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

[Stathis Voukelatos]

Hi Florian,

On 26/01/15 22:30, Florian Fainelli wrote:
> On 23/01/15 02:07, 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.
> Is there any latency penalty involved in capturing (or not) packets as
> opposed to having this capture HW unused?

There is no additional latency introduced by the sniffer at the H/W level,
if that is what you mean. Only the S/W overhead for handling the
sniffer interrupt for each match event.

> > 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.
> Instead of having this new generic netlink family to control sniffing,
> could we imagine registering a netdevice which does not nothing but
> still allows for tools like tcpdump, af_packet and other capture tools
> to work transparently and just leverage the HW capture?
Thanks, I will work on that change. It has been suggested by a previous
reviewer too and it makes sense to go down that route.

Stathis

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