rust: str: implement strip_prefix for BStr

Implement `strip_prefix` for `BStr` by deferring to `slice::strip_prefix`
on the underlying `&[u8]`.

Reviewed-by: Gary Guo <[email protected]>
Reviewed-by: Alice Ryhl <[email protected]>
Reviewed-by: Daniel Almeida <[email protected]>
Tested-by: Daniel Almeida <[email protected]>
Signed-off-by: Andreas Hindborg <[email protected]>
Tested-by: Daniel Gomez <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
[ Pluralized section name. Hid `use`. - Miguel ]
Signed-off-by: Miguel Ojeda <[email protected]>

Author: Andreas Hindborg

rust/kernel/str.rs

@@ -31,6 +31,23 @@ impl BStr {
         // SAFETY: `BStr` is transparent to `[u8]`.
         unsafe { &*(bytes as *const [u8] as *const BStr) }
     }
+
+    /// Strip a prefix from `self`. Delegates to [`slice::strip_prefix`].
+    ///
+    /// # 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())
+            .map(Self::from_bytes)
+    }
 }
 
 impl fmt::Display for BStr {