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kernel源码（十四）exit.c
本文主要是介绍kernel源码（十四）exit.c，对大家解决编程问题具有一定的参考价值，需要的程序猿们随着小编来一起学习吧！
该源码主要实现进程退出或终止的相关功能
源码
/*
* linux/kernel/exit.c
*
* (C) 1991 Linus Torvalds
*/
#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)
{
int i;
if (!p)
return;
for (i=1 ; i<NR_TASKS ; i++)
if (task[i]==p) {
task[i]=NULL;
free_page((long)p);
schedule();
return;
}
panic("trying to release non-existent task");
}
static inline int send_sig(long sig,struct task_struct * p,int priv)
{
if (!p || sig<1 || sig>32)
return -EINVAL;
if (priv || (current->euid==p->euid) || suser())
p->signal |= (1<<(sig-1));
else
return -EPERM;
return 0;
}
static void kill_session(void)
{
struct task_struct **p = NR_TASKS + task;
while (--p > &FIRST_TASK) {
if (*p && (*p)->session == current->session)
(*p)->signal |= 1<<(SIGHUP-1);
}
}
/*
* XXX need to check permissions needed to send signals to process
* groups, etc. etc. kill() permissions semantics are tricky!
*/
int sys_kill(int pid,int sig)
{
struct task_struct **p = NR_TASKS + task;
int err, retval = 0;
if (!pid) while (--p > &FIRST_TASK) {
if (*p && (*p)->pgrp == current->pid)
if (err=send_sig(sig,*p,1))
retval = err;
} else if (pid>0) while (--p > &FIRST_TASK) {
if (*p && (*p)->pid == pid)
if (err=send_sig(sig,*p,0))
retval = err;
} else if (pid == -1) while (--p > &FIRST_TASK)
if (err = send_sig(sig,*p,0))
retval = err;
else while (--p > &FIRST_TASK)
if (*p && (*p)->pgrp == -pid)
if (err = send_sig(sig,*p,0))
retval = err;
return retval;
}
static void tell_father(int pid)
{
int i;
if (pid)
for (i=0;i<NR_TASKS;i++) {
if (!task[i])
continue;
if (task[i]->pid != pid)
continue;
task[i]->signal |= (1<<(SIGCHLD-1));
return;
}
/* if we don't find any fathers, we just release ourselves */
/* This is not really OK. Must change it to make father 1 */
printk("BAD BAD - no father found\n\r");
release(current);
}
int do_exit(long code)
{
int i;
free_page_tables(get_base(current->ldt[1]),get_limit(0x0f));
free_page_tables(get_base(current->ldt[2]),get_limit(0x17));
for (i=0 ; i<NR_TASKS ; i++)
if (task[i] && task[i]->father == current->pid) {
task[i]->father = 1;
if (task[i]->state == TASK_ZOMBIE)
/* assumption task[1] is always init */
(void) send_sig(SIGCHLD, task[1], 1);
}
for (i=0 ; i<NR_OPEN ; i++)
if (current->filp[i])
sys_close(i);
iput(current->pwd);
current->pwd=NULL;
iput(current->root);
current->root=NULL;
iput(current->executable);
current->executable=NULL;
if (current->leader && current->tty >= 0)
tty_table[current->tty].pgrp = 0;
if (last_task_used_math == current)
last_task_used_math = NULL;
if (current->leader)
kill_session();
current->state = TASK_ZOMBIE;
current->exit_code = code;
tell_father(current->father);
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,unsigned long * stat_addr, int options)
{
int flag, code;
struct task_struct ** p;
verify_area(stat_addr,4);
repeat:
flag=0;
for(p = &LAST_TASK ; p > &FIRST_TASK ; --p) {
if (!*p || *p == current)
continue;
if ((*p)->father != current->pid)
continue;
if (pid>0) {
if ((*p)->pid != pid)
continue;
} else if (!pid) {
if ((*p)->pgrp != current->pgrp)
continue;
} else if (pid != -1) {
if ((*p)->pgrp != -pid)
continue;
}
switch ((*p)->state) {
case TASK_STOPPED:
if (!(options & WUNTRACED))
continue;
put_fs_long(0x7f,stat_addr);
return (*p)->pid;
case TASK_ZOMBIE:
current->cutime += (*p)->utime;
current->cstime += (*p)->stime;
flag = (*p)->pid;
code = (*p)->exit_code;
release(*p);
put_fs_long(code,stat_addr);
return flag;
default:
flag=1;
continue;
}
}
if (flag) {
if (options & WNOHANG)
return 0;
current->state=TASK_INTERRUPTIBLE;
schedule();
if (!(current->signal &= ~(1<<(SIGCHLD-1))))
goto repeat;
else
return -EINTR;
}
return -ECHILD;
}
View Code
进程释放
void release(struct task_struct * p)
{
int i;
if (!p)
return;
for (i=1 ; i<NR_TASKS ; i++) //遍历所有进程
if (task[i]==p) { //找到进程p
task[i]=NULL; 进程指针置为空
free_page((long)p); //释放内存页
schedule(); //重新调度
return; //返回
}
panic("trying to release non-existent task"); //死机了
}
向指定的任务p发送sig信号
static inline int send_sig(long sig,struct task_struct * p,int priv) //priv表示权限
{
if (!p || sig<1 || sig>32)
return -EINVAL;
if (priv || (current->euid==p->euid) || suser()) //如果priv置位，或者是超级用户，或者有效用户id和当前进程的euid相等
p->signal |= (1<<(sig-1)); //则把p进程信号位图的sig信号置位
else
return -EPERM;
return 0;
}
终止会话
static void kill_session(void)
{
struct task_struct **p = NR_TASKS + task;//任务数组的最末一个任务
while (--p > &FIRST_TASK) { //从最末一个任务开始往前循环，但是不包括任务0
if (*p && (*p)->session == current->session) //如果*p的session和当前进程的session相等
(*p)->signal |= 1<<(SIGHUP-1); //向*p发送SIGHUP(挂断)信号
}
}
系统调用kill的实现。
int sys_kill(int pid,int sig)
{
struct task_struct **p = NR_TASKS + task;
int err, retval = 0;
if (!pid) while (--p > &FIRST_TASK) { //如果pid为0时
if (*p && (*p)->pgrp == current->pid)
if (err=send_sig(sig,*p,1))
retval = err;
} else if (pid>0) while (--p > &FIRST_TASK) { //如果pis>0时
if (*p && (*p)->pid == pid)
if (err=send_sig(sig,*p,0))
retval = err;
} else if (pid == -1) while (--p > &FIRST_TASK) //如果pid==-1时
if (err = send_sig(sig,*p,0))
retval = err;
else while (--p > &FIRST_TASK) //如果pid<-1时
if (*p && (*p)->pgrp == -pid)
if (err = send_sig(sig,*p,0))
retval = err;
return retval;
}
通知父进程，向pid发送SIGCHLD信号
static void tell_father(int pid)
{
int i;
if (pid)
for (i=0;i<NR_TASKS;i++) {
if (!task[i])
continue;
if (task[i]->pid != pid)
continue;
task[i]->signal |= (1<<(SIGCHLD-1)); //向task[i]进程发送SIGCHLD信号
return;
}
/* if we don't find any fathers, we just release ourselves */
/* This is not really OK. Must change it to make father 1 */
printk("BAD BAD - no father found\n\r");
release(current); //如果没找到父进程，则释放进程
}
int do_exit(long code)
{
int i;
free_page_tables(get_base(current->ldt[1]),get_limit(0x0f));//释放当前代码段和数据段所在的内存页
free_page_tables(get_base(current->ldt[2]),get_limit(0x17));
for (i=0 ; i<NR_TASKS ; i++)
if (task[i] && task[i]->father == current->pid) { //如果当前进程有子进程，则设置子进程的father为1
task[i]->father = 1;
if (task[i]->state == TASK_ZOMBIE) //如果子进程已处于僵死状态，则向进程1发送SIGCHLD信号
/* assumption task[1] is always init */
(void) send_sig(SIGCHLD, task[1], 1);
}
for (i=0 ; i<NR_OPEN ; i++) //关闭进程打开的所有的文件
if (current->filp[i])
sys_close(i);
iput(current->pwd);
current->pwd=NULL;
iput(current->root);
current->root=NULL;
iput(current->executable);
current->executable=NULL;
if (current->leader && current->tty >= 0) //如果当前进程是头进程，并且有控制终端
tty_table[current->tty].pgrp = 0; //则把终端释放掉
if (last_task_used_math == current) //如果进程上次使用过协处理器
last_task_used_math = NULL;
if (current->leader) //如果当前进程是头进程
kill_session(); //终止会话相关的进程
current->state = TASK_ZOMBIE; //把当前进程的状态设置为僵死状态。
current->exit_code = code; //退出代码
tell_father(current->father); //通知父进程，向当前进程的父进程发送SIGCHLD信号
schedule(); //重新调度
return (-1); /* just to suppress warnings */
}
系统调用exit的实现
int sys_exit(int error_code) //error_code是用户程序提供的退出状态信息
{
return do_exit((error_code&0xff)<<8);
}
int sys_waitpid(pid_t pid,unsigned long * stat_addr, int options)
{
int flag, code;
struct task_struct ** p;
verify_area(stat_addr,4);
repeat:
flag=0;
for(p = &LAST_TASK ; p > &FIRST_TASK ; --p) {
if (!*p || *p == current)
continue;
if ((*p)->father != current->pid)
continue;
if (pid>0) {
if ((*p)->pid != pid)
continue;
} else if (!pid) {
if ((*p)->pgrp != current->pgrp)
continue;
} else if (pid != -1) {
if ((*p)->pgrp != -pid)
continue;
}
switch ((*p)->state) {
case TASK_STOPPED:
if (!(options & WUNTRACED))
continue;
put_fs_long(0x7f,stat_addr);
return (*p)->pid;
case TASK_ZOMBIE:
current->cutime += (*p)->utime;
current->cstime += (*p)->stime;
flag = (*p)->pid;
code = (*p)->exit_code;
release(*p);
put_fs_long(code,stat_addr);
return flag;
default:
flag=1;
continue;
}
}
if (flag) {
if (options & WNOHANG)
return 0;
current->state=TASK_INTERRUPTIBLE;
schedule();
if (!(current->signal &= ~(1<<(SIGCHLD-1))))
goto repeat;
else
return -EINTR;
}
return -ECHILD;
}
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