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

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Message-ID: <Z8HXkmtrMMD1dATZ@smile.fi.intel.com>
Date: Fri, 28 Feb 2025 17:34:42 +0200
From: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To: Alice Ryhl <aliceryhl@...gle.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 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?

> +#endif

-- 
With Best Regards,
Andy Shevchenko