[C++] 纯文本查看 复制代码
asmlinkage long sys_getpgid(pid_t pid)
{
if (!pid) {
return current->pgrp;
} else {
int retval;
struct task_struct *p;
read_lock(&tasklist_lock);
p = find_task_by_pid(pid);
retval = -ESRCH;
if (p)
retval = p->pgrp;
read_unlock(&tasklist_lock);
return retval;
}
}
/*
* This needs some heavy checking ...
* I just haven't the stomach for it. I also don't fully
* understand sessions/pgrp etc. Let somebody who does explain it.
*
* OK, I think I have the protection semantics right.... this is really
* only important on a multi-user system anyway, to make sure one user
* can't send a signal to a process owned by another. -TYT, 12/12/91
*
* Auch. Had to add the 'did_exec' flag to conform completely to POSIX.
* LBT 04.03.94
*/
asmlinkage long sys_setpgid(pid_t pid, pid_t pgid)
{
struct task_struct * p;
int err = -EINVAL;
if (!pid)
pid = current->pid;
if (!pgid)
pgid = pid;
if (pgid < 0)
return -EINVAL;
/* From this point forward we keep holding onto the tasklist lock
* so that our parent does not change from under us. -DaveM
*/
read_lock(&tasklist_lock);
/*第一前提: 先要验证要设定的进程是否存在,不存在的话不能做事*/
err = -ESRCH;
p = find_task_by_pid(pid);
if (!p)
goto out;
/* 第二前提: 先要检查做这个操作的权限:
当前进程只能将自身和其子进程设置为进程组id,并且
当前进程和其子进程必须属于同一次会话
(同组的进程一定属于同一次会话)
*/
if (p->p_pptr == current || p->p_opptr == current)
{
err = -EPERM;
/*如果不属于同一次会话(同一次控制台),不可以*/
if (p->session != current->session)
goto out;
err = -EACCES;
/*某个子进程调用 exec 函数之后, 就不能再将该子进程的 id 作为进程组 id*/
if (p->did_exec)
goto out;
}
else if (p != current)
goto out;
err = -EPERM;
/*boolean value for session group leader */
/*如果是一次会话的leader,也不可以
注意进程组的首领进程也是可以改变组id的*/
if (p->leader)
goto out;
/*好!几个前提条件全满足了,要做正事了:
但是是不是组号的合法性还没有验证?见后话!*/
/*要设进程号不是要设定的组号,如果是,直接设,因为这
意味着是增加了以自己的pid作为新的组号的进程组,这个
进程也将成为新进程组的首领进程,所以在此根本不用比较
会话号,自己对自己肯定是同一次会话.如果条件不满足,则
要做这些判断*/
if (pgid != pid)
{
struct task_struct * tmp;
for_each_task (tmp)
{
/*能不能找到一个进程,组号正好是要设定的组号,
并且和要设定的进程属于同一个控制台(同一个会话)
找到才可以设定,其实这里就是要判定组号的合法性,
即必须是一个已经存在的组,而且和当前同一次会话才
可以操作,这个也不能忘记,其实就是说:同组的进程
一定属于同一次会话*/
if (tmp->pgrp == pgid &&
tmp->session == current->session)
goto ok_pgid;
}
goto out;
}
ok_pgid:
p->pgrp = pgid;
err = 0;
out:
/* All paths lead to here, thus we are safe. -DaveM */
read_unlock(&tasklist_lock);
return err;
}
asmlinkage long sys_getsid(pid_t pid)
{
if (!pid) {
return current->session;
} else {
int retval;
struct task_struct *p;
read_lock(&tasklist_lock);
p = find_task_by_pid(pid);
retval = -ESRCH;
if(p)
retval = p->session;
read_unlock(&tasklist_lock);
return retval;
}
}
asmlinkage long sys_setsid(void)
{
struct task_struct * p;
int err = -EPERM;
read_lock(&tasklist_lock);
for_each_task(p)
{
/*如果当前进程是一个进程组的首领进程,
则不能建立一个新的会话*/
if (p->pgrp == current->pid)
goto out;
}
/*将新创建会话的leader设定为创建者就是当前进程*/
current->leader = 1;
/*清楚看见一个新的进程组诞生了
当前进程成为新进程组的首领进程
新会话的id 是当前进程号,也是新会话的leader
*/
current->session = current->pgrp = current->pid;
/*当前进程失去控制终端*/
current->tty = NULL;
current->tty_old_pgrp = 0;
err = current->pgrp;
out:
read_unlock(&tasklist_lock);
return err;
}