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    SubjectRe: BUG: mmapfile/writev spurious zero bytes (x86_64/not i386, bisected, reproducable)
    On Tue, Jun 17, 2008 at 02:20:49PM -0700, Linus Torvalds wrote:
    > On Tue, 17 Jun 2008, Linus Torvalds wrote:
    > >
    > > Hmm. Something like this *may* salvage it.
    > >
    > > Untested, so far (I'll reboot and test soon enough), but even if it fixes
    > > things, it's not really very good.
    > Ok, so I just rebooted with this, and it does indeed fix the bug.
    > I'd be happier with a more complete fix (ie being byte-accurate and
    > actually doing the partial copy when it hits a fault in the middle), but
    > this seems to be the minimal fix, and at least fixes the totally bogus
    > return values from the x86-64 __copy_user*() functions.
    > Not that I checked that I got _all_ cases correct (and maybe there are
    > other versions of __copy_user that I missed entirely), but Bron's
    > test-case at least seems to work properly for me now.
    > Bron? If you have a more complete test-suite (ie the real-world case that
    > made you find this), it would be good to verify the whole thing.

    I have a real world test case using "cyr_dbtool" from Cyrus 2.3.12 on a
    known-bug-inducing piece of data (the key and value sizes in the example
    code were taken from that. Indeed, the example code started off
    building byte-for-byte identical files, then I changed it to write only
    a single character across the entire key and value so the hexdump was

    I'll give it a go.


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