linux-kernel - Re: [PATCH v4 26/28] rust: str: test: replace `alloc::format`

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Message-ID: <d7e43b0d-e76e-4a23-9225-261ca1484b02@kernel.org>
Date: Mon, 12 Aug 2024 15:07:54 +0200
From: Danilo Krummrich <dakr@...nel.org>
To: Benno Lossin <benno.lossin@...ton.me>
Cc: ojeda@...nel.org, alex.gaynor@...il.com, wedsonaf@...il.com,
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Subject: Re: [PATCH v4 26/28] rust: str: test: replace `alloc::format`

On 8/8/24 9:22 AM, Benno Lossin wrote:
> On 05.08.24 17:19, Danilo Krummrich wrote:
>> The current implementation of tests in str.rs use `format!` to format
>> strings for comparison, which, internally, creates a new `String`.
>>
>> In order to prepare for getting rid of Rust's alloc crate, we have to
>> cut this dependency. Instead, implement `format!` for `CString`.
>>
>> Note that for userspace tests, `Kmalloc`, which is backing `CString`'s
>> memory, is just a type alias to `Cmalloc`.
>>
>> Signed-off-by: Danilo Krummrich <dakr@...nel.org>
>> ---
>>   rust/kernel/str.rs | 23 ++++++++++++++++++++++-
>>   1 file changed, 22 insertions(+), 1 deletion(-)
>>
>> diff --git a/rust/kernel/str.rs b/rust/kernel/str.rs
>> index 0b6ffbade521..8f234224cbf5 100644
>> --- a/rust/kernel/str.rs
>> +++ b/rust/kernel/str.rs
>> @@ -523,7 +523,28 @@ macro_rules! c_str {
>>   #[cfg(test)]
>>   mod tests {
>>       use super::*;
>> -    use alloc::format;
>> +
>> +    struct String(CString);
>> +
>> +    impl String {
>> +        fn from_fmt(args: fmt::Arguments<'_>) -> Self {
>> +            String(CString::try_from_fmt(args).unwrap())
>> +        }
>> +    }
>> +
>> +    impl Deref for String {
>> +        type Target = str;
>> +
>> +        fn deref(&self) -> &str {
>> +            self.0.to_str().unwrap()
>> +        }
>> +    }
> 
> Don't actually think we need this newtype.

Right, but I thought it's a bit more extensible and cleaner than...

> 
>> +
>> +    macro_rules! format {
>> +        ($($f:tt)*) => ({
>> +            &*String::from_fmt(kernel::fmt!($($f)*))
> 
> We could just do this:
> 
>      CString::try_from_fmt(kernel::fmt!($(f)*)).unwrap().to_str().unwrap()

...doing it inline.

I'm fine either way, but unless you really want me to change it, I'd
rather keep it as it is.

> 
> ---
> Cheers,
> Benno
> 
>> +        })
>> +    }
>>
>>       const ALL_ASCII_CHARS: &'static str =
>>           "\\x01\\x02\\x03\\x04\\x05\\x06\\x07\\x08\\x09\\x0a\\x0b\\x0c\\x0d\\x0e\\x0f\
>> --
>> 2.45.2
>>
>