Help with filing a [maybe] ZFS/mmap bug.

[Steven Hartland]

----- Original Message ----- 
From: "Andriy Gapon" <avg at FreeBSD.org>

>>> I was able recreate the problem on a 10-BETA-something-or-other
>>> recently (I'd only been using 9 up until then).  Andriy's patches
>>> didn't make a difference.  I haven't heard anything since reporting
>>> back to him.
>> 
>> I've pretty much confirmed mmap support is causing the corruption when
>> running rrdcached as since rebuilding with mmap disabled I've had no
>> further corruption.
> 
> Well, this is not a _proof_, of course...

Proof that mmap is causing the corruption, not that ZFS mmap support
is the point at fault,  as the code in rrdtool takes a different path
so could still be an application error, but without mmap enabled I've
seen zero corruption so...

>> @George when you got corruption what did the files look like? I ask as
>> here I see lots of zeros as through the file size was correct but pretty
>> much blanked.
> 
> Steve, could you please provide a little bit more of description of the
> corruption that you got.  Lengths of those zeroed regions, their offsets (modulo
> page size).
> Anything that could establish a pattern (if any exists).

They all seem to be corrupted to the same file which when dumped using
hexdump -C <file> results in:
00000000  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
*
00001000  00 00 00 00 00 00 f8 ff  00 00 00 00 00 00 f8 ff  |................|
*
000a8000  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
*
000af000  00 00 00 00 00 00 f8 ff  00 00 00 00 00 00 f8 ff  |................|
*
00113de0

    Regards
    Steve

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