FreeBSD 5 内核源代码分析之中断处理(3)
同系统调用一样，这里的调用栈struct intrframe既是atpic_handle_intr()的参数，也是中断
返回时用以恢复现场的寄存器状态。
代码:
/* Interrupt stack frame */
struct intrframe {
int if_vec;
int if_fs;
int if_es;
int if_ds;
int if_edi;
int if_esi;
int if_ebp;
int :32;
int if_ebx;
int if_edx;
int if_ecx;
int if_eax;
int :32; /* for compat with trap frame - trapno */
int :32; /* for compat with trap frame - err */
/* below portion defined in 386 hardware */
int if_eip;
int if_cs;
int if_eflags;
/* below only when crossing rings (e.g. user to kernel) */
int if_esp;
int if_ss;
};
void
atpic_handle_intr(struct intrframe iframe)
{
struct intsrc *isrc;
KASSERT((uint)iframe.if_vec < ICU_LEN,
("unknown int %d\n", iframe.if_vec));
isrc = &atintrs[iframe.if_vec].at_intsrc;
/*
* If we don't have an ithread, see if this is a spurious
* interrupt.
*/
if (isrc->is_ithread == NULL &&
(iframe.if_vec == 7 || iframe.if_vec == 15)) {
int port, isr;
/*
* Read the ISR register to see if IRQ 7/15 is really
* pending. Reset read register back to IRR when done.
*/
port = ((struct atpic *)isrc->is_pic)->at_ioaddr;
mtx_lock_spin(&icu_lock);
outb(port, OCW3_SEL | OCW3_RR | OCW3_RIS);
isr = inb(port);
outb(port, OCW3_SEL | OCW3_RR);
mtx_unlock_spin(&icu_lock);
if ((isr & IRQ7) == 0)
return;
}
intr_execute_handlers(isrc, &iframe);
}
经过简单的有关8259A特有的检查，atpic_handle_intr()就转到intr_execute_handlers()
继续处理。
intr_execute_handlers()是一个重要的函数，它先得到IRQ号，然后判断是否是快速中断，
如果是，则直接在当前线程的上下文中运行，如果不是，则调度对应的中断线程来运行。
这个处理是被critical_enter()/critical_exit()保护起来的，以保证不会嵌套调度中断线程。
代码:
void
intr_execute_handlers(struct intsrc *isrc, struct intrframe *iframe)
{
struct thread *td;
struct ithd *it;
struct intrhand *ih;
int error, vector;
td = curthread;
td->td_intr_nesting_level++;
/*
* We count software interrupts when we process them. The
* code here follows previous practice, but there's an
* argument for counting hardware interrupts when they're
* processed too.
*/
atomic_add_long(isrc->is_count, 1);
atomic_add_int(&cnt.v_intr, 1);
it = isrc->is_ithread;
if (it == NULL)
ih = NULL;
else
ih = TAILQ_FIRST(&it->it_handlers);
/*
* XXX: We assume that IRQ 0 is only used for the ISA timer
* device (clk).
*/
vector = isrc->is_pic->pic_vector(isrc);
if (vector == 0)
clkintr_pending = 1;
critical_enter();
if (ih != NULL && ih->ih_flags & IH_FAST) {
/*
* Execute fast interrupt handlers directly.
* To support clock handlers, if a handler registers
* with a NULL argument, then we pass it a pointer to
* a trapframe as its argument.
*/
TAILQ_FOREACH(ih, &it->it_handlers, ih_next) {
MPASS(ih->ih_flags & IH_FAST);
CTR3(KTR_INTR, "%s: executing handler %p(%p)",
__func__, ih->ih_handler,
ih->ih_argument == NULL ? iframe :
ih->ih_argument);
if (ih->ih_argument == NULL)
ih->ih_handler(iframe);
else
ih->ih_handler(ih->ih_argument);
}
isrc->is_pic->pic_eoi_source(isrc);
error = 0;
凡是总是有例外，fast中断不在中断线程的上下文中运行，而是直接在用户进程的上下文中运行
代码:
} else {
/*
* For stray and threaded interrupts, we mask and EOI the
* source.
*/
isrc->is_pic->pic_disable_source(isrc);
isrc->is_pic->pic_eoi_source(isrc);
if (ih == NULL)
error = EINVAL;
else
error = ithread_schedule(it, !cold);
}
其他的非快速中断则需要调度。这里先应答中断控制器，然后调度。
代码:
critical_exit();
if (error == EINVAL) {
atomic_add_long(isrc->is_straycount, 1);
if (*isrc->is_straycount < MAX_STRAY_LOG)
log(LOG_ERR, "stray irq%d\n", vector);
else if (*isrc->is_straycount == MAX_STRAY_LOG)
log(LOG_CRIT,
"too many stray irq %d's: not logging anymore\n",
vector);
}
td->td_intr_nesting_level--;
}
中断线程调度函数ithread_schedule()处理有关中断线程调度的工作。
代码:
int
ithread_schedule(struct ithd *ithread, int do_switch)
{
struct int_entropy entropy;
struct thread *td;
struct thread *ctd;
struct proc *p;
/*
* If no ithread or no handlers, then we have a stray interrupt.
*/
if ((ithread == NULL) || TAILQ_EMPTY(&ithread->it_handlers))
return (EINVAL);
ctd = curthread;
/*
* If any of the handlers for this ithread claim to be good
* sources of entropy, then gather some.
*/
if (harvest.interrupt && ithread->it_flags & IT_ENTROPY) {
entropy.vector = ithread->it_vector;
entropy.proc = ctd->td_proc;
random_harvest(&entropy, sizeof(entropy), 2, 0,
RANDOM_INTERRUPT);
}
如果该中断线程有IT_ENTROPY标志，说明可以当作随机数的来源。
代码:
td = ithread->it_td;
p = td->td_proc;
KASSERT(p != NULL, ("ithread %s has no process", ithread->it_name));
CTR4(KTR_INTR, "%s: pid %d: (%s) need = %d",
__func__, p->p_pid, p->p_comm, ithread->it_need);
/*
* Set it_need to tell the thread to keep running if it is already
* running. Then, grab sched_lock and see if we actually need to
* put this thread on the runqueue. If so and the do_switch flag is
* true and it is safe to switch, then switch to the ithread
* immediately. Otherwise, set the needresched flag to guarantee
* that this ithread will run before any userland processes.
*/
ithread->it_need = 1;
设置it_need，可以保证中断线程不会在还有中断的情况下，错过中断而去睡眠，见ithread_loop()。
代码:
mtx_lock_spin(&sched_lock);
if (TD_AWAITING_INTR(td)) {
CTR2(KTR_INTR, "%s: setrunqueue %d", __func__, p->p_pid);
TD_CLR_IWAIT(td);
setrunqueue(td);
if (do_switch &&
(ctd->td_critnest == 1) ) {
KASSERT((TD_IS_RUNNING(ctd)),
("ithread_schedule: Bad state for curthread."));
ctd->td_proc->p_stats->p_ru.ru_nivcsw++;
if (ctd->td_flags & TDF_IDLETD)
ctd->td_state = TDS_CAN_RUN; /* XXXKSE */
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