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Re: [PATCH v2 RFC] userns: Convert xfs to use kuid/kgid where appropriat

To: Dave Chinner <david@xxxxxxxxxxxxx>
Subject: Re: [PATCH v2 RFC] userns: Convert xfs to use kuid/kgid where appropriate
From: Serge Hallyn <serge.hallyn@xxxxxxxxxx>
Date: Thu, 27 Jun 2013 08:02:05 -0500
Cc: Dwight Engen <dwight.engen@xxxxxxxxxx>, "Eric W. Biederman" <ebiederm@xxxxxxxxx>, xfs@xxxxxxxxxxx, Brian Foster <bfoster@xxxxxxxxxx>
Delivered-to: xfs@xxxxxxxxxxx
In-reply-to: <20130626224410.GB28426@dastard>
References: <20130619110948.0bfafa2b@xxxxxxxxxx> <20130620001341.GM29338@dastard> <20130620095410.1917d235@xxxxxxxxxx> <20130620220311.GT29376@dastard> <20130621111420.5592707e@xxxxxxxxxx> <20130624003316.GH29376@dastard> <20130624091035.6274800f@xxxxxxxxxx> <20130626020924.GD29376@dastard> <20130626173017.5100327a@xxxxxxxxxx> <20130626224410.GB28426@dastard>
User-agent: Mutt/1.5.21 (2010-09-15)
Quoting Dave Chinner (david@xxxxxxxxxxxxx):
> On Wed, Jun 26, 2013 at 05:30:17PM -0400, Dwight Engen wrote:
> > On Wed, 26 Jun 2013 12:09:24 +1000
> > Dave Chinner <david@xxxxxxxxxxxxx> wrote:
> > > > We do need to decide on the di_uid that comes back from bulkstat.
> > > > Right now it is returning on disk (== init_user_ns) uids. It looks
> > > > to me like xfsrestore is using the normal vfs routines (chown,

I might not be helpful here, (as despite having used xfs for years
I've not used these features) but feel like I should try based on
what I see in the manpages.  Here is my understanding:

Assume you're a task in a child userns, where you have host uids
100000-110000 mapped to container uids 0-10000,

1. bulkstat is an xfs_ioctl command, right?  It should return the mapped
uids (0-10000).

2. xfsdump should store the uids as seen in the caller's namespace.  If
xfsdump is done from the container, the dump should show uids 0-10000.

3. xfsrestore should use be run from the desired namespace.  If you did
xfsdump from the host ns, you should then xfsrestore from the host ns.
Then inside the container those uids (100000-110000) will be mapped
to your uids (0-10000).

4. If you xfsdump in this container, then xfsrestore in another
container where you have 200000-210000 mapped to 0-10000, the dump
image will have uids 0-10000.  The restored image will have container
uids 0-10000, while on the underlying host media it will be uids
200000-210000.

5. If you xfsdump in this container then xfsrestore on the host, then
the host uids 0-10000 will be used on the underlying media.  The
container would be unable to read this files as the uids do not map
into the container.

-serge

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