On Fri, Mar 20, 2009 at 01:58:08AM +0100, Robert Schwebel wrote:Greg,
On Wed, Mar 18, 2009 at 11:32:32AM -0700, Greg KH wrote:If anyone has any questions that this summary doesn't answer, please let meLet me take this as an opportunity to discuss the epl (Ethernet
know.
Powerlink) driver in staging. Taken aside the eye-cancer thing while
looking at the code (this could be fixed in the staging model), I
suppose the whole design is questionable.
Sure it's questionable, and it's horrid code, but it is being used by
people and is the only public implementation of EPL on Linux that I can
find.
We have ported similar commercial EPL stacks to linux-rt in the past,
and what we simply did is to implement the code completely in userspace,
ontop of a raw socket. It worked out pretty well and with reasonable
realtime performance. For the high level API, we used the process data
model provided by libpv [1], which gives you an abstraction that follows
both, automation-people's "process variable" concept and a modern object
oriented desing (in C, modeled after the POSIX object model for example
like pthread_create() & friends).
Doing this kind of network protocols in kernel space may be possible in
general, but IMHO the first thing that has to be done for a sane design
is:
"Invent proper APIs and abstractions"
Agreed.
Unfortunately, industry people have somehow missed the last 10 years of
software engineering, so even recent ethernet fieldbus designs like
PowerLink or EtherCAT use the CANopen Object Dictionary [1] as their
"abstraction" between the stack and the application. So writing
applications in the EPL/CANopen/EtherCAT world works by PEEK and POKE on
a variable-length global variable array. Welcome to software design of
the 80es. Nevertheless, "Object Dictionary" is a standard API for
industry people which cannot be discussed away, because automation
people are used to this terminology.
So if we want to do any kind of EPL/CANopen/EtherCAT work in the kernel,
let's start with the question what it buys us in comparism with a pure
userspace solution like outlined above.
Are userspace solutions for this opensource today?
<snip>
What do others think? Is it worth the effort to invent a proper objdict
API for linux?
I suggest discussing this on netdev, that's the proper place for network
protocol discussions like this, right?