Re: [PATCH v3 5/5] panic_qr: use new #[export] macro

[Jocelyn Falempe <jfalempe@redhat.com>]

On 03/03/2025 09:45, 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}`
> 
> The signature declarations are moved to a header file so it can be
> included in the Rust bindings helper, and the extern keyword is removed
> as it is unnecessary.

Thanks, it looks good to me.

Reviewed-by: Jocelyn Falempe <jfalempe@redhat.com>

> 
> Reviewed-by: Andreas Hindborg <a.hindborg@kernel.org>
> Reviewed-by: Tamir Duberstein <tamird@gmail.com>
> Acked-by: Simona Vetter <simona.vetter@ffwll.ch>
> Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> Signed-off-by: Alice Ryhl <aliceryhl@google.com>
> ---
>   drivers/gpu/drm/drm_panic.c     |  5 -----
>   drivers/gpu/drm/drm_panic_qr.rs | 15 +++++++++++----
>   include/drm/drm_panic.h         |  7 +++++++
>   rust/bindings/bindings_helper.h |  5 +++++
>   4 files changed, 23 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_panic.c b/drivers/gpu/drm/drm_panic.c
> index f128d345b16d..dee5301dd729 100644
> --- a/drivers/gpu/drm/drm_panic.c
> +++ b/drivers/gpu/drm/drm_panic.c
> @@ -486,11 +486,6 @@ static void drm_panic_qr_exit(void)
>   	stream.workspace = NULL;
>   }
>   
> -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);
> -
>   static int drm_panic_get_qr_code_url(u8 **qr_image)
>   {
>   	struct kmsg_dump_iter iter;
> diff --git a/drivers/gpu/drm/drm_panic_qr.rs b/drivers/gpu/drm/drm_panic_qr.rs
> index bcf248f69252..906943b02beb 100644
> --- a/drivers/gpu/drm/drm_panic_qr.rs
> +++ b/drivers/gpu/drm/drm_panic_qr.rs
> @@ -27,7 +27,10 @@
>   //! * <https://github.com/bjguillot/qr>
>   
>   use core::cmp;
> -use kernel::str::CStr;
> +use kernel::{
> +    prelude::*,
> +    str::CStr,
> +};
>   
>   #[derive(Debug, Clone, Copy, PartialEq, Eq, Ord, PartialOrd)]
>   struct Version(usize);
> @@ -929,7 +932,7 @@ fn draw_all(&mut self, data: impl Iterator<Item = u8>) {
>   /// * `tmp` must be valid for reading and writing for `tmp_size` bytes.
>   ///
>   /// They must remain valid for the duration of the function call.
> -#[no_mangle]
> +#[export]
>   pub unsafe extern "C" fn drm_panic_qr_generate(
>       url: *const kernel::ffi::c_char,
>       data: *mut u8,
> @@ -980,8 +983,12 @@ fn draw_all(&mut self, data: impl Iterator<Item = u8>) {
>   /// * If `url_len` > 0, remove the 2 segments header/length and also count the
>   ///   conversion to numeric segments.
>   /// * If `url_len` = 0, only removes 3 bytes for 1 binary segment.
> -#[no_mangle]
> -pub extern "C" fn drm_panic_qr_max_data_size(version: u8, url_len: usize) -> usize {
> +///
> +/// # Safety
> +///
> +/// Always safe to call.
> +#[export] // required to be unsafe due to this annotation
> +pub unsafe extern "C" fn drm_panic_qr_max_data_size(version: u8, url_len: usize) -> usize {
>       #[expect(clippy::manual_range_contains)]
>       if version < 1 || version > 40 {
>           return 0;
> diff --git a/include/drm/drm_panic.h b/include/drm/drm_panic.h
> index f4e1fa9ae607..ff78d00c3da5 100644
> --- a/include/drm/drm_panic.h
> +++ b/include/drm/drm_panic.h
> @@ -163,4 +163,11 @@ static inline void drm_panic_unlock(struct drm_device *dev, unsigned long flags)
>   
>   #endif
>   
> +#if defined(CONFIG_DRM_PANIC_SCREEN_QR_CODE)
> +size_t drm_panic_qr_max_data_size(u8 version, size_t url_len);
> +
> +u8 drm_panic_qr_generate(const char *url, u8 *data, size_t data_len, size_t data_size,
> +			 u8 *tmp, size_t tmp_size);
> +#endif
> +
>   #endif /* __DRM_PANIC_H__ */
> diff --git a/rust/bindings/bindings_helper.h b/rust/bindings/bindings_helper.h
> index 55354e4dec14..607e90a682ca 100644
> --- a/rust/bindings/bindings_helper.h
> +++ b/rust/bindings/bindings_helper.h
> @@ -36,6 +36,11 @@
>   #include <linux/workqueue.h>
>   #include <trace/events/rust_sample.h>
>   
> +#if defined(CONFIG_DRM_PANIC_SCREEN_QR_CODE)
> +// Used by #[export] in drivers/gpu/drm/drm_panic_qr.rs
> +#include <drm/drm_panic.h>
> +#endif
> +
>   /* `bindgen` gets confused at certain things. */
>   const size_t RUST_CONST_HELPER_ARCH_SLAB_MINALIGN = ARCH_SLAB_MINALIGN;
>   const size_t RUST_CONST_HELPER_PAGE_SIZE = PAGE_SIZE;
>