linux-kernel - Re: [RFC PATCH] getvalues(2) prototype

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Message-ID: <CAJfpegvwTmaw0bp70-nYQAvs8T=wYyxnDEoA=rOvX8HDZnxCTg@mail.gmail.com>
Date:   Wed, 23 Mar 2022 15:00:01 +0100
From:   Miklos Szeredi <miklos@...redi.hu>
To:     Casey Schaufler <casey@...aufler-ca.com>
Cc:     Christian Brauner <brauner@...nel.org>,
        Miklos Szeredi <mszeredi@...hat.com>,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        Linux API <linux-api@...r.kernel.org>,
        linux-man <linux-man@...r.kernel.org>,
        LSM <linux-security-module@...r.kernel.org>,
        Karel Zak <kzak@...hat.com>, Ian Kent <raven@...maw.net>,
        David Howells <dhowells@...hat.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        Christian Brauner <christian@...uner.io>,
        Amir Goldstein <amir73il@...il.com>,
        James Bottomley <James.Bottomley@...senpartnership.com>
Subject: Re: [RFC PATCH] getvalues(2) prototype

On Wed, 23 Mar 2022 at 14:51, Casey Schaufler <casey@...aufler-ca.com> wrote:

> You also need a way to get a list off what attributes are available
> and/or a way to get all available attributes. Applications and especially
> libraries shouldn't have to guess what information is relevant. If the
> attributes change depending on the filesystem and/or LSM involved, and
> they do, how can a general purpose library function know what data to
> ask for?

Oh, yes.  Even the current prototype does that:

# ~/getvalues / ""
[] = "mnt" "mntns" "xattr" "data" (len=21)
# ~/getvalues / "mnt"
[mnt] = "id" "parentid" "root" "mountpoint" "options" "shared"
"master" "propagate_from" "unbindable" (len=76)
# ~/getvalues / "mntns"
[mntns] = "21" "22" "24" "25" "23" "26" "27" "28" "29" "30" "31" "32" (len=36)
 ~/getvalues / "mntns:21"
[mntns:21] = "id" "parentid" "root" "mountpoint" "options" "shared"
"master" "propagate_from" "unbindable" (len=76)

I didn't implement enumeration for "data" and "xattr" but that is
certainly possible and not even difficult to do.

Thanks,
Miklos