[v9,1/4] rust: move `CStr`'s `Display` to helper struct

Commit Message

Tamir Duberstein March 17, 2025, 3:30 p.m. UTC

Remove `impl Display for CStr` in preparation for replacing `CStr` with
`core::ffi::CStr` which doesn't impl `Display`. Add `CStr::display`
returning a helper struct to replace the lost functionality; this
matches the APIs exposed by `std::ffi::OSstr` and `std::path::Path` for
printing non-Unicode data.

Signed-off-by: Tamir Duberstein <[e-mail]>
---
 rust/kernel/kunit.rs |  9 +++++---
 rust/kernel/str.rs   | 63 ++++++++++++++++++++++++++++++++++++++++++----------
 2 files changed, 57 insertions(+), 15 deletions(-)

Patch

diff --git a/rust/kernel/kunit.rs b/rust/kernel/kunit.rs
index 824da0e9738a..630b947c708c 100644
--- a/rust/kernel/kunit.rs
+++ b/rust/kernel/kunit.rs
@@ -56,6 +56,7 @@  macro_rules! kunit_assert {
                 break 'out;
             }
 
+            static NAME: &'static $crate::str::CStr = $crate::c_str!($name);
             static FILE: &'static $crate::str::CStr = $crate::c_str!($file);
             static LINE: i32 = core::line!() as i32 - $diff;
             static CONDITION: &'static $crate::str::CStr = $crate::c_str!(stringify!($condition));
@@ -71,11 +72,13 @@  macro_rules! kunit_assert {
                 //
                 // This mimics KUnit's failed assertion format.
                 $crate::kunit::err(format_args!(
-                    "    # {}: ASSERTION FAILED at {FILE}:{LINE}\n",
-                    $name
+                    "    # {NAME}: ASSERTION FAILED at {FILE}:{LINE}\n",
+                    NAME = NAME.display(),
+                    FILE = FILE.display(),
                 ));
                 $crate::kunit::err(format_args!(
-                    "    Expected {CONDITION} to be true, but is false\n"
+                    "    Expected {CONDITION} to be true, but is false\n",
+                    CONDITION = CONDITION.display(),
                 ));
                 $crate::kunit::err(format_args!(
                     "    Failure not reported to KUnit since this is a non-KUnit task\n"
diff --git a/rust/kernel/str.rs b/rust/kernel/str.rs
index 28e2201604d6..50eb4266047a 100644
--- a/rust/kernel/str.rs
+++ b/rust/kernel/str.rs
@@ -376,27 +376,66 @@  pub fn to_ascii_uppercase(&self) -> Result<CString, AllocError> {
 
         Ok(s)
     }
-}
 
-impl fmt::Display for CStr {
-    /// Formats printable ASCII characters, escaping the rest.
+    /// Returns an object that implements [`Display`] for safely printing a [`CStr`] that may
+    /// contain non-Unicode data. If you would like an implementation which escapes the [`CStr`]
+    /// please use [`Debug`] instead.
+    ///
+    /// [`Display`]: fmt::Display
+    /// [`Debug`]: fmt::Debug
+    ///
+    /// # Examples
     ///
     /// ```
     /// # use kernel::c_str;
     /// # use kernel::fmt;
-    /// # use kernel::str::CStr;
     /// # use kernel::str::CString;
     /// let penguin = c_str!("