sysctl+kern_sysctl: Honor SKIP for descendant nodes

[freqlabs]

Summary

Ensure we also skip descendants of SKIP nodes when iterating through children of an explicitly specified node.

Reported by: np
Sponsored by: iXsystems, Inc.

[np]

I don't see any change in behavior. My test setup has a T6 card and cxgbe(4) is loaded. Then I run

# sysctl dev.t6nex.0

I do not expect to see dev.t6nex.0.misc or anything underneath it because misc is marked SKIP. But it shows up, even after applying the patch in this review to /sbin/sysctl.

[freqlabs]

Ok I see the problem. We don't get nodes when iterating, so the skip node never gets seen for this to skip its descendants. Back to the drawing board, then.

[freqlabs]

The page fault in t4_get_lb_stats with my T580-LP-SO-CR was fun.
I have fixed CTL_SYSCTL_NEXTNOSKIP so it doesn't skip nodes, will update the diffs soon.

[np]

In D26833#598620, @freqlabs wrote:

The page fault in t4_get_lb_stats with my T580-LP-SO-CR was fun.

Please file a bug for this, stack included, and assign it to me.

[freqlabs]

Don't skip nodes when iterating with NEXTNOSKIP.

[freqlabs]

Fixed edge cases where first child is a skip node and where descendants of a skip node are also flagged with skip.

[freqlabs]

Actually works now after testing with fixed cxl driver.