Allow RAID-6 check to be passed only the
MD device, start and length.
The three parameters are mandatory.
All necessary information is collected using
the "sysfs_read()" call.
Furthermore, if "length" is "0", then the check
is performed until the end of the array.
Some checks are done, for example if the md device
is really a RAID-6. Nevertheless I guess it is not
bullet proof...
Next patch will include the "suspend" action.
My idea is to do it "per stripe", please let me
know if you've some better options.