Date: Thu, 10 Apr 2008 11:48:44 -0400 From: John Baldwin <jhb@freebsd.org> To: freebsd-drivers@freebsd.org Cc: Rick Hunnicutt <rk_hunnicutt@yahoo.com> Subject: Re: New driver writer Message-ID: <200804101148.44612.jhb@freebsd.org> In-Reply-To: <535058.32207.qm@web37606.mail.mud.yahoo.com>
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On Tuesday 08 April 2008 03:29:07 pm Rick Hunnicutt wrote:
> Hello all,
>
> I'm writing a BSD PCI character driver and have many questions. I have the
architecture handbook and it answers some questions but leaves much
unaddressed. For example, the parameters on the open/close/read/write calls
don't seems to be address. Am I expected to dig around the code base to
decipher their purpose or have I missed a vital area of documentation?
>
> Thank you for your help.
Yeah, you'll have to dig for now. :( The way you normally do cdev's though is
something like this:
struct foo_softc {
device_t foo_dev;
...
struct cdev *foo_cdev;
...
};
static int
static int
foo_attach(device_t dev)
{
struct foo_softc *sc;
sc = device_get_softc(dev);
....
sc->foo_cdev = make_dev(&foo_cdevsw, unit2minor(device_get_unit(dev)),
UID_ROOT, GID_WHEEL, 0600, "foo%d", device_get_unit(dev));
if (sc->foo_cdev == NULL)
/* error handling */
sc->foo_cdev->si_drv1 = sc;
...
}
static int
foo_detach(device_t dev)
{
...
if (sc->foo_cdev)
destroy_dev(sc->foo_cdev);
...
}
static int
foo_open(struct cdev *dev, int flag, int mode, struct thread *td)
{
struct foo_softc *sc;
sc = dev->si_drv1;
/* Now you have the foo_softc structure and can do whatever you want */
}
That is, the trick is for the driver to store a pointer to its softc structure
in the 'si_drv1' member of the cdev when you create the cdev. You can then
get the softc pointer out of 'si_drv1' in your cdevsw routines. There are
also 'si_drv0' (u_int) and 'si_drv2' (another void * like 'si_drv1') fields
in 'struct cdev' that the driver "owns" and is free to put whatever data is
desired in.
--
John Baldwin
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