[PATCH 5/6] rust: add `CStr` methods matching `core::ffi::CStr`
Tamir Duberstein
tamird at gmail.com
Fri Jul 4 20:14:56 UTC 2025
Prepare for replacing `CStr` with `core::ffi::CStr` by soft-deprecating
methods which don't exist on `core::ffi::CStr`.
We could keep `as_bytes{,_with_nul}` through an extension trait but
seeing as we have to introduce `as_char_ptr_in_const_context` as a free
function, we may as well introduce `to_bytes{,_with_nul}` here to allow
downstream code to migrate in one cycle rather than two.
Link: https://github.com/Rust-for-Linux/linux/issues/1075
Signed-off-by: Tamir Duberstein <tamird at gmail.com>
---
rust/kernel/str.rs | 37 ++++++++++++++++++++++++++++++++++---
1 file changed, 34 insertions(+), 3 deletions(-)
diff --git a/rust/kernel/str.rs b/rust/kernel/str.rs
index f326f0c40ab0..cbb357fc0111 100644
--- a/rust/kernel/str.rs
+++ b/rust/kernel/str.rs
@@ -175,6 +175,15 @@ macro_rules! b_str {
}};
}
+/// Returns a C pointer to the string.
+// It is a free function rather than a method on an extension trait because:
+//
+// - error[E0379]: functions in trait impls cannot be declared const
+#[inline]
+pub const fn as_char_ptr_in_const_context(c_str: &CStr) -> *const c_char {
+ c_str.0.as_ptr()
+}
+
/// Possible errors when using conversion functions in [`CStr`].
#[derive(Debug, Clone, Copy)]
pub enum CStrConvertError {
@@ -294,23 +303,45 @@ pub unsafe fn from_bytes_with_nul_unchecked_mut(bytes: &mut [u8]) -> &mut CStr {
}
/// Returns a C pointer to the string.
+ ///
+ /// Using this function in a const context is deprecated in favor of
+ /// [`as_char_ptr_in_const_context`] in preparation for replacing `CStr` with `core::ffi::CStr`
+ /// which does not have this method.
#[inline]
pub const fn as_char_ptr(&self) -> *const c_char {
- self.0.as_ptr()
+ as_char_ptr_in_const_context(self)
}
/// Convert the string to a byte slice without the trailing `NUL` byte.
#[inline]
- pub fn as_bytes(&self) -> &[u8] {
+ pub fn to_bytes(&self) -> &[u8] {
&self.0[..self.len()]
}
+ /// Convert the string to a byte slice without the trailing `NUL` byte.
+ ///
+ /// This function is deprecated in favor of [`Self::to_bytes`] in preparation for replacing
+ /// `CStr` with `core::ffi::CStr` which does not have this method.
+ #[inline]
+ pub fn as_bytes(&self) -> &[u8] {
+ self.to_bytes()
+ }
+
/// Convert the string to a byte slice containing the trailing `NUL` byte.
#[inline]
- pub const fn as_bytes_with_nul(&self) -> &[u8] {
+ pub const fn to_bytes_with_nul(&self) -> &[u8] {
&self.0
}
+ /// Convert the string to a byte slice containing the trailing `NUL` byte.
+ ///
+ /// This function is deprecated in favor of [`Self::to_bytes_with_nul`] in preparation for
+ /// replacing `CStr` with `core::ffi::CStr` which does not have this method.
+ #[inline]
+ pub const fn as_bytes_with_nul(&self) -> &[u8] {
+ self.to_bytes_with_nul()
+ }
+
/// Yields a [`&str`] slice if the [`CStr`] contains valid UTF-8.
///
/// If the contents of the [`CStr`] are valid UTF-8 data, this
--
2.50.0
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