Re: Why no XML in the Kernel?

[Nix <nix@esperi.org.uk>]

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.

Indeed.

(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
chance.)

-- 
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and home of the General Grant Home for Compulsive Arsonists).'
            --- James Nicoll