linux-kernel - Re: [PATCH] overlayfs: ignore empty NFSv4 ACLs in ext4 upperdir

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Date:   Thu, 2 May 2019 19:53:13 +0200
From:   Andreas Gruenbacher <agruenba@...hat.com>
To:     "J. Bruce Fields" <bfields@...ldses.org>
Cc:     Andreas Grünbacher <andreas.gruenbacher@...il.com>,
        Miklos Szeredi <miklos@...redi.hu>, NeilBrown <neilb@...e.com>,
        Amir Goldstein <amir73il@...il.com>,
        Patrick Plagwitz <Patrick_Plagwitz@....de>,
        "linux-unionfs@...r.kernel.org" <linux-unionfs@...r.kernel.org>,
        Linux NFS list <linux-nfs@...r.kernel.org>,
        Linux FS-devel Mailing List <linux-fsdevel@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] overlayfs: ignore empty NFSv4 ACLs in ext4 upperdir

On Thu, 2 May 2019 at 19:16, J. Bruce Fields <bfields@...ldses.org> wrote:
> On Thu, May 02, 2019 at 05:08:14PM +0200, Andreas Grünbacher wrote:
> > You'll still see permissions that differ from what the filesystem
> > enforces, and copy-up would change that behavior.
>
> That's always true, and this issue isn't really specific to NFSv4 ACLs
> (or ACLs at all), it already exists with just mode bits.  The client
> doesn't know how principals may be mapped on the server, doesn't know
> group membership, etc.
>
> That's the usual model, anyway.  Permissions are almost entirely the
> server's responsibility, and we just provide a few attributes to set/get
> those server-side permissions.

Sure, if the client and server don't share the same user and group
databases, ACLs can get a very different meaning.

Andreas

> The overlayfs/NFS case is different, I think: the nfs filesystem may be
> just a static read-only template for a filesystem that's only ever used
> by clients, and for all I know maybe permissions should only be
> interpreted on the client side in that case.
>
> --b.