This corrects a bug where stale dhcp packets would get reprocessed,
causing very bad behavior; an issue that was introduced in the
coroutine conversion.
If ndhc were a high-performance program that handled lots of events,
this change would harm performance. But it is not, and it implicitly
believes that events come in one at a time. Processing batches
would make it harder to assure correctness while also never allocating
memory at runtime.
The previous structure was fine when everything was handled
immediately by callbacks, but it isn't now.
This change makes it much easier to reason about ndhc's behavior
and properly handle errors.
It is a very large changeset, but there is no way to make this
sort of change incrementally. Lease acquisition is tested to
work.
It is highly likely that some bugs were both introduced and
squashed here. Some obvious code cleanups will quickly follow.
This change paves the way for allowing ifch to notify the core ndhc
about failures. It would be far too difficult to reason about the
state machine if the requests to ifch were asynchronous.
Currently ndhc assumes that ifch requests never fail, but this
is not always true because of eg, rfkill.
In order for this to work, the correct rfkill index must be specified
with the rfkill-idx option.
It might be possible to auto-detect the corresponding rfkill-idx option,
but I'm not sure if there's a guaranteed mapping between rfkill name and
interface name, as it seems that rfkills should represent phy devices
and not wlan devices.
The rfkill indexes can be found by checking
/sys/class/rfkill/rfkill<IDX>.
AF_UNIX SOCK_STREAM sockets between the master processes and each subprocess,
and poll for the HUP event.
At the same time, be specific about the events that are checked in epoll
when dispatching on an event.
The pipes wouldn't do this job anymore because they were unused and thus
never performed writes that would generate SIGPIPEs, so the pipes are
removed, too.
