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

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Date:   Fri, 14 Aug 2020 10:05:09 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Jeffrey E Altman <jaltman@...istor.com>
Cc:     David Howells <dhowells@...hat.com>,
        Miklos Szeredi <miklos@...redi.hu>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        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 Wed, Aug 12, 2020 at 8:53 PM Jeffrey E Altman <jaltman@...istor.com> wrote:
>
> For the AFS community, fsinfo offers a method of exposing some server
> and volume properties that are obtained via "path ioctls" in OpenAFS and
> AuriStorFS.  Some example of properties that might be exposed include
> answers to questions such as:

Note that several of the questions you ask aren't necessarily
mount-related at all.

Doing it by mount ends up being completely the wrong thing.

For example, at a minimum, these guys may well be per-directory (or
even possibly per-file):

>  * where is a mounted volume hosted? which fileservers, named by uuid
>  * what is the block size? 1K, 4K, ...
>  * are directories just-send-8, case-sensitive, case-preserving, or
>    case-insensitive?
>  * if not just-send-8, what character set is used?
>  * if Unicode, what normalization rules? etc.
>  * what volume security policy (authn, integ, priv) is assigned, if any?
>  * what is the replication policy, if any?
>  * what is the volume encryption policy, if any?

and trying to solve this with some kind of "mount info" is pure garbage.

Honestly, I really think you may want an extended [f]statfs(), not
some mount tracking.

                 Linus