Re: [PATCH] rust: Add `container_of` and `offset_of` macros

[Andreas Hindborg <nmi@metaspace.dk>]

Hi Maira,

Maíra Canal <mcanal@igalia.com> writes:

> From: Asahi Lina <lina@asahilina.net>
>
> Add Rust counterparts to these C macros. `container_of` is useful for C
> struct subtyping, to recover the original pointer to the container
> structure. `offset_of` is useful for struct-relative addressing.
>
> Co-authored-by: Miguel Ojeda <ojeda@kernel.org>
> Signed-off-by: Miguel Ojeda <ojeda@kernel.org>
> Co-authored:by: Léo Lanteri Thauvin <leseulartichaut@gmail.com>
> Signed-off-by: Léo Lanteri Thauvin <leseulartichaut@gmail.com>
> Co-authored-by: Wedson Almeida Filho <wedsonaf@google.com>
> Signed-off-by: Wedson Almeida Filho <wedsonaf@google.com>
> Signed-off-by: Asahi Lina <lina@asahilina.net>
> Signed-off-by: Maíra Canal <mcanal@igalia.com>
> ---
>
> Hi,
>
> `container_of` is a essential macro to build any sort of driver in the
> Linux Kernel. Therefore, we need a good and reliable implementation of
> this macro for the Rust abstractions.
>
> Although I checked the version sent by Matt [1], I don't really like the
> fact that such an essential part of the foundation of any driver would
> be an unsafe macro. Therefore, I propose this alternative to Matt's
> implementation, which is Lina's implementation that it is actually safe.
>
> `container_of` is a dependency for the rustgem driver and this is part
> of my current efforts to upstream the driver.
>

`offset_of!()` is available as `core::mem::offset_of!()` under unstable
feature gate, which is currently enabled and used in the workqueue
abstractions. So at least that macro is not required.

Best regards,
Andreas