Subject: Re: Networking strangeness Solution?
From: Charles McLachlan (cim@uk.research.att.com)
Date: Tue May 09 2000 - 11:59:15 MDT
On Tue, 09 May 2000, you wrote:
> My (kernel newbie's) intuition is that there's a layering problem in how
> the sheep_net driver's doing it's job.
Spot on. See my post to Brian for fully details
> Similar products, like VMware (www.vmware.com), don't have this kind of
> difficulty.
But they use a similar mechanism, a kernel module feeds packets into a user
land process that feeds them onto a network driver running on the virtual
machine.
> I've done some
> coding for this kind of thing on VMS, and I'd be happy to take a crack at
> the Linux flavor: can anyone point me at a document that describes how
> the Linux kernel does internal packet routing?
The sheep_net code is actually very simple (I think). It just reads /dev/eth0,
spools the packets and waits for someone (i.e. the osi_enet driver) to read from
/dev/sheepnet.
osi_enet seems to do pretty mush exactly the same thing, it reads from
/dev/sheepnet, spools and waits for LinuxOSIGetPacket from the Mac driver.
The virtual Mac is told about waiting data by a spoofed irq transition.
In my nieve way I can see a few things that might jolly things along.
1) Cut out the spool in osi_enet. Have a thread in MOL that polls /dev/sheepnet
and spoofs an irq when there's data ready. Then, when the Mac calls
LinuxOSIGetPacket, thats when you do the read on /dev/sheepnet.
2) (I'm not totally sure on this one as I am vague about all the
nuances of sheep_net's operation) Cut out sheep net for reading entirely. Get
osi_enet to poll/ read directly on eth0. (Would this upset other things using
eth0?)
3) Put a timeout on spoofing irqs up to the Mac. The Mac's STREAMS driver gets
bogged down if too many irqs come too quickly so maybe get osi_enet to
collect packets into groups and send one irq per group. (Will this work, or is
it one irq per packet?)
4) Get the Mac STREAMS module to grab more memory (so it can deal with more
packets before barfing).
By the way, I really have no idea about what I'm talking about, this is my
first venture into network/ kernel module/ STREAMS hackery so please don't
freak if I'm talking dreck.
--
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Charlie McLachlan
AT&T Research Lab. Cambridge.
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