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    SubjectRe: Why no XML in the Kernel?
    On Mon, 3 Oct 2005, Al Viro moaned:
    > Another fun consideration in that area is that XML (or s-exp, or trees,
    > whatever representation you prefer) has nothing to help with dynamic data
    > structures. Exporting snapshots does not work since the real state
    > includes the information about locks being held - without that you
    > can't tell which invariants hold at the moment, since the real ones
    > include lock state.

    Oh yes; the only practical way to get the system into a consistent state
    would be to take out the BKL (the old, non-preemptible variant),
    generate all that XML (for all of /proc and all of /sys!) and then
    release it again.

    Efficient this is *not*.

    (at least, not the loony everything-in-one-big-file variant. Keeping the
    current smaller files but making them XML is possible, but pointless:
    the filesystem already provides the hierarchical structure in /sys, and
    nothing can make /proc regular, so what's the point of adding an extra
    layer of hierarchy that serves only to complicate parsing and make it
    hard for *humans* to use?)

    > And forcing all locks involved into known state
    > is nowhere near feasible, of course. OTOH, exporting dynamic state
    > including locks and walking the damn thing is
    > a) not feasible with XML

    It's feasible, if you don't mind ps(1) becoming a DoS attack, and one
    running instance of top(1) damn-nearly freezing the system.

    It's just not *sane*.

    > b) would require giving userland way too much access to locking,
    > creating a nightmare wrt deadlock potential.


    (Current rant: DRM churn, forcing one of abandonment of decent 3D
    support, or upgrading of the X server to the bleeding-edge, or using an
    old kernel with known security holes, or becoming enough of a DRI
    developer to backport the changes, or using nothing but distro kernels
    <=2.6.11. Most of these are not terribly feasible for me right now. Ah
    well, my 3D card is total crap anyway. It's just a shame the X server
    crashes whenever asked to do in-software 3D rendering... time to
    debug. I thought I might actually get some work done this evening. Fat

    `Next: FEMA neglects to take into account the possibility of
    fire in Old Balsawood Town (currently in its fifth year of drought
    and home of the General Grant Home for Compulsive Arsonists).'
    --- James Nicoll
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