linux-kernel - Re: [PATCH v3 1/2] rust: Introduce file_from

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Message-ID: <aFGenbg8S36G1aeP@tardis.local>
Date: Tue, 17 Jun 2025 09:58:05 -0700
From: Boqun Feng <boqun.feng@...il.com>
To: Miguel Ojeda <miguel.ojeda.sandonis@...il.com>
Cc: linux-kernel@...r.kernel.org, rust-for-linux@...r.kernel.org,
	ojeda@...nel.org, alex.gaynor@...il.com, gary@...yguo.net,
	bjorn3_gh@...tonmail.com, benno.lossin@...ton.me,
	a.hindborg@...sung.com, aliceryhl@...gle.com, tmgross@...ch.edu,
	dakr@...nel.org, mingo@...hat.com, peterz@...radead.org,
	juri.lelli@...hat.com, vincent.guittot@...aro.org,
	dietmar.eggemann@....com, rostedt@...dmis.org, bsegall@...gle.com,
	mgorman@...e.de, vschneid@...hat.com, pmladek@...e.com,
	fujita.tomonori@...il.com, mingo@...nel.org
Subject: Re: [PATCH v3 1/2] rust: Introduce file_from_location()

On Tue, Jun 17, 2025 at 05:28:41PM +0200, Miguel Ojeda wrote:
> On Tue, Jun 17, 2025 at 3:42 PM Boqun Feng <boqun.feng@...il.com> wrote:
> >
> > Will do, one thing though: the comment lines seem to wrap at 78 or 80
> > chars, so do other lines for conditional features in rust/kernel/lib.rs.
> > However I believe in Rust code we use 100 chars text width, any
> > particular reason that I should keep these new lines the same (wrapping
> > at 80 characters)? Otherwise I will make the new lines wrap at 100.
> 
> We have both styles, so up to you.
> 

I will use 100 characters then.

> It would have been nice to at least know already if `rustfmt` would
> eventually land on 80 or 100 for this, even if the automatically
> wrapping is not stable :(
> 
> > Sure, will do, but I'm afraid there is only case, unless I misunderstood
> > you:
> 
> I meant the "If `file_with_nul()` is not available" vs. the available
> one (since it is mentioned in the docs already).
> 

Yes, but the example would be one, just the output would be different,
hence I said the "only case", but see below:

> > /// use kernel::file_from_location;
> 
> I would hide this line, since it is a single import of the item itself.
> 
> > ///     pr_info!("{}\n", file_from_location(caller));
> 
> I would suggest adding a comment on top of this line mentioning the
> output it could potentially show, e.g.
> 
>     // Output: ...
> 

This actually helped me find a bug in the current implementation: I
should use core::ffi::CStr::to_bytes_with_nul() instead of to_bytes().
Please see below for the update "Examples" section:

/// # Examples
///
/// ```
/// # use kernel::file_from_location;
///
/// #[track_caller]
/// fn foo() {
///     let caller = core::panic::Location::caller();
///
///     // Output:
///     // - If file_with_nul() available: "rust/doctests_kernel_generated.rs"
///     // - otherwise: "<Location::file_with_nul() not supported>"
///     pr_info!("{}\n", file_from_location(caller));
/// }
///
/// # foo();

> Thanks for this!
> 

Thank you!

Regards,
Boqun

> Cheers,
> Miguel