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    SubjectRe: silent semantic changes with reiser4
    Christoph Hellwig wrote:
    > or placing this into a userspace helper that the kernel can invoke
    > transparently.

    Yes, exactly this for most file formats.
    Ideally, with _some_ user control over the handlers for their own
    files a bit like Hurd.

    Not just archive files: metadata pulled from audio files, images,
    distro packages, etc. In other words much the same as Gnome and KDE's
    things, but with more emphasis on metadata extractors and efficient
    on-disk cache interaction, and a sane page-cache coherency interface
    (possibly FUSE).

    Metadata extraction is useful for search and indexing purposes.
    (That, and a way to hook change notifications up with indexers --
    again comes with any proper coherency interface).

    For new applications using a container, it's tempting to want one
    format which is optimised for this. But really many applications want
    to write XML or compressed XML, or something else that isn't
    especially efficient but is easy to work with on many OSes. We should
    support applications whatever format they need to work with, if
    providing an interior view as a directory is useful for them. (This
    implies applications can introduce their own formats for files they
    need to operate on.) By the way, lazy updating of containers is an
    even bigger advantage if you have to use XML as the flat format,
    because the savings from not serialising when you don't need to are
    more pronounced.

    For some applications the "content" isn't structured in a way which
    maps naturally to a plain archive file. Hans' /etc/passwd is a simple
    example: at least one of the "flat" representations, when there are
    enough entries, probably ought to be a DB file for faster lookup.
    (Though, it would be great if /etc/passwd could automagically get fast
    lookup due to an automagic underlying representation, while still
    appearing to be a flat file when you cat it).

    Also, imagine "cd" into a MySQL table file. It might just work.

    By the way, we don't need containers to waste huge amounts of space
    like the Microsoft Word "fast save" documents did. Because our
    containers are created on demand, there is no performance advantage in
    them having unused holes, unlike the case were Word was saving changes
    periodically.

    -- Jamie

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