【linux驱动】简单字符设备驱动
1. 设备文件相关结构体和函数
一个 Linux 系统，默认最大的主设备号是 255，结构体如下
// include/linux/fs.h
#define CHRDEV_MAJOR_HASH_SIZE 255
// /fs/char_dev.c
static struct char_device_struct {
struct char_device_struct *next;
unsigned int major;
unsigned int baseminor;
int minorct;
char name[64];
struct cdev *cdev; /* will die */
} *chrdevs[CHRDEV_MAJOR_HASH_SIZE];
设备注册函数
// include/linux/fs.h
// 向内核注册了一个字符设备
static inline int register_chrdev(unsigned int major, const char *name,
const struct file_operations *fops)
{
return __register_chrdev(major, 0, 256, name, fops);
}
/**
* __register_chrdev() - create and register a cdev occupying a range of minors
* @major: major device number or 0 for dynamic allocation 主设备号或者为 0 就是动态分配
* @baseminor: first of the requested range of minor numbers 次设备号，register_chrdev 直接使用了 0
* @count: the number of minor numbers required
* @name: name of this range of devices 设备名字
* @fops: file operations associated with this devices 文件结构体（Linux 万物皆文件，靠的就是这个结构体）
*
* If @major == 0 this functions will dynamically allocate a major and return
* its number.
*
* If @major > 0 this function will attempt to reserve a device with the given
* major number and will return zero on success.
*
* Returns a -ve errno on failure.
*
* The name of this device has nothing to do with the name of the device in
* /dev. It only helps to keep track of the different owners of devices. If
* your module name has only one type of devices it's ok to use e.g. the name
* of the module here.
*/
int __register_chrdev(unsigned int major, unsigned int baseminor,
unsigned int count, const char *name,
const struct file_operations *fops)
{
struct char_device_struct *cd;
struct cdev *cdev;
int err = -ENOMEM;
cd = __register_chrdev_region(major, baseminor, count, name);
if (IS_ERR(cd))
return PTR_ERR(cd);
cdev = cdev_alloc();
if (!cdev)
goto out2;
cdev->owner = fops->owner;
cdev->ops = fops;
kobject_set_name(&cdev->kobj, "%s", name);
err = cdev_add(cdev, MKDEV(cd->major, baseminor), count);
if (err)
goto out;
cd->cdev = cdev;
return major ? 0 : cd->major;
out:
kobject_put(&cdev->kobj);
out2:
kfree(__unregister_chrdev_region(cd->major, baseminor, count));
return err;
}
3. 例子代码
chrdevbase.c
#include Makefile
obj-m += chrdevbase.o
#generate the path
CURRENT_PATH:=$(shell pwd)
#the current kernel version number
LINUX_KERNEL:=$(shell uname -r)
#the absolute path
LINUX_KERNEL_PATH:=/usr/src/linux-headers-$(LINUX_KERNEL)
#complie object
all:
make -C $(LINUX_KERNEL_PATH) M=$(CURRENT_PATH) modules
#clean
clean:
make -C $(LINUX_KERNEL_PATH) M=$(CURRENT_PATH) clean
- 编译：
make，生成*.ko文件，它就是内核模块。 - 插入内核模块：
insmod chrdevbase.ko - 查看内核模块是否成功：
dmesg | tail -n 20
[ 9.261691] rfkill: input handler disabled
[ 345.463456] kauditd_printk_skb: 32 callbacks suppressed
[ 345.463458] audit: type=1400 audit(1697963648.793:43): apparmor="STATUS" operation="profile_replace" info="same as current profile, skipping" profile="unconfined" name="/snap/core/16202/usr/lib/snapd/snap-confine" pid=2103 comm="apparmor_parser"
[ 345.463466] audit: type=1400 audit(1697963648.793:44): apparmor="STATUS" operation="profile_replace" info="same as current profile, skipping" profile="unconfined" name="/snap/core/16202/usr/lib/snapd/snap-confine//mount-namespace-capture-helper" pid=2103 comm="apparmor_parser"
[ 346.309668] audit: type=1400 audit(1697963649.640:45): apparmor="STATUS" operation="profile_replace" profile="unconfined" name="snap.gnome-system-monitor.hook.configure" pid=2107 comm="apparmor_parser"
[ 346.777464] audit: type=1400 audit(1697963650.108:46): apparmor="STATUS" operation="profile_replace" profile="unconfined" name="snap.gnome-system-monitor.gnome-system-monitor" pid=2106 comm="apparmor_parser"
[ 348.399012] audit: type=1400 audit(1697963651.727:47): apparmor="STATUS" operation="profile_replace" profile="unconfined" name="snap-update-ns.gnome-system-monitor" pid=2105 comm="apparmor_parser"
[ 348.403846] audit: type=1400 audit(1697963651.731:48): apparmor="STATUS" operation="profile_replace" info="same as current profile, skipping" profile="unconfined" name="snap-update-ns.core" pid=2109 comm="apparmor_parser"
[ 348.405261] audit: type=1400 audit(1697963651.735:49): apparmor="STATUS" operation="profile_replace" info="same as current profile, skipping" profile="unconfined" name="snap.core.hook.configure" pid=2110 comm="apparmor_parser"
[13529.015625] chrdevbase: loading out-of-tree module taints kernel.
[13529.015665] chrdevbase: module verification failed: signature and/or required key missing - tainting kernel
[13529.016265] chrdevbase driver register success
[13529.016266] chrdevbase_init()
- 查看设备列表：
cat /proc/devices
......
180 usb
189 usb_device
200 chrdevbase # 设备号 200 就是我们代码中的设备号
204 ttyMAX
216 rfcomm
226 drm
238 kfd
- 创建设备，跟设备号绑定：
mknod /dev/chrdevbase c 200 0
4. 测试
- 测试文件
test.c
#include "stdio.h"
#include "unistd.h"
#include "sys/types.h"
#include "sys/stat.h"
#include "fcntl.h"
#include "stdlib.h"
#include "string.h"
static char usrdata[] = {"usr data!"};
/**
* @brief main 函数
*
* @param argc
* @param argv
* @return int
*/
int main(int argc, char *argv[])
{
int fd, retvalue;
char *filename;
char readbuf[100], writebuf[100];
if (argc != 3)
{
printf("Error Usage!\r\n");
return -1;
}
filename = argv[1];
/* 打开驱动文件 */
fd = open(filename, O_RDWR);
if (fd < 0)
{
printf("Can't open file %s\r\n", filename);
return -1;
}
if (atoi(argv[2]) == 1)
{
/* 从驱动文件读取数据 */
retvalue = read(fd, readbuf, 50);
if (retvalue < 0)
{
printf("read file %s failed!\r\n", filename);
}
else
{
/* 读取成功，打印出读取成功的数据 */
printf("read data:%s\r\n", readbuf);
}
}
if (atoi(argv[2]) == 2)
{
/* 向设备驱动写数据 */
memcpy(writebuf, usrdata, sizeof(usrdata));
retvalue = write(fd, writebuf, 50);
if (retvalue < 0)
{
printf("write file %s failed!\r\n", filename);
}
}
/* 关闭设备 */
retvalue = close(fd);
if (retvalue < 0)
{
printf("Can't close file %s\r\n", filename);
return -1;
}
return 0;
}
- 编译：
gcc -o test test.c - 运行：
从设备文件读：./test /dev/chrdevbase 1， 往设备文件写：/test /dev/chrdevbase 2