linux-kernel - Re: [RFC][PATCH 05/11] pids: Move the pgrp and session pid pointers from task_struct to signal

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Message-ID: <20180717115952.GA29647@redhat.com>
Date:   Tue, 17 Jul 2018 13:59:52 +0200
From:   Oleg Nesterov <oleg@...hat.com>
To:     "Eric W. Biederman" <ebiederm@...ssion.com>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-kernel@...r.kernel.org, Wen Yang <wen.yang99@....com.cn>,
        majiang <ma.jiang@....com.cn>
Subject: Re: [RFC][PATCH 05/11] pids: Move the pgrp and session pid pointers
 from task_struct to signal_struct

This is a bit offtopic/cosmetic and we can do this later, just for record
before I forget this...

On 07/10, Eric W. Biederman wrote:
>
> +static struct pid **task_pid_ptr(struct task_struct *task, enum pid_type type)
> +{
> +	return (type == PIDTYPE_PID) ?
> +		&task->thread_pid :
> +		(type == __PIDTYPE_TGID) ?
> +		&task->signal->leader_pid :
> +		&task->signal->pids[type];
> +}

This new helper is (simplified after you removed __PIDTYPE_TGID/leader_pid) can
have more users: task_pid_type(), init_task_pid(). In fact even (say) task_tgid()
can use it if we export it inline.

And if we make task_pid_ptr() the only user of signal->pids[] array we can shrink
it, signal->pids[0] is not used. Or may be we can simply redefine enum pid_type,
we can define PIDTYPE_PID == -1 or move it at the end, or do something else.

Once again, this is just random/minor thoughts, feel free to ignore.

Oleg.