linux-kernel - Re: [RFC v2 09/20] PCI/CMA: Expose in sysfs whether devices are authenticated

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Message-ID: <2025022752-pureblood-renovator-84a8@gregkh>
Date: Thu, 27 Feb 2025 04:00:28 -0800
From: Greg KH <gregkh@...uxfoundation.org>
To: Alice Ryhl <aliceryhl@...gle.com>
Cc: Alistair Francis <alistair@...stair23.me>, linux-cxl@...r.kernel.org,
	linux-kernel@...r.kernel.org, lukas@...ner.de,
	linux-pci@...r.kernel.org, bhelgaas@...gle.com,
	Jonathan.Cameron@...wei.com, rust-for-linux@...r.kernel.org,
	akpm@...ux-foundation.org, boqun.feng@...il.com,
	bjorn3_gh@...tonmail.com, wilfred.mallawa@....com, ojeda@...nel.org,
	alistair23@...il.com, a.hindborg@...nel.org, tmgross@...ch.edu,
	gary@...yguo.net, alex.gaynor@...il.com, benno.lossin@...ton.me,
	Alistair Francis <alistair.francis@....com>
Subject: Re: [RFC v2 09/20] PCI/CMA: Expose in sysfs whether devices are
 authenticated

On Thu, Feb 27, 2025 at 12:52:02PM +0100, Alice Ryhl wrote:
> On Thu, Feb 27, 2025 at 12:17 PM Greg KH <gregkh@...uxfoundation.org> wrote:
> >
> > On Thu, Feb 27, 2025 at 01:09:41PM +1000, Alistair Francis wrote:
> > > +     return rust_authenticated_show(spdm_state, buf);
> >
> > Here you have C code calling into Rust code.  I'm not complaining about
> > it, but I think it will be the first use of this, and I didn't think
> > that the rust maintainers were willing to do that just yet.
> >
> > Has that policy changed?
> >
> > The issue here is that the C signature for this is not being
> > auto-generated, you have to manually keep it in sync (as you did above),
> > with the Rust side.  That's not going to scale over time at all, you
> > MUST have a .h file somewhere for C to know how to call into this and
> > for the compiler to check that all is sane on both sides.
> >
> > And you are passing a random void * into the Rust side, what could go
> > wrong?  I think this needs more thought as this is fragile-as-f***.
> 
> I don't think we have a policy against it? I'm pretty sure the QR code
> thing does it.

Sorry, you are right, it does, and of course it happens (otherwise how
would bindings work), but for small functions like this, how is the C
code kept in sync with the rust side?  Where is the .h file that C
should include?

thanks,

greg "I need more coffee" k-h