Fix building warnings

    fix typos, clean up some code, correct function prototype.

    Signed-off-by: Bo Yang <boyang@suse.com>
    Add handler for metadata update.

    After receiving metadata update message, reload
    superblock from disk.

    Signed-off-by: Bo Yang <boyang@suse.com>
Merge pull request #5 from thesues/master

fix warnings,Add handler for metadata update from boyang