Date: Wed, 18 Jun 2014 09:44:17 -0400 From: John Baldwin <jhb@freebsd.org> To: freebsd-current@freebsd.org Cc: Hans Petter Selasky <hps@selasky.org> Subject: Re: [RFC] Huge sysctl patch for the kernel coming - work in progress Message-ID: <201406180944.17762.jhb@freebsd.org> In-Reply-To: <53A179D5.8020604@selasky.org> References: <53A179D5.8020604@selasky.org>
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On Wednesday, June 18, 2014 7:36:53 am Hans Petter Selasky wrote:
> Hi,
>
> Sometimes sysctl's default value needs to be setup at boot time and not
> when the rc.d/sysctl is running. Currently this is done by having two
> statements in the kernel:
>
> TUNABLE_INT("net.graph.mppe.log_max_rekey", &mppe_log_max_rekey);
> SYSCTL_INT(_net_graph_mppe, OID_AUTO, log_max_rekey, CTLFLAG_RW,
>
> I want to simplify this to:
>
> SYSCTL_INT(_net_graph_mppe, OID_AUTO, log_max_rekey, CTLFLAG_RWTUN,
>
> In other words if the existing CTLFLAG_TUN is set, the sysctl will
> automatically be pre-loaded with values from /boot/loader.conf.
>
> The reason we don't want the current approach is:
>
> 1) It duplicates the sysctl path in the TUNABLE statement.
> 2) It does not work very well for dynamically attached sysctls. There is
> a lot of code overhead computing the TUNABLE() path before the TUNABLE()
> can be fetched.
>
> Here is a work in progress:
>
> http://home.selasky.org:8192/sysctl_tunable.diff
>
> In most cases my patch is fine, but in some other cases I need some
> input, like in the VM subsystem when doing init, I'm not sure if the
> SYSINIT() for subsystem SI_SUB_KMEM, which sysctl's are using, has
> already been executed.
I think this is a good idea, but it's also true you can just leave separate
TUNABLE_ statements without setting the CTLFLAG_TUN flag for cases you aren't
sure about for now. It probably makes sense to do these changes in stages.
I was going to suggest using sbuf() for building the tunable name, but that
doesn't work since you have to build it in reverse.
--
John Baldwin
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