Re: pkg.c revision 367687 breaks pkg

On Sun, Nov 15, 2020 at 2:05 PM Stefan Esser <se_at_freebsd.org> wrote:
>
> Am 15.11.20 um 20:41 schrieb Kyle Evans:
> > This is a separate (valid) problem, but not directly related to
> > Scott's work here. sysctlbyname now goes directly to the kernel with
> > no chance for the user.* sysctls to intercept. That should
> > independently be fixed to maintain the illusion that they're real
> > sysctl's.
>
> user.localbase is a real sysctl, but with a default value returned
> when sysctl(3) is used.
>

Yup.

> The getlocalbase() function should not depend on this default value,
> since it contains an identicl default value that can be returned if
> sysctlbyname fails (or rather returns a zero length string in case
> no other value has been written to the kernel).
>

I don't care about this particular application, to be honest, but
about the general problem. libc has a sizable chunk of code in
sysctl(3) dealing with user.* sysctls, and sysctlbyname will never see
it. This isn't documented in the manpage, and IMO it's really just an
oversight; libc should still be able to provide the values as seen in
^/lib/libc/gen/sysctl.c whether you've invoked sysctl() or
sysctlbyname(). At a glance, it looks like localbase is the only one
that's also tunable, most of these don't really even need to take a
trip to the kernel to read.

Thanks,

Kyle Evans