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    SubjectRe: silent semantic changes with reiser4
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    Christophe Saout wrote:

    | Yes, the main compound stream unaware applications would see would just
    | be a writable view of its contents. Probably not trivial to implement
    | but doable.

    Not the main stream, I think, but we do need a way to make "eight-stream
    octopus" files portable. But there needs to be a copy(2) syscall, and
    apps need to start supporting it. After all, copy-on-write was planned
    for Reiser4, now 4.1*. And don't anyone dare suggest "userland library".

    | It should be a simple format. Something simliar to tar. The worst thing

    Simple, yes. Similar to tar, no.

    How about a serializer plugin? foo.mp3/serialize (say) should return
    some single stream which contains all of foo.mp3. It could work for
    directories as well, recursively, at least on the same filesystem --
    you'd back up by doing

    cp /serialize /backup/20040826

    This has two potential problems. One is security -- I want to be able
    to serialize foo.mp3 without being root, but root doesn't want me to be
    able to serialize /etc and thus get access to shadow.

    The second problem is that in order to actually be used for backup, we
    need snapshots, which are not done yet*. Currently, it'd have to lock
    the file/directory (recursively), which you don't want to do to entire
    live filesystems... So, no massive backups of live systems yet, but
    definitely useful for sending around mp3s and such.

    | that can happen is people start writing plugins for every existing
    | compound format out there. It should be the other way around, agree on a
    | simple compound format and encourage applications to use this one if the
    | want to use this advantage.

    For the format, I vote for whatever format we're using at the storage
    layer. It'd be a lot faster that way, both in execution time (I think)
    and in development time (I'm sure). Plus, imagine the restore:

    cat /backup/20040826 > /dev/hda5
    resizefs_reiser4 /dev/hda5


    * Disclaimer -- all this is "I think, last I checked".


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