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Date:      Sat, 17 Mar 2012 08:45:20 +0100
From:      Luigi Rizzo <rizzo@iet.unipi.it>
To:        grarpamp <grarpamp@gmail.com>
Cc:        freebsd-net@freebsd.org
Subject:   Re: netmap
Message-ID:  <20120317074520.GB69097@onelab2.iet.unipi.it>
In-Reply-To: <CAD2Ti28W3JoBEyBqzkRkTzPh2VhmT3bM9EYe1-NnSFbaPXzHDg@mail.gmail.com>
References:  <CAD2Ti2-%2BRQZA8Tx6F746k%2Bz01yztZcKYUoptCYwFsp7odffExw@mail.gmail.com> <20120316231337.GA62350@onelab2.iet.unipi.it> <CAD2Ti28W3JoBEyBqzkRkTzPh2VhmT3bM9EYe1-NnSFbaPXzHDg@mail.gmail.com>

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On Fri, Mar 16, 2012 at 08:22:45PM -0400, grarpamp wrote:
> > yes this is the long term plan (actually, kind of works now too
> > if the netmap-attached client then passes the packets to the host
> > stack).
> 
> I would not know how to do that as a common user.


the "bridge" application in tools/tools/examples does exactly that
-- it can pass all packets (bidirectionally) between the host stack
and an interface in netmap mode. With little modifications it can
decide to look at the packets, keep some for itself, modify them, etc.

And the OS still believes the interface is there so playing with
addresses, forwarding tables, etc still works as always.

To come to the rest of your message: sure it would be great if
netmap could at the same time do all what is available in the
standard stack _and_ go much faster. But life is typically
a tradeoff and this case is no different: at the moment i can only
offer the option of run-time switching between the standard
stack and netmap mode, where you can do some things much faster
but you have a bit of inconvenience with other features
(e.g. you cannot do bpf in netmap mode, although netmap itself
is a much faster way of doing capture/inject). 

cheers
luigi



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