linux-kernel - Re: [PATCH v7 1/2] fork: extend clone3() to support setting a PID

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Date:   Mon, 11 Nov 2019 17:32:10 +0100
From:   Oleg Nesterov <oleg@...hat.com>
To:     Christian Brauner <christian.brauner@...ntu.com>
Cc:     Adrian Reber <areber@...hat.com>,
        Eric Biederman <ebiederm@...ssion.com>,
        Pavel Emelyanov <ovzxemul@...il.com>,
        Jann Horn <jannh@...gle.com>,
        Dmitry Safonov <0x7f454c46@...il.com>,
        linux-kernel@...r.kernel.org, Andrei Vagin <avagin@...il.com>,
        Mike Rapoport <rppt@...ux.ibm.com>,
        Radostin Stoyanov <rstoyanov1@...il.com>
Subject: Re: [PATCH v7 1/2] fork: extend clone3() to support setting a PID

On 11/11, Christian Brauner wrote:
>
> On Mon, Nov 11, 2019 at 04:40:28PM +0100, Adrian Reber wrote:
> > > note also that this way we can easily allow set_tid[some_level] == 0, we can
> > > simply do
> > >
> > > 	-	if (xxx < 1 || xxx >= pid_max)
> > > 	+	if (xxx < 0 || xxx >= pid_max)
> > >
> > > although I don't think this is really useful.
> >
> > Yes. I explicitly didn't allow 0 as a PID as I didn't thought it would
> > be useful (or maybe even valid).
>
> How do you express: I don't care about a specific pid in pidns level
> <n>,

Yes,

> Wouldn't that be potentially useful?

As I said above, I don't think this is really useful. Just I was thinking
out loud.

I suggested to cache set_tid[pos] rather than pos because this makes the
code simpler, not because this allows this allows to "naturally" handle
the case when set_tid[pos] == 0. Sorry it it was not clear.

Oleg.