Re: [PATCH] rust: driver: let probe() return impl PinInit<Self, Error>

["Benno Lossin" <lossin@kernel.org>]

On Fri Oct 17, 2025 at 4:12 AM CEST, Alexandre Courbot wrote:
> On Thu Oct 16, 2025 at 9:55 PM JST, Danilo Krummrich wrote:
>> The driver model defines the lifetime of the private data stored in (and
>> owned by) a bus device to be valid from when the driver is bound to a

>> device (i.e. from successful probe()) until the driver is unbound from
>> the device.
>>
>> This is already taken care of by the Rust implementation of the driver
>> model. However, we still ask drivers to return a Result<Pin<KBox<Self>>>
>> from probe().
>>
>> Unlike in C, where we do not have the concept of initializers, but
>> rather deal with uninitialized memory, drivers can just return an
>> impl PinInit<Self, Error> instead.
>>
>> This contributed to more clarity to the fact that a driver returns it's
>
> nit: s/it's/its
>
>> device private data in probe() and the Rust driver model owns the data,
>> manages the lifetime and - considering the lifetime - provides (safe)
>> accessors for the driver.
>>
>> Hence, let probe() functions return an impl PinInit<Self, Error> instead
>> of Result<Pin<KBox<Self>>>.
>>
>> Signed-off-by: Danilo Krummrich <dakr@kernel.org>
>
> Short anecdote: I was curious about measuring the footprint impact of
> pin initializers, so I did a `size vmlinux` before and after this patch
> to compare the size of the `text` section. This patch removes exactly 60
> bytes of binary code, which I guess corresponds to the duplicated `KBox`
> allocations that are now gone. It's great to confirm once again how Rust
> abstractions are indeed zero-overhead! :)

Thanks for the test! If you find that at any point they aren't, let me
know, then we can fix that :)

---
Cheers,
Benno