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exit.c 代码分析笔记
release
释放进程的函数release() 主要根据指定进程的任务数据结构指针，在任务数组中删除指定的进程指针，释放相关内存页，并立刻让内核重新调度进程的运行。
void release(struct task_struct * p) //释放p指向的进程
{int i;if (!p) //常规检测p是否为0return;if (p == current) { //不能把自己给释放了printk("task releasing itself\n\r");return;}for (i=1 ; i<NR_TASKS ; i++) //扫描所有的进程if (task[i]==p) { //找出p进程task[i]=NULL; //把p置空/* Update links */if (p->p_osptr) //调整链表p->p_osptr->p_ysptr = p->p_ysptr;if (p->p_ysptr)p->p_ysptr->p_osptr = p->p_osptr;elsep->p_pptr->p_cptr = p->p_osptr;free_page((long)p); //释放p进程占用的内存页schedule();//任务调度return;}panic("trying to release non-existent task");
}bad_task_ptr 和audit_ptree
#ifdef DEBUG_PROC_TREE //下面这部分代码是调试用的
/** Check to see if a task_struct pointer is present in the task[] array* Return 0 if found, and 1 if not found.*/
int bad_task_ptr(struct task_struct *p)
{int i;if (!p)return 0;for (i=0 ; i<NR_TASKS ; i++)if (task[i] == p)return 0;return 1; //如果p不在task数组里面，那这个指针就有问题！
}/** This routine scans the pid tree and make sure the rep invarient still* holds. Used for debugging only, since it's very slow....** It looks a lot scarier than it really is.... we're doing ænothing more* than verifying the doubly-linked list foundæin p_ysptr and p_osptr,* and checking it corresponds with the process tree defined by p_cptr and* p_pptr;*/
void audit_ptree() //其实不难，就是打印进程树的相关信息，方便调试用
{int i;for (i=1 ; i<NR_TASKS ; i++) {if (!task[i])continue;if (bad_task_ptr(task[i]->p_pptr))printk("Warning, pid %d's parent link is bad\n",task[i]->pid);if (bad_task_ptr(task[i]->p_cptr))printk("Warning, pid %d's child link is bad\n",task[i]->pid);if (bad_task_ptr(task[i]->p_ysptr))printk("Warning, pid %d's ys link is bad\n",task[i]->pid);if (bad_task_ptr(task[i]->p_osptr))printk("Warning, pid %d's os link is bad\n",task[i]->pid);if (task[i]->p_pptr == task[i])printk("Warning, pid %d parent link points to self\n");if (task[i]->p_cptr == task[i])printk("Warning, pid %d child link points to self\n");if (task[i]->p_ysptr == task[i])printk("Warning, pid %d ys link points to self\n");if (task[i]->p_osptr == task[i])printk("Warning, pid %d os link points to self\n");if (task[i]->p_osptr) {if (task[i]->p_pptr != task[i]->p_osptr->p_pptr)printk("Warning, pid %d older sibling %d parent is %d\n",task[i]->pid, task[i]->p_osptr->pid,task[i]->p_osptr->p_pptr->pid);if (task[i]->p_osptr->p_ysptr != task[i])printk("Warning, pid %d older sibling %d has mismatched ys link\n",task[i]->pid, task[i]->p_osptr->pid);}if (task[i]->p_ysptr) {if (task[i]->p_pptr != task[i]->p_ysptr->p_pptr)printk("Warning, pid %d younger sibling %d parent is %d\n",task[i]->pid, task[i]->p_osptr->pid,task[i]->p_osptr->p_pptr->pid);if (task[i]->p_ysptr->p_osptr != task[i])printk("Warning, pid %d younger sibling %d has mismatched os link\n",task[i]->pid, task[i]->p_ysptr->pid);}if (task[i]->p_cptr) {if (task[i]->p_cptr->p_pptr != task[i])printk("Warning, pid %d youngest child %d has mismatched parent link\n",task[i]->pid, task[i]->p_cptr->pid);if (task[i]->p_cptr->p_ysptr)printk("Warning, pid %d youngest child %d has non-NULL ys link\n",task[i]->pid, task[i]->p_cptr->pid);}}
}
#endif /* DEBUG_PROC_TREE */send_sig
static inline int send_sig(long sig,struct task_struct * p,int priv) //给进程p，发送信号。priv 是强制发送信号的标识
{if (!p) //常规的p非空检测return -EINVAL;if (!priv && (current->euid!=p->euid) && !suser())//如果不具有超级用户权限，又不是当前session里面的进程，且没有强制发送信号，进入if，returnreturn -EPERM;if ((sig == SIGKILL) || (sig == SIGCONT)) { //如果要发送的信号是SIGKILL或者SIGCONTif (p->state == TASK_STOPPED) //如果当前进程处于stop状态，则将其置于TASK_RUNNING状态p->state = TASK_RUNNING;p->exit_code = 0;p->signal &= ~( (1<<(SIGSTOP-1)) | (1<<(SIGTSTP-1)) |(1<<(SIGTTIN-1)) | (1<<(SIGTTOU-1)) ); //消除SIGSTOP SIGTSTP SIGTTIN SIGTTOU}/* If the signal will be ignored, don't even post it */if ((int) p->sigaction[sig-1].sa_handler == 1) //如果handler是 ignore 就不要送信号鸟。。return 0;/* Depends on order SIGSTOP, SIGTSTP, SIGTTIN, SIGTTOU */if ((sig >= SIGSTOP) && (sig <= SIGTTOU))//如果信号含有 SIGSTOP, SIGTSTP, SIGTTIN, SIGTTOU其中任何信号，那么就消除SIGCONT信号p->signal &= ~(1<<(SIGCONT-1));/* Actually deliver the signal */p->signal |= (1<<(sig-1)); //最后这里才把信号写入信号变量return 0;
}session_of_pgrp
int session_of_pgrp(int pgrp) //获取process group的session ID ，没有找到返回-1
{struct task_struct **p;for (p = &LAST_TASK ; p > &FIRST_TASK ; --p)if ((*p)->pgrp == pgrp)return((*p)->session);return -1;
}kill_pg
int kill_pg(int pgrp, int sig, int priv) //给指定的进程组发送信号
{struct task_struct **p;int err,retval = -ESRCH; //指定的进程不存在int found = 0;if (sig<1 || sig>32 || pgrp<=0)return -EINVAL;for (p = &LAST_TASK ; p > &FIRST_TASK ; --p)if ((*p)->pgrp == pgrp) { //对每一个属于process group的进程发送信号sigif (sig && (err = send_sig(sig,*p,priv)))retval = err;elsefound++;}return(found ? 0 : retval);
}kill_proc
int kill_proc(int pid, int sig, int priv) //给指定进程发送信号
{struct task_struct **p;if (sig<1 || sig>32)return -EINVAL;for (p = &LAST_TASK ; p > &FIRST_TASK ; --p)if ((*p)->pid == pid)return(sig ? send_sig(sig,*p,priv) : 0);return(-ESRCH);
}
sys_kill
系统调用sys_kill 用于项进程发送任何指定的信号，根据参数pid不同的数值，该系统调用会向不同的进或进程组发送信号。
/** POSIX specifies that kill(-1,sig) is unspecified, but what we have* is probably wrong. Should make it like BSD or SYSV.*/
int sys_kill(int pid,int sig)
{struct task_struct **p = NR_TASKS + task;int err, retval = 0;if (!pid) //如果是进程0 init ，用最高权限发送信号，将信号发送给当前进程所处进程组的所有进程return(kill_pg(current->pid,sig,0));if (pid == -1) { //如果 pid是-1，把信号发送到除了init进程外的所有进程！while (--p > &FIRST_TASK)if (err = send_sig(sig,*p,0))retval = err;return(retval);}if (pid < 0) //如果pid<0，发送到|pid| 所处进程组的所有进程return(kill_pg(-pid,sig,0));/* Normal kill */return(kill_proc(pid,sig,0)); //否则，发送到进程pid
}is_orphaned_pgrp
关于孤儿进程组的探讨
/** Determine if a process group is "orphaned", according to the POSIX* definition in 2.2.2.52. Orphaned process groups are not to be affected* by terminal-generated stop signals. Newly orphaned process groups are* to receive a SIGHUP and a SIGCONT.** "I ask you, have you ever known what it is to be an orphan?"*/
int is_orphaned_pgrp(int pgrp) //判断是否为一个孤儿进程组
{struct task_struct **p;for (p = &LAST_TASK ; p > &FIRST_TASK ; --p) {if (!(*p) || //如果进程不存在，下一个((*p)->pgrp != pgrp) || // 如果进程所处的进程组不是pgrp，下一个((*p)->state == TASK_ZOMBIE) || // 进程的状态是zombie，下一个((*p)->p_pptr->pid == 1)) //进程parent是init ,下一个continue;if (((*p)->p_pptr->pgrp != pgrp) && //如果父进程所在的组不在pgrp，但是父进程所在的session存在((*p)->p_pptr->session == (*p)->session))return 0;}return(1); /* (sighing) "Often!" */
}
has_stopped_jobs
static int has_stopped_jobs(int pgrp) //判断进程组内是否有进程处于TASK_STOPPED状态
{struct task_struct ** p;for (p = &LAST_TASK ; p > &FIRST_TASK ; --p) {if ((*p)->pgrp != pgrp)continue;if ((*p)->state == TASK_STOPPED)return(1);}return(0);
}do_exit
volatile void do_exit(long code)
{struct task_struct *p;int i;free_page_tables(get_base(current->ldt[1]),get_limit(0x0f));free_page_tables(get_base(current->ldt[2]),get_limit(0x17));/*这里采用的两个参数0x0f即1111B，因此他指向的段优先级为3，存储在LDT表中，索引为1。也就是当前任务段的代码段描述符。另外一个参数0x17即10111B，因此他指向的段优先级为3，存储在LDT表中，索引为2.也就是当前任务的数及堆栈段描述符。这样，通过get_limit(0x0f)和get_limit(0x17)就得到了当前任务代码段和数据堆栈段的长度。因此，
free_page_tables(get_base(current->ldt[1]),get_limit(0x0f));
free_page_tables(get_base(current->ldt[2]),get_limit(0x17));就释放了当前任务的代码段和数据堆栈段。*/for (i=0 ; i<NR_OPEN ; i++)if (current->filp[i]) //filp文件结构指针表，filp[i]就是文件i被打开的IDsys_close(i); //关闭进程当前打开的文件iput(current->pwd); //和fs inode有关系current->pwd = NULL; //当前进程的工作目录置为NULLiput(current->root);//和fs inode有关系current->root = NULL;//当前进程的根目录置为NULLiput(current->executable);//和fs inode有关系current->executable = NULL;//当前进程的执行程序文件的i节点置为NULLiput(current->library);//和fs inode有关系current->library = NULL;//当前进程的库文件置为NULLcurrent->state = TASK_ZOMBIE; //状态置为TASK_ZOMBIEcurrent->exit_code = code; //设置进程退出码/** Check to see if any process groups have become orphaned* as a result of our exiting, and if they have any stopped* jobs, send them a SIGUP and then a SIGCONT. (POSIX 3.2.2.2)** Case i: Our father is in a different pgrp than we are* and we were the only connection outside, so our pgrp* is about to become orphaned.*/if ((current->p_pptr->pgrp != current->pgrp) &&(current->p_pptr->session == current->session) &&is_orphaned_pgrp(current->pgrp) &&has_stopped_jobs(current->pgrp)) { //如果当前进程组是个orphaned groupkill_pg(current->pgrp,SIGHUP,1);//用于只是这些进程和当前session 断开联系，我这里不是很明白为什么要发送SIGHUP 和 SIGCONTkill_pg(current->pgrp,SIGCONT,1);}/* Let father know we died */current->p_pptr->signal |= (1<<(SIGCHLD-1)); // 告诉parent process 当前进程要挂掉鸟/** This loop does two things:** A. Make init inherit all the child processes* B. Check to see if any process groups have become orphaned* as a result of our exiting, and if they have any stopped* jons, send them a SIGUP and then a SIGCONT. (POSIX 3.2.2.2)*/if (p = current->p_cptr) { //如果当前进程的child process 非空，进入ifwhile (1) {p->p_pptr = task[1]; //让init进程领养current 进程的child 进程if (p->state == TASK_ZOMBIE) //p进程沦为zombietask[1]->signal |= (1<<(SIGCHLD-1)); //向init进程发送SIGCHLD信号/** process group orphan check* Case ii: Our child is in a different pgrp* than we are, and it was the only connection* outside, so the child pgrp is now orphaned.*/if ((p->pgrp != current->pgrp) &&(p->session == current->session) &&is_orphaned_pgrp(p->pgrp) &&has_stopped_jobs(p->pgrp)) {//判断p进程所在进程组是否是orphaned group，如果是。发送SIGHUP和SIGCONT信号kill_pg(p->pgrp,SIGHUP,1);kill_pg(p->pgrp,SIGCONT,1);}if (p->p_osptr) { //如果p_osptr非空，则把p->p_osptr赋值给pp = p->p_osptr;continue; //下一轮循环，知道p_osptr为NULL}/** This is it; link everything into init's children* and leave*/p->p_osptr = task[1]->p_cptr;task[1]->p_cptr->p_ysptr = p;task[1]->p_cptr = current->p_cptr; //这三句把这个child process —— p 更新为 init 进程的 最年轻的child processcurrent->p_cptr = 0; //处理完所有的child process ，把 当前进程的p_cptr置为NULLbreak; //处理完了跳出while}}if (current->leader) { //如果当前进程是session leaderstruct task_struct **p;struct tty_struct *tty;if (current->tty >= 0) { //切断当前进程和terminal 的联系tty = TTY_TABLE(current->tty); //tty 还没看布吉岛。。。if (tty->pgrp>0)kill_pg(tty->pgrp, SIGHUP, 1);tty->pgrp = 0;tty->session = 0;}for (p = &LAST_TASK ; p > &FIRST_TASK ; --p) //把所有和当前进程同一个session的进程的tty都置为-1if ((*p)->session == current->session)(*p)->tty = -1;}if (last_task_used_math == current)//数字协处理器木有看。。。布吉岛，//但是语句的意思是上次用过协处理器的进程是当前进程的话酒吧last_task_used_math 置为NULLlast_task_used_math = NULL;
#ifdef DEBUG_PROC_TREEaudit_ptree();
#endifschedule(); //进程调度
}sys_exit
int sys_exit(int error_code) //系统调用sys_exit函数，通过调用do_exit 函数来实现
{do_exit((error_code&0xff)<<8);//error_code是用户程序提供的退出状态信息，只有低字节有效//把error_code 左移八位是空出第八位供wait()和waitpid()函数使用
}sys_waitpid
用于挂起当前进程，知道pid指定的进程退出或者收到要求该进程终止的信号，或者是需要调用一个signal handler。如果pid 所指的进程早已退出(zombie)则本调用立刻返回。子进程的所有资源将被释放。
int sys_waitpid(pid_t pid,unsigned long * stat_addr, int options)//其实我一般都木有怎么用stat_addr 这边选项，一般我都NULL了 <—_<—
//waitpid居然放在。。。exit.c 里，木有别的，只有惊奇
{int flag;struct task_struct *p;unsigned long oldblocked;verify_area(stat_addr,4); //验证stat_addr 地址处4byte 可写
repeat:flag=0;for (p = current->p_cptr ; p ; p = p->p_osptr) {if (pid>0) {if (p->pid != pid) //找到pid描述的child进程的指针continue;} else if (!pid) { //如果pid等于0， 找到pid 所在的进程组if (p->pgrp != current->pgrp)continue;} else if (pid != -1) { //如果pid < -1 ，找到|pid|所在的进程组if (p->pgrp != -pid)continue;}// 如果以上判断田间都没进if去，pid = -1 ，这里不是很明白，看完fork之后回头再updateswitch (p->state) {case TASK_STOPPED: //如果进程p处于TASK_STOPPED状态if (!(options & WUNTRACED) || //如果option的WUNTRACED 没有置位或者 exit_code 等于0 ,对下一个older child进行检测!p->exit_code)continue;put_fs_long((p->exit_code << 8) | 0x7f,stat_addr);//把第一个参数写入第二个参数指向的地址p->exit_code = 0; //正常退出return p->pid; //返回结束child 的pidcase TASK_ZOMBIE:current->cutime += p->utime;current->cstime += p->stime; //更新时间参数flag = p->pid;put_fs_long(p->exit_code, stat_addr); //把p->exit_code 写入stat_addrrelease(p); //释放进程p占用的内存页
#ifdef DEBUG_PROC_TREEaudit_ptree();
#endifreturn flag;default:flag=1;continue;}}if (flag) { //存在不处于TASK_STOPPED 和TASK_ZOMBIE状态的进程if (options & WNOHANG) //如果WNOHANG(表示若没有子进程处于退出或者终止状态就返回)在options中置位，就立刻返回0；return 0; //一般我是不会用WNOHANG的。。。坦白的说我都没用过current->state=TASK_INTERRUPTIBLE; //更新进程状态，置为TASK_INTERRUPTIBLEoldblocked = current->blocked; //当前进程阻塞的信号储存于oldblocked中current->blocked &= ~(1<<(SIGCHLD-1)); //消除当前进程中的SIGCHLD信号schedule();//进程调度current->blocked = oldblocked; //回复原来的信号图if (current->signal & ~(current->blocked | (1<<(SIGCHLD-1))))//如果收到了除了SIGCHLD之外的其他信号，return 挂掉return -ERESTARTSYS;elsegoto repeat; //否则goto到repeat 继续重复，直到return 出去。。。。。原来是这样waitpid的啊！}return -ECHILD; //没有找到pid对应的child process，返回错误码
}
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