linux-kernel - Re: [RFC 1/1] shiftfs: uid/gid shifting bind mount

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Date:   Mon, 6 Feb 2017 09:50:44 -0500
From:   Theodore Ts'o <tytso@....edu>
To:     James Bottomley <James.Bottomley@...senPartnership.com>
Cc:     "J. R. Okajima" <hooanon05g@...il.com>,
        Djalal Harouni <tixxdz@...il.com>, Chris Mason <clm@...com>,
        Josh Triplett <josh@...htriplett.org>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        Andy Lutomirski <luto@...nel.org>,
        Seth Forshee <seth.forshee@...onical.com>,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-security-module@...r.kernel.org,
        Dongsu Park <dongsu@...ocode.com>,
        David Herrmann <dh.herrmann@...glemail.com>,
        Miklos Szeredi <mszeredi@...hat.com>,
        Alban Crequy <alban.crequy@...il.com>,
        Al Viro <viro@...IV.linux.org.uk>,
        "Serge E. Hallyn" <serge@...lyn.com>, Phil Estes <estesp@...il.com>
Subject: Re: [RFC 1/1] shiftfs: uid/gid shifting bind mount

On Sun, Feb 05, 2017 at 10:46:23PM -0800, James Bottomley wrote:
> Yes, I know the problem.  However, I believe most current linux
> filesystems no longer guarantee stable, for the lifetime of the file,
> inode numbers.  The usual docker container root is overlayfs, which,
> similarly doesn't support stable inode numbers.  I see the odd
> complaint about docker with overlayfs having unstable inode numbers,
> but none seems to have any serious repercussions.

Um, no.  Most current linux file systems *do* guarantee stable inode
numbers.  For one thing, NFS would break horribly if you didn't have
stable inode numbers.  Never mind applications which depend on POSIX
semantics.  And you wouldn't be able to save games in rogue or
nethack, either.  :-)

Overlayfs may not, currently, but it's considered a bug.

	      	   	      	       - Ted