内核实验（五）：传统简单字符设备驱动

一、篇头

目标是把内核相关部分的实验都再做一次，虽然有现成源码，但从以往学习经历看，自己还是得多少做一些改动，对于要自虐的，可以从头打一遍，这样效果会好很多，练习完后，做个总结。实验简单，花的时间也不多，温故而知新。

二、源码

2.1 驱动关键部分

static int __init test_3_init(void)
{
   
   
    int ret;

        pr_info("test_3_init\n");

    ret = alloc_chrdev_region(&dev, 0, count, DEMO_NAME);
    if (ret) {
   
   
        pr_err("failed to allocate char device region");
        return ret;
    }

    test_3_cdev = cdev_alloc();
    if (!test_3_cdev) {
   
   
        pr_err("cdev_alloc failed\n");
        goto unregister_chrdev;
    }

    cdev_init(test_3_cdev, &test_3_fops);

        /*
          (1) 下面语句会创建 /proc/devices/test_3_dev， 但不会创建/dev下的设备节点
        */
    ret = cdev_add(test_3_cdev, dev, count);
    if (ret) {
   
   
        pr_err("cdev_add failed\n");
        goto cdev_fail;
    }

    pr_err("succeeded register char device: %s\n", DEMO_NAME);
    pr_err("Major number = %d, minor number = %d\n",
            MAJOR(dev), MINOR(dev));
// …… 省略 …… 
    return ret;
}

2.2 APP：test_3_app.c

• 完成的linux app源码

#include <stdio.h>
#include <fcntl.h>
#include <unistd.h>

#define MY_DEV_NAME "/dev/test_3_dev"

int main()
{
   
   
    char buffer[64];
    int fd;

    fd = open(MY_DEV_NAME, O_RDONLY);
    if (fd < 0) {
   
   
        printf("open device %s failded\n", MY_DEV_NAME);
        return -1;
    }
    read(fd, buffer, 64);
    close(fd);
    return 0;
}

2.3 驱动完整源码

• test_3.c

#include <linux/module.h>
#include <linux/fs.h>
#include <linux/uaccess.h>
#include <linux/init.h>
#include <linux/cdev.h>

#define DEMO_NAME "test_3_dev"
static dev_t dev;
static struct cdev *test_3_cdev;
static signed count = 1;

static int test_3_open(struct inode *inode, struct file *file)
{
   
   
    int major = MAJOR(inode->i_rdev);
    int minor = MINOR(inode->i_rdev);

    pr_info("%s: major=%d, minor=%d\n", __func__, major, minor);
    return 0;
}

static int test_3_release(struct inode *inode, struct file *file)
{
   
   
    pr_info("%s \n", __func__);

    return 0;
}

static ssize_t
test_3_read(struct file *file, char __user *buf, size_t lbuf, loff_t *ppos)
{
   
   
    pr_info("%s \n", __func__);
    return 0;
}

static ssize_t
test_3_write(struct file *file, const char __user *buf, size_t count, loff_t *f_pos)
{
   
   
    pr_info("%s \n", __func__);
    return 0;

}

static const struct file_operations test_3_fops = {
   
   
    .owner = THIS_MODULE,
    .open = test_3_open,
    .release = test_3_release,
    .read = test_3_read,
    .write = test_3_write
};


static int __init test_3_init(void)
{
   
   
    int ret;

        pr_info("test_3_init\n");

    ret = alloc_chrdev_region(&dev, 0, count, DEMO_NAME);
    if (ret) {
   
   
        pr_err("failed to allocate char device region");
        return ret;
    }

    test_3_cdev = cdev_alloc();
    if (!test_3_cdev) {
   
   
        pr_err("cdev_alloc failed\n");
        goto unregister_chrdev;
    }

    cdev_init(test_3_cdev, &test_3_fops);

    ret = cdev_add(test_3_cdev, dev, count);
    if (ret) {
   
   
        pr_err("cdev_add failed\n");
        goto cdev_fail;
    }

    pr_err("succeeded register char device: %s\n", DEMO_NAME);
    pr_err("Major number = %d, minor number = %d\n",
            MAJOR(dev), MINOR(dev));

    return 0;

cdev_fail:
    cdev_del(test_3_cdev);
unregister_chrdev:
    unregister_chrdev_region(dev, count);

    return ret;
}

static void __exit test_3_exit(void)
{
   
   
    pr_info("test_3_exit\n");

    if (test_3_cdev)
        cdev_del(test_3_cdev);

    unregister_chrdev_region(dev, count);
}

module_init(test_3_init);
module_exit(test_3_exit);

MODULE_LICENSE("Dual BSD/GPL");
MODULE_AUTHOR("szhou <66176468@qq.com>");
MODULE_DESCRIPTION("test_1, simple char kernel module");

2.4 Makefile

• 实验和之前几篇文章有集成性，本文实验只需要在 obj-m 后面添加 test_3.o 即可

KDIR := /home/szhou/works/qemu_linux/linux-stable


obj-m := test_1.o test_2.o test_3.o


all :
    $(MAKE) -C $(KDIR) M=$(PWD) modules

clean:
    $(MAKE) -C $(KDIR) SUBDIRS=$(PWD) clean
    rm -f *.ko

三、编译

3.1 编译ko

szhou@bc01:~/works/qemu_linux/linux-stable/my_kmodules$ ls
Makefile  modules.order  Module.symvers  test_1.c  test_1.ko  test_1.mod  test_1.mod.c  test_1.mod.o  test_1.o  test_2.c  test_2.ko  test_2.mod  test_2.mod.c  test_2.mod.o  test_2.o  test_3_app.c  test_3.c
szhou@bc01:~/works/qemu_linux/linux-stable/my_kmodules$ make
make -C /home/szhou/works/qemu_linux/linux-stable M=/home/szhou/works/qemu_linux/linux-stable/my_kmodules modules
make[1]: Entering directory '/home/szhou/works/qemu_linux/linux-stable'
  CC [M]  /home/szhou/works/qemu_linux/linux-stable/my_kmodules/test_3.o
  MODPOST /home/szhou/works/qemu_linux/linux-stable/my_kmodules/Module.symvers
  CC [M]  /home/szhou/works/qemu_linux/linux-stable/my_kmodules/test_1.mod.o
  LD [M]  /home/szhou/works/qemu_linux/linux-stable/my_kmodules/test_1.ko
  CC [M]  /home/szhou/works/qemu_linux/linux-stable/my_kmodules/test_2.mod.o
  LD [M]  /home/szhou/works/qemu_linux/linux-stable/my_kmodules/test_2.ko
  CC [M]  /home/szhou/works/qemu_linux/linux-stable/my_kmodules/test_3.mod.o
  LD [M]  /home/szhou/works/qemu_linux/linux-stable/my_kmodules/test_3.ko
make[1]: Leaving directory '/home/szhou/works/qemu_linux/linux-stable'
szhou@bc01:~/works/qemu_linux/linux-stable/my_kmodules$

3.2 编译app

• 因为使用qemu模拟，而我们之前建立的mini Linux系统尚未添加 so 等各种依赖库，所以需要在编译app时候添加 --static标志，使用静态链接，这样就可以不依赖于so文件。

szhou@bc01:~/works/qemu_linux/linux-stable/my_kmodules$ arm-linux-gnueabi-gcc test_3_app.c -o test_3_app --static
szhou@bc01:~/works/qemu_linux/linux-stable/my_kmodules$ file test_3_app
test_3_app: ELF 32-bit LSB executable, ARM, EABI5 version 1 (SYSV), statically linked, BuildID[sha1]=1a479f0e5a7f3cba6fb0ea4121337f56623cb5a5, for GNU/Linux 3.2.0, not stripped
szhou@bc01:~/works/qemu_linux/linux-stable/my_kmodules$

四、测试

4.1 部署

• 透过NFS部署，不了解的，请参考之前的内核实验（四）
• 将测试文件复制到nfs共享目录下

szhou@bc01:~/works/qemu_linux/linux-stable/my_kmodules$ cp test_3.ko ~/works/nfs_share/
szhou@bc01:~/works/qemu_linux/linux-stable/my_kmodules$ cp test_3_app ~/works/nfs_share/

4.2 测试

4.2.1 启动qemu虚拟机

qemu-system-arm   -nographic  -M vexpress-a9 -m 1024M -kernel arch/arm/boot/zImage   -initrd ../busybox/rootfs.ext4.img.gz    -dtb arch/arm/boot/dts/vexpress-v2p-ca9.dtb

4.2.2 运行测试文件

----------------------------------------
Welcome to szhou's tiny Linux
----------------------------------------

Please press Enter to activate this console. 
~ # 
~ # 
~ #  mount -t nfs -o nolock 192.168.3.67:/home/szhou/works/nfs_share /mnt
~ # cd /mnt/
/mnt # ls
abc_client  bcd_server  test_3.ko
/mnt # insmod test_3.ko 
test_3: loading out-of-tree module taints kernel.
test_3_init
succeeded register char device: test_3_dev
Major number = 248, minor number = 0
/mnt # 
/mnt # mknod /dev/test_3_dev c 248 0
/mnt # ./test_3_app 
test_3_open: major=248, minor=0
test_3_read 
test_3_release 
/mnt # 
/mnt # rmmod  test_3.ko 
test_3_exit
/mnt #

4.2.3 查看设备情况

• 注意，此处尚未使用mknod手动创建设备文件

（1） insmod ko
/mnt # insmod test_3.ko 
test_3: loading out-of-tree module taints kernel.
test_3_init
succeeded register char device: test_3_dev
Major number = 248, minor number = 0


（2）查看 /dev 可见无目标设备


（3）查看 /proc/devices ，则创建了test_3_dev
/dev # cat /proc/devices 
Character devices:
  1 mem
  2 pty
  3 ttyp
  4 /dev/vc/0
  4 tty
  5 /dev/tty
  5 /dev/console
// …… 省略 ……
248 test_3_dev
// …… 省略 ……

Block devices:
// …… 省略 ……
/dev #

五、篇尾

略……
用这个简单的实验， 再次检验了内核实验四，NFS环境的高效。