PROPOSAL: "creates" option to improve support for ifupdown front ends

[Thomas Hood <jdthood@yahoo.co.uk>]

Authors of front ends for ifupdown would like to be able
to compile a list of interfaces that, at a particular point
in time, could be enabled.  Some of these interfaces are
listed in /proc/net/dev -- no problem there.  However, some
interfaces only appear when ifup is run to configure them.
For example, on my system (using the experimental ifupdown)
if I run:

    ifup ppp0=foo

then pppd is started using the options listed in the "iface foo"
stanza in /etc/network/interfaces and pppd creates interface ppp0.
The problem is that, in this example, 'ppp0' does not appear
anywhere in /etc/network/interfaces.  So how can the front end
know that ppp0 is one of the interfaces that the user could bring
up?

To solve this problem it is proposed that logical interface
definitions in /etc/network/interfaces include a new option:

    iface foo inet ppp
        creates ppp0

This option would be, er, optional.  Its effect would be to place
a restriction on which physical interface could be configured as
the logical interface in question.  If this option is used where
appropriate then front ends for ifupdown could include the
arguments of all "creates" options in the list of available
interfaces.

Does anyone have any better ideas?
-- 
Thomas Hood