linux-kernel - Re: file metadata via fs API (was: [GIT PULL] Filesystem Information)

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Message-ID: <CAJfpegvUBpb+C2Ab=CLAwWffOaeCedr-b7ZZKZnKvF4ph1nJrw@mail.gmail.com>
Date:   Tue, 11 Aug 2020 22:28:31 +0200
From:   Miklos Szeredi <miklos@...redi.hu>
To:     Casey Schaufler <casey@...aufler-ca.com>
Cc:     Andy Lutomirski <luto@...capital.net>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        David Howells <dhowells@...hat.com>,
        Al Viro <viro@...iv.linux.org.uk>, Karel Zak <kzak@...hat.com>,
        Jeff Layton <jlayton@...hat.com>,
        Miklos Szeredi <mszeredi@...hat.com>,
        Nicolas Dichtel <nicolas.dichtel@...nd.com>,
        Christian Brauner <christian@...uner.io>,
        Lennart Poettering <lennart@...ttering.net>,
        Linux API <linux-api@...r.kernel.org>,
        Ian Kent <raven@...maw.net>,
        LSM <linux-security-module@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: file metadata via fs API (was: [GIT PULL] Filesystem Information)

On Tue, Aug 11, 2020 at 6:17 PM Casey Schaufler <casey@...aufler-ca.com> wrote:

> Since a////////b has known meaning, and lots of applications
> play loose with '/', its really dangerous to treat the string as
> special. We only get away with '.' and '..' because their behavior
> was defined before many of y'all were born.

So the founding fathers have set things in stone and now we can't
change it.   Right?

Well that's how it looks... but let's think a little; we have '/' and
'\0' that can't be used in filenames.  Also '.' and '..' are
prohibited names. It's not a trivial limitation, so applications are
probably not used to dumping binary data into file names.  And that
means it's probably possible to find a fairly short combination that
is never used in practice (probably containing the "/." sequence).
Why couldn't we reserve such a combination now?

I have no idea how to find such it, but other than that, I see no
theoretical problem with extending the list of reserved filenames.

Thanks,
Miklos