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

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Date:   Mon, 20 Feb 2017 14:26:24 -0500
From:   Vivek Goyal <vgoyal@...hat.com>
To:     James Bottomley <James.Bottomley@...senPartnership.com>
Cc:     Al Viro <viro@...IV.linux.org.uk>,
        Djalal Harouni <tixxdz@...il.com>, Chris Mason <clm@...com>,
        Theodore Tso <tytso@....edu>,
        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>,
        "Serge E. Hallyn" <serge@...lyn.com>, Phil Estes <estesp@...il.com>
Subject: Re: [RFC 1/1] shiftfs: uid/gid shifting bind mount

On Sat, Feb 18, 2017 at 07:24:38PM -0800, James Bottomley wrote:

[..]
> > > Yes, this is a known characteristic of stacked filesystems.  Is 
> > > there some magic I don't know about that would make it easier to 
> > > reflect hard links as aliases?
> > 
> > I think overlayfs had the same issue in the beginning and miklos
> > fixed it.
> > 
> > commit 51f7e52dc943468c6929fa0a82d4afac3c8e9636
> > Author: Miklos Szeredi <mszeredi@...hat.com>
> > Date:   Fri Jul 29 12:05:24 2016 +0200
> > 
> >     ovl: share inode for hard link
> 
> That's rather complex, but the principle is simple: use the inode hash
> for all upper inodes that may have aliases.  Aliasable means the
> underlying inode isn't a directory and has i_nlink > 1, so all I have
> to do is perform a lookup through the hash if the underlying is
> aliasable, invalidate the dentry in d_revalidate if the aliasing
> conditions to the underlying change and manually handle hard links and
> it should all work.
> 
> Like this?

Sounds reasonable to me. I did basic testing and this seems to work for me.

In general, I am having random crashes. I just get following on serial
console

------[Cut Here]----------

And nothing after that.

Still trying to narrow down.

Vivek