linux-kernel - Re: [PATCH v3 1/2] Rust: kernel patch series

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Message-ID: <42c3fc0c-46a8-4502-ad53-d3b886fad5e8@gmail.com>
Date: Mon, 11 Aug 2025 15:22:18 -0300
From: AI Talking about AI <aitalkingai@...il.com>
To: rust-for-linux@...r.kernel.org
Cc: linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 1/2] Rust: kernel patch series

>From 21a3d2a2dcff13f445915602c06a17af07835ee7 Mon Sep 17 00:00:00 2001
From: AI talking about AI <aitalkingai@...il.com>
Date: Thu, 7 Aug 2025 07:53:56 -0700
Subject: [PATCH 1/2] rust: mark CStr::to_str #[must_use] and update docs

Add explanation about handling UTF-8 errors and mark CStr::to_str as #[must_use] to prevent silent error ignoring. Also document safety requirements of as_str_unchecked.

Signed-off-by: AI talking about AI <aitalkingai@...il.com>
---
 rust/kernel/str.rs | 29 +++++++++++++++++++++--------
 1 file changed, 21 insertions(+), 8 deletions(-)

diff --git a/rust/kernel/str.rs b/rust/kernel/str.rs
index 6c89255..290031b 100644
--- a/rust/kernel/str.rs
+++ b/rust/kernel/str.rs
@@ -37,12 +37,8 @@ impl BStr {
     /// # Examples
     ///
     /// ```
-    /// # use kernel::b_str;
-    /// assert_eq!(Some(b_str!("bar")), b_str!("foobar").strip_prefix(b_str!("foo")));
-    /// assert_eq!(None, b_str!("foobar").strip_prefix(b_str!("bar")));
-    /// assert_eq!(Some(b_str!("foobar")), b_str!("foobar").strip_prefix(b_str!("")));
-    /// assert_eq!(Some(b_str!("")), b_str!("foobar").strip_prefix(b_str!("foobar")));
-    /// ```
+
+///
     pub fn strip_prefix(&self, pattern: impl AsRef<Self>) -> Option<&BStr> {
         self.deref()
             .strip_prefix(pattern.as_ref().deref())
@@ -346,7 +342,7 @@ impl CStr {
     ///
     /// If the contents of the [`CStr`] are valid UTF-8 data, this
     /// function will return the corresponding [`&str`] slice. Otherwise,
-    /// it will return an error with details of where UTF-8 validation failed.
+    /// it will return an [`Err`] with details of where UTF-8 validation failed.
     ///
     /// # Examples
     ///
@@ -356,7 +352,21 @@ impl CStr {
     /// assert_eq!(cstr.to_str(), Ok("foo"));
     /// # Ok::<(), kernel::error::Error>(())
     /// ```
+
+    ///
+    /// # Errors
+    ///
+    /// This function returns an [`Err`] when the underlying bytes are not
+    /// valid UTF-8. The [`Err`] must be handled; it cannot be discarded,
+    /// as indicated by the `#[must_use]` annotation on this method.
+    ///
+    /// This method returns a [`Result`] because not all C strings contain
+    /// valid UTF-8. To avoid accidentally ignoring a failed conversion,
+    /// the return type is marked `#[must_use]`. Code that calls this
+    /// function should handle the error case explicitly (e.g. by logging or
+    /// propagating it), rather than silently discarding it.
     #[inline]
+    #[must_use]
     pub fn to_str(&self) -> Result<&str, core::str::Utf8Error> {
         core::str::from_utf8(self.as_bytes())
     }
@@ -380,7 +390,10 @@ impl CStr {
     /// ```
     #[inline]
     pub unsafe fn as_str_unchecked(&self) -> &str {
-        // SAFETY: TODO.
+        // SAFETY: The data behind `self` are bytes from a `CStr`, i.e. a NUL-terminated sequence
+        // of u8 values. `from_utf8_unchecked` requires that the byte slice be valid UTF-8; the
+        // caller of this method must therefore guarantee that the `CStr` contains valid UTF-8
+        // data before calling this function. See [`to_str`] for a checked version.
         unsafe { core::str::from_utf8_unchecked(self.as_bytes()) }
     }
 
-- 
2.39.5