linux-kernel - Re: [PATCH v6 1/3] rust: configfs: introduce rust support for configfs

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Message-ID: <87msbw1s9e.fsf@kernel.org>
Date: Thu, 01 May 2025 13:31:57 +0200
From: Andreas Hindborg <a.hindborg@...nel.org>
To: "Miguel Ojeda" <miguel.ojeda.sandonis@...il.com>
Cc: "Danilo Krummrich" <dakr@...nel.org>,  "Miguel Ojeda"
 <ojeda@...nel.org>,  "Alex Gaynor" <alex.gaynor@...il.com>,  "Boqun Feng"
 <boqun.feng@...il.com>,  "Gary Guo" <gary@...yguo.net>,  Björn Roy Baron
 <bjorn3_gh@...tonmail.com>,  "Benno Lossin" <benno.lossin@...ton.me>,
  "Alice Ryhl" <aliceryhl@...gle.com>,  "Trevor Gross" <tmgross@...ch.edu>,
  "Joel Becker" <jlbec@...lplan.org>,  "Peter Zijlstra"
 <peterz@...radead.org>,  "Ingo Molnar" <mingo@...hat.com>,  "Will Deacon"
 <will@...nel.org>,  "Waiman Long" <longman@...hat.com>,  "Fiona Behrens"
 <me@...enk.dev>,  "Charalampos Mitrodimas" <charmitro@...teo.net>,
  "Daniel Almeida" <daniel.almeida@...labora.com>,  "Breno Leitao"
 <leitao@...ian.org>,  <rust-for-linux@...r.kernel.org>,
  <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v6 1/3] rust: configfs: introduce rust support for configfs

"Miguel Ojeda" <miguel.ojeda.sandonis@...il.com> writes:

> On Thu, May 1, 2025 at 12:15 PM Andreas Hindborg <a.hindborg@...nel.org> wrote:
>>
>> Signed-off-by: Andreas Hindborg <a.hindborg@...nel.org>
>>
>> ---
>>
>
> Spurious newlines.

The one just before the cut?

>
>> This patch is a direct dependency for `rnull`, the rust null block driver.
>> ---
>
> By the way, you don't need this `---`.

b4 adds it 🤷

>
>> +//! `configfs` interface.
>
> I don't know if configfs is supposed to be written in code spans, but
> I appreciate you are trying to be throughout in your Markdown use ;)
> It may be easier to read to not have it in code spans, since we have
> many already and it is not code anyway.

OK

>
> By the way, you may want to mention somehow the title they use in
> their docs: "Userspace-driven Kernel Object Configuration".

Will do.

>
>> +//! See the [rust_configfs.rs] sample for a full example use of this module.
>
> Files are, though, like the C header below, so: [`rust_configfs.rs`]

OK

>
>> +/// with configfs, embed a field of this type into your kernel module struct.
>
> Either with or without a code span, i.e. being consistent is best.

I am! Consistently inconsistent. Very much so in this series. Will fix.

>
>> +    /// Return the address of the `bindings::config_group` embedded in `Self`.
>
> I think you may be able to use intra-doc links for [`Self`].

Thanks. Would be nice with a lint for missed intra-doc links.

>
>> +        let c_group: *mut bindings::config_group =
>> +        // SAFETY: By function safety requirements, `item` is embedded in a
>> +        // `config_group`.
>> +            unsafe { container_of!(item, bindings::config_group, cg_item) }.cast_mut();
>
> It doesn't work to put the safety comment on top? (We had issues
> similar to this in the past, so if it is intentional, that is fine).

Clippy gets mad if we move it up. Because rustfmt wants the unsafe block
to a new line:

  warning: unsafe block missing a safety comment
    --> rust/kernel/configfs.rs:557:13
      |
  557 |             unsafe { container_of!(item, bindings::config_group, cg_item) }.cast_mut();
      |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
      |
      = help: consider adding a safety comment on the preceding line
      = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#undocumented_unsafe_blocks
      = note: requested on the command line with `-W clippy::undocumented-unsafe-blocks`

>
>> +/// This type is constructed statically at compile time and is by the
>> +/// [`kernel::configfs_attrs`] macro.
>
> Sentence is missing something. Also, we never used `# Note` yet, but I
> guess it is fine.

Thanks, rephrased:

  # Note
  
  Instances of this type are constructed statically at compile by the
  [`kernel::configfs_attrs`] macro.

>
>> +    /// Null terminated Array of pointers to `Attribute`. The type is `c_void`
>
> Intar-doc link(s)?
>
>> +        // We need a space at the end of our list for a null terminator.
>> +        if I >= N - 1 {
>> +            kernel::build_error!("Invalid attribute index");
>> +        }
>
> Would the following work instead?
>
>     const { assert!(I < N - 1, "Invalid attribute index") };
>
> (Please double-check it actually catches the cases you need)

The reason I choose build_error is that if this should somehow end up
being evaluated in non-const context at some point, I want the build to
fail if the condition is not true. I don't think I get that with assert?


Best regards,
Andreas Hindborg