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    SubjectRe: [RFC] Heads up on sys_fallocate()
    On Monday 05 March 2007, Jörn Engel wrote:
    > That actually causes an interesting problem for compressing filesystems.
    > The space consumed by blocks depends on their contents and how well it
    > compresses.  At the moment, the only option I see to support
    > posix_fallocate for LogFS is to set an inode flag disabling compression,
    > then allocate the blocks.
    > But if the file already contains large amounts of compressed data, I
    > have a problem.  Disabling compression for a range within a file is not
    > supported, so I can only return an error.  But which one?

    Using the current glibc implementation on a compressed file system ideally
    should be a very expensive no-op because you won't actually allocate much
    space for a file when writing zeroes to it. You also don't benefit of a
    contiguous allocation in logfs, since flash has uniform seek times over
    all the medium.

    I'd suggest you implement posix_fallocate as an real nop and just return
    success without doing anything. You could also return ENOSPC in case
    the blocks requested by posix_fallocate don't fit on the medium without
    compression, but that is more or less just guesswork (like statfs is).

    Arnd <><
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      Last update: 2007-03-05 01:41    [W:0.020 / U:7.488 seconds]
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