Re: [PATCH bpf-next v1 0/6] Introduce eBPF support for HID devices

Greg KH
2022-02-25T16:21:54Z

On Fri, Feb 25, 2022 at 05:06:32PM +0100, Benjamin Tissoires wrote:
> On Thu, Feb 24, 2022 at 6:21 PM Yonghong Song <yhs@fb.com> wrote:
> >
> >
> >
> > On 2/24/22 5:49 AM, Benjamin Tissoires wrote:
> > > Hi Greg,
> > >
> > > Thanks for the quick answer :)
> > >
> > > On Thu, Feb 24, 2022 at 12:31 PM Greg KH <gregkh@linuxfoundation.org> wrote:
> > >>
> > >> On Thu, Feb 24, 2022 at 12:08:22PM +0100, Benjamin Tissoires wrote:
> > >>> Hi there,
> > >>>
> > >>> This series introduces support of eBPF for HID devices.
> > >>>
> > >>> I have several use cases where eBPF could be interesting for those
> > >>> input devices:
> > >>>
> > >>> - simple fixup of report descriptor:
> > >>>
> > >>> In the HID tree, we have half of the drivers that are "simple" and
> > >>> that just fix one key or one byte in the report descriptor.
> > >>> Currently, for users of such devices, the process of fixing them
> > >>> is long and painful.
> > >>> With eBPF, we could externalize those fixups in one external repo,
> > >>> ship various CoRe bpf programs and have those programs loaded at boot
> > >>> time without having to install a new kernel (and wait 6 months for the
> > >>> fix to land in the distro kernel)
> > >>
> > >> Why would a distro update such an external repo faster than they update
> > >> the kernel? Many sane distros update their kernel faster than other
> > >> packages already, how about fixing your distro? :)
> > >
> > > Heh, I'm going to try to dodge the incoming rhel bullet :)
> > >
> > > It's true that thanks to the work of the stable folks we don't have to
> > > wait 6 months for a fix to come in. However, I think having a single
> > > file to drop in a directory would be easier for development/testing
> > > (and distribution of that file between developers/testers) than
> > > requiring people to recompile their kernel.
> > >
> > > Brain fart: is there any chance we could keep the validated bpf
> > > programs in the kernel tree?
> >
> > Yes, see kernel/bpf/preload/iterators/iterators.bpf.c.
>
> Thanks. This is indeed interesting.
> I am not sure the exact usage of it though :)
>
> One thing I wonder too while we are on this topic, is it possible to
> load a bpf program from the kernel directly, in the same way we can
> request firmwares?

We used to be able to do that, putting bpf programs inside a module.
But that might have gotten removed because no one actually used it. I
thought it was a nice idea.

> Because if we can do that, in my HID use case we could replace simple
> drivers with bpf programs entirely and reduce the development cycle to
> a bare minimum.

How would the development cycle change? You could get rid of many
in-kernel hid drivers and replace them with bpf code perhaps? Maybe
that's a good use case :)

thanks,

greg k-h