netdev - Re: [PATCH iproute2 -next] tc, bpf: finalize eBPF support for cls and act front-end

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Message-ID: <20150402121003.GA21588@casper.infradead.org>
Date:	Thu, 2 Apr 2015 13:10:03 +0100
From:	Thomas Graf <tgraf@...g.ch>
To:	Hannes Frederic Sowa <hannes@...essinduktion.org>
Cc:	Daniel Borkmann <daniel@...earbox.net>, stephen@...workplumber.org,
	ast@...mgrid.com, jiri@...nulli.us, netdev@...r.kernel.org,
	Jamal Hadi Salim <jhs@...atatu.com>
Subject: Re: [PATCH iproute2 -next] tc, bpf: finalize eBPF support for cls
 and act front-end

On 04/02/15 at 01:30pm, Hannes Frederic Sowa wrote:
> On Thu, Apr 2, 2015, at 12:19, Daniel Borkmann wrote:
> > I'm probably missing something, would that need changes to bash?
> > 
> > I mean exec could bind an fd in the shell to sockets and use that,
> > for example ...
> > 
> >    exec 3<>/dev/tcp/www.slashdot.org/80
> >    echo -e "GET / HTTP/1.1\r\nhost:
> >    http://www.slashdot.org\r\nConnection: close\r\n\r\n" >&3
> >    cat <&3
> > 
> > ... perhaps such a built-in fake device for retrieving bpf map fds
> > might be interesting, e.g. exec 4<>/dev/bpf/<obj-file>/<map-name> if
> > that has been given to bash?
> > 
> > Anyway, I think to have some utility for shell scripts, as you
> > suggest, certainly sounds interesting!
> 
> All file descriptors will be inherited by exec as long as the O_CLOEXEC
> flag wasn't specified on them. So you can retrieve the fds via af_unix
> and just exec a new shell. The file descriptors will stay open and you
> can pass the numbers of the fds via environment. This wouldn't need
> changes to bash or kernel.

We also have to consider implementing a way to reopen the fds after
the original process has crashed but I agree this is a great start
for the tc environment.
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