ipoe: flush sessions left by a previous instance with a single command

On startup accel-pppd is expected to drop everything a previous instance
left behind in the kernel. For sessions it did so by dumping them with
IPOE_CMD_GET and sending one IPOE_CMD_DELETE per ifindex. That dump was
written for the session backup code removed in 1972a7e5c and was never
adapted to its new, destructive role:

 - it was issued on the socket subscribed to the packet multicast group,
   so it competed with the notifications that the still attached stale
   rx handlers keep generating; on a loaded box the receive buffer
   overruns and rtnl_dump_filter() gives up with ENOBUFS,
 - its return value was discarded, so such a failure was silent,
 - it ran before the interfaces were detached, which is what produces
   those notifications in the first place,
 - it was skipped entirely when the multicast group could not be
   resolved, again with nothing but a warning about packet handling,
 - and every session cost a socket, a round trip, a grace period and a
   full unregister_netdev().

Whatever it missed stays in the kernel forever: the daemon has no record
of those sessions, so nothing ever deletes them, and every subscriber
later assigned one of their addresses is refused with EEXIST by
IPOE_CMD_MODIFY.

Add IPOE_CMD_FLUSH, which unlinks all sessions in one go, waits for a
single grace period and unregisters the devices with
unregister_netdevice_many(), and use it instead. The old path is kept as
a fallback for a module predating the command, which is reported as
EOPNOTSUPP, and now checks its return value and uses a private socket.

Reorder init() so the interfaces are detached before the multicast group
is joined, and so the flush also runs when only the group lookup failed.

0 files changed, 0 insertions, 0 deletions