I'm trying to wrap my mind around the full sequence of events from an interface coming up (or its address changing) to the scripts in /etc/hotplug.d/iface being called. I'm specifically interested in this for ddns purposes (ddns-scripts packages drops a 25-ddns script there), but the discussion should apply more generally.
I start in the kernel, where subsystems can inject a uevent using kobject_uevent:
http://lxr.linux.no/linux+v3.12.6/lib/k … ent.c#L322
That takes an enum for the action, which is stringified according to this LUT for inclusion in the netlink message as "ACTION=":
http://lxr.linux.no/linux+v3.12.6/lib/k … vent.c#L45
The possible values are: add, remove, change, move, online, offline.
I looked around linux/net/ for call sites of kobject_uevent and it seems like net only delivers add/remove for devices as a whole, plus change for a few protocol/driver specific cases like rfkill. No interface address change events? Anyway, let's continue..
From here procd appears to create a netlink socket and pump events out of it:
http://nbd.name/gitweb.cgi?p=luci2/proc … =HEAD#l451
There doesn't seem to be much event-specific handling in C code, but there is a mini domain-specific language (why a new language instead of bash or lua?) expressed in JSON that takes care of certain subsystems specially:
https://dev.openwrt.org/browser/trunk/p … ?rev=36994
netifd *also* creates a netlink socket and pumps events out of it:
http://nbd.name/gitweb.cgi?p=luci2/neti … =HEAD#l141
netifd seems to handle "add" and "remove" events only, using them to update internal state about device presence and to rebroadcast state changes to internal subscribers. I see calls to device_claim in alias.c, bridge.c, vlan.c, a few others. Do these events somehow end up on ubus? Are there any bash scripts (ala /etc/hotplug.d) executed as a result of these events? examples/hotplug-cmd seems to be a hotplug script, when does this come into play?
Going back to procd, the openwrt hotplug.json, for "net" events, runs /sbin/hotplug-call %SUBSYSTEM%. This runs the scripts in /etc/hotplug.d/net with environment from the uevent:
https://dev.openwrt.org/browser/trunk/p … =36994#L71
hotplug.json has no configuration for SUBSYSTEM=iface. Are these events swallowed? What about the "ifup" and "ifdown" values for ACTION? (these are documented on the wiki: http://wiki.openwrt.org/doc/techref/hotplug and used by the scripts in /etc/hotplug.d/iface) I'm starting to think SUBSYSTEM=iface may not actually exist..
Does uevent deliver events only for device add/remove, or also when an interface alias is created? What about when the addresses of an interface change? I tried answering some of these questions by running 'strace -f -p 1' (stracing procd) and bringing up an alias of lo (ifconfig lo:1 188.8.131.52 netmask 255.255.255.0) but it didn't seem to get any events. I also tried stracing netifd, again with no visible effects. I can't easily play with the other interface on this router because it's in active use.
The reason I'm doing this is I suspect ddns-scripts is not being triggered when my WAN interface gets an IP. It has the following script in /etc/hotplug.d/iface/25-ddns:
if [ "$ACTION" = "ifup" ]; then
In my case the WAN proto is DHCP - I want an event when WAN gets an IP (*after* the underlying network device has come up). What is the best hook to trigger for this? I have another router that uses PPP on wan so I'm looking for a generic solution.
(Last edited by eigma on 26 Dec 2013, 05:01)