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    SubjectRe: Loop Devices over NFS don't work?

    > > > You could fall back to read/write in theory. There is an interesting project
    > > > for you 8)
    > >
    > > Really? Think about deadlocks. Both nbd and loop are _evil_. Mount
    > > sparse file over loopback, then write to both filessytems in heavy way
    > > to see why. THIS IS NOT EASY.
    > Time to embarrass myself once more on l-k ;) Intuition tells me that deadlocks
    > and races need to be thought about, but unfortunately I can't see what they
    > are.
    > How is writing to a filesystem on the loopbacked device simultaneously with
    > the hosting filesystem any different from writing to two files on the hosted
    > filesystem simultaneously?

    Because for writing _datablock_ on loopfs you need to write
    _indirectblock_ on hosting filesystem. Something that could not have
    happened before. And now imagine writing _indirectblock_ on loop,
    which results into write of _indirectblock_ on hosting fs. I am not
    telling you I understand those issues. I just see it is not easy.

    > Swapping, of course, is a different issue. Do we have any flags at the moment
    > which prevent people from trying to swap to inappropriate block devices (nbd,
    > certain raid levels with md, etc.)?

    No and I'd like to see such patch.


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