linux-kernel - Re: [PATCH v12 2/3] rust: add parameter support to the `module!` macro

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Message-Id: <DAKE43J2GFVF.18KWPFWPZKDM@kernel.org>
Date: Thu, 12 Jun 2025 09:52:30 +0200
From: "Benno Lossin" <lossin@...nel.org>
To: "Andreas Hindborg" <a.hindborg@...nel.org>
Cc: "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>, "Masahiro Yamada" <masahiroy@...nel.org>,
 "Nathan Chancellor" <nathan@...nel.org>, "Luis Chamberlain"
 <mcgrof@...nel.org>, "Danilo Krummrich" <dakr@...nel.org>, "Nicolas Schier"
 <nicolas.schier@...ux.dev>, "Trevor Gross" <tmgross@...ch.edu>, "Adam
 Bratschi-Kaye" <ark.email@...il.com>, <rust-for-linux@...r.kernel.org>,
 <linux-kernel@...r.kernel.org>, <linux-kbuild@...r.kernel.org>, "Petr
 Pavlu" <petr.pavlu@...e.com>, "Sami Tolvanen" <samitolvanen@...gle.com>,
 "Daniel Gomez" <da.gomez@...sung.com>, "Simona Vetter"
 <simona.vetter@...ll.ch>, "Greg KH" <gregkh@...uxfoundation.org>, "Fiona
 Behrens" <me@...enk.dev>, "Daniel Almeida" <daniel.almeida@...labora.com>,
 <linux-modules@...r.kernel.org>
Subject: Re: [PATCH v12 2/3] rust: add parameter support to the `module!`
 macro

On Wed Jun 11, 2025 at 12:31 PM CEST, Andreas Hindborg wrote:
> "Benno Lossin" <lossin@...nel.org> writes:
>> On Tue May 6, 2025 at 3:02 PM CEST, Andreas Hindborg wrote:
>>> diff --git a/rust/macros/helpers.rs b/rust/macros/helpers.rs
>>> index a3ee27e29a6f..16d300ad3d3b 100644
>>> --- a/rust/macros/helpers.rs
>>> +++ b/rust/macros/helpers.rs
>>> @@ -10,6 +10,17 @@ pub(crate) fn try_ident(it: &mut token_stream::IntoIter) -> Option<String> {
>>>      }
>>>  }
>>>  
>>> +pub(crate) fn try_sign(it: &mut token_stream::IntoIter) -> Option<char> {
>>> +    let peek = it.clone().next();
>>> +    match peek {
>>> +        Some(TokenTree::Punct(punct)) if punct.as_char() == '-' => {
>>
>> Should we also allow a leading `+`?
>
> I would argue no, because rust literals cannot start with `+`.

Makes sense.

>>> +            let _ = it.next();
>>> +            Some(punct.as_char())
>>> +        }
>>> +        _ => None,
>>> +    }
>>> +}
>>> +
>>>  pub(crate) fn try_literal(it: &mut token_stream::IntoIter) -> Option<String> {
>>>      if let Some(TokenTree::Literal(literal)) = it.next() {
>>>          Some(literal.to_string())
>>> @@ -86,3 +97,17 @@ pub(crate) fn function_name(input: TokenStream) -> Option<Ident> {
>>>      }
>>>      None
>>>  }
>>> +
>>> +/// Parse a token stream of the form `expected_name: "value",` and return the
>>> +/// string in the position of "value".
>>> +///
>>> +/// # Panics
>>> +///
>>> +/// - On parse error.
>>> +pub(crate) fn expect_string_field(it: &mut token_stream::IntoIter, expected_name: &str) -> String {
>>> +    assert_eq!(expect_ident(it), expected_name);
>>> +    assert_eq!(expect_punct(it), ':');
>>> +    let string = expect_string(it);
>>> +    assert_eq!(expect_punct(it), ',');
>>
>> This won't allow omitting the trailing comma.
>
> This is in line with the rest of the module macro.

Then we should change that:

    https://github.com/Rust-for-Linux/linux/issues/1172

>>> +    string
>>> +}
>>
>> [...]
>>
>>> @@ -186,33 +336,35 @@ pub(crate) fn module(ts: TokenStream) -> TokenStream {
>>>      let info = ModuleInfo::parse(&mut it);
>>>  
>>>      let mut modinfo = ModInfoBuilder::new(info.name.as_ref());
>>> -    if let Some(author) = info.author {
>>> -        modinfo.emit("author", &author);
>>> +    if let Some(author) = &info.author {
>>> +        modinfo.emit("author", author);
>>>      }
>>> -    if let Some(authors) = info.authors {
>>> +    if let Some(authors) = &info.authors {
>>>          for author in authors {
>>> -            modinfo.emit("author", &author);
>>> +            modinfo.emit("author", author);
>>>          }
>>>      }
>>> -    if let Some(description) = info.description {
>>> -        modinfo.emit("description", &description);
>>> +    if let Some(description) = &info.description {
>>> +        modinfo.emit("description", description);
>>>      }
>>>      modinfo.emit("license", &info.license);
>>> -    if let Some(aliases) = info.alias {
>>> +    if let Some(aliases) = &info.alias {
>>>          for alias in aliases {
>>> -            modinfo.emit("alias", &alias);
>>> +            modinfo.emit("alias", alias);
>>>          }
>>>      }
>>> -    if let Some(firmware) = info.firmware {
>>> +    if let Some(firmware) = &info.firmware {
>>>          for fw in firmware {
>>> -            modinfo.emit("firmware", &fw);
>>> +            modinfo.emit("firmware", fw);
>>
>> I don't like that you have to change all of these.
>
> Why not? If I was to write this code in the first place, I would have
> used a reference rather than pass by value.

That's fine, but do it in a separate commit then.

>> Can't you just take a
>> `&[Parameter]` argument in `emit_params` instead of the whole
>> `ModuleInfo` struct?
>
> I don't think that is a nice solution. I would have to pass the name
> field as well, increasing the number of parameters to the function.

Ah right makes sense.

---
Cheers,
Benno