1/ Introduce "mddev->resync_max_sectors" so that an md personality
can ask for resync to cover a different address range than that of a
single drive.  raid10 will use this.

2/ fix is_mddev_idle so that if there seem to be a negative number
 of events, it doesn't immediately assume activity.

3/ make "sync_io" (the count of IO sectors used for array resync)
 an atomic_t to avoid SMP races. 

4/ Pass md_sync_acct a "block_device" rather than the containing "rdev",
  as the whole rdev isn't needed. Also make this an inline function.

5/ Make sure recovery gets interrupted on any error.
Signed-off-by: Neil Brown <neilb@cse.unsw.edu.au>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>