Reading configuration file from driver during load

[Warner Losh]

From: Oliver Fromme <olli at lurza.secnetix.de>
Subject: Re: Reading configuration file from driver during load
Date: Tue, 19 Sep 2006 15:46:09 +0200 (CEST)

> Gireesh wrote:
>  > I have a driver which has some parameters hardcoded as of now. It requires
>  > values of these parameters to be available during load (during attach
>  > function). My requirement is to read these parameters from a configuration
>  > file so that we can load driver with different values to parameters without
>  > rebuilding driver. 
> 
> I think that sysctl or kenv variables are best suited for
> that purpose.  There are a lot of examples for that in
> existing drivers.

The 'kenv' variables are best wrapped in the tunable interfaces.  For
example: 

u_long cbb_start_16_io = CBB_START_16_IO;
TUNABLE_ULONG("hw.cbb.start_16_io", &cbb_start_16_io);
SYSCTL_ULONG(_hw_cbb, OID_AUTO, start_16_io, CTLFLAG_RW,
    &cbb_start_16_io, CBB_START_16_IO,
    "Starting ioport for 16-bit cards");

This is from the cbb driver.  It is a hint/tunable that can also set
the starting I/O port address range to use for 16-bit cards.  Users
can either place the following line in /boot/loader.conf or in
/etc/sysctl.conf.

	hw.cbb.start_16_io=0x300

The former sets it at attach time, while the latter sets it early in
the boot process, but after it has attached.  You can also set it at
run-time:

	sysctl hw.cbb.start_16_io=0x300

Warner