Efficient use of Dummynet pipes in IPFW

[Luigi Rizzo]

On Mon, Sep 19, 2005 at 09:11:33AM -0600, Brett Glass wrote:
> At 01:59 AM 9/19/2005, Luigi Rizzo wrote:
> 
> >Same for as the 'resume' option. It might be nice to have,
> >however but there is already a two-rule version (the one i
> >suggested, follow the non-terminating action with a skipto rule)
> >so its absence is not blocking you from doing what you want.
> 
> That option requires repeating ALL of the matching on the packet.

absolutely not. it is the same as your 'resume' only split on two lines.

> >in terms of implementation, if you want to add it, the best place
> >would be to add the 'skipto' fields to each 'action' opcode.
> >I am not very interested in implementing it, though, because i still see
> >ipfw as a low-level language.
> 
> I don't see it that way, because low level languages like assembler 
> are normally very efficient and highly granular. The underlying
> opcode language of IPFW is low level for sure. But I would classify 
> IPFW's "language," as presented by the userland utility, as "high 
> level but limited." Sort of like the MS-DOS shell.

whatever. feel free to write a high level interpreter,
since i don't see it that way you can't expect me to do that :)

	cheers
	luigi
> >> I've looked at the source and it's fragmented and virtually undocumented,
> >
> >are you talking about the userland part or the kernel code ?
> 
> Both. There are some parts that are better than others; for
> example, the kernel part is more straightforward than the
> userland part and has more comments.
> 
> Yes, I know: some coders (the NetBSD folks are notorious for this) 
> seem to think that if you don't want to read (and mentally reverse-
> engineer) all of the C code, you shouldn't be touching it. But this 
> leads to bugs, because even a good coder won't know about "contracts" 
> involving code in other places.
> 
> >i agree the userland part is a mess.
> >But the kernel code i believe is reasonably documented
> >(of course it could be documented better - patches welcome).
> >the first 250 or so lines in ip_fw2.h are almost all comments
> >describing the opcode formats.
> >ip_fw2.c tries to describe rule parsing in the body of ipfw_chk()
> 
> Yep, I see that. But there are implicit contracts with the userland
> side.... Some are obvious but some seem to be subtle.
> 
> --Brett Glass