linux-kernel - Re: [PATCH v2] rust: str: add conversion from `CStr` to `CString`

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Date:   Mon, 8 May 2023 12:41:27 +0100
From:   Gary Guo <gary@...yguo.net>
To:     Alice Ryhl <aliceryhl@...gle.com>
Cc:     Miguel Ojeda <ojeda@...nel.org>,
        Wedson Almeida Filho <wedsonaf@...il.com>,
        Alex Gaynor <alex.gaynor@...il.com>,
        Boqun Feng <boqun.feng@...il.com>,
        "Björn Roy Baron" <bjorn3_gh@...tonmail.com>,
        Benno Lossin <benno.lossin@...ton.me>,
        Martin Rodriguez Reboredo <yakoyoku@...il.com>,
        rust-for-linux@...r.kernel.org, linux-kernel@...r.kernel.org,
        patches@...ts.linux.dev
Subject: Re: [PATCH v2] rust: str: add conversion from `CStr` to `CString`

On Wed,  3 May 2023 14:10:16 +0000
Alice Ryhl <aliceryhl@...gle.com> wrote:

> These methods can be used to copy the data in a temporary c string into
> a separate allocation, so that it can be accessed later even if the
> original is deallocated.
> 
> The API in this change mirrors the standard library API for the `&str`
> and `String` types. The `ToOwned` trait is not implemented because it
> assumes that allocations are infallible.

How about add a `TryToOwned` trait to the kernel crate and implement
that trait for `CStr` instead?

Best,
Gary

> 
> Reviewed-by: Benno Lossin <benno.lossin@...ton.me>
> Signed-off-by: Alice Ryhl <aliceryhl@...gle.com>
> ---
>  rust/kernel/str.rs | 22 ++++++++++++++++++++++
>  1 file changed, 22 insertions(+)
> 
> diff --git a/rust/kernel/str.rs b/rust/kernel/str.rs
> index b771310fa4a4..f3dc5b24ea55 100644
> --- a/rust/kernel/str.rs
> +++ b/rust/kernel/str.rs
> @@ -2,6 +2,7 @@
>  
>  //! String representations.
>  
> +use alloc::alloc::AllocError;
>  use alloc::vec::Vec;
>  use core::fmt::{self, Write};
>  use core::ops::{self, Deref, Index};
> @@ -199,6 +200,12 @@ impl CStr {
>      pub unsafe fn as_str_unchecked(&self) -> &str {
>          unsafe { core::str::from_utf8_unchecked(self.as_bytes()) }
>      }
> +
> +    /// Convert this [`CStr`] into a [`CString`] by allocating memory and
> +    /// copying over the string data.
> +    pub fn to_cstring(&self) -> Result<CString, AllocError> {
> +        CString::try_from(self)
> +    }
>  }
>  
>  impl fmt::Display for CStr {
> @@ -584,6 +591,21 @@ impl Deref for CString {
>      }
>  }
>  
> +impl<'a> TryFrom<&'a CStr> for CString {
> +    type Error = AllocError;
> +
> +    fn try_from(cstr: &'a CStr) -> Result<CString, AllocError> {
> +        let mut buf = Vec::new();
> +
> +        buf.try_extend_from_slice(cstr.as_bytes_with_nul())
> +            .map_err(|_| AllocError)?;
> +
> +        // INVARIANT: The `CStr` and `CString` types have the same invariants for
> +        // the string data, and we copied it over without changes.
> +        Ok(CString { buf })
> +    }
> +}
> +
>  /// A convenience alias for [`core::format_args`].
>  #[macro_export]
>  macro_rules! fmt {
> 
> base-commit: ea76e08f4d901a450619831a255e9e0a4c0ed162