[adding -doc, which is more appropriate for some of the questions]
On Saturday, 22 January 2000 at 23:06:41 -0500, Bill Maniatty wrote:
> Hello All:
>
> I have a student this semester in my Operating Systems class who would like
> to become a bit more knowledgeable about systems software. I suggested
> that he learn a bit about how device drivers are written in FreeBSD
> as a minor project. My questions are:
>
> 1) Does any current documentation of how to write and/or install a
> device driver exist in English (note C != English)?
Yes, with reservations.
> We would love to have a level documentation like the document by
> Pragmatic at http://thc.pimmel.com/files/thc/bsdkern.html, we are
> looking for a how to guide.
Somewhere we have a tutorial. I think it's been retired because it's
out of date, but it could be a very rewarding starting point for
somebody who wanted to work his way into the material and either
update it or bring out a new document based on the structure. This
would also give the student good visibility in the (Free)BSD
community.
> 2) If no existing documentation exists, would it be a good idea to
> put together a sort of how to guide for a simple driver (with an
> eye to generalization later if warranted)?
>
> 3) If the answer to 2 is yes, can we get constructive help from the FreeBSD
> community?
Definitely. -hackers would be the right forum there. I would also
personally commit to helping within the constraints of my other work.
> Assuming that this constitutes an interesting project, what would be
> a good initial approach? I was considering:
> 1) Get and build the FreeBSD kernel (4.0?)
> 2) Choose a non-essential device with a simple preexisting driver.
> 3) Remove all trace of the driver from the kernel source.
> 4) Reapply the changes used to install the driver (perhaps one step at a time).
> We could suggest some simple sanity checks to support stepwise refinement.
(1) and (2) are a good start. You don't need to remove the old
driver; it would in fact make it easier for debugging purposes if it
remained. Instead, choose another major number and name, and write a
new driver. This procedure is definitely *not* documented, but it's
the way we introduce new drivers, and I think a couple of other people
who have done it would be pleased to help.
A possibly better alternative is to find a device which isn't
currently supported by FreeBSD and write a driver for it. This would
have the advantage that the work would also be a contribution to
FreeBSD. The question that I can't answer here is: what would be an
appropriate device?
> If this is a good idea, I would like the following help from the FreeBSD
> community:
> 1) Identify a simple driver (perhaps something like a joystick
> driver?)
I don't know if anybody uses it any more.
> 2) Identify all source code associated with the driver (including configuration
> files, makefiles etc...). Some files may have only one or two lines
> devoted to the driver, so we will need to know how to recognize such lines
> and would appreciate pointers to such lines.
That should be relatively straightforward after examination of the old
tutorial, the sources and hier(7). If not, ask away. Important
directories are:
/sys symlink to /usr/src/sys; I'll use it below
/sys/config generic configuration files
/sys/i386/config configuration files for i386
/sys/dev sources for generic device drivers
/sys/isa sources for generic ISA device drivers
/sys/i386/isa sources for i386-only ISA device drivers
Greg
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