linux-kernel - Re: [PATCH 1/2] pid: add pidfd

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Date:   Fri, 17 May 2019 00:53:41 +1000
From:   Aleksa Sarai <cyphar@...har.com>
To:     Christian Brauner <christian@...uner.io>
Cc:     Daniel Colascione <dancol@...gle.com>,
        Jann Horn <jannh@...gle.com>, Oleg Nesterov <oleg@...hat.com>,
        Al Viro <viro@...iv.linux.org.uk>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Arnd Bergmann <arnd@...db.de>,
        David Howells <dhowells@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        elena.reshetova@...el.com, Kees Cook <keescook@...omium.org>,
        Andy Lutomirski <luto@...capital.net>,
        Andy Lutomirski <luto@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-alpha@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-ia64@...r.kernel.org, linux-m68k@...ts.linux-m68k.org,
        linux-mips@...r.kernel.org, linux-parisc@...r.kernel.org,
        linuxppc-dev@...ts.ozlabs.org, linux-s390@...r.kernel.org,
        linux-sh@...r.kernel.org, sparclinux@...r.kernel.org,
        linux-xtensa@...ux-xtensa.org,
        Linux API <linux-api@...r.kernel.org>,
        linux-arch@...r.kernel.org,
        "open list:KERNEL SELFTEST FRAMEWORK" 
        <linux-kselftest@...r.kernel.org>
Subject: Re: [PATCH 1/2] pid: add pidfd_open()

On 2019-05-16, Christian Brauner <christian@...uner.io> wrote:
> On Wed, May 15, 2019 at 10:45:06AM -0700, Daniel Colascione wrote:
> > On Wed, May 15, 2019 at 3:04 AM Christian Brauner <christian@...uner.io> wrote:
> > > +       if (pid <= 0)
> > > +               return -EINVAL;
> > 
> > WDYT of defining pid == 0 to mean "open myself"?
> 
> I'm torn. It be a nice shortcut of course but pid being 0 is usually an
> indicator for child processes. So unless the getpid() before
> pidfd_open() is an issue I'd say let's leave it as is. If you really
> want the shortcut might -1 be better?

I'd suggest not using negative numbers, and instead reserving them for
PIDTYPE_TGID if we ever want to have that in the future. IMHO, doing

  pfd = pidfd_open(getpid(), 0);

is not the end of the world.


-- 
Aleksa Sarai
Senior Software Engineer (Containers)
SUSE Linux GmbH
<https://www.cyphar.com/>

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