git: HAMMER - Add version 3 meta-data features

[Matthew Dillon]

:commit 83f2a3aae851887c1143dd5174eade5b66682dce
:Author: Matthew Dillon <dillon at apollo.backplane.com>
:Date:   Wed Oct 14 11:44:59 2009 -0700
:
:    HAMMER - Add version 3 meta-data features

    Please note that this is considered EXPERIMENTAL, which is why HAMMER v3 is
    marked as a work in progress.   Do not upgrade your production systems yet.
    We need to test these features for a good month and work out the kinks.

    The work is also not quite finished yet.  The hammer cleanup directive
    still stores its cycle files in <fs>/snapshots, and still stores the
    snapshot softlinks there as well.

    What I would like to do is move the cycle files to /var/db and create a
    /var/snapshots, but I am not yet sure how best to name the files (ideas
    are welcome!).  Getting it all moved out of <fs>/snapshots will allow us to
    get rid of <fs>/snapshots entirely.

    With the snapshots as filesystem meta-data it will be possible to
    regenerate snapshot softlinks from the meta-data in cases where the softlinks
    get blown away (e.g. by a mistaken rm -rf or something like that), plus
    hammer cleanup will not mistakenly blow away the snapshots because it
    also uses the meta-data to create its definitive list of transaction ids
    for pruning purposes.

    These changes will also make manaing mirroring slaves a whole lot easier.
    Mirroring slaves have the particular issue of <fs>/snapshots being a mirror
    of the master, meaning the snapshot data and config info is all for the
    master rather than for the slave.  Once the new work is all finished that
    will no longer be an issue and slaves can be managed with their own independant
    configs.

						-Matt