/***********************Linux-2.6.32************************************/
//include/linux/hardirq.h
in_irq()       //CPU正服务于硬件中断时，返回True
in_softirq()   //CPU正服务于软件中断时，返回True
in_interrupt() //CPU正在服务于一个硬件中断或软件中断，或抢占功能关闭时，返回True  
 
//arch/x86/include/asm/hardirq.h
local_softirq_pending()  //本地CPU至少有一个IRQ出于未决状态时，返回True
 
//include/linux/interrupt.h
__raise_softirq_irqoff()  //设置与软IRQ相关联的标识，将IRQ标记为未决
raise_softirq_irqoff()    //__raise_softirq_irqoff包裹函数，当in_interrupt为False时，唤醒ksoftirqd
raise_softirq()           //包裹raise_softirq_irqoff，调用raise_softirq_irqoff前先关中断
 
//kernel/softirq.c
__local_bh_enable()   //开启本地CPU的下半部 
local_bh_enable()     //如果有任何软IRQ未决，且in_interrupt返回False，则invoke_softirq
local_bh_disable()    //关闭CPU下半部
 
//include/linux/irqflags.h
local_irq_enable()    //开启本地CPU中断功能
local_irq_disable()   //关闭本地CPU中断功能
local_irq_save()      //先把本地CPU中断状态保存，再予以关闭
local_irq_restore()   //恢复本地CPU之前的中断状态，恢复local_irq_save保存的中断信息
 
//include/linux/spinlock.h
spin_lock_bh()      //取得回旋锁，关闭下半部及抢占功能
spin_unlock_bh()    //释放回旋锁，重启下半部抢占功能

//inculde/linux/preempt.h
preempt_disable()          //为当前任务关闭抢占功能。可重复调用，递增引用计数器
preempt_enable()           //抢占功能再度开启，（需要先检查引用计数器是否为0）
preempt_enable_no_resch()  //递减引用计数器，只有引用计数器为0时，抢占功能才能再度开启
preempt_check_resched()    //由preempt_enable调用，检查引用计数器是否为0.
 
// arch/x86/include/asm/thread_info.h
struct thread_info {
    ……
    int         preempt_count;  /* 0 => preemptable,
                           <0 => BUG */ //抢占计数器，指定进程是否能被抢占
    ……
};

enum {
    TIMER_BH = 0,
    CONSOLE_BH,
    TQUEUE_BH,
    DIGI_BH,
    SERIAL_BH,
    RISCOM8_BH,
    SPECIALIX_BH,
    AURORA_BH,
    ESP_BH,
    NET_BH,      //网络下半部
    SCSI_BH,
    IMMEDIATE_BH,
    KEYBOARD_BH,
    CYCLADES_BH,
    CM206_BH,
    JS_BH,
    MACSERIAL_BH,
    ISICOM_BH
};

引入软IRQ

//include/linux/interrupt.h
enum
{
    HI_SOFTIRQ=0,     //高优先级微任务
    TIMER_SOFTIRQ,
    NET_TX_SOFTIRQ,  //网络软IRQ
    NET_RX_SOFTIRQ,  //网络软IRQ
    BLOCK_SOFTIRQ,
    BLOCK_IOPOLL_SOFTIRQ,
    TASKLET_SOFTIRQ,  //低优先级微任务软IRQ
    SCHED_SOFTIRQ,
    HRTIMER_SOFTIRQ,
    RCU_SOFTIRQ,    /* Preferable RCU should always be the last softirq */
 
    NR_SOFTIRQS
};      

/*
 * Incoming packets are placed on per-cpu queues so that
 * no locking is needed.
 */
struct softnet_data
{
    struct Qdisc        *output_queue;      //qdisc是queueing discipline的简写，也就是排队规则，即qos.这里也就是输出帧的控制。
    struct sk_buff_head input_pkt_queue;    //当输入帧被驱动取得之前，就保存在这个队列里，（不适用与napi驱动，napi有自己的私有队列）
    struct list_head    poll_list;          //表示有输入帧待处理的设备链表。 
    struct sk_buff      *completion_queue;  //表示已经成功被传递出的帧的链表。
 
    struct napi_struct  backlog;            //用来兼容非napi的驱动。                                                                    
};

// kernel/softirq.c
void open_softirq(int nr, void (*action)(struct softirq_action *))                            
{
    softirq_vec[nr].action = action;
}

/*
 * Tasklets
 */
struct tasklet_head
{
    struct tasklet_struct *head;                                                                                                        
    struct tasklet_struct **tail;
};
 
static DEFINE_PER_CPU(struct tasklet_head, tasklet_vec);
static DEFINE_PER_CPU(struct tasklet_head, tasklet_hi_vec);

struct tasklet_struct
{
    struct tasklet_struct *next;  //把关联到同一个CPU的结构链接起来                                                                                                   
    unsigned long state;          //位图标识，其可能的取值由TASKLET_STATE_XXX枚举
    atomic_t count;               //计数器，0表示微任务被关闭，不可执行。非0表示微任务已经开启
    void (*func)(unsigned long);  //要执行的函数
    unsigned long data;           //上面函数的参数
}; 
 
enum
{
    TASKLET_STATE_SCHED,    /* Tasklet is scheduled for execution */
    TASKLET_STATE_RUN   /* Tasklet is running (SMP only) */
};