exit.c

linux的内核源码

#include <errno.h>
#include <signal.h>
#include <sys/wait.h>

#include <linux/sched.h>
#include <linux/kernel.h>
#include <linux/tty.h>
#include <asm/segment.h>

int sys_pause(void);
int sys_close(int fd);

void release(struct task_struct * p)	//释放该任务的资源
{
	int i;

	if (!p)
		return;
	for (i=1 ; i<NR_TASKS ; i++)
		if (task[i]==p) {		//找到该进程的任务号
			task[i]=NULL;
			free_page((long)p);	//释放该任务的页
			schedule();		//重新调度所有任务
			return;
		}
	panic("trying to release non-existent task");
}

static inline void send_sig(long sig,struct task_struct * p,int priv)	//向进程任务传送信号
{
	if (!p || sig<1 || sig>32)
		return;
	if (priv ||
		current->uid==p->uid ||
		current->euid==p->uid ||
		current->uid==p->euid ||
		current->euid==p->euid)
		p->signal |= (1<<(sig-1));			//接收信号
}

void do_kill(long pid,long sig,int priv)
{
	struct task_struct **p = NR_TASKS + task;		//指针指向最后一个任务

	if (!pid) while (--p > &FIRST_TASK) {		//如果进程号为0（初始进程）
		if (*p && (*p)->pgrp == current->pid)
			send_sig(sig,*p,priv);
	} else if (pid>0) while (--p > &FIRST_TASK) {	//如果进程号不是初始进程号
		if (*p && (*p)->pid == pid)
			send_sig(sig,*p,priv);
	} else if (pid == -1) while (--p > &FIRST_TASK)	//如果PID=-1，那么就给所有的任务发信号
		send_sig(sig,*p,priv);
	else while (--p > &FIRST_TASK)			//如果PID〈-1
		if (*p && (*p)->pgrp == -pid)
			send_sig(sig,*p,priv);
}

int sys_kill(int pid,int sig)
{
	do_kill(pid,sig,!(current->uid || current->euid));
	return 0;
}

int do_exit(long code)
{
	int i;

	free_page_tables(get_base(current->ldt[1]),get_limit(0x0f));	//释放本进程的代码段的页表
	free_page_tables(get_base(current->ldt[2]),get_limit(0x17));	//释放本进程的数据段的页表
	for (i=0 ; i<NR_TASKS ; i++)		//将本进程的子进程的父设为0，那么这些子任务不就成了孤儿？
		if (task[i] && task[i]->father == current->pid)
			task[i]->father = 0;
	for (i=0 ; i<NR_OPEN ; i++)			//关闭该进程打开的所有文件
		if (current->filp[i])
			sys_close(i);			//在open.c中定义
	iput(current->pwd);				//释放本进程所在目录的INODE
	current->pwd=NULL;
	iput(current->root);				//释放本进程根目录的INODE
	current->root=NULL;
	if (current->leader && current->tty >= 0)		//释放本进程占用的TTY
		tty_table[current->tty].pgrp = 0;
	if (last_task_used_math == current)
		last_task_used_math = NULL;
	if (current->father) {			//如果该进程有父进程
		current->state = TASK_ZOMBIE;
		do_kill(current->father,SIGCHLD,1);	//给相应的任务发信号
		current->exit_code = code;
	} else
		release(current);			//释放当前任务资源
	schedule();
	return (-1);	/* just to suppress warnings */
}

int sys_exit(int error_code)
{
	return do_exit((error_code&0xff)<<8);
}

int sys_waitpid(pid_t pid,int * stat_addr, int options)
{
	int flag=0;
	struct task_struct ** p;

	verify_area(stat_addr,4);
repeat:
	for(p = &LAST_TASK ; p > &FIRST_TASK ; --p)
		if (*p && *p != current &&
		   (pid==-1 || (*p)->pid==pid ||
		   (pid==0 && (*p)->pgrp==current->pgrp) ||
		   (pid<0 && (*p)->pgrp==-pid)))
			if ((*p)->father == current->pid) {	//如果任务是当前任务的子任务
				flag=1;
				if ((*p)->state==TASK_ZOMBIE) {
					put_fs_long((*p)->exit_code,
						(unsigned long *) stat_addr);	//保存本任务的退出码到stat_addr
					current->cutime += (*p)->utime;	//当前进程的时间加上要释放的子进程时间
					current->cstime += (*p)->stime;
					flag = (*p)->pid;
					release(*p);		//释放子进程
					return flag;
				}
			}
	if (flag) {
		if (options & WNOHANG)
			return 0;
		sys_pause();				//暂停当前任务
		if (!(current->signal &= ~(1<<(SIGCHLD-1))))	//如果当前任务没有接收到SIGCHLD信号，循环
			goto repeat;
		else
			return -EINTR;
	}
	return -ECHILD;
}