linux-kernel - Re: [PATCH] vfs: add faccessat2 syscall

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Message-ID: <CAOssrKe7RNyReAFLoQGBDm79qMdXEubhP5QhG_+UmGZXgeXBkA@mail.gmail.com>
Date:   Sat, 18 Apr 2020 21:00:05 +0200
From:   Miklos Szeredi <mszeredi@...hat.com>
To:     Stefan Metzmacher <metze@...ba.org>
Cc:     Al Viro <viro@...iv.linux.org.uk>,
        lkml <linux-kernel@...r.kernel.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        Linux API <linux-api@...r.kernel.org>,
        Eric Sandeen <sandeen@...deen.net>
Subject: Re: [PATCH] vfs: add faccessat2 syscall

On Sat, Apr 18, 2020 at 8:36 PM Stefan Metzmacher <metze@...ba.org> wrote:
>
> Hi Miklos,
>
> > POSIX defines faccessat() as having a fourth "flags" argument, while the
> > linux syscall doesn't have it.  Glibc tries to emulate AT_EACCESS and
> > AT_SYMLINK_NOFOLLOW, but AT_EACCESS emulation is broken.
> >
> > Add a new faccessat(2) syscall with the added flags argument and implement
> > both flags.
> >
> > The value of AT_EACCESS is defined in glibc headers to be the same as
> > AT_REMOVEDIR.  Use this value for the kernel interface as well, together
> > with the explanatory comment.
>
> It would be nice if resolv_flags would also be passed in addition to the
> at flags.
> See:https://lore.kernel.org/linux-api/CAHk-=wiaL6zznNtCHKg6+MJuCqDxO=yVfms3qR9A0czjKuSSiA@mail.gmail.com/
>
> We should avoid expecting yet another syscall in near future.

What is the objection against

openat(... O_PATH)
foobarat(fd, AT_EMPTY_PATH, ...)

?

Thanks,
Miklos