linux-kernel - Re: [PATCH v3 1/2] rust: add static_key

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Date: Thu, 27 Jun 2024 09:26:46 -0700
From: Boqun Feng <boqun.feng@...il.com>
To: Alice Ryhl <aliceryhl@...gle.com>
Cc: Steven Rostedt <rostedt@...dmis.org>,
	Masami Hiramatsu <mhiramat@...nel.org>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	Peter Zijlstra <peterz@...radead.org>,
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 Ard Biesheuvel <ardb@...nel.org>,	Miguel Ojeda <ojeda@...nel.org>,
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	Björn Roy Baron <bjorn3_gh@...tonmail.com>,
	Benno Lossin <benno.lossin@...ton.me>,
	Andreas Hindborg <a.hindborg@...sung.com>,
	linux-trace-kernel@...r.kernel.org, rust-for-linux@...r.kernel.org,
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 Fuad Tabba <tabba@...gle.com>,	linux-arm-kernel@...ts.infradead.org,
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	WANG Xuerui <kernel@...0n.name>, Bibo Mao <maobibo@...ngson.cn>,
	Tiezhu Yang <yangtiezhu@...ngson.cn>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Tianrui Zhao <zhaotianrui@...ngson.cn>, loongarch@...ts.linux.dev
Subject: Re: [PATCH v3 1/2] rust: add static_key_false

On Thu, Jun 27, 2024 at 10:34:39AM +0200, Alice Ryhl wrote:
> On Tue, Jun 25, 2024 at 6:18 PM Boqun Feng <boqun.feng@...il.com> wrote:
> >
> > Hi Alice,
> >
> > On Fri, Jun 21, 2024 at 10:35:26AM +0000, Alice Ryhl wrote:
> > > Add just enough support for static key so that we can use it from
> > > tracepoints. Tracepoints rely on `static_key_false` even though it is
> > > deprecated, so we add the same functionality to Rust.
> > >
> > > It is not possible to use the existing C implementation of
> > > arch_static_branch because it passes the argument `key` to inline
> > > assembly as an 'i' parameter, so any attempt to add a C helper for this
> > > function will fail to compile because the value of `key` must be known
> > > at compile-time.
> > >
> > > Signed-off-by: Alice Ryhl <aliceryhl@...gle.com>
> >
> > [Add linux-arch, and related arch maintainers Cced]
> >
> > Since inline asms are touched here, please consider copying linux-arch
> > and arch maintainers next time ;-)
> 
> Will do.
> 
> > For x86_64 and arm64 bits:
> >
> > Acked-by: Boqun Feng <boqun.feng@...il.com>
> >
> > One thing though, we should split the arch-specific impls into different
> > files, for example: rust/kernel/arch/arm64.rs or rust/arch/arm64.rs.
> > That'll be easier for arch maintainers to watch the Rust changes related
> > to a particular architecture.
> 
> Is that how you would prefer to name these files? You don't want
> static_key somewhere in the filename?
> 

I could have been more explicit. My preference is (for example ARM64)

*	we have a rust/kernel/arch.rs, where we do:

		#[cfg(CONFIG_ARM64)]
		mod arm64::*;

		#[cfg(CONFIG_ARM64)]
		pub use arm64::*;

*	we have a rust/kernel/arch/arm64.rs:

		pub(crate) mod jump_label;

*	we have a rust/kernel/arch/arm64/jump_label.rs, where we put
	ARM64 arch_static_branch() there. (or static_key.rs and
	arch_static_key_false()).

Then linux-arch can watch:

	rust/kernel/arch.rs
	rust/kernel/arch/

And ARM64 maintainers can watch:

	rust/kernel/arch/arm64.rs
	rust/kernel/arch/arm64

This is similar to how <asm/*.h> are organized today.

Does this make sense?

Regards,
Boqun

> > Another thought is that, could you implement an arch_static_branch!()
> > (instead of _static_key_false!()) and use it for static_key_false!()
> > similar to what we have in C? The benefit is that at least for myself
> > it'll be easier to compare the implementation between C and Rust.
> 
> I can try to include that.
> 
> Alice