md/raid6: support read-modify-write v3: s-o-b comment Once again thanks to an older patch from Kumar Sundararajan and Dan Williams that helped me to understand RAID6 logic inside md better. Everything is based on ideas & discussions that started with http://marc.info/?l=linux-raid&m=136624783417452&w=1 Another try to implement RMW support for RAID6. This time improve syndrome calculation too. A few things to note: 1) Patches are based on official 3.16 kernel git. 2) The required optimized syndrome functions were implemented if possible. Generic & SSE2 are the ones that I could write & test on my machine. If you want to test/benchmark this patch ensure that you force select one of the two. Programmers with appropriate hardware in their hands are encouraged to send the missing algorithms. 3) raid6 test program was enhanced to verify algorithm correctness. Additionaly this release was checked with a self written single threaded test tool I called wprd (write predictable random data). Checked features include raid expansion, rebuild of failed drives, different RAID6 geometries, ... /dev/md0 and the underlying block devices contents were checked with sha256sum against an expected result of the unpatched module. Knock on wood so far no failures. Thanks Neil for your support. Markus
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