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From:   Linus Torvalds <torvalds@linux-foundation.org>
Date:   Fri, 14 Aug 2020 10:05:09 -0700
Message-ID: <CAHk-=whLhwum2E+qperD=TypGHXxoBtXOu-HHDd9L9_XFFyiaA@mail.gmail.com>
Subject: Re: file metadata via fs API (was: [GIT PULL] Filesystem Information)
To:     Jeffrey E Altman <jaltman@auristor.com>
Cc:     David Howells <dhowells@redhat.com>,
        Miklos Szeredi <miklos@szeredi.hu>,
        linux-fsdevel <linux-fsdevel@vger.kernel.org>,
        Al Viro <viro@zeniv.linux.org.uk>, Karel Zak <kzak@redhat.com>,
        Jeff Layton <jlayton@redhat.com>,
        Miklos Szeredi <mszeredi@redhat.com>,
        Nicolas Dichtel <nicolas.dichtel@6wind.com>,
        Christian Brauner <christian@brauner.io>,
        Lennart Poettering <lennart@poettering.net>,
        Linux API <linux-api@vger.kernel.org>,
        Ian Kent <raven@themaw.net>,
        LSM <linux-security-module@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
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On Wed, Aug 12, 2020 at 8:53 PM Jeffrey E Altman <jaltman@auristor.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