Need help with network device driver development

[Ollie Lho]

"Stuart Summerville (Deimus)" wrote:
> 
> Hi there,
> 
> I'm toying with the idea of writing (hacking actually..) a psuedo network
> device driver that doesn't actually interface to nic hardware, but uses a
> custom packet transmision system. eg. I would have an eth-x interface
> connected to the psuedo-nic module on one machine, which is connected (by
> the custom comms system) to an eth-x interface on another machine (possibly
> the same one).
> 
> I've browsed the source for several net drivers (3com, ne, re100, and
> loopback) and the skeleton driver and have some idea as to whats involved.
> The "Network buffers & memory management" article from LinuxJournal
> (http://www2.linuxjournal.com/lj-issues/issue30/1312.html) proved very
> informative, but I still have some questions:
> 
> 1) the loopback driver source defines that device as being type
> ARPHRD_LOOPBACK. The would seem to inform the kernel that the device will be
> different to normal nic drivers, such as that there will be no interrupt
> mechanism (should it? I guess there's no rx function required) employed by
> the driver. My driver needs such distinctions made also (being totally
> software driven), so how do I find out which ARP_HARDWARE type best matches
> the requirements of my driver?
> 
> Yes, the source is all there, but I'd prefer to read existing literature (or
> have someone who's "been there, done that" tell me) before diving into the
> source.
> 
> 2) How does one debug the way that the kernel brings these modules and
> interfaces to life? With a hacked version of one of the above drivers
> properly configured (ie. alias added to /etc/conf.modules, the
> module "installed" in /lib/mod... & eth if added via linuxconf) all I see
> when the kernel (RH 6.1) tries to bring up that eth interface on reboot is
> something like "Bringing up ethx, delayed ethx init..." indicating that
> something went wrong. The corresponding kernel log (as recorded by dmesg, or
> seen in /var/log/messages is loaded with
> insmod) shows test log messages from the start of my driver. No, the fact
> that the hardware for that driver wasn't present shouldn't matter - I've
> forced the return of init_module to be 0. Obviously something deeper into
> the nic probing (or even further) is broken.
> 
> What I really need/want is to see more info from the kernel about why it
> decided to delay init of that eth interface.
> 
> 3) If these network device drivers must operate in an interrupt driven mode
> (I'd really rather have the kernel (or ip stack...) poll my driver for
> received data), can you suggest a way of generating a software interrupt to
> do this? Can I generate a timer interrupt for my task to prompt the polling
> of rx'd data, or should I run my custom comms system as a separate task in a
> polled fashion, which then interrupts the driver for handling of the
> received data?
> 
> 4) Any advice about juicy books that might cover this? Any other web pages
> that elaborate further? I couldn't find anything on the LDP development
> pages & others....
> 
> Thanks, sTu.
> 

The "Linux Device Driver Programming" by Rubini has a chapter on Network
device driver, you should start from there.

Take a look on my SiS 900 driver, the comments sould be clear for
novice driver writer. (hey, it was the first driver I maintained !!)

Ollie

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