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    SubjectRe: [PATCH 0/5] hybrid union filesystem prototype
    On Thu, 2 Sep 2010 15:15:37 +0200 (CEST)
    Jan Engelhardt <> wrote:

    > On Monday 2010-08-30 12:18, Miklos Szeredi wrote:
    > >
    > >> My comment about set-theory unions being commutative set me thinking. I
    > >> really don't think "union" is the right name for this thing. There is
    > >> nothing about it which really fits that proper definition of a union.
    > >
    > >We could call it overlayfs. People learn new names quickly :)
    > There is a much larger issue that you should be very well aware about —
    > "The name wanted to be a clever acronym for "Filesystem in
    > USErspace", but it turned out to be an unfortunate choice. The author
    > has since vowed never to name a project after a common term, not even
    > anything found more than a handful of times on Google."
    > overlayfs already exists. Right next to fuse on sourceforge...


    No, I mean it. "Linux Over-Lays". :-)

    > Oh and I what I like to see is support for multiple readonly branches :)

    I think we very nearly have that, assuming I understand your requirement
    The lower filesystem can itself be an overlay, providing it is mounted

    So if /mnt/ro1 /mnt/ro2 /mnt/ro3 are all read-only branches then

    mount -o ro,lowerdir=/mnt/ro1,upperdir=/mnt/ro2 meaninglessstring /mnt/ov1
    mount -o ro,lowerdir=/mnt/ov1,upperdir=/mnt/ro3 meaninglessstring /mnt/ov2
    mount -o lowerdir=/mnt/ov2,upperdir=/mnt/rw ignoreme /mnt/overlay

    and /mnt/overlay will be the combination of 3 read-only filesystems and one
    writable one.
    (this doesn't work with the code as-is, but it is really just a few bug-fixes

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