On 06/18/14 15:44, John Baldwin wrote:
On Wednesday, June 18, 2014 7:36:53 am Hans Petter Selasky wrote:

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:


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.


After going through a lot of existing code, I've decided to make a new flag, CTLFLAG_FETCH rather than overload CTLFLAG_TUN, so that the new functionality can be added to drivers and tested. For example sysctls which implement function callbacks and are not trivial, this might cause locking of non-initialized mutexes and so on. And also I see some dependencies, that values are fetched at a certain point in the boot process and that existing CTLFLAG_TUN might confuse existing logic.

I've updated my patch (same link):


BTW: Can someone which have a beefy machine run a universe with this patch applied?

I'll probably put it into the tree next week.

freebsd-current@freebsd.org mailing list
To unsubscribe, send any mail to "freebsd-current-unsubscr...@freebsd.org"

Reply via email to