrdev_region() 함수에 의해 등록된 장치 번호를 반환합니다.
copy_from_user() 함수를 이용하여 사용자 공간으로 부터 전달 받은 데이터(buf)를 "p→buffer" 변수에 복사합니다.
#include <linux/init.h>
#include <linux/module.h>
#include <linux/types.h>
#include <linux/kernel.h>
#include <linux/fs.h>
#include <linux/cdev.h>
#include <linux/sched.h>
#include <linux/device.h>
#include <linux/slab.h>
#include <asm/current.h>
#include <linux/uaccess.h>
MODULE_LICENSE("Dual BSD/GPL");
#define DRIVER_NAME "chardev"
#define BUFFER_SIZE 256
static const unsigned int MINOR_BASE = 0;
static const unsigned int MINOR_NUM = 2;
static unsigned int chardev_major;
static struct cdev chardev_cdev;
static struct class *chardev_class = NULL;
static int chardev_open(struct inode *, struct file *);
static int chardev_release(struct inode *, struct file *);
static ssize_t chardev_read(struct file *, char *, size_t, loff_t *);
static ssize_t chardev_write(struct file *, const char *, size_t, loff_t *);
struct file_operations chardev_fops = {
.open = chardev_open,
.release = chardev_release,
.read = chardev_read,
.write = chardev_write,
};
struct data {
unsigned char buffer[BUFFER_SIZE];
};
static int chardev_init(void)
{
int alloc_ret = 0;
int cdev_err = 0;
int minor;
dev_t dev;
printk("The chardev_init() function has been called.");
alloc_ret = alloc_chrdev_region(&dev, MINOR_BASE, MINOR_NUM, DRIVER_NAME);
if (alloc_ret != 0) {
printk(KERN_ERR "alloc_chrdev_region = %d\n", alloc_ret);
return -1;
}
//Get the major number value in dev.
chardev_major = MAJOR(dev);
dev = MKDEV(chardev_major, MINOR_BASE);
//initialize a cdev structure
cdev_init(&chardev_cdev, &chardev_fops);
chardev_cdev.owner = THIS_MODULE;
//add a char device to the system
cdev_err = cdev_add(&chardev_cdev, dev, MINOR_NUM);
if (cdev_err != 0) {
printk(KERN_ERR "cdev_add = %d\n", alloc_ret);
unregister_chrdev_region(dev, MINOR_NUM);
return -1;
}
chardev_class = class_create(THIS_MODULE, "chardev");
if (IS_ERR(chardev_class)) {
printk(KERN_ERR "class_create\n");
cdev_del(&chardev_cdev);
unregister_chrdev_region(dev, MINOR_NUM);
return -1;
}
for (minor = MINOR_BASE; minor < MINOR_BASE + MINOR_NUM; minor++) {
device_create(chardev_class, NULL, MKDEV(chardev_major, minor), NULL, "chardev%d", minor);
}
return 0;
}
static void chardev_exit(void)
{
int minor;
dev_t dev = MKDEV(chardev_major, MINOR_BASE);
printk("The chardev_exit() function has been called.");
for (minor = MINOR_BASE; minor < MINOR_BASE + MINOR_NUM; minor++) {
device_destroy(chardev_class, MKDEV(chardev_major, minor));
}
class_destroy(chardev_class);
cdev_del(&chardev_cdev);
unregister_chrdev_region(dev, MINOR_NUM);
}
static int chardev_open(struct inode *inode, struct file *file)
{
char *str = "helloworld";
int ret;
struct data *p = kmalloc(sizeof(struct data), GFP_KERNEL);
printk("The chardev_open() function has been called.");
if (p == NULL) {
printk(KERN_ERR "kmalloc - Null");
return -ENOMEM;
}
ret = strlcpy(p->buffer, str, sizeof(p->buffer));
if(ret > strlen(str)){
printk(KERN_ERR "strlcpy - too long (%d)",ret);
}
file->private_data = p;
return 0;
}
static int chardev_release(struct inode *inode, struct file *file)
{
printk("The chardev_release() function has been called.");
if (file->private_data) {
kfree(file->private_data);
file->private_data = NULL;
}
return 0;
}
static ssize_t chardev_write(struct file *filp, const char __user *buf, size_t count, loff_t *f_pos)
{
struct data *p = filp->private_data;
printk("The chardev_write() function has been called.");
printk("Before calling the copy_from_user() function : %p, %s",p->buffer,p->buffer);
if (copy_from_user(p->buffer, buf, count) != 0) {
return -EFAULT;
}
printk("After calling the copy_from_user() function : %p, %s",p->buffer,p->buffer);
return count;
}
static ssize_t chardev_read(struct file *filp, char __user *buf, size_t count, loff_t *f_pos)
{
struct data *p = filp->private_data;
printk("The chardev_read() function has been called.");
if(count > BUFFER_SIZE){
count = BUFFER_SIZE;
}
if (copy_to_user(buf, p->buffer, count) != 0) {
return -EFAULT;
}
return count;
}
module_init(chardev_init);
module_exit(chardev_exit); |
obj-m := chardev.o all: make -C /lib/modules/$(shell uname -r)/build M=$(shell pwd) modules clean: make -C /lib/modules/$(shell uname -r)/build M=$(shell pwd) clean |
#include <stdio.h>
#include <stdlib.h>
#include <fcntl.h>
#include <unistd.h>
#include <errno.h>
#define TEXT_LEN 12
int main()
{
static char buff[256];
int fd;
if ((fd = open("/dev/chardev0", O_RDWR)) < 0){
printf("Cannot open /dev/chardev0. Try again later.\n");
}
if (write(fd, "lazenca0x0", TEXT_LEN) < 0){
printf("Cannot write there.\n");
}
if (read(fd, buff, TEXT_LEN) < 0){
printf("An error occurred in the read.\n");
}else{
printf("%s\n", buff);
}
if (close(fd) != 0){
printf("Cannot close.\n");
}
return 0;
} |
lazenca0x0@ubuntu:~/Kernel/Module/WR$ make make -C /lib/modules/4.18.0-11-generic/build M=/home/lazenca0x0/Kernel/Module/WR modules make[1]: Entering directory '/usr/src/linux-headers-4.18.0-11-generic' Makefile:982: "Cannot use CONFIG_STACK_VALIDATION=y, please install libelf-dev, libelf-devel or elfutils-libelf-devel" CC [M] /home/lazenca0x0/Kernel/Module/WR/chardev.o Building modules, stage 2. MODPOST 1 modules CC /home/lazenca0x0/Kernel/Module/WR/chardev.mod.o LD [M] /home/lazenca0x0/Kernel/Module/WR/chardev.ko make[1]: Leaving directory '/usr/src/linux-headers-4.18.0-11-generic' lazenca0x0@ubuntu:~/Kernel/Module/WR$ |
lazenca0x0@ubuntu:~/Kernel/Module/WR$ echo 'KERNEL == "chardev[0-9]*",GROUP="root",MODE="0666"' >> /etc/udev/rules.d/80-chardev.rules lazenca0x0@ubuntu:~/Kernel/Module/WR$ sudo insmod chardev.ko [sudo] password for lazenca0x0: lazenca0x0@ubuntu:~/Kernel/Module/WR$ ls -al /dev/chardev* crw-rw-rw- 1 root root 240, 0 Nov 27 22:39 /dev/chardev0 crw-rw-rw- 1 root root 240, 1 Nov 27 22:39 /dev/chardev1 lazenca0x0@ubuntu:~/Kernel/Module/WR$ |
lazenca0x0@ubuntu:~/Kernel/Module/WR$ gcc -o test test.c lazenca0x0@ubuntu:~/Kernel/Module/WR$ ./test lazenca0x0 lazenca0x0@ubuntu:~/Kernel/Module/WR$ dmesg |tail [ 10.899284] random: 7 urandom warning(s) missed due to ratelimiting [ 11.942688] [drm:vmw_stdu_crtc_page_flip [vmwgfx]] *ERROR* Page flip error -16. [ 130.546522] chardev: loading out-of-tree module taints kernel. [ 130.546570] chardev: module verification failed: signature and/or required key missing - tainting kernel [ 130.547051] The chardev_init() function has been called. [ 133.948317] The chardev_open() function has been called. [ 133.948320] The chardev_write() function has been called. [ 133.948322] Before calling the copy_from_user() function : 0000000012f53a81, helloworld [ 133.948323] After calling the copy_from_user() function : 0000000012f53a81, lazenca0x0 [ 133.948324] The chardev_read() function has been called. lazenca0x0@ubuntu:~/Kernel/Module/WR$ |
#include <stdio.h>
#include <stdlib.h>
#include <fcntl.h>
#include <unistd.h>
#include <errno.h>
int main()
{
static char buff[256];
int fd0_A, fd0_B, fd1_A;
if ((fd0_A = open("/dev/mydevice0", O_RDWR)) < 0) perror("open");
if ((fd0_B = open("/dev/mydevice0", O_RDWR)) < 0) perror("open");
if ((fd1_A = open("/dev/mydevice1", O_RDWR)) < 0) perror("open");
if (write(fd0_A, "0_A", 4) < 0) perror("write");
if (write(fd0_B, "0_B", 4) < 0) perror("write");
if (write(fd1_A, "1_A", 4) < 0) perror("write");
if (read(fd0_A, buff, 4) < 0) perror("read");
printf("%s\n", buff);
if (read(fd0_B, buff, 4) < 0) perror("read");
printf("%s\n", buff);
if (read(fd1_A, buff, 4) < 0) perror("read");
printf("%s\n", buff);
if (close(fd0_A) != 0) perror("close");
if (close(fd0_B) != 0) perror("close");
if (close(fd1_A) != 0) perror("close");
return 0;
} |
lazenca0x0@ubuntu:~/Kernel/Module/WR$ ./test1 0_A 0_B 1_A lazenca0x0@ubuntu:~/Kernel/Module/WR$ [ 1837.876449] The chardev_open() function has been called. [ 1837.876452] The chardev_open() function has been called. [ 1837.876484] The chardev_open() function has been called. [ 1837.876486] The chardev_write() function has been called. [ 1837.876488] Before calling the copy_from_user() function : 000000000affca99, helloworld [ 1837.876489] After calling the copy_from_user() function : 000000000affca99, 0_A [ 1837.876489] The chardev_write() function has been called. [ 1837.876490] Before calling the copy_from_user() function : 00000000d881b9fa, helloworld [ 1837.876491] After calling the copy_from_user() function : 00000000d881b9fa, 0_B [ 1837.876491] The chardev_write() function has been called. [ 1837.876492] Before calling the copy_from_user() function : 00000000ecd9f924, helloworld [ 1837.876492] After calling the copy_from_user() function : 00000000ecd9f924, 1_A [ 1837.876493] The chardev_read() function has been called. [ 1837.876559] The chardev_read() function has been called. [ 1837.876561] The chardev_read() function has been called. [ 1837.876563] The chardev_release() function has been called. [ 1837.876564] The chardev_release() function has been called. lazenca0x0@ubuntu:~/Kernel/Module/WR$ |