一、篇头

继续使用qemu调试内核的实验。本章复习阻塞与非阻塞IO的概念和机制，然后对之前实验（八）的代码做少许修改，添加阻塞的IO读写。

二、系列文章

略……

三、实验环境

• 编译服务器+NFS：ubuntu 22.04
• Qemu 虚拟机：Linux version 5.15.102 + Buysbox 1.3.36 + ARM_32bit

Qemu 启动命令：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

四、源码

4.1 概念及接口介绍

非阻塞IO

进程发起I/O系统调用后，如果设备驱动的缓冲区没有数据，那么进程返回一个错误而不会被阻塞。如果驱动缓冲区中有数据，那么设备驱动把数据直接返回给用户进程。

阻塞

进程发起I/O系统调用后，如果设备的缓冲区没有数据，那么需要到硬件I/O中重新获取新数据，进程会被阻塞，也就是睡眠等待。直到数据准备好，进程才会被唤醒，并重新把数据返回给用户空间。

睡眠等待

Linux内核提供了简单的睡眠方式，并封装成wait_event()的宏以及其他几个扩展宏，主要功能是在让进程睡眠时也检查进程的唤醒条件。

wait_event(wq, condition)
wait_event_interruptible(wq, condition)
wait_event_timeout(wq, condition, timeout)
wait_event_interruptible_timeout(wq, condition, timeout)

wq表示等待队列头。condition是一个布尔表达式，在condition变为真之前，进程会保持睡眠状态。timeout表示当timeout时间到达之后，进程会被唤醒，因此它只会等待限定的时间。当给定的时间到了之后，wait_event_timeout()和wait_event_interruptible_timeout()这两个宏无论condition是否为真，都会返回0。
wait_event_interruptible()会让进程进入可中断睡眠状态，而wait_event()会让进程进入不可中断睡眠态，也就是说不受干扰，对信号不做任何反应，不可能发送 SIGKILL 信号使它停止，因为它们不响应信号。因此，一般驱动程序不会采用这个睡眠模式。

唤醒

wake_up(x)
wake_up_interruptible(x)wake_up()会唤醒等待队列中所有的进程;
wake_up()应该和 wait_event()或者wait_event_timeout()配对使用;
wake_up_interruptible()应该和 wait_event_interruptible()和wait_event_interruptible_timeout()配对使用。

4.2 驱动源码

• 文件名：linux-stable\my_kmodules\test_9.c

#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include  #define MY_DEV_NAME "my_dev"struct my_device_st {const char *name;struct device *dev;struct miscdevice *miscdev;wait_queue_head_t read_queue;wait_queue_head_t write_queue;	
};static struct my_device_st *my_device; DEFINE_KFIFO(my_kfifo, char, 128);static int test_9_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);file->private_data = my_device;pr_info("%s: file->private_data=0x%x \n", __func__, (unsigned int)file->private_data);	return 0;
}static int test_9_release(struct inode *inode, struct file *file)
{	struct my_device_st *data = file->private_data;pr_info("%s: file->private_data=0x%x \n", __func__, (unsigned int)file->private_data);	kfree(data);file->private_data = NULL;return 0;
}static ssize_t test_9_read(struct file *file, char __user *buf, size_t count, loff_t *ppos)
{int ret;unsigned int copied_count=0;struct my_device_st *my_device = file->private_data;pr_info("%s \n", __func__);/** (1)add for O_NONBLOCK reading*/if(kfifo_is_empty(&my_kfifo)){if(file->f_flags & O_NONBLOCK)return  -EAGAIN;// （2）若用户发起的是非BLOCK读，则因为空间为空，调度进程到等等队列，进程睡眠pr_info("%s: pid=%d, going to sleep\n", __func__, current->pid);ret = wait_event_interruptible(my_device->read_queue,!kfifo_is_empty(&my_kfifo));if (ret)return ret;}ret = kfifo_to_user(&my_kfifo, buf,  count, &copied_count);if(ret != 0) return -EFAULT;// （3）如果FIFI有空余，唤醒等待写入的其他进程if (!kfifo_is_full(&my_kfifo))wake_up_interruptible(&my_device->write_queue);pr_info("%s, pid=%d, actual_readed=%d, pos=%lld\n",__func__,current->pid, copied_count, *ppos);return copied_count;
}static ssize_t test_9_write(struct file *file, const char __user *buf, size_t count, loff_t *f_pos)
{int ret;unsigned int copied_count=0;struct my_device_st *data = file->private_data;pr_info("%s \n", __func__);/** (1)add for O_NONBLOCK writing*/if(kfifo_is_full(&my_kfifo)){if(file->f_flags & O_NONBLOCK){return  -EAGAIN;}// （2）若用户发起的是非BLOCK写，则因为空间已满，调度进程到等等队列，进程睡眠pr_info("%s: pid=%d, going to sleep\n", __func__, current->pid);ret = wait_event_interruptible(data->write_queue,!kfifo_is_empty(&my_kfifo));if (ret)return ret;}ret = kfifo_from_user(&my_kfifo, buf, count, &copied_count);if(ret != 0) return -EFAULT;// （3）如果数据非空，唤醒等待读取的其他进程if (!kfifo_is_empty(&my_kfifo))wake_up_interruptible(&data->read_queue);pr_info("%s, pid=%d, actual_readed=%d, pos=%lld\n",__func__,current->pid, copied_count, *f_pos);return copied_count;}static const struct file_operations test_fops = {.owner = THIS_MODULE,.open = test_9_open,.release = test_9_release,.read = test_9_read,.write = test_9_write
};static struct miscdevice test_9_misc_device ={.minor = MISC_DYNAMIC_MINOR,.name = MY_DEV_NAME,.fops = &test_fops,
};static int __init test_9_init(void)
{int ret;pr_info("test_9_init\n");//（1） 创建共享的数据结构，包含IO读和写的等待队列my_device = kmalloc(sizeof(struct my_device_st), GFP_KERNEL);if (!my_device)return -ENOMEM;my_device->miscdev = &test_9_misc_device;init_waitqueue_head(&my_device->read_queue);init_waitqueue_head(&my_device->write_queue);ret = misc_register(&test_9_misc_device);if (ret != 0 ) {pr_err("failed to misc_register");return ret;}pr_err("Minor number = %d\n", test_9_misc_device.minor);return 0;
}static void __exit test_9_exit(void)
{pr_info("test_9_exit\n");if(my_device)kfree(my_device);misc_deregister(&test_9_misc_device);
}module_init(test_9_init);
module_exit(test_9_exit);MODULE_LICENSE("Dual BSD/GPL");
MODULE_AUTHOR("szhou <66176468@qq.com>");
MODULE_DESCRIPTION("test_9, 使用misc、KFIFO开发设备驱动非阻塞+阻塞的设备驱动。");

4.3 APP源码

• 简单起见，用echo和cat分别启2个进程进行读写。

4.4 Makefile

• 文件名：linux-stable\my_kmodules\Makefile
• 如下，继续追加 test_9.o 即可编译出test_9.ko

KDIR := /home/szhou/works/qemu_linux/linux-stableobj-m := test_1.o test_2.o test_3.o test_4.o  test_5.o test_6.o test_7.o test_9.o
all :$(MAKE) -C $(KDIR) M=$(PWD) modules
clean:$(MAKE) -C $(KDIR) SUBDIRS=$(PWD) cleanrm -f *.ko

五、编译及部署

（1）执行驱动KO编译
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_9.oMODPOST /home/szhou/works/qemu_linux/linux-stable/my_kmodules/Module.symversCC [M]  /home/szhou/works/qemu_linux/linux-stable/my_kmodules/test_9.mod.oLD [M]  /home/szhou/works/qemu_linux/linux-stable/my_kmodules/test_9.ko
make[1]: Leaving directory '/home/szhou/works/qemu_linux/linux-stable'（2）执行app编译
szhou@bc01:~/works/qemu_linux/linux-stable/my_kmodules$ arm-linux-gnueabi-gcc app_test_9.c -o app_test_9 --static（3）将KO和APP存放到NFS共享目录
szhou@bc01:~/works/qemu_linux/linux-stable/my_kmodules$ cp test_9.ko app_test_9  ~/works/nfs_share/
szhou@bc01:~/works/qemu_linux/linux-stable/my_kmodules$ 

六、运行及测试

（1）启动之前编译组建的QEMU虚拟机
----------------------------------------
Welcome to szhou's tiny Linux
----------------------------------------Please press Enter to activate this console. 
~
（2）挂载NFS共享目录
~ #  mount -t nfs -o nolock 192.168.3.67:/home/szhou/works/nfs_share /mnt（3） 加载ko
~ # cd /mnt/
/mnt # 
/mnt # insmod test_9.ko 
test_9: loading out-of-tree module taints kernel.
test_9_init
Minor number = 125
/mnt # 
/mnt # mdev -s（4） 运行app测试
/mnt # cat /dev/my_dev  &
/mnt # test_9_open: major=10, minor=125
test_9_open: file->private_data=0x81b8bb00 
test_9_read 
test_9_read: pid=489, going to sleep/mnt # echo "Hellow, do block reading ."  >  /dev/my_dev 
test_9_open: major=10, minor=125
test_9_open: file->private_data=0x81b8bb00 
test_9_write 
test_9_write, pid=457, actual_readed=27, pos=0
test_9_read, pid=489, actual_readed=27, pos=0
Hellow, do block reading .
test_9_read 
test_9_read: pid=489, going to sleep
test_9_release: file->private_data=0x81b8bb00 
/mnt # 

操作画面如下图：