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Date:   Fri, 19 Jul 2019 12:19:31 +1000
From:   Aleksa Sarai <cyphar@cyphar.com>
To:     "Dmitry V. Levin" <ldv@altlinux.org>
Cc:     Al Viro <viro@zeniv.linux.org.uk>,
        Jeff Layton <jlayton@kernel.org>,
        "J. Bruce Fields" <bfields@fieldses.org>,
        Arnd Bergmann <arnd@arndb.de>,
        David Howells <dhowells@redhat.com>,
        Shuah Khan <shuah@kernel.org>,
        Shuah Khan <skhan@linuxfoundation.org>,
        Christian Brauner <christian@brauner.io>,
        Eric Biederman <ebiederm@xmission.com>,
        Andy Lutomirski <luto@kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Alexei Starovoitov <ast@kernel.org>,
        Kees Cook <keescook@chromium.org>,
        Jann Horn <jannh@google.com>, Tycho Andersen <tycho@tycho.ws>,
        David Drysdale <drysdale@google.com>,
        Chanho Min <chanho.min@lge.com>,
        Oleg Nesterov <oleg@redhat.com>, Aleksa Sarai <asarai@suse.de>,
        Linus Torvalds <torvalds@linux-foundation.org>,
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Subject: Re: [PATCH v9 08/10] open: openat2(2) syscall
Message-ID: <20190719021931.ypwvcvp3imbgjjx6@yavin>
References: <20190706145737.5299-1-cyphar@cyphar.com>
 <20190706145737.5299-9-cyphar@cyphar.com>
 <20190719015933.GA18022@altlinux.org>
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On 2019-07-19, Dmitry V. Levin <ldv@altlinux.org> wrote:
> On Sun, Jul 07, 2019 at 12:57:35AM +1000, Aleksa Sarai wrote:
> [...]
> > +/**
> > + * Arguments for how openat2(2) should open the target path. If @extra=
 is zero,
> > + * then openat2(2) is identical to openat(2).
> > + *
> > + * @flags: O_* flags (unknown flags ignored).
>=20
> What was the rationale for implementing this semantics?
> Ignoring unknown flags makes potential extension of this new interface
> problematic.  This has bitten us many times already, so ...

I am mirroring the semantics of open(2) and openat(2).

To be clear, I am in favour of doing it -- and it would definitely be
possible to implement it with -EINVAL (you would just mask off
~VALID_OPEN_FLAGS for the older syscalls). But Linus' response to my
point about (the lack of) -EINVAL for unknown open(2) flags gave me the
impression he would be against this idea (though I might be
misunderstanding the point he was making).

--=20
Aleksa Sarai
Senior Software Engineer (Containers)
SUSE Linux GmbH
<https://www.cyphar.com/>

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