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From: Doug Ambrisko <ambrisko@ambrisko.com>
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To: John Baldwin <jhb@freebsd.org>
Date: Thu, 11 Aug 2005 16:21:02 -0700 (PDT)
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Cc: freebsd-hackers@freebsd.org, Dan Nelson <dnelson@allantgroup.com>
Subject: Re: Checking sysctl values from within the kernel.
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John Baldwin writes:
| On Friday 05 August 2005 10:50 am, Dan Nelson wrote:
| > In the last episode (Aug 05), Thordur I. Bjornsson said:
| > > If I want to check a sysctl value from within the kernel (e.g. an
| > > KLD), should I use the system calls described in sysctl(3) ?
| > >
| > > If not, what is the propper way to do so ?
| >
| > Since most sysctls are direct mappings onto integer variables in the
| > kernel, just check the variable directly.
| 
| There's also a kernel_sysctl() function available in the kernel for in-kernel 
| access to sysctls.  You might have to lookup the OID for a given name 
| yourself though.  Actually, there's a kernel_sysctlbyname() as well.

This could be a fragile interface though.  I used this scheme to do 
"soft-linking" between modules that could be kldloaded into the kernel
or static.  We called it several times every few seconds.  Over time
the system would wedge on a setjmp or something like that.  We changed
it to a function call since in a static kernel then the problem went away.

Doug A.