前言

编写Linux驱动的时候对于work_struct的使用还是很普遍的，很早之前就在阅读驱动源码的时候就看到了它的踪影，根据其命名大概知道了它的具体作用，但是仍然不知所以，同时，伴随出现的还有delayed_work以及workqueue_struct，抱着知其然并知其所以然的态度，在这里归纳总结一下work_struct，以及如何在驱动中使用，因为工作队列相对来说比较复杂，篇幅和能力有限，只能介绍相对重要的部分。

workqueue

内核里一直运行类似worker thread，它会对工作队列中的work进行处理，大致的工作流程原理可以参考下图所示；

在这里的work则是work_struct变量，并且绑定一个执行函数——typedef void (*work_func_t)(struct work_struct *work);。在worker thread中会对非空的工作队列进行工作队列的出队操作，并运行work绑定的函数。

work_struct

work_struct的数据结构如下，暂时我们还无法关注其原理，只关注如何去开启一个work

#include <linux/include/workqueue.h>
typedef void (*work_func_t)(struct work_struct *work);
struct work_struct {
	atomic_long_t data;
	struct list_head entry;
	work_func_t func;
#ifdef CONFIG_LOCKDEP
	struct lockdep_map lockdep_map;
#endif
};

通过数据结构可以知道，每当我们定义一个work_struct变量的时候，需要绑定一个work_func_t类型的函数指针。

例程

下面写了 一个demo，模块初始化之后会每隔5秒调度work开始运行，最终demo_work_func会运行规定的次数，并打印传递的参数和进程信息。

#include <linux/init.h>
#include <linux/module.h>
#include <linux/time.h>
#include <linux/jiffies.h>
#include <linux/workqueue.h>
#include <linux/slab.h> //kmalloc kfree
#include <linux/sched.h>
#include <linux/delay.h>
static char data[] = "test for demo work";
struct work_ctx{
	struct work_struct real_work;
	char *str;
	int arg;
}work_ctx;
struct work_ctx *demo_work;
static void demo_work_func(struct work_struct *work){
	struct work_ctx *temp_work = container_of(work,struct work_ctx,real_work);
	printk(KERN_INFO "[work]=> PID: %d; NAME: %s\n", current->pid, current->comm);
	printk(KERN_INFO "[work]=> sleep 1 seconds\n");
	set_current_state(TASK_INTERRUPTIBLE);
	schedule_timeout(1 * HZ); //Wait 1 seconds
	printk(KERN_INFO "[work]=> data is: %d  %s\n", temp_work->arg,temp_work->str);
}
static int __init demo_thread_init(void){
	int count = 10;
	demo_work = kmalloc(sizeof(*demo_work),GFP_KERNEL);	
	INIT_WORK(&demo_work->real_work, demo_work_func);
	demo_work->str = data;
	while(count--){
		msleep(5000);
		demo_work->arg = count;
		schedule_work(&demo_work->real_work);
	}
	return 0;
}
module_init(demo_thread_init);
static void __exit demo_thread_exit(void){
	flush_work(&demo_work->real_work);
	kfree(demo_work);
}
module_exit(demo_thread_exit);
MODULE_LICENSE("GPL");	

运行结果

[    8.500146] [work]=> PID: 37; NAME: kworker/0:1
[    8.500216] [work]=> sleep 1 seconds
[    9.499783] [work]=> data is: 9  test for demo work
[   13.503165] [work]=> PID: 37; NAME: kworker/0:1
[   13.503213] [work]=> sleep 1 seconds
[   14.503122] [work]=> data is: 8  test for demo work
[   18.506493] [work]=> PID: 37; NAME: kworker/0:1
[   18.506534] [work]=> sleep 1 seconds
[   19.506460] [work]=> data is: 7  test for demo work
[   23.509833] [work]=> PID: 37; NAME: kworker/0:1
[   23.509874] [work]=> sleep 1 seconds
[   24.510060] [work]=> data is: 6  test for demo work
[   28.513161] [work]=> PID: 37; NAME: kworker/0:1
[   28.513206] [work]=> sleep 1 seconds
[   29.513121] [work]=> data is: 5  test for demo work
[   33.516502] [work]=> PID: 37; NAME: kworker/0:1
[   33.516545] [work]=> sleep 1 seconds
[   34.516452] [work]=> data is: 4  test for demo work
[   38.519819] [work]=> PID: 37; NAME: kworker/0:1
[   38.519860] [work]=> sleep 1 seconds
[   39.519782] [work]=> data is: 3  test for demo work
[   43.523151] [work]=> PID: 37; NAME: kworker/0:1
[   43.523191] [work]=> sleep 1 seconds
[   44.523117] [work]=> data is: 2  test for demo work
[   48.526495] [work]=> PID: 37; NAME: kworker/0:1
[   48.526542] [work]=> sleep 1 seconds
[   49.526444] [work]=> data is: 1  test for demo work
[   53.539699] [work]=> PID: 37; NAME: kworker/0:1
[   53.539763] [work]=> sleep 1 seconds
[   54.542925] [work]=> data is: 0  test for demo work

参考

https://www.oreilly.com/library/view/understanding-the-linux/0596005652/ch04s08.html

https://kukuruku.co/post/multitasking-in-the-linux-kernel-workqueues/