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    Subject[ANNOUNCE] ddtree: A git kernel tree for storage servers
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    Hi all,

    I have set up a new git tree to better serve the needs of those
    interested in advanced storage applications and development.

    This ddtree git repository aims to provide a congenial forum for
    development of forward looking storage features such as replication and
    clustering; and to provide improved kernels for those who consider it
    important that their storage servers run efficiently under heavy load
    without deadlocking.

    What will be in this ddtree?

    * Block layer deadlock fixes (Status: production)
    * bio allocation optimizations (Status: functional)
    * bio support for stacking block devices (Status: functional)
    * vm dirty limit eradication (Status: prototype)
    * vm dirty rate balancing (Status: prototype)
    * ddlink generic device driver control library (Status: functional)
    * ddsetup device mapper frontend rewrite (Status: incomplete)
    * ddman kernel cluster harness (Status: upcoming)
    * ddraid distributed raid (Status: prototype)
    * ddsnap replicating snapshot device (Status: alpha)

    Patch set tracking

    One task that git does not support well at all is maintaining the
    identity of patches and patch sets. This is no doubt due to the fact
    that Graydon Hoare[1] never implemented the second of my two
    suggestions for improving Monotone's database schema[2], which is to
    say that patches and patch sets should be first class, versioned
    objects in the revision control database. One could fairly say that
    git caters more to maintainers than submitters, the latter being
    largely left to their own devices when it comes to splitting deltas up
    into the modular form wanted for peer review. My partial solution to
    this deficiency is to embed the interesting patches in a directory
    called "patches", each named in such a way that:

    ls patches/* | sort -r | xargs cat | patch -p1 -RE

    will reverse them, and:

    cat patches/* | patch -p1

    will re-apply them. This is similar to the way Quilt works, less its
    series file, which is replaced by a naming convention that is obvious
    from inspection. No doubt I should really begin using Quilt, but I can
    always learn that art later. For now, the important thing is to carry
    along patch identities in a way that makes life easier for me.

    At present, ddtree only carries six patches, all in its main "dd"
    branch. These patches are based off of the "ddbase" branch, which is
    in turn derived from either a two-dot or a three-dot stable kernel
    release. Thus, I intend to track Linus's tree at coarse intervals and
    selected stable releases at finer intervals, which will most likely
    coincide with significant distributor branch points such as that of
    Ubuntu Hardy (long term stable server release).

    So for today:

    $ tree patches
    patches
    |-- bio-alloc
    |-- bio-alloc-hide-endio
    |-- bio-alloc-stack
    |-- bio-alloc-stack-reduce-dm-allocs
    |-- ddlink
    `-- ddlink-ddsetup

    Other patches expected to land here over the next few days:

    * bio.throttle (avoid bio write deadlock)
    * ddsnap (snapshots and replication)
    * ramback (backing store for ramdisks)

    I am still learning git and developing my workflow, so it will take a
    few days for that to settle down, during which period I will tear down
    and rebase the content several times. Currently I have very limited
    bandwidth available, so please be gentle and avoid clone - just clone
    a linus tree and pull into that instead. (hpa...?)

    To browse ddtree:

    http://phunq.net/ddtree

    To pull from ddtree:

    http://phunq.net/git/ddtree (please do not clone for now)

    For now there is no git:protocol access because git-daemon manifests
    some strange issue I have not yet had time to track down. The symptom
    is this:

    $ tail /var/log/git-daemon/current
    2008-03-19_03:49:26.67922 [1068] Request upload-pack for '/ddtree'
    2008-03-19_03:49:26.68142 fatal: packfile ./objects/pack/pack-d37a0c64e9ce1c8b29ad9c02a39636ca9c609c31.pack cannot be mapped.

    Invitation

    Anybody who wants to participate in the ongoing design, development and
    debugging of lvm3, among other things: we hang out on irc.oftc.net
    #zumastor. Everybody welcome, and see http://zumastor.org.

    Regards,

    Daniel

    [1] Graydon Hoare: see quicksort, then see grandfather.

    [2] Fortunately, Graydon did implement the first suggestion, that
    directories should become first class versioned objects, thus setting
    the stage for the development of git[3].

    [3] Monotone, http://en.wikipedia.org/wiki/Monotone_%28software%29


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