From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-fsdevel-owner@vger.kernel.org>
Received: from bedivere.hansenpartnership.com ([66.63.167.143]:59748 "EHLO
        bedivere.hansenpartnership.com" rhost-flags-OK-OK-OK-OK)
        by vger.kernel.org with ESMTP id S1750922AbdBUAiW (ORCPT
        <rfc822;linux-fsdevel@vger.kernel.org>);
        Mon, 20 Feb 2017 19:38:22 -0500
Message-ID: <1487637498.2337.42.camel@HansenPartnership.com>
Subject: Re: [RFC 1/1] shiftfs: uid/gid shifting bind mount
From: James Bottomley <James.Bottomley@HansenPartnership.com>
To: Vivek Goyal <vgoyal@redhat.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>
Date: Mon, 20 Feb 2017 16:38:18 -0800
In-Reply-To: <20170220192624.GC9464@redhat.com>
References: <1486235880.2484.17.camel@HansenPartnership.com>
         <1486235972.2484.19.camel@HansenPartnership.com>
         <20170215203441.GA22585@redhat.com>
         <1487260590.2944.21.camel@HansenPartnership.com>
         <20170217025516.GD29622@ZenIV.linux.org.uk>
         <1487352847.4351.23.camel@HansenPartnership.com>
         <20170217203529.GC15841@redhat.com>
         <1487474678.15793.2.camel@HansenPartnership.com>
         <20170220192624.GC9464@redhat.com>
Content-Type: text/plain; charset="UTF-8"
Mime-Version: 1.0
Content-Transfer-Encoding: 7bit
Sender: linux-fsdevel-owner@vger.kernel.org
List-ID: <linux-fsdevel.vger.kernel.org>

On Mon, 2017-02-20 at 14:26 -0500, Vivek Goyal wrote:
> 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
> 
> ------[Cut Here]----------
> 
> And nothing after that.

That's indicative of some hard lockup.  I don't see this, but I'm also
using a second laptop for testing, which is suboptimal.  I'm going to
try moving to xfstests inside a VM tomorrow (that's what long aeroplane
flights are for).

> Still trying to narrow down.

Thanks.  There've been a lot of patches flying around, so I'll do a
collected repost under a v2 header to make sure we're all in sync.

James