xenomai 3.0.2 -任务切换《xnarch_switch_to》

1.xnarch_switch_to

void xnarch_switch_to(struct xnthread *out, struct xnthread *in)
{
    struct xnarchtcb *out_tcb = &out->tcb, *in_tcb = &in->tcb;
    struct mm_struct *prev_mm, *next_mm;
    struct task_struct *next;

    next = in_tcb->core.host_task;
    prev_mm = out_tcb->core.active_mm;

    next_mm = in_tcb->core.mm;
    //首先，检查是否为内核线程还是用户进程
    if (next_mm == NULL) {
        //kernel thread,copy mm from previous process.
        in_tcb->core.active_mm = prev_mm;
        enter_lazy_tlb(prev_mm, next);
    } else {
        ipipe_switch_mm_head(prev_mm, next_mm, next);
        /*
         * We might be switching back to the root thread,
         * which we preempted earlier, shortly after "current"
         * dropped its mm context in the do_exit() path
         * (next->mm == NULL). In that particular case, the
         * kernel expects a lazy TLB state for leaving the mm.
         */
        if (next->mm == NULL)
            enter_lazy_tlb(prev_mm, next);
    }

    __asm_thread_s.witch(out_tcb->core.tip, in_tcb->core.tip);
}