linux-kernel - Re: [PATCH v7 23/26] rust: str: test: replace `alloc::format`

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Message-ID: <20240928203710.40bbb24d.gary@garyguo.net>
Date: Sat, 28 Sep 2024 20:37:10 +0100
From: Gary Guo <gary@...yguo.net>
To: Danilo Krummrich <dakr@...nel.org>
Cc: ojeda@...nel.org, alex.gaynor@...il.com, wedsonaf@...il.com,
 boqun.feng@...il.com, bjorn3_gh@...tonmail.com, benno.lossin@...ton.me,
 a.hindborg@...sung.com, aliceryhl@...gle.com, akpm@...ux-foundation.org,
 daniel.almeida@...labora.com, faith.ekstrand@...labora.com,
 boris.brezillon@...labora.com, lina@...hilina.net, mcanal@...lia.com,
 zhiw@...dia.com, cjia@...dia.com, jhubbard@...dia.com, airlied@...hat.com,
 ajanulgu@...hat.com, lyude@...hat.com, linux-kernel@...r.kernel.org,
 rust-for-linux@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH v7 23/26] rust: str: test: replace `alloc::format`

On Thu, 12 Sep 2024 00:52:59 +0200
Danilo Krummrich <dakr@...nel.org> 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`.
> 
> Reviewed-by: Alice Ryhl <aliceryhl@...gle.com>
> Reviewed-by: Benno Lossin <benno.lossin@...ton.me>
> Signed-off-by: Danilo Krummrich <dakr@...nel.org>

Reviewed-by: Gary Guo <gary@...yguo.net>

> ---
>  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 209ad1bb1a49..726329530338 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()
> +        }
> +    }
> +
> +    macro_rules! format {
> +        ($($f:tt)*) => ({
> +            &*String::from_fmt(kernel::fmt!($($f)*))
> +        })
> +    }
>  
>      const ALL_ASCII_CHARS: &'static str =
>          "\\x01\\x02\\x03\\x04\\x05\\x06\\x07\\x08\\x09\\x0a\\x0b\\x0c\\x0d\\x0e\\x0f\