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

From: Vivek Goyal <vgoyal@redhat.com>
To: James Bottomley <James.Bottomley@HansenPartnership.com>
Cc: Al Viro <viro@ZenIV.linux.org.uk>,
	Djalal Harouni <tixxdz@gmail.com>, Chris Mason <clm@fb.com>,
	Theodore Tso <tytso@mit.edu>,
	Josh Triplett <josh@joshtriplett.org>,
	"Eric W. Biederman" <ebiederm@xmission.com>,
	Andy Lutomirski <luto@kernel.org>,
	Seth Forshee <seth.forshee@canonical.com>,
	linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
	linux-security-module@vger.kernel.org,
	Dongsu Park <dongsu@endocode.com>,
	David Herrmann <dh.herrmann@googlemail.com>,
	Miklos Szeredi <mszeredi@redhat.com>,
	Alban Crequy <alban.crequy@gmail.com>,
	"Serge E. Hallyn" <serge@hallyn.com>,
	Phil Estes <estesp@gmail.com>
Subject: Re: [RFC 1/1] shiftfs: uid/gid shifting bind mount
Date: Mon, 20 Feb 2017 14:26:24 -0500	[thread overview]
Message-ID: <20170220192624.GC9464@redhat.com> (raw)
In-Reply-To: <1487474678.15793.2.camel@HansenPartnership.com>

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@redhat.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

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And nothing after that.

Still trying to narrow down.

Vivek