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Re: processing order for configuration files in /etc/network/interfaces.d




On Mon 27 Aug 2018 at 19:24:01 (+0300), Reco wrote:
> 	Hi.
> 
> On Mon, Aug 27, 2018 at 12:01:23PM -0400, Greg Wooledge wrote:
> > On Mon, Aug 27, 2018 at 06:41:25PM +0300, Reco wrote:
> > > Last sentence says to me that wordexp output should be always sorted.
> > 
> > This only tells us that it *reads* the config files in glob-sorted order.
> > And peeking into the actual source code of ifupdown, yes, it appears to
> > do this.  (File config.c starting at line 436, in the stretch source.)
> > It even uses wordexp() as advertised.
> > 
> > What's less clear to me at this moment is what happens *after* the
> > interface configuration file(s) have been read into memory.
> > 
> > Moving over to main.c, it looks like it reads the interfaces (line 639),
> > and that function was called from line 1190.  After line 1190, it loops
> > over the "target_iface" array, and processes them in the order they appear
> > in that array.
> > 
> > So... next question is how they get packed into that array.
> > 
> > Returning to the select_interfaces function, it looks like the ordering
> > is created by a call to find_allowup.
> > 
> > And... this is where I stopped reading, because it got confusing.  Maybe
> > someone else can take a stab at deciphering that part.
> 
> select_interfaces() is called on "ifup -a" invocation.
> read_interfaces() is called by it.
> read_interfaces() calls read_interfaces_defn().
> read_interfaces_defn() parses "iface" and "source" directives, and calls
> read_interfaces_defn() once again on each file specified by "source" in
> order defined by wordexp(3).
> 
> Therefore defn[] array should be filled in this order (assuming that one
> specifies "source" only at /e/n/i):
> 
> 1) any interface definition at /e/n/i in order encountered, until
> "source" directive.
> 2) any interface definition provided by "source" directive in order
> defined by wordexp(3).
> 3) any interface definition at /e/n/i in order encountered, after the
> "source" directive.
> 
> I'd use ltrace(1) to check it, but building test environment is
> something that I lack the time to do.

That's still the order in which the stanzas are read. Don't we now
need to know what the contents of each stanza is, ie is it an "auto"
or an "allow-hotplug" stanza, etc?

Cheers,
David.