Re: [PATCH 1/5 2.6.21-rc4] l2tp: pppol2tp core

James Chapman wrote:

Patrick McHardy wrote:

quoted

The interaction with UDP sockets looks pretty horrible IMO. On the
send side I don't see why you can't simply build the UDP header
yourself instead of doing these set_fs + sendmsgs hacks. 

Wouldn't that effectively duplicate the code in udp_sendmsg()? If I
don't use a socket, I'd also have to build an IP header and feed the
frame into the IP stack for outbound routing. It doesn't feel like the
right thing to do.

Thats what other tunnel drivers do. Sending UDP is pretty simple, I'd
expect that it comes down to less code than now.

One reason for using the L2TP tunnel's UDP socket directly was to have
the data traffic carried by all sessions in that tunnel use the tunnel's
socket buffer, thereby ensuring that one tunnel's data can't starve
another tunnel.

If you use encapsulation sockets and process packets immediately
that should still not be possible.

quoted

On the
receive side I it would be nice if you could use the encapsulation
socket stuff thats also used by IPsec.

Can you point me at some example code, please?

net/ipv4/udp.c: udp_encap_rcv()

quoted

- pppol2tp_fget: why do you want to open sockets for other processes?
  I hope this can go together with the sendmsg hacks

There are two userspace daemons: l2tpd and pppd. L2ptd opens a UDP
tunnel socket and sets up one or more L2TP sessions in that tunnel. When
a new session is established, l2tpd spawns a pppd process (per session).
The pppd process creates a PPPoL2TP socket (this driver). The PPPoL2TP
socket is associated with the tunnel UDP socket that was created by
l2tpd. So on creating a new PPPoX socket, the connect() handling needs
to find the UDP socket of the tunnel. Since connect() runs in the
context of pppd, it needs a way of doing a sock lookup to find the UDP
socket that was created by l2tpd.

How about just passing the file descriptor from l2tpd to pppd?