Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
MIME-Version: 1.0
References: <20220322192712.709170-1-mszeredi@redhat.com> <20220323114215.pfrxy2b6vsvqig6a@wittgenstein>
 <CAJfpegsCKEx41KA1S2QJ9gX9BEBG4_d8igA0DT66GFH2ZanspA@mail.gmail.com> <d3333dbe-b4b7-8eb9-4a50-8526d95b5394@schaufler-ca.com>
In-Reply-To: <d3333dbe-b4b7-8eb9-4a50-8526d95b5394@schaufler-ca.com>
From:   Miklos Szeredi <miklos@szeredi.hu>
Date:   Wed, 23 Mar 2022 15:00:01 +0100
Message-ID: <CAJfpegvwTmaw0bp70-nYQAvs8T=wYyxnDEoA=rOvX8HDZnxCTg@mail.gmail.com>
Subject: Re: [RFC PATCH] getvalues(2) prototype
To:     Casey Schaufler <casey@schaufler-ca.com>
Cc:     Christian Brauner <brauner@kernel.org>,
        Miklos Szeredi <mszeredi@redhat.com>,
        linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
        Linux API <linux-api@vger.kernel.org>,
        linux-man <linux-man@vger.kernel.org>,
        LSM <linux-security-module@vger.kernel.org>,
        Karel Zak <kzak@redhat.com>, Ian Kent <raven@themaw.net>,
        David Howells <dhowells@redhat.com>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Al Viro <viro@zeniv.linux.org.uk>,
        Christian Brauner <christian@brauner.io>,
        Amir Goldstein <amir73il@gmail.com>,
        James Bottomley <James.Bottomley@hansenpartnership.com>
Content-Type: text/plain; charset="UTF-8"
Precedence: bulk

On Wed, 23 Mar 2022 at 14:51, Casey Schaufler <casey@schaufler-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