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    SubjectRe: [RFC 12/26] ext2 white-out support
    On Wed, Aug 01, 2007 at 12:00:42PM +0200, Hans-Peter Jansen wrote:
    > Am Dienstag, 31. Juli 2007 19:00 schrieb Jan Blunck:
    > > On Tue, Jul 31, Josef Sipek wrote:
    > > > On Mon, Jul 30, 2007 at 06:13:35PM +0200, Jan Blunck wrote:
    > > > > Introduce white-out support to ext2.
    > > >
    > > > I think storing whiteouts on the branches is wrong. It creates all sort
    > > > of nasty cases when people actually try to use unioning. Imagine a
    > > > (no-so unlikely) scenario where you have 2 unions, and they share a
    > > > branch. If you create a whiteout in one union on that shared branch,
    > > > the whiteout magically affects the other union as well! Whiteouts are a
    > > > union-level construct, and therefore storing them at the branch level
    > > > is wrong.
    > >
    > > So you think that just because you mounted the filesystem somewhere else
    > > it should look different? This is what sharing is all about. If you share
    > > a filesystem you also share the removal of objects.
    >
    > No. At least I don't.
    >
    > Usage case: I heavily depend on using union mounts in diskless nfs setups,
    > since it drops the amount of administration of many systems _near_ one. It
    > boils down on installing the distribution of your choice in a directory,
    > union mount it ro, overlayed with a node private one (doing this in initrd
    > on the client for several reasons),

    You're not sharing the rw layer so it's a different scenario, and will not
    have the problem I'm talking about. See my other post [1] for exact scenario
    where storing whiteouts on a branch would cause problems.

    > add a little boot and automatic setup
    > machinery and be done. Since all changes are persistant, any system can be
    > set up individually, and still mostly only one tree is needed to keep up to
    > date.. Being in production in an office environment since two years without
    > major hassle (*).

    Unionfs is used by many people in this way.

    Josef 'Jeff' Sipek.

    [1] http://lkml.org/lkml/2007/7/31/365

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