ifup async race problem

[Warren Togami <wtogami-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>]

modules.d/40network/60-net.rules

ACTION=="add", SUBSYSTEM=="net", RUN+="/sbin/ifup $env{INTERFACE}"
ACTION=="online", SUBSYSTEM=="net", RUN+="/sbin/netroot $env{INTERFACE}"

This works just fine if you have a single interface.  But if you have 
more than one interface bad things can happen.  If you have two or more 
interfaces and root=dhcp, the ifup udev rule attempts to dhclient on all 
interfaces simultaneously.

This can be a problem in cases where two or more interfaces are on DHCP 
networks.  The udev rule kicked off both interfaces simultaneously, so 
there is no way to guarantee which of the two will succeed to mount the 
rootfs.  In my testing this means eth0 or eth1 unpredictably mounted the 
rootfs.  The other interface meanwhile is configured to an IP address 
and has routes added.  DNS and routes configured could be either 
interface as well.

Locking so only one interface can ifup at a time wont exactly help here, 
because you still cannot predict which interface will go first.

It seems we have no way to make it predictable (eth0 attempts before 
eth1) while doing ifup from a udev event?

Warren Togami
wtogami-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org
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