netdev - Re: [PATCH] net: Linn Ethernet Packet Sniffer driver

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Message-ID: <54C7736C.8090704@linn.co.uk>
Date:	Tue, 27 Jan 2015 11:15:56 +0000
From:	Stathis Voukelatos <stathis.voukelatos@...n.co.uk>
To:	Daniel Borkmann <dborkman@...hat.com>
CC:	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"abrestic@...omium.org" <abrestic@...omium.org>
Subject: Re: [PATCH] net: Linn Ethernet Packet Sniffer driver

Hi Daniel,

On 26/01/15 10:10, Daniel Borkmann wrote:
>> Hello Daniel. Thank you for your feedback.
>> Packet sockets could also be used for the driver interface to
>> user space, however I think that both approaches would require the same
>> amount of maintenance. We need to maintain a protocol consisting of
>> a set of messages or commands that user space can use to communicate
>> with the driver in order to configure the H/W and retrieve results.
>> We could use packet sockets to send those messages  too, but I thought
>> netlink already provides a message exchange framework that we could
>> make use of.
>
> When using packet sockets and your driver as a backend feeding them,
> users can see that there's an extra capturing/monitoring netdev present,
> all libpcap-based tools such as tcpdump et al would work out of the box
> w/o adapting any code, and as an admin you can also see what users/tools
> are making of use of the device through packet sockets. I couldn't parse
> the exact motivation from the commit message of why avoiding all this is
> better?
>
> Thanks,
> Daniel
>
>
Just wanted to clarify some implementation details for your approach.
- The driver would need to create and register two net_device instances.
One for sniffing Ethernet TX packets and one for RX.
- Would the control interface for the sniffer in that case need to be
through private socket ioctls (ie SIOCDEVPRIVATE + x ioctl ids)?
- For each ethernet packet that matches the command string the sniffer
returns some data bytes and optionally a timestamp (depending on the
command string). Would a new protocol need to be added in
<linux/if_ether.h> in order to deliver that data to user space through
a packet socket?

Thanks,
Stathis

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