Limitation in the badblocks routines

Limitation in the badblocks routines

[Verma, Vishal L]

I think I've found a limitation in the badblocks implementation
(block/badblocks.c), which we now also use for nvdimm badblocks. 

Consider the following operations:

badblocks_set(bb, 32, 1);
badblocks_set(bb, 34, 1);
badblocks_set(bb, 36, 1);

badblocks_show will now correctly report:
32 1
34 1
36 1

Now if I do:
badblocks_set(bb, 32, 12);

Ideally, this should collapse all ranges into a single (32, 12).. But
looks like badblocks_set only merges one set of adjacent mergeable
ranges, and then returns, resulting in:

32 3
36 1

Now if I add the same (32, 12) range again, I get:

32 5

as one more set is merged. And finally after adding (32, 12) one final
time, I get the expected

32 12.

Neil - do you think it will be relatively straightforward to extend
badblocks_set to be aware of multi-overlap ranges like above? I haven't
really looked at the internals of it (I'll take a look tomorrow), but I
wanted to get this out in the meantime.

Thanks,
	-Vishal
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