Date:	Mon, 26 Jan 2015 09:49:44 +0000
From:	Stathis Voukelatos <stathis.voukelatos@...n.co.uk>
To:	Daniel Borkmann <dborkman@...hat.com>,
	Stathis Voukelatos <stathisv70@...il.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


On 23/01/15 11:20, Daniel Borkmann wrote:
> On 01/23/2015 11:07 AM, Stathis Voukelatos wrote:
>> This patch adds support the Ethernet Packet Sniffer H/W module
>> developed by Linn Products Ltd and found in the IMG Pistachio SoC.
>> The module allows Ethernet packets to be parsed, matched against
>> a user-defined pattern and timestamped. It sits between a 100M
>> Ethernet MAC and PHY and is completely passive with respect to
>> Ethernet frames.
>>
>> Matched packet bytes and timestamp values are returned through a
>> FIFO. Timestamps are provided to the module through an externally
>> generated Gray-encoded counter.
>>
>> The command pattern for packet matching is stored in module RAM
>> and consists of a sequence of 16-bit entries. Each entry includes
>> an 8-bit command code and and 8-bit data value. Valid command
>> codes are:
>> 0 - Don't care
>> 1 - Match: packet data must match command string byte
>> 2 - Copy: packet data will be copied to FIFO
>> 3 - Match/Stamp: if packet data matches string byte, a timestamp
>>                    is copied into the FIFO
>> 4 - Copy/Done: packet data will be copied into the FIFO.
>>                  This command terminates the command string.
>>
>> The driver consists of two modules:
>> - Core: it provides an API to user space using the Generic Netlink
>>           framework. Specific backend implementations, like the
>>           Ethernet Packet Sniffer, register one or more channels
>>           with the Core. For each channel a Genl family is created.
>>           User space can access a channel by sending Genl messages
>>           to the Genl family associated with the channel. Packet
>>           matching events are multicast.
>>
>> - Ethernet Packet Sniffer backend: provides the driver for the
>>           Linn Ethernet Packet Sniffer H/W modules.
>>
>> The split between a core and backend modules allows software-only
>> implementations to be added for platforms where no H/W support
>> is available.
>>
>> Based on 3.19-rc5
>>
>> Signed-off-by: Stathis Voukelatos <stathis.voukelatos@...n.co.uk>
> Please have a look at packet sockets, they offer already all the
> functionality (if not more) your driver interface to the user space
> resembles, are transparent to the underlying hardware, and easily
> can cope with 100Mbit.
>
> If I understand this correctly, you are effectively introducing a
> parallel API *next* to packet sockets to user space that we have to
> maintain forever ...
>
> Thanks !
>

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.

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