kernel enviroment in sysctl MIB

[Peter Pentchev]

On Tue, Nov 11, 2003 at 06:01:55PM +0100, Reinier Kleipool wrote:
> Hello,
> 
>   I am investigating the possiblilies for looking at the kernel boot
> parameters from within a userland utility. (Possibly a new FreeBSD install
> facility) The idea is that by looking at sysctl kern.environment.* you
> should be able to see the BTX variables. An install program could use this
> to see an INSTALL_SERVER=install.company.com variable (etc...) to use as
> install server. The BTX loader could provide these variables at install boot
> time, thus enableing fully automated installs.
[snip]
> My question is this: When looking at kern/kern_environmet.c I see routines
> that install a SYSCTL_NODE kern.environment. The sysctl_kernenv routine
> handles this node. What I do not understand is how the environment is
> returned from this routine.

Take a look at the kenv(1) utility - its source is in the
src/usr.bin/kenv/kenv.c file.  There is a weird comment at line 74,
where the kern.environment sysctl is accessed in a really 'magic &
undocumented' way.  Look at what it does - basically enumerating oid's
from a given starting point, the starting point being obtained in said
'magic & undocumented' way - and see if you could use the same approach.
Alternatively, you could just invoke kenv(1) with your variables as
command-line parameters from your program/script, although this might
incur a performance cost.

G'luck,
Peter

-- 
Peter Pentchev	roam at ringlet.net    roam at sbnd.net    roam at FreeBSD.org
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