linux-kernel - Re: [PATCH v4 4/4] rust: add parameter support to the `module!` macro

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Message-ID: <874j1q1umv.fsf@kernel.org>
Date: Wed, 22 Jan 2025 21:06:00 +0100
From: Andreas Hindborg <a.hindborg@...nel.org>
To: "Petr Pavlu" <petr.pavlu@...e.com>
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>,  "Nicolas Schier" <nicolas@...sle.eu>,  "Luis
 Chamberlain" <mcgrof@...nel.org>,  "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>,  "Sami Tolvanen"
 <samitolvanen@...gle.com>,  "Daniel Gomez" <da.gomez@...sung.com>,
  "Simona Vetter" <simona.vetter@...ll.ch>,  "Greg KH"
 <gregkh@...uxfoundation.org>,  <linux-modules@...r.kernel.org>
Subject: Re: [PATCH v4 4/4] rust: add parameter support to the `module!` macro

"Petr Pavlu" <petr.pavlu@...e.com> writes:

> On 1/9/25 11:54, Andreas Hindborg wrote:
>> This patch includes changes required for Rust kernel modules to utilize
>> module parameters. This code implements read only support for integer
>> types without `sysfs` support.
>>

[cut]

>> +
>> +        // SAFETY: `old_value` is valid for writes, as we have exclusive
>> +        // access. `old_value` is pointing to an initialized static, an
>
> Typo: an -> and

Thanks.

[cut]

>> +
>> +    fn emit_params(&mut self, info: &ModuleInfo) {
>> +        let Some(params) = &info.params else {
>> +            return;
>> +        };
>> +
>> +        for param in params {
>> +            let ops = param_ops_path(&param.ptype);
>> +
>> +            // Note: The spelling of these fields is dictated by the user space
>> +            // tool `modinfo`.
>> +            self.emit_param("parmtype", &param.name, &param.ptype);
>> +            self.emit_param("parm", &param.name, &param.description);
>> +
>> +            write!(
>> +                self.param_buffer,
>> +                "
>> +                    pub(crate) static {param_name}:
>> +                        ::kernel::module_param::ModuleParamAccess<{param_type}> =
>> +                            ::kernel::module_param::ModuleParamAccess::new({param_default});
>> +
>> +                    #[link_section = \"__param\"]
>> +                    #[used]
>> +                    static __{module_name}_{param_name}_struct:
>> +                        ::kernel::module_param::RacyKernelParam =
>> +                        ::kernel::module_param::RacyKernelParam(::kernel::bindings::kernel_param {{
>> +                            name: if cfg!(MODULE) {{
>> +                                c\"{module_name}.{param_name}\"
>> +                            }} else {{
>> +                                c\"{param_name}\"
>> +                            }}.as_ptr(),
>
> This should be the other way around? Running
> 'insmod rust_minimal.ko test_parameter=2' reports for me that the
> parameter is unknown while specifying 'rust_minimal.test_parameter=2'
> works. The prefix should be used only if the module is built-in so the
> parameter can be distinguished on the kernel command line.

Thanks for testing! This actually gave me quite a headache when I was
using the series elsewhere. I forgot to resend the series with the fix,
sorry.


Best regards,
Andreas Hindborg