[Bug 275632] process being killed which has a big file mmap'ed and performs writes to it

https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=275632

--- Comment #3 from Martin Birgmeier <d8zNeCFG@aon.at> ---
The issue is certainly reproducible - it happens every time I let the program
run.

Some background: "cawic" stands for "compare and write if changed". It is
basically a fancy way of copying stdin to a pre-existing file, but only those
portions which have changed are actually written. The pre-existing file is
actually a disk image; it is being updated from the physical disk every few
months (backup).

The 128 block size was chosen to match the ZFS default block size. Writing only
changed portions is intended to minimize snapshot sizes of the ZFS filesystem
the file resides on.

The current workaround is to restart the program until it runs to completion -
the parts which have already been written will only be read, then the next part
is partially rewritten and either fails there or finally succeeds.

-- Martin

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