Re: [PATCH v3 1/7] rust: firmware: add request_into_buf()

On Fri Jul 3, 2026 at 4:27 AM JST, Timur Tabi wrote:
> Add request_into_buf(), a Rust wrapper around the
> request_firmware_into_buf() function. This variant loads the firmware
> image directly into a caller-provided buffer rather than a
> kernel-allocated one.
>
> Signed-off-by: Timur Tabi <[email protected]>
> ---
>  rust/kernel/firmware.rs | 47 +++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 47 insertions(+)
>
> diff --git a/rust/kernel/firmware.rs b/rust/kernel/firmware.rs
> index 71168d8004e2..4460fb2cd5d8 100644
> --- a/rust/kernel/firmware.rs
> +++ b/rust/kernel/firmware.rs
> @@ -120,6 +120,53 @@ fn drop(&mut self) {
>      }
>  }
>  
> +/// Load firmware directly into the caller-provided `buf`.
> +///
> +/// On success the firmware image has been copied into `buf`; the caller accesses the data
> +/// through `buf` itself.
> +///
> +/// This is intentionally a stand-alone function rather than a `Firmware` constructor. For
> +/// the `into_buf` path, the firmware data lives in the caller's `buf`, not in a
> +/// kernel-owned buffer, so returning a `Firmware` would expose `Firmware::data()` as a
> +/// second handle aliasing `buf` (and `release_firmware()` does not free `buf` anyway).
> +pub fn request_into_buf(name: &CStr, dev: &Device, buf: &mut [u8]) -> Result {

Sashiko is correct to point out that this doesn't return the number of
bytes actually written into `buf`. We might not use that information in
nova-core, but this is a kernel-wide API.

Returning a `Result<&[u8]>` would take care of this and cover the
general use-case nicely.