Re: Anyone using binmiscctl for interesting things?

(top posting because I've only had one coffee so far)

I like it!


-a

On Thu, 18 Jun 2026 at 06:56, Kyle Evans <[email protected]> wrote:
>
> Hi,
>
> I was chatting with Warner about this last night and he received it positively, so wider audience: I'd like to rewrite the binmiscctl interface into the kernel to allow scoping activator rules and that could have broader impact, so I'd like to hear about any uses that *aren't* qemu-user-static.
>
> Background: in today's world, imgact_binmisc.c exposes a sysctl that's only usable in prison0, and it registers interpreters for the whole system. I think that's suboptimal for $reasons that I'm happy to expand on, but the short version is that I'd like to replace the sysctl interface with a cdev/ioctl that can optionally be revealed in a child devfs, so that we can delegate control *and* implement per-jail activators.
>
> binmiscctl would likely grow a pair of flags, --inherit/--no-inherit, so that today's usage could still work just fine by using --inherit'ed rules in prison0.  Eventually --no-inherit would become the default, but we'd probably want to first teach poudriere to stand-up binmiscctl rules in a jail as needed; ideally, we'd probably take the current set of activators from the qemu_user_static rc script[0] and install config file(s) that describe how TARGET/TARGET_ARCH pairs map to binmiscctl params that poudriere can ingest to make that maintainable.  (CC'd bdrewery in case he already hates that idea just upon hearing it)
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> The control interface will probably get split out to an imgact_binmisc_ctl.c at the start of this effort to try and clean some things up a little bit, since the sysctl interface should probably be retained in COMPAT_FREEBSD15- we could maybe debate later if the feature is niche enough that compatibility can drop once all supported releases have a binmiscctl(8) doing cdev things, but it's still worth making it maintainable up front.
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> Thanks,
>
> Kyle Evans
>
> [0] https://cgit.freebsd.org/ports/tree/emulators/qemu-user-static/files/qemu_user_static.in
>