Re: [PATCH v8 6/6] rust: samples: Add debugfs sample

[Danilo Krummrich <dakr@kernel.org>]

On Tue, Jul 01, 2025 at 10:24:04AM -0700, Matthew Maurer wrote:
> On Tue, Jul 1, 2025 at 7:03 AM Greg Kroah-Hartman
> <gregkh@linuxfoundation.org> wrote:
> >
> > On Fri, Jun 27, 2025 at 11:18:29PM +0000, Matthew Maurer wrote:
> > > +        // An `Arc<Mutex<usize>>` doesn't implement display, so let's give explicit instructions on
> > > +        // how to print it
> > > +        let file_2 = sub.fmt_file(c_str!("arc_backed"), my_arc.clone(), &|val, f| {
> > > +            writeln!(f, "locked value: {:#010x}", *val.lock())
> > > +        });
> >
> > While cute, is this really going to be the way to describe all "custom"
> > debugfs function callbacks?  No other way to point to a function itself
> > instead?  Look at "fun" debugfs functions like qh_lines() in
> > drivers/usb/host/ehci-dbg.c that is dumping tons of data out.  Putting
> > that inline here is going to be a bit ackward :)
> 
> Good news, function pointers are legal to pass in here as well
> already, I can add that usage to make it clear.
> 
> >
> > So can you show an example of a "traditional" debugfs file output with
> > multiple lines that is dealing with a dynamically allocated device that
> > is associated with the module (not the static example you showed here),
> > as that's going to be the real way this is used, not with static
> > variables.
> 
> Sure, do we want to:
> * Finish creating the driver struct early in `init`, then call dynamic
> `.create(&str)` or `.destroy(&str)` `.modify(&str)` type things on it
> in `init` to show how it would work
> * Actually wire up an input source to drive create/destroy/modify
> dynamically (e.g. I could implement a miscdevice) - if you want this
> one, do you have a preference on where I get my input signal from?

I think the idea was to show how it works in a real driver context, e.g. a
platform driver, just like what samples/rust/rust_driver_platform.rs does. Not a
miscdevice registered from a module, which is a rather rare use-case.

If you rebase on the latest driver-core-next, you can write a platform driver
with an ACPI ID table, which can easily probed by passing
`-acpitable file=ssdt.aml` to qemu, i.e. no need to mess with OF.