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

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Message-ID: <CAJfpegvFBdp3v9VcCp-wNDjZnQF3q6cufb-8PJieaGDz14sbBg@mail.gmail.com>
Date:   Wed, 12 Aug 2020 16:46:20 +0200
From:   Miklos Szeredi <miklos@...redi.hu>
To:     Al Viro <viro@...iv.linux.org.uk>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Jann Horn <jannh@...gle.com>,
        Casey Schaufler <casey@...aufler-ca.com>,
        Andy Lutomirski <luto@...capital.net>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        David Howells <dhowells@...hat.com>,
        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 Wed, Aug 12, 2020 at 4:40 PM Al Viro <viro@...iv.linux.org.uk> wrote:
>
> On Wed, Aug 12, 2020 at 09:23:23AM +0200, Miklos Szeredi wrote:
>
> > Anyway, starting with just introducing the alt namespace without
> > unification seems to be a good first step. If that turns out to be
> > workable, we can revisit unification later.
>
> Start with coming up with answers to the questions on semantics
> upthread.  To spare you the joy of digging through the branches
> of that thread, how's that for starters?
>
> "Can those suckers be passed to
> ...at() as starting points?

No.

>  Can they be bound in namespace?

No.

> Can something be bound *on* them?

No.

>  What do they have for inodes
> and what maintains their inumbers (and st_dev, while we are at
> it)?

Irrelevant.  Can be some anon dev + shared inode.

The only attribute of an attribute that I can think of that makes
sense would be st_size, but even that is probably unimportant.

>  Can _they_ have secondaries like that (sensu Swift)?

Reference?

> Is that a flat space, or can they be directories?"

Yes it has a directory tree.   But you can't mkdir, rename, link,
symlink, etc on anything in there.

Thanks,
Miklos