From owner-freebsd-hackers  Tue Jun 30 16:05:22 1998
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From: wjw@digi.digiware.nl (Willem Jan Withagen)
Message-Id: <199806302303.XAA07485@digi.digiware.nl>
Subject: Variant Link implementation, continued
In-Reply-To: <199806080712.AAA09745@antipodes.cdrom.com> from Mike Smith at "Jun 8, 98 00:12:57 am"
To: mike@smith.net.au (Mike Smith)
Date: Wed, 1 Jul 1998 01:03:37 +0200 (CEST)
Cc: hackers@FreeBSD.ORG
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=>  > >> If we really wanted to get variant symlinks, I would suggest copying
=>  > >> the already-fairly-well-known syntax of AFS, `@name_of_parameter'.  As
=>  > >> the metasyntactic variable suggests, these should be (a fairly small
=>  > >> number of) parameters which hold system-wide.  (Indeed, given the
=>  > >> existence of the sysctlbyname interface in the kernel, one could
=>  > >> simply kick them off in that direction.)
=>  > >
=>  > >Ok.  I did actually look at how this could be implemented last time it 
=>  > >came up, and I think it would be *reasonably* straightforward.

I have actual working code for this. 
At the moment every variantlink gets replaced by '2.2.6', since that is my
current OS version.

And /usr/local is thus pointing to /usr/local.${OSVERSION}
lrwxrwxrwx   1 root  wheel    20 Jul  1 00:50 local@ -> ./.local.${OSVERSION}
lrwxrwxrwx   1 root  wheel    12 Mar  1 23:08 .local.2.2.6@ -> /home2/local
lrwxrwxrwx   1 root  wheel    12 Mar  1 23:08 .local.@ -> /home2/local

Which is running for quite a while (1-2 weeks). The last link is to be used
in case I run a kernel with actual variant translation but OSVERSION is not
defined.

So I'm up for the next challenge:
=>  Start small; once this is working for you, the next step is the
=>  'defaults' space, which should be sysctl-accessible.  Then you can 
=>  start worrying about how to become more process-specific.

* sysctl-accessable variant parameters.
Currently all I know about this comes from 'man 3 sysctl' and browsing
through the kernel-source. But I've never finished my reading on MIB's so
any help an/or suggestion is welcom. 

My 2 major questions:
    -	How can I efficiently obtain the value of a sysctl value?
	And should they look like 'variant.name', or would/should a
	variant link be able to look like: 
		kern.osrelease: 2.2.6-STABLE
    -	It seems that names are allocated from within the kernel 
	upon startup, nothing dynamic. Is there any work in progress to make
	this more flexible? I could start by first creating a standard set
	of names.

    *	An alternative would be: How do I obtain the environment of the
	process using the link? (assuming it has nog messed with its
	*env-pointer)

Thanx,
--WjW

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