netdev - Re: [RFC PATCH 0/2] add ppp_generic ioctl to bridge channels

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Message-ID: <20201109155237.69c2b867@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com>
Date:   Mon, 9 Nov 2020 15:52:37 -0800
From:   Jakub Kicinski <kuba@...nel.org>
To:     Tom Parkin <tparkin@...alix.com>
Cc:     netdev@...r.kernel.org, gnault@...hat.com, jchapman@...alix.com
Subject: Re: [RFC PATCH 0/2] add ppp_generic ioctl to bridge channels

On Fri,  6 Nov 2020 18:16:45 +0000 Tom Parkin wrote:
> This small RFC series implements a suggestion from Guillaume Nault in
> response to my previous submission to add an ac/pppoe driver to the l2tp
> subsystem[1].
> 
> Following Guillaume's advice, this series adds an ioctl to the ppp code
> to allow a ppp channel to be bridged to another.  Quoting Guillaume:
> 
> "It's just a matter of extending struct channel (in ppp_generic.c) with
> a pointer to another channel, then testing this pointer in ppp_input().
> If the pointer is NULL, use the classical path, if not, forward the PPP
> frame using the ->start_xmit function of the peer channel."
> 
> This allows userspace to easily take PPP frames from e.g. a PPPoE
> session, and forward them over a PPPoL2TP session; accomplishing the
> same thing my earlier ac/pppoe driver in l2tp did but in much less code!

I have little understanding of the ppp code, but I can't help but
wonder why this special channel connection is needed? We have great
many ways to redirect traffic between interfaces - bpf, tc, netfilter,
is there anything ppp specific that is required here?