Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
MIME-Version: 1.0
References: <20190329155425.26059-1-christian@brauner.io> <CAHk-=wjq4dTPcz-qsvhpm5F42SDHCoqEWv1V=rs_kt6MC=ZThA@mail.gmail.com>
 <BCD99947-5F55-4116-8F74-D6832E50340B@brauner.io> <CAHk-=whcA0kAWGqet9oJdyttjhP7J4PcU2Ly=n_Qyo6rMJNxRg@mail.gmail.com>
 <CAKOZuevv_QgvzmusA+yey76vo4hn9bEVwud2RumuOr0K4++15A@mail.gmail.com>
 <CAHk-=wj0o8BiUrYiM5ZcTS6JxBh1M60O36Ms8-EqLQ139=1L4g@mail.gmail.com>
 <20190330171215.3yrfxwodstmgzmxy@brauner.io> <CAHk-=whF6gnRVbJaArZna4e=tejfrzmNQtRbWjnuSSKpBn+jQg@mail.gmail.com>
 <132107F4-F56B-4D6E-9E00-A6F7C092E6BD@amacapital.net> <CAHk-=wiaLtH41Mc5qAjOeCWavPqV0DhS581KYa0QBt8uraTK1Q@mail.gmail.com>
 <20190331211041.vht7dnqg4e4bilr2@brauner.io>
In-Reply-To: <20190331211041.vht7dnqg4e4bilr2@brauner.io>
From:   Linus Torvalds <torvalds@linux-foundation.org>
Date:   Sun, 31 Mar 2019 14:17:48 -0700
Message-ID: <CAHk-=wi3AE1-iRQ_7LOeSMNAMrGxRdC=gTjD30duVw4XRchcNQ@mail.gmail.com>
Subject: Re: [PATCH v2 0/5] pid: add pidfd_open()
To:     Christian Brauner <christian@brauner.io>
Cc:     Andy Lutomirski <luto@amacapital.net>,
        Daniel Colascione <dancol@google.com>,
        Jann Horn <jannh@google.com>,
        Andrew Lutomirski <luto@kernel.org>,
        David Howells <dhowells@redhat.com>,
        "Serge E. Hallyn" <serge@hallyn.com>,
        Linux API <linux-api@vger.kernel.org>,
        Linux List Kernel Mailing <linux-kernel@vger.kernel.org>,
        Arnd Bergmann <arnd@arndb.de>,
        "Eric W. Biederman" <ebiederm@xmission.com>,
        Konstantin Khlebnikov <khlebnikov@yandex-team.ru>,
        Kees Cook <keescook@chromium.org>,
        Alexey Dobriyan <adobriyan@gmail.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Michael Kerrisk-manpages <mtk.manpages@gmail.com>,
        Jonathan Kowalski <bl0pbl33p@gmail.com>,
        "Dmitry V. Levin" <ldv@altlinux.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Oleg Nesterov <oleg@redhat.com>,
        Nagarathnam Muthusamy <nagarathnam.muthusamy@oracle.com>,
        Aleksa Sarai <cyphar@cyphar.com>,
        Al Viro <viro@zeniv.linux.org.uk>,
        Joel Fernandes <joel@joelfernandes.org>
Content-Type: text/plain; charset="UTF-8"
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Sun, Mar 31, 2019 at 2:10 PM Christian Brauner <christian@brauner.io> wrote:
>
> I don't think that we want or can make them equivalent since that would
> mean we depend on procfs.

Sure we can.

If /proc is enabled, then you always do that dance YOU ALREADY WROTE
THE CODE FOR to do the stupid ioctl.

And if /procfs isn't enabled, then you don't do that.

Ta-daa. Done. No stupid ioctl, and now /proc and pidfd_open() return
the same damn thing.

And guess what? If /proc isn't enabled, then obviously pidfd_open()
gives you the /proc-less thing, but at least there is no crazy "two
different file descriptors for the same thing" situation, because then
the /proc one doesn't exist.

Notice? No incompatibility. No crazy stupid new "convert one to the
other", because "the other model" NEVER EXISTS. There is only one
pidfd - it might be proc-less if CONFIG_PROC isn't there, but let's
face it, nobody even cares, because nobody ever disabled /proc anyway.

And no need for some new "convert" interface (ioctl or other).

Problem solved.

                   Linus