Writing Drivers for NetBSD - of index.html

3 THE AUTOCONF(9) PART OF THE RF(4) DRIVER 25
available as a preprocessor constant RFCCF DRIVE DEFAULT and in is our example
-1. (See 3.1.2 and 2.4 for the reason.)
Thus, the driver gets the value of the locators from two sides of the interface
attribute to which it attaches, i.e. the position, adress, ID, ... under which it is
known to its parent. The one side from which the driver receives the value of
the locator is the cf loc array of the cfdata data structure. These values are the
same as the ones give in the kernels configuration file; they are statically given
at compilation time. The other side is the attach args data structure passed to
the rfmatch function as void *aux. That structure is passed from the parent to
the child when the kernel boots. It therefore contains the locator values, that are
actually found in the hardware.
In the above if conditional, the child is checking two conditions: first,
whether or not a wildcard was given as the locator. If so, then the position, address,
ID, ... under which it is known to the parent matches, it returns 1 and the
child driver is attached. If the kernel configuration file did not contain a precise
position, address, ID, ... for the child, it has to use the match function to check
if the value of the configuration file is identical to the one actually found. If so,
then all’s peachy and the child driver is attached. If not, then the found hardware
configuration does not match the kernel configuration an the child driver must not
be attached. Therefore, the match function returns 0. This check is necessary to
“nail down” certain locators in the kernels configuration file. For example:
sd2 at scsibus1 target 6 lun 0
Using this mechanism, it is possible to on the one hand use wildcards and
at the same time to “nail down” certain instances of a driver to a specific position.
That is another reason why config found() calls config search().
config search() iterates over all children. That’s the only way to find the
“right” child, if no wildcards are used.
3.3.4 rf attach()
void
rf_attach(struct device *parent, struct device *self, void *aux)
{
struct rf_softc *rf_sc = (struct rf_softc *)self;
struct rfc_attach_args *rfc_aa = (struct rfc_attach_args *)aux;
struct rfc_softc *rfc_sc;
struct disklabel *dl;