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    SubjectRe: Is there a "make hole" (truncate in middle) syscall?
    On Thu, Dec 11, 2003 at 08:48:15PM +0100, Jörn Engel wrote:
    > On Thu, 11 December 2003 11:15:28 -0800, Hua Zhong wrote:
    > > Hey, I think when I get some cycles I can try to implement this for
    > > tmpfs (since it's simpler) myself, and post a patch. :-) But before
    > > that, I want to make sure it's doable.
    >
    > If you really do it, please don't add a syscall for it. Simply check
    > each written page if it is completely filled with zero. (This will be
    > a very quick check for most pages, as they will contain something
    > nonzero in the first couple of words)

    Um, no.

    That is a very bad idea. Your suggestion would make it impossible to
    actually write a block of all-zeros to the disk. That makes it
    impossible to pre-allocate disk space.

    Another syscall is precisely the correct thing to do. (I don't think
    make_hole() is a special case of any extant syscall.)

    -andy
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