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【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];- 1
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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); }- 1
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/** * __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; }- 1
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3. 例子代码
chrdevbase.c
#include#include #include #include #include #include #define CHRDEVBASE_MAJOR 200 /* 主设备号 */ #define CHRDEVBASE_NAME "chrdevbase" /* 设备名 */ static char readbuf[100]; /* 读缓冲区 */ static char writebuf[100]; /* 写缓冲区 */ static char kerneldata[] = {"kernel data!"}; /* * @description : 打开设备 * @param – inode : 传递给驱动的 inode * @param - filp : 设备文件，file 结构体有个叫做 private_data 的成员变量 * 一般在 open 的时候将 private_data 指向设备结构体。 * @return : 0 成功;其他 失败 */ static int chrdevbase_open(struct inode *inode, struct file *filp) { // printk("chrdevbase open!\r\n"); return 0; } /* * @description : 从设备读取数据 * @param - filp : 要打开的设备文件(文件描述符) * @param - buf : 返回给用户空间的数据缓冲区 * @param - cnt : 要读取的数据长度 * @param - offt : 相对于文件首地址的偏移 * @return : 读取的字节数，如果为负值，表示读取失败 */ static ssize_t chrdevbase_read(struct file *filp, char __user *buf, size_t cnt, loff_t *offt) { int retvalue = 0; /* 向用户空间发送数据 */ memcpy(readbuf, kerneldata, sizeof(kerneldata)); retvalue = copy_to_user(buf, readbuf, cnt); if (retvalue == 0) { printk("kernel senddata ok!\r\n"); } else { printk("kernel senddata failed!\r\n"); } // printk("chrdevbase read!\r\n"); return 0; } /* * @description : 向设备写数据 * @param - filp : 设备文件，表示打开的文件描述符 * @param - buf : 要写给设备写入的数据 * @param - cnt : 要写入的数据长度 * @param - offt : 相对于文件首地址的偏移 * @return : 写入的字节数，如果为负值，表示写入失败 */ static ssize_t chrdevbase_write(struct file *filp, const char __user *buf, size_t cnt, loff_t *offt) { int retvalue = 0; /* 接收用户空间传递给内核的数据并且打印出来 */ retvalue = copy_from_user(writebuf, buf, cnt); if (retvalue == 0) { printk("kernel recevdata:%s\r\n", writebuf); } else { printk("kernel recevdata failed!\r\n"); } // printk("chrdevbase write!\r\n"); return 0; } /* * @description : 关闭/释放设备 * @param - filp : 要关闭的设备文件(文件描述符) * @return : 0 成功;其他 失败 */ static int chrdevbase_release(struct inode *inode, struct file *filp) { // printk("chrdevbase release！\r\n"); return 0; } /* * 设备操作函数结构体 */ static struct file_operations chrdevbase_fops = { .owner = THIS_MODULE, .open = chrdevbase_open, .read = chrdevbase_read, .write = chrdevbase_write, .release = chrdevbase_release, }; /* * @description : 驱动入口函数 * @param : 无 * @return : 0 成功;其他 失败 */ static int __init chrdevbase_init(void) { int retvalue = 0; /* 注册字符设备驱动 */ retvalue = register_chrdev(CHRDEVBASE_MAJOR, CHRDEVBASE_NAME, &chrdevbase_fops); if (retvalue < 0) { printk("chrdevbase driver register failed\r\n"); } printk("chrdevbase_init()\r\n"); return 0; } /* * @description : 驱动出口函数 * @param : 无 * @return : 无 */ static void __exit chrdevbase_exit(void) { /* 注销字符设备驱动 */ unregister_chrdev(CHRDEVBASE_MAJOR, CHRDEVBASE_NAME); printk("chrdevbase_exit()\r\n"); } /* * 将上面两个函数指定为驱动的入口和出口函数 */ module_init(chrdevbase_init); module_exit(chrdevbase_exit); /* * LICENSE 和作者信息 */ MODULE_LICENSE("GPL"); MODULE_AUTHOR("chenzhiyong"); - 1
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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- 1
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- 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()- 1
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- 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- 1
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- 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; }- 1
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- 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
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- 原文地址：https://blog.csdn.net/yong1585855343/article/details/133822999
