Date: Wed, 8 Dec 2004 22:05:03 -0600 From: Dan Nelson <dnelson@allantgroup.com> To: cm c <beatlelittle@yahoo.com.cn> Cc: freebsd-questions@freebsd.org Subject: Re: How to write driver with load time parameter support? Message-ID: <20041209040502.GJ2629@dan.emsphone.com> In-Reply-To: <20041209034201.11670.qmail@web15307.mail.bjs.yahoo.com> References: <20041208035709.GF2629@dan.emsphone.com> <20041209034201.11670.qmail@web15307.mail.bjs.yahoo.com>
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In the last episode (Dec 09), cm c said:
> I'm still not very clear the way to do this. Does this method do set
> the parameters at load time or after load ? Cause Linux can
> insmod abc.o param=123;
> param is set to 123 when abc is linked to the kernel.
You would put something like
abc.param="123" in loader.conf or add it via kenv, and then in your
variable declaration area:
static int myparam = 0;
TUNABLE_INT("abc.param", &myparam);
That works for a module that can only be loaded once, and a static
tuneable name. If you don't know the name of the tunable until your
driver is loaded, you can use the TUNABLE_INT_FETCH() macro in a
function. Sysctls are recommended if you have a value that can be
changed after the module is loaded.
If you are writing a device driver, take a look at how if_fxp.c pulls
in per-device tunable/sysctls (search for bundle_max).
--
Dan Nelson
dnelson@allantgroup.com
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