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From:   Andy Lutomirski <luto@amacapital.net>
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Subject: Re: [PATCH v2 0/5] pid: add pidfd_open()
Date:   Mon, 1 Apr 2019 10:10:01 -0600
Message-Id: <190D1581-ADD6-4E8B-93A3-5F3C6B1D8154@amacapital.net>
References: <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> <CAHk-=wi3AE1-iRQ_7LOeSMNAMrGxRdC=gTjD30duVw4XRchcNQ@mail.gmail.com> <18C7FCB9-2CBA-4237-94BB-9C4395A2106B@amacapital.net> <20190401114059.7gdsvcqyoz2o5bbz@yavin> <CAHk-=wgKqBQznZdTQaM6yQ+_5dcz-+q8=2sbQsAoDh55hQTLMA@mail.gmail.com>
Cc:     Aleksa Sarai <cyphar@cyphar.com>,
        Christian Brauner <christian@brauner.io>,
        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>,
        Al Viro <viro@zeniv.linux.org.uk>,
        Joel Fernandes <joel@joelfernandes.org>
In-Reply-To: <CAHk-=wgKqBQznZdTQaM6yQ+_5dcz-+q8=2sbQsAoDh55hQTLMA@mail.gmail.com>
To:     Linus Torvalds <torvalds@linux-foundation.org>
Sender: linux-kernel-owner@vger.kernel.org
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> On Apr 1, 2019, at 9:36 AM, Linus Torvalds <torvalds@linux-foundation.org>=
 wrote:
>=20
>> On Mon, Apr 1, 2019 at 4:41 AM Aleksa Sarai <cyphar@cyphar.com> wrote:
>>=20
>> Eric pitched a procfs2 which would *just* be the PIDs some time ago (in
>> an attempt to make it possible one day to mount /proc inside a container
>> without adding a bunch of masked paths), though it was just an idea and
>> I don't know if he ever had a patch for it.
>=20
> I wonder if we really want a fill procfs2, or maybe we could just make
> the pidfd readable (yes, it's a directory file descriptor, but we
> could allow reading).


There were patches to make procfs mount options work sensibly, and I think t=
hey got merged. So we could probably avoid a whole procfs2 by instead having=
 it be procfs plus a special (maybe purely internal) mount option to restric=
t it.