to prevent deadlock on media unbind (which is called with
the interface wlock()'ed), the medias reader processes
that unbind was waiting for used to discard packets when
the interface could not be rlocked.
this has the unfortunate side effect that when we change
addresses on a interface that packets are getting lost.
this is problematic for the processing of ipv6 router
advertisements when multiple RA's are getting received
in quick succession.
this change removes that packet dropping behaviour and
instead changes the unbind process to avoid the deadlock
by wunlock()ing the interface temporarily while waiting
for the reader processes to finish. the interface media
is also changed to the mullmedium before unlocking (see
the comment).
avm fritzbox uses very long RA period so it effectively only
responds after a router solicitation. when there are multiple
fritzbox routers on the lan, then while configuring one prefix
of the first RA, the ip stack can drop the second router
advertisement and we would never get the second route.
packets can always get lost. so we just keep on sending router
solicitations (up to 3 times) to make sure we got all the RA's.
This patch makes 3 changes:
- It makes upas/fs send plumb messages when a message
changes in the background (eg, someone on another imap
connection opens a message and sets the read flag)
- It makes faces not complain when it gets one of these
new modify messages.
- It makes acme/Mail update the flags in the display
when it gets one of these messages.
on systems with serial console and graphics such as the raspberry pi,
it is nice to get a system shell on the serial console even when no
monitor is connected.
the console command runs a command or the system shell under
a new instance of kbdfs, optionally providing a serial console
when $console environment variable is set.
