linux-ext4 - Re: [PATCH 00/18] VFS: Filesystem information [ver #21]

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Message-ID: <2329129.1596647628@warthog.procyon.org.uk>
Date:   Wed, 05 Aug 2020 18:13:48 +0100
From:   David Howells <dhowells@...hat.com>
To:     James Bottomley <James.Bottomley@...senPartnership.com>
Cc:     dhowells@...hat.com, viro@...iv.linux.org.uk,
        Theodore Ts'o <tytso@....edu>,
        Andreas Dilger <adilger.kernel@...ger.ca>,
        Eric Biggers <ebiggers@...nel.org>,
        Jeff Layton <jlayton@...nel.org>, linux-ext4@...r.kernel.org,
        Carlos Maiolino <cmaiolino@...hat.com>,
        "Darrick J. Wong" <darrick.wong@...cle.com>,
        linux-api@...r.kernel.org, torvalds@...ux-foundation.org,
        raven@...maw.net, mszeredi@...hat.com, christian@...uner.io,
        jannh@...gle.com, kzak@...hat.com, jlayton@...hat.com,
        linux-fsdevel@...r.kernel.org,
        linux-security-module@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 00/18] VFS: Filesystem information [ver #21]

James Bottomley <James.Bottomley@...senPartnership.com> wrote:

> It sort of petered out into a long winding thread about why not use
> sysfs instead, which really doesn't look like a good idea to me.

It seemed to turn into a set of procfs symlinks that pointed at a bunch of
sysfs stuff - or possibly some special filesystem.

> Could I make a suggestion about how this should be done in a way that
> doesn't actually require the fsinfo syscall at all: it could just be
> done with fsconfig.

I'd prefer to keep it separate.  The interface for fsconfig() is intended to
move stuff into the kernel, not out of it.  Better to add a parallel syscall
to go the other way (kind of like we have setxattr/getxattr, sendmsg/recvmsg).

Further, fsinfo() can refer directly to a file/fd/mount/whatever, but
fsconfig() doesn't do that.  You have to use fspick() to get a context before
you can use fsconfig().  Now, that's fine if you want to gather several pieces
of information from a particular object, but it's not so good if you want to
get one piece of information from each of several objects.

> ... make it table configured...

I did, kind of (though I didn't call it that).  Al rewrote the code to get rid
of it.

David