linux-kernel - Re: [PATCH 0/4] Re-export Zeroable and zeroed() from ffi module

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Message-ID: <CAH5fLggAfRkjSmYuYAZioXn3OP31Fwr=VGd2znnaHQvPL3tKHg@mail.gmail.com>
Date: Mon, 26 Jan 2026 17:14:43 +0100
From: Alice Ryhl <aliceryhl@...gle.com>
To: Gary Guo <gary@...yguo.net>
Cc: Benno Lossin <lossin@...nel.org>, Miguel Ojeda <ojeda@...nel.org>, 
	Boqun Feng <boqun.feng@...il.com>, Björn Roy Baron <bjorn3_gh@...tonmail.com>, 
	Andreas Hindborg <a.hindborg@...nel.org>, Trevor Gross <tmgross@...ch.edu>, 
	Danilo Krummrich <dakr@...nel.org>, "Rafael J. Wysocki" <rafael@...nel.org>, 
	Viresh Kumar <viresh.kumar@...aro.org>, Igor Korotin <igor.korotin.linux@...il.com>, 
	Daniel Almeida <daniel.almeida@...labora.com>, Len Brown <lenb@...nel.org>, 
	rust-for-linux@...r.kernel.org, linux-kernel@...r.kernel.org, 
	linux-pm@...r.kernel.org, linux-acpi@...r.kernel.org
Subject: Re: [PATCH 0/4] Re-export Zeroable and zeroed() from ffi module

On Mon, Jan 26, 2026 at 5:11 PM Gary Guo <gary@...yguo.net> wrote:
>
> On Mon Jan 26, 2026 at 4:08 PM GMT, Benno Lossin wrote:
> > On Mon Jan 26, 2026 at 2:25 PM CET, Alice Ryhl wrote:
> >> On Mon, Jan 26, 2026 at 01:15:53PM +0000, Gary Guo wrote:
> >>> On Mon Jan 26, 2026 at 1:05 PM GMT, Alice Ryhl wrote:
> >>> > Currently, the Zeroable trait is defined by pin-init because pin-init
> >>> > happens to use the trait. However, zeroed types are useful for many
> >>> > purposes other than pin-init. Also, we wish to implement Zeroable for
> >>> > types generated by bindgen. For both of these reasons, re-export
> >>> > Zeroable from the ffi crate, which is a already dependency of the crates
> >>> > with bindgen output.
> >>>
> >>> I don't see a benefit of re-exporting these from the `ffi` crate? Especially
> >>> that we re-export `ffi` crate from kernel crate anyway, and `Zeroable` is
> >>> already in the kernel prelude.
> >>>
> >>> We already derive `Zeroable` for bindgen via `MaybeZeroable` derive in
> >>> rust/bindgen_parameters.
> >>
> >> I can't find the convo now, but this change is on my list from when we
> >> discussed also implementing FromBytes / IntoBytes for the bindings
> >> types. To do that, we need to move our FromBytes / IntoBytes traits
> >> somewhere that bindings/uapi can access, and we agreed that the ffi
> >> crate was a good place for it.
> >>
> >> And then for consistency, also reexport Zeroable from the same location.
> >
> > I think you also mentioned at some point that using `pin_init` from
> > `bindings` seemed strange and also using the `pin_init::zeroed()`
> > function also doesn't fit, since it doesn't have to do with pinned
> > initialization.
>
> Shouldn't it be that a crate that implements Zeroable / FromBytes / IntoBytes
> and then pin_init becoming an user of that crate, then?

The Zeroable trait has to be in pin-init because it's also outside the
kernel. You *could* add yet another crate just for this and let
pin-init depend on it, but just putting it in the existing ffi seems
reasonable to me, and ffi is not a bad name for the owner of those
traits anyway.

Though I guess if we add zerocopy, that concern goes away.

Alice