Jeff Garzik [off-list ref] writes:

No!  procfs additions are discouraged.  sysfs in 2.5.x if you _must_
do this, but SIOCDEVPRIVATE or just flat out maintaining a kernel
patch against a stable kernel tree would be much preferred, I think.

Still, SIOCDEVPRIVATE should _not_, in my opinion, be used for anything
but hacks.
For example, we should stop using it for configuring ethernet bridges:

net/bridge/br_device.c: if (cmd != SIOCDEVPRIVATE)
-- 
Krzysztof Halasa
Network Administrator