I/O errors on Hammer volume

[Matthew Dillon]

    I have pushed a new hammer directive to HEAD called 'checkmap'.
    It isn't complete yet but it should be good enough to verify that
    all record data references are accounted for in the blockmap.  I still
    need to have it check B-Tree node allocations and other stuff.

    hammer -f <device> checkmap

    If it does not output any blockmap info then everything that it checks
    (so far) is ok.

    If you specify verbose (-v) it will output the blockmap info it
    collects whether good or bad.

    The directive scans the B-Tree so it will take a little while, but
    nowhere near as long as 'show' because it doesn't dive the record data.

    Also in the same commit I pushed some changes to the 'show' directive
    to hopefully detect and report zone mismatches instead of assert.

    --

    Hopefully this will narrow down the problem space.  I'd like you to
    run both the hammer show and hammer checkmap operations with this
    latest hammer utility and report back.  bzip2'ing the output and
    making it available would also be helpful.

						-Matt