Linux驱动实践：中断处理中的【工作队列】 workqueue 是什么鬼？

struct workqueue_struct {
    struct list_head        pwqs;           /* WR: all pwqs of this wq */
    struct list_head        list;           /* PR: list of all workqueues */
    ...
    char                    name[WQ_NAME_LEN]; /* I: workqueue name */
    ...
    /* hot fields used during command issue, aligned to cacheline */
    unsigned int            flags ____cacheline_aligned; /* WQ: WQ_* flags */
    struct pool_workqueue __percpu *cpu_pwqs; /* I: per-cpu pwqs */
    struct pool_workqueue __rcu *numa_pwq_tbl[]; /* PWR: unbound pwqs indexed by node */
};

struct work_struct {
        atomic_long_t data;
        struct list_head entry;
        work_func_t func;   // 指向处理函数
#ifdef CONFIG_LOCKDEP                                                                                   
        struct lockdep_map lockdep_map;
#endif
};

/*
 * System-wide workqueues which are always present.
 *
 * system_wq is the one used by schedule[_delayed]_work[_on]().
 * Multi-CPU multi-threaded.  There are users which expect relatively
 * short queue flush time.  Don't queue works which can run for too
 * long.
 *
 * system_highpri_wq is similar to system_wq but for work items which
 * require WQ_HIGHPRI.
 *
 * system_long_wq is similar to system_wq but may host long running
 * works.  Queue flushing might take relatively long.
 *
 * system_unbound_wq is unbound workqueue.  Workers are not bound to
 * any specific CPU, not concurrency managed, and all queued works are
 * executed immediately as long as max_active limit is not reached and
 * resources are available.
 *
 * system_freezable_wq is equivalent to system_wq except that it's
 * freezable.
 *
 * *_power_efficient_wq are inclined towards saving power and converted
 * into WQ_UNBOUND variants if 'wq_power_efficient' is enabled; otherwise,
 * they are same as their non-power-efficient counterparts - e.g.
 * system_power_efficient_wq is identical to system_wq if
 * 'wq_power_efficient' is disabled.  See WQ_POWER_EFFICIENT for more info.
 */

extern struct workqueue_struct *system_wq;
extern struct workqueue_struct *system_highpri_wq;
extern struct workqueue_struct *system_long_wq;
extern struct workqueue_struct *system_unbound_wq;
extern struct workqueue_struct *system_freezable_wq;
extern struct workqueue_struct *system_power_efficient_wq;
extern struct workqueue_struct *system_freezable_power_efficient_wq;

int __init workqueue_init_early(void)
{
    ...    
    system_wq = alloc_workqueue("events", 0, 0);
    system_highpri_wq = alloc_workqueue("events_highpri", WQ_HIGHPRI, 0);                           
    system_long_wq = alloc_workqueue("events_long", 0, 0);
    system_unbound_wq = alloc_workqueue("events_unbound", WQ_UNBOUND,
                                            WQ_UNBOUND_MAX_ACTIVE);
    system_freezable_wq = alloc_workqueue("events_freezable",
                                              WQ_FREEZABLE, 0);
    system_power_efficient_wq = alloc_workqueue("events_power_efficient",
                                              WQ_POWER_EFFICIENT, 0);
    system_freezable_power_efficient_wq = alloc_workqueue("events_freezable_power_efficient",
                                              WQ_FREEZABLE | WQ_POWER_EFFICIENT,
                                              0);
    ...
}

/**
 * schedule_work - put work task in global workqueue
 * @work: job to be done
 *
 * Returns %false if @work was already on the kernel-global workqueue and
 * %true otherwise.
 *
 * This puts a job in the kernel-global workqueue if it was not already
 * queued and leaves it in the same position on the kernel-global
 * workqueue otherwise.
 */

static inline bool schedule_work(struct work_struct *work){ 　　
    return queue_work(system_wq, work);
}

$ cd tmp/linux-4.15/drivers
$ mkdir my_driver_interrupt_wq
$ touch my_driver_interrupt_wq.c
$ touch Makefile

#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/interrupt.h>

static int irq;					
static char * devname;		

static struct work_struct mywork;	
			
 // 接收驱动模块加载时传入的参数
module_param(irq, int, 0644);
module_param(devname, charp, 0644);

// 定义驱动程序的 ID，在中断处理函数中用来判断是否需要处理			
#define MY_DEV_ID	   		1226

// 驱动程序数据结构
struct myirq
{
    int devid;
};
 
struct myirq mydev  ={ MY_DEV_ID };

#define KBD_DATA_REG        0x60  
#define KBD_STATUS_REG      0x64
#define KBD_SCANCODE_MASK   0x7f
#define KBD_STATUS_MASK     0x80

// 工作项绑定的处理函数
static void mywork_handler(struct work_struct *work)
{
    printk("mywork_handler is called. \n");
    // do some other things
}
		
//中断处理函数
static irqreturn_t myirq_handler(int irq, void * dev)
{
    struct myirq mydev;
    unsigned char key_code;
    mydev = *(struct myirq*)dev;	
	
	// 检查设备 id，只有当相等的时候才需要处理
	if (MY_DEV_ID == mydev.devid)
	{
		// 读取键盘扫描码
		key_code = inb(KBD_DATA_REG);
	
		if (key_code == 0x01)
		{
			printk("ESC key is pressed! \n");
			
			// 初始化工作项
			INIT_WORK(&mywork, mywork_handler);
			
			// 加入到工作队列 system_wq
        	        schedule_work(&mywork);
		}
	}	

	return IRQ_HANDLED;
}
 
// 驱动模块初始化函数
static int __init myirq_init(void)
{
    printk("myirq_init is called. \n");

	// 注册中断处理函数
    if(request_irq(irq, myirq_handler, IRQF_SHARED, devname, &mydev)!=0)
    {
        printk("register irq[%d] handler failed. \n", irq);
        return -1;
    }

    printk("register irq[%d] handler success. \n", irq);
    return 0;
}
 
// 驱动模块退出函数
static void __exit myirq_exit(void)
{
    printk("myirq_exit is called. \n");

	// 释放中断处理函数
    free_irq(irq, &mydev);
}
 
MODULE_LICENSE("GPL");
module_init(myirq_init);
module_exit(myirq_exit);

ifneq ($(KERNELRELEASE),)
	obj-m := my_driver_interrupt_wq.o
else
	KERNELDIR ?= /lib/modules/$(shell uname -r)/build
	PWD := $(shell pwd)
default:
	$(MAKE) -C $(KERNELDIR) M=$(PWD) modules
clean:
	$(MAKE) -C $(KERNEL_PATH) M=$(PWD) clean
endif

$ make
$ sudo insmod my_driver_interrupt_wq.ko irq=1 devname=mydev

$ lsmod | grep my_driver_interrupt_wq
my_driver_interrupt_wq    16384  0

$ dmesg
...
[  188.247636] myirq_init is called. 
[  188.247642] register irq[1] handler success.

if (key_code == 0x01)
{
	printk("ESC key is pressed! \n");
	INIT_WORK(&mywork, mywork_handler);
	schedule_work(&mywork);
}

[  305.053155] ESC key is pressed! 
[  305.053177] mywork_handler is called.