linux-kernel - Re: [PATCH 08/24] proc: pick out a function to iterate task children

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Message-ID: <20150718212223.GA10240@redhat.com>
Date:	Sat, 18 Jul 2015 23:22:23 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Andrew Vagin <avagin@...il.com>
Cc:	Andrey Vagin <avagin@...nvz.org>, linux-kernel@...r.kernel.org,
	linux-api@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Cyrill Gorcunov <gorcunov@...nvz.org>,
	Pavel Emelyanov <xemul@...allels.com>,
	Roger Luethi <rl@...lgate.ch>, Arnd Bergmann <arnd@...db.de>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	David Ahern <dsahern@...il.com>,
	Andy Lutomirski <luto@...capital.net>,
	Pavel Odintsov <pavel.odintsov@...il.com>
Subject: Re: [PATCH 08/24] proc: pick out a function to iterate task
	children

On 07/17, Andrew Vagin wrote:
>
> On Tue, Jul 14, 2015 at 08:02:35PM +0200, Oleg Nesterov wrote:
> > On 07/06, Andrey Vagin wrote:
> > >
> > > -static struct pid *
> > > -get_children_pid(struct inode *inode, struct pid *pid_prev, loff_t pos)
> > > +static struct task_struct *
> > > +task_next_child(struct task_struct *parent, struct task_struct *prev, unsigned int pos)
> > >  {
> >
> > I won't really argue, just a question...
> >
> > So this patch changes it to accept/return task_struct rather pid. Why?
> > it is better to get/put "struct pid" only, not the whole task_struct.
> >
> > If another caller want task_struct, the necessary conversion is simple.
>
> Another caller wants task_struct.
>
> Currently this function receives pid and converts it into task_struct, then
> gets the next child and returns its pid.

Exactly because we try to avoid get_task_struct() if possible.

> So I try to avoid extra
> conversion in task_diag code.

Which is simple. And perhaps even iter->task can actually be iter->pid.

But as I said I won't really argue. And just in case, I personally think
this series makes sense, although I can't review the netlink interface.

Oleg.

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