Re: [PATCH v5] rust: str: add {make,to}_{upper,lower}case() to CString

[Danilo Krummrich <dakr@redhat.com>]

On Mon, Mar 04, 2024 at 01:22:17PM +0100, Danilo Krummrich wrote:
> On 2/23/24 17:37, Danilo Krummrich wrote:
> > Add functions to convert a CString to upper- / lowercase, either
> > in-place or by creating a copy of the original CString.
> > 
> > Naming followes the one from the Rust stdlib, where functions starting
> > with 'to' create a copy and functions starting with 'make' perform an
> > in-place conversion.
> > 
> > This is required by the Nova project (GSP only Rust successor of
> > Nouveau) to convert stringified enum values (representing different GPU
> > chipsets) to strings in order to generate the corresponding firmware
> > paths. See also [1].
> 
> Gentle ping.

It doesn't seem there's any further feedback, thus can this be merged?

- Danilo

> 
> > 
> > [1] https://rust-for-linux.zulipchat.com/#narrow/stream/288089-General/topic/String.20manipulation.20in.20kernel.20Rust
> > 
> > Reviewed-by: Alice Ryhl <aliceryhl@google.com>
> > Signed-off-by: Danilo Krummrich <dakr@redhat.com>
> > ---
> > Changes in V5:
> >    - remove unneeded return statements
> >    - use Vec::as_mut_slice() instead of a dereference
> > Changes in V4:
> >    - move to_ascii_{lower,upper}case() to CStr
> >    - add a few comments suggested by Alice
> > Changes in V3:
> >    - add an `impl DerefMut for CString`, such that these functions can be defined
> >      for `CStr` as `&mut self` and still be called on a `CString`
> > Changes in V2:
> >    - expand commit message mentioning the use case
> >    - expand function doc comments to match the ones from Rust's stdlib
> >    - rename to_* to make_* and add the actual to_* implementations
> > ---
> >   rust/kernel/str.rs | 87 +++++++++++++++++++++++++++++++++++++++++++++-
> >   1 file changed, 86 insertions(+), 1 deletion(-)
> > 
> > diff --git a/rust/kernel/str.rs b/rust/kernel/str.rs
> > index 7d848b83add4..c1c8ccc80c52 100644
> > --- a/rust/kernel/str.rs
> > +++ b/rust/kernel/str.rs
> > @@ -5,7 +5,7 @@
> >   use alloc::alloc::AllocError;
> >   use alloc::vec::Vec;
> >   use core::fmt::{self, Write};
> > -use core::ops::{self, Deref, Index};
> > +use core::ops::{self, Deref, DerefMut, Index};
> >   use crate::{
> >       bindings,
> > @@ -143,6 +143,19 @@ pub const fn from_bytes_with_nul(bytes: &[u8]) -> Result<&Self, CStrConvertError
> >           unsafe { core::mem::transmute(bytes) }
> >       }
> > +    /// Creates a mutable [`CStr`] from a `[u8]` without performing any
> > +    /// additional checks.
> > +    ///
> > +    /// # Safety
> > +    ///
> > +    /// `bytes` *must* end with a `NUL` byte, and should only have a single
> > +    /// `NUL` byte (or the string will be truncated).
> > +    #[inline]
> > +    pub unsafe fn from_bytes_with_nul_unchecked_mut(bytes: &mut [u8]) -> &mut CStr {
> > +        // SAFETY: Properties of `bytes` guaranteed by the safety precondition.
> > +        unsafe { &mut *(bytes as *mut [u8] as *mut CStr) }
> > +    }
> > +
> >       /// Returns a C pointer to the string.
> >       #[inline]
> >       pub const fn as_char_ptr(&self) -> *const core::ffi::c_char {
> > @@ -206,6 +219,70 @@ pub unsafe fn as_str_unchecked(&self) -> &str {
> >       pub fn to_cstring(&self) -> Result<CString, AllocError> {
> >           CString::try_from(self)
> >       }
> > +
> > +    /// Converts this [`CStr`] to its ASCII lower case equivalent in-place.
> > +    ///
> > +    /// ASCII letters 'A' to 'Z' are mapped to 'a' to 'z',
> > +    /// but non-ASCII letters are unchanged.
> > +    ///
> > +    /// To return a new lowercased value without modifying the existing one, use
> > +    /// [`to_ascii_lowercase()`].
> > +    ///
> > +    /// [`to_ascii_lowercase()`]: #method.to_ascii_lowercase
> > +    pub fn make_ascii_lowercase(&mut self) {
> > +        // INVARIANT: This doesn't introduce or remove NUL bytes in the C
> > +        // string.
> > +        self.0.make_ascii_lowercase();
> > +    }
> > +
> > +    /// Converts this [`CStr`] to its ASCII upper case equivalent in-place.
> > +    ///
> > +    /// ASCII letters 'a' to 'z' are mapped to 'A' to 'Z',
> > +    /// but non-ASCII letters are unchanged.
> > +    ///
> > +    /// To return a new uppercased value without modifying the existing one, use
> > +    /// [`to_ascii_uppercase()`].
> > +    ///
> > +    /// [`to_ascii_uppercase()`]: #method.to_ascii_uppercase
> > +    pub fn make_ascii_uppercase(&mut self) {
> > +        // INVARIANT: This doesn't introduce or remove NUL bytes in the C
> > +        // string.
> > +        self.0.make_ascii_uppercase();
> > +    }
> > +
> > +    /// Returns a copy of this [`CString`] where each character is mapped to its
> > +    /// ASCII lower case equivalent.
> > +    ///
> > +    /// ASCII letters 'A' to 'Z' are mapped to 'a' to 'z',
> > +    /// but non-ASCII letters are unchanged.
> > +    ///
> > +    /// To lowercase the value in-place, use [`make_ascii_lowercase`].
> > +    ///
> > +    /// [`make_ascii_lowercase`]: str::make_ascii_lowercase
> > +    pub fn to_ascii_lowercase(&self) -> Result<CString, AllocError> {
> > +        let mut s = self.to_cstring()?;
> > +
> > +        s.make_ascii_lowercase();
> > +
> > +        Ok(s)
> > +    }
> > +
> > +    /// Returns a copy of this [`CString`] where each character is mapped to its
> > +    /// ASCII upper case equivalent.
> > +    ///
> > +    /// ASCII letters 'a' to 'z' are mapped to 'A' to 'Z',
> > +    /// but non-ASCII letters are unchanged.
> > +    ///
> > +    /// To uppercase the value in-place, use [`make_ascii_uppercase`].
> > +    ///
> > +    /// [`make_ascii_uppercase`]: str::make_ascii_uppercase
> > +    pub fn to_ascii_uppercase(&self) -> Result<CString, AllocError> {
> > +        let mut s = self.to_cstring()?;
> > +
> > +        s.make_ascii_uppercase();
> > +
> > +        Ok(s)
> > +    }
> >   }
> >   impl fmt::Display for CStr {
> > @@ -593,6 +670,14 @@ fn deref(&self) -> &Self::Target {
> >       }
> >   }
> > +impl DerefMut for CString {
> > +    fn deref_mut(&mut self) -> &mut Self::Target {
> > +        // SAFETY: A `CString` is always NUL-terminated and contains no other
> > +        // NUL bytes.
> > +        unsafe { CStr::from_bytes_with_nul_unchecked_mut(self.buf.as_mut_slice()) }
> > +    }
> > +}
> > +
> >   impl<'a> TryFrom<&'a CStr> for CString {
> >       type Error = AllocError;
> > 
> > base-commit: 39133352cbed6626956d38ed72012f49b0421e7b