Linux Interrupts and Exceptions - 3

I/O Interrupt (硬體裝置的中斷) 處理函式是以 request_irq() 來向核心註冊的，並且以 free_irq() 來清除

定義於 include/linux/interrupt.h

int request_irq(
　　　　unsigned int　　irq,
　　　　irqreturn_t 　　(*handler)(int, void *, struct pt_regs *),
　　　　unsigned long 　irqflags,
　　　　const char 　　*devname,
　　　　void　　　　　 *dev_id
　　);

void free_irq(
　　　　unsigned int　irq,
　　　　void 　　　　*dev_id
　　);

struct irqaction {
　　irqreturn_t (*handler)(int, void *, struct pt_regs *);
　　unsigned long flags;
　　cpumask_t mask;
　　const char *name;
　　void *dev_id;
　　struct irqaction *next;
　　int irq;
　　struct proc_dir_entry *dir;
};

request_irq() 函式內部則是呼叫 setup_irq() 來進行 IRQ Line 的註冊
其動作是將要求中斷處理的資訊包裝成 struct irqaction 的結構，然後記錄於 irq_desc 陣列中的 IRQ Line 的位置
若有共用 IRQ Line 的中斷，則會以鏈結串列的方式掛在同一個陣列的位置上，如下圖所示

圖中的 hw_interrupt_type 是一個描述中斷控制器的資料結構，用來抽象化不同的中斷控制硬體
例如：舊式的 8259A，或新式的 APIC，也可能是無任何中斷控制器

定義於 include/linux/irq.h

/*
* Interrupt controller descriptor. This is all we need
* to describe about the low-level hardware.
*/
struct hw_interrupt_type {
　　const char * typename;
　　unsigned int (*startup)(unsigned int irq);
　　void (*shutdown)(unsigned int irq);
　　void (*enable)(unsigned int irq);
　　void (*disable)(unsigned int irq);
　　void (*ack)(unsigned int irq);
　　void (*end)(unsigned int irq);
　　void (*set_affinity)(unsigned int irq, cpumask_t dest);
};

typedef struct hw_interrupt_type　hw_irq_controller;

定義於 arch/i386/kernel/i8259.c

static struct hw_interrupt_type i8259A_irq_type = {
　　"XT-PIC",
　　startup_8259A_irq,
　　shutdown_8259A_irq,
　　enable_8259A_irq,
　　disable_8259A_irq,
　　mask_and_ack_8259A,
　　end_8259A_irq,
　　NULL
};

定義於 arch/i386/kernel/io_apic.c

/*
* Level and edge triggered IO-APIC interrupts need different handling,
* so we use two separate IRQ descriptors. Edge triggered IRQs can be
* handled with the level-triggered descriptor, but that one has slightly
* more overhead. Level-triggered interrupts cannot be handled with the
* edge-triggered handler, without risking IRQ storms and other ugly
* races.
*/
static struct hw_interrupt_type ioapic_edge_type = {
　　.typename　　= "IO-APIC-edge",
　　.startup　　　= startup_edge_ioapic,
　　.shutdown　　= shutdown_edge_ioapic,
　　.enable　　　 = enable_edge_ioapic,
　　.disable　　　= disable_edge_ioapic,
　　.ack　　　　 = ack_edge_ioapic,
　　.end　　　　= end_edge_ioapic,
　　.set_affinity = set_ioapic_affinity,
};

static struct hw_interrupt_type ioapic_level_type = {
　　.typename　　 = "IO-APIC-level",
　　.startup　　　= startup_level_ioapic,
　　.shutdown　　 = shutdown_level_ioapic,
　　.enable　　　 = enable_level_ioapic,
　　.disable　　　= disable_level_ioapic,
　　.ack　　　　　= mask_and_ack_level_ioapic,
　　.end　　　　　= end_level_ioapic,
　　.set_affinity = set_ioapic_affinity,
};

定義於 kernel/irq/handle.c

struct hw_interrupt_type no_irq_type = {
　　.typename = "none",
　　.startup = startup_none,
　　.shutdown = shutdown_none,
　　.enable = enable_none,
　　.disable = disable_none,
　　.ack = ack_none,
　　.end = end_none,
　　.set_affinity = NULL
};