Re: Python or Perl for a Debian maintainance project?

[Philip Brown <phil@bolthole.com>]

On Thu, Feb 19, 2004 at 10:42:56AM +0800, Isaac To wrote:
> ...
> Perhaps you want to enlighten the kernel developers.  A typical kernel
> function, say sys_getpgid, is implemented (in 2.4.24 kernel) like this:
> 
> asmlinkage long sys_setpgid(pid_t pid, pid_t pgid)
> {
>     ....
> 
>         /* 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);
> 
>         err = -ESRCH;
>         p = find_task_by_pid(pid);
>         if (!p)
>                 goto out;
> 
>         if (p->p_pptr == current || p->p_opptr == current) {
>                 err = -EPERM;
>                 if (p->session != current->session)
>                         goto out;
>...
> out:
>         /* All paths lead to here, thus we are safe. -DaveM */
>         read_unlock(&tasklist_lock);
>         return err;
> }




An alternative method in C, if you dont want to write a new function,
is to fake one in-line, using a one-shot while loop.
No goto required. Just an indent level.
Which has a nice side effect of very clearly demarking,
"Hey, something special is going on here"
 (ie: I'm HOLDING A LOCK)



asmlinkage long sys_setpgid(pid_t pid, pid_t pgid)
{
	int err=0;

	....

	read_lock(&tasklist_lock);
	do {
		p = find_task_by_pid(pid);
		if (!p){
			err=-ESRCH;
			break;
		}
		if (p->session != current->session){
			err = -EPERM;
			break;
		}

		... /* do stuff... */

	} while (0); /* allow for early termination */

	read_unlock(&tasklist_lock);
	return err;
}