linux-kernel - Re: [PATCH v2 5/5] panic_qr: use new #[export] macro

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Message-ID: <CAH5fLghO2BhDqs50_ke1ci7kR0ze66qAWQUxzX5-M4403Yc-8w@mail.gmail.com>
Date: Fri, 28 Feb 2025 18:06:10 +0100
From: Alice Ryhl <aliceryhl@...gle.com>
To: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>, Miguel Ojeda <ojeda@...nel.org>, 
	Petr Mladek <pmladek@...e.com>, Steven Rostedt <rostedt@...dmis.org>, 
	Rasmus Villemoes <linux@...musvillemoes.dk>, Sergey Senozhatsky <senozhatsky@...omium.org>, 
	Andrew Morton <akpm@...ux-foundation.org>, Boqun Feng <boqun.feng@...il.com>, 
	Gary Guo <gary@...yguo.net>, Björn Roy Baron <bjorn3_gh@...tonmail.com>, 
	Benno Lossin <benno.lossin@...ton.me>, Andreas Hindborg <a.hindborg@...nel.org>, 
	Trevor Gross <tmgross@...ch.edu>, Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>, 
	Maxime Ripard <mripard@...nel.org>, Thomas Zimmermann <tzimmermann@...e.de>, 
	David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>, linux-kernel@...r.kernel.org, 
	rust-for-linux@...r.kernel.org, dri-devel@...ts.freedesktop.org
Subject: Re: [PATCH v2 5/5] panic_qr: use new #[export] macro

On Fri, Feb 28, 2025 at 4:34 PM Andy Shevchenko
<andriy.shevchenko@...ux.intel.com> wrote:
>
> On Fri, Feb 28, 2025 at 12:39:34PM +0000, Alice Ryhl wrote:
> > This validates at compile time that the signatures match what is in the
> > header file. It highlights one annoyance with the compile-time check,
> > which is that it can only be used with functions marked unsafe.
> >
> > If the function is not unsafe, then this error is emitted:
> >
> > error[E0308]: `if` and `else` have incompatible types
> >    --> <linux>/drivers/gpu/drm/drm_panic_qr.rs:987:19
> >     |
> > 986 | #[export]
> >     | --------- expected because of this
> > 987 | pub extern "C" fn drm_panic_qr_max_data_size(version: u8, url_len: usize) -> usize {
> >     |                   ^^^^^^^^^^^^^^^^^^^^^^^^^^ expected unsafe fn, found safe fn
> >     |
> >     = note: expected fn item `unsafe extern "C" fn(_, _) -> _ {kernel::bindings::drm_panic_qr_max_data_size}`
> >                found fn item `extern "C" fn(_, _) -> _ {drm_panic_qr_max_data_size}`
>
> ...
>
> > +#if defined(CONFIG_DRM_PANIC_SCREEN_QR_CODE)
> > +extern size_t drm_panic_qr_max_data_size(u8 version, size_t url_len);
> > +
> > +extern u8 drm_panic_qr_generate(const char *url, u8 *data, size_t data_len, size_t data_size,
> > +                             u8 *tmp, size_t tmp_size);
>
> Is extern needed?

I doubt it. I just copied the declaration without changing it.

Alice