void sys_exit()
{
/*
a) Free the data structures and resources of this process (physical memory, task_struct,
and so). It uses the free_frame function to free physical pages.
b) Use the scheduler interface to select a new process to be executed and make a context
switch.*/
update_user_to_system();
free_user_pages(current());
update_current_state_rr(&freequeue);
sched_next_rr();
}
* 使用次数，若是共享的，则分配一个新的页目录，并将原页目录引用数减1。
*/
BOOL pre_replace_user_zone(void)
{
free_user_pages(current->code_start,
current->data_end-current->code_start, 1);
if(1 < mem_map[M2MAP(current->tss.cr3)]) {
unsigned long addr = current->tss.cr3;
if(!copy_kernel_page_dir(&(current->tss.cr3))) {
k_printf("free_user_zone: have no free-page!");
return FALSE;
}
load_cr3(current->tss.cr3);
--mem_map[M2MAP(addr)];
d_printf("set cr3 finished, cr3 = %x.\n", current->tss.cr3);
}
