Automagic SYSCTLs

[Garrett Cooper]

On Sat, Jan 15, 2011 at 4:12 PM,  <mdf at freebsd.org> wrote:
> I started out with a plan to import a patch from Isilon that adds
> type-safety to the existing SYSCTLs for scalar variables in the
> kernel.  After the discussion on the svn mailing list here
> (http://lists.freebsd.org/pipermail/svn-src-head/2011-January/024097.html)
> I now have a prototype patch for SYSCTL_ADD_SCALAR that could replace
> most uses of SYSCTL_ADD_{INT, UINT, LONG, ULONG, QUAD} and is suitable
> for the SYSCTL_ADD_FOO that are used on 16 and 8 bit members (without
> type checking) today.
>
> The gist is that the handler knows the sizeof the variable in the
> kernel and uses this to copy out.  For the case of a long, there's
> some goop for SCTL_MASK32.  For the case of 8 and 16 bit variables,
> they are still copied in and out as 32-bit quantities.
>
> Let me know if this seems like the right or wrong direction in which
> to move.  I haven't tackled the static sysctls as the code I have does
> some run-time evaluation because the code is easier to write that way.
>  One possibility is to change the sysctl_oid struct or at least add a
> SIGNED flag; this would also have the advantage of making it possible
> to clean up the CTLTYPE_[U]INT issue where there is no real difference
> between the two CTLTYPEs.
>
> http://people.freebsd.org/~mdf/bsd-sysctl-scalar.diff

Looks interesting, but what are the performance implications of the new logic?
Thanks,
-Garrett