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    SubjectRe: [PATCH 1/6] fs: add hole punching to fallocate
    On Tue, Nov 09, 2010 at 12:12:22PM +1100, Dave Chinner wrote:
    > Hole punching was not included originally in fallocate() for a
    > variety of reasons. IIRC, they were along the lines of:
    >
    > 1 de-allocating of blocks in an allocation syscall is wrong.
    > People wanted a new syscall for this functionality.
    > 2 no glibc interface needs it
    > 3 at the time, only XFS supported punching holes, so there
    > is not need to support it in a generic interface
    > 4 the use cases presented were not considered compelling
    > enough to justify the additional complexity (!)
    >
    > In the end, I gave up arguing for it to be included because just
    > getting the FALLOC_FL_KEEP_SIZE functionality was a hard enough
    > battle.
    >
    > Anyway, #3 isn't the case any more, #4 was just an excuse not to
    > support anything ext4 couldn't do and lots of apps are calling
    > fallocate directly (because glibc can't use FALLOC_FL_KEEP_SIZE) so
    > #2 isn't an issue, either.

    I don't recall anyone arguing #4 because of ext4, but I get very tired
    of the linux-fsdevel bike-shed painting parties, so I often will
    concede whatever is necessary just to get the !@#! interface in,
    assuming we could add more flags later....

    glibc does support fallocate(), BTW; it's just posix_fallocate() that
    doesn't use FALLOC_FL_KEEP_SIZE.

    > I guess that leaves #1 to be debated;
    > I don't think there is any problem with doing what you propose.

    I don't have a problem either.

    As a completely separate proposal, what do people think about an
    FALLOCATE_FL_ZEROIZE after which time the blocks are allocated, but
    reading from them returns zero. This could be done either by (a)
    sending a discard in the case of devices where discard_zeros_data is
    true and discard_granularty is less than the fs block size, or (b) by
    setting the uninitialized flag in the extent tree.

    - Ted


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