[PATCH 0/5, v2] repair: sector size and blkmap fixes

[Dave Chinner]

Hi Alex,

Here's the fixes I posted a few days ago with all the review
comments fixed up.

Version 2:
- fixed typos in sector size comments
- fixed setting default sector size so that the ioctl doesn't wipe
  it out
- separate out prefetch valgrind error fix.
- separate out large blkmap allocation caching fix
- separate out handling of blkmap memory allocation failure during a
  grow to avoid a buffer overrun situation when moving extents
  around in the array
- avoid modifying blkmap->naexts when allocation fails.
- separate extent count overflow checking in blkmap allocation and
  growing
- use #if BITS_PER_LONG == 32
- Introduce BLKMAP_NEXTS_MAX and use it unconditionally rather than
  open code it and only include the check on 32 bit builds
- add checking for negative extent counts to avoid grow overflows
  past INT_MAX going undetected.