Re: [PATCH v2 1/2] rust: introduce abstractions for fwctl

[Zhi Wang <zhiw@nvidia.com>]

On Tue, 27 Jan 2026 21:07:37 +0100
"Danilo Krummrich" <dakr@kernel.org> wrote:

> On Tue Jan 27, 2026 at 8:57 PM CET, Zhi Wang wrote:
> > The fwctl_alloc_device() helper allocates a raw struct fwctl_device
> > without private driver data here. The Rust driver object should be
> > already allocated and initialized separately before reaching this
> > point.
> >
> > We rely on the standard dev->parent chain to access the rust driver
> > object from the fwctl callbacks.
> 
> (I will go for a thorough review soon, but for now a quick drive-by
> comment.)
> 
> IIUC, you are saying that the user is supposed to use the private data
> of the parent device in fwctl callbacks. Let's not make this a design
> choice please. Instead, allow the user pass in separate private data for
> the fwctl device as well.
> 
> This serves the purpose of clear ownership and lifetime of the data.
> E.g. the fwctl device does not necessarily exist as long as the parent
> device is bound.
> 
> It is a good thing if driver authors are forced to take a decision about
> which object owns the data and what's the scope of the data.

I wrote a version like this before. My initial concern of mixing Rust
objects together with C objecs within C-allocated memory was about
potential memory alignment issues when rust side doing CAST on the memory.

I agree that providing a way to attach private data directly to the
fwctl_device also has quite some benetifs.

IMO, if we go this way, the private data from rust side needs to have
#[repr(C)] to address the above issue all the time?

Z.