linux-kernel - [PATCH v4 2/4] rust: str: implement `strip

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Message-Id: <20250109-module-params-v3-v4-2-c208bcfbe11f@kernel.org>
Date: Thu, 09 Jan 2025 11:54:57 +0100
From: Andreas Hindborg <a.hindborg@...nel.org>
To: Miguel Ojeda <ojeda@...nel.org>, Alex Gaynor <alex.gaynor@...il.com>, 
 Boqun Feng <boqun.feng@...il.com>, Gary Guo <gary@...yguo.net>, 
 Björn Roy Baron <bjorn3_gh@...tonmail.com>, 
 Benno Lossin <benno.lossin@...ton.me>, Alice Ryhl <aliceryhl@...gle.com>, 
 Masahiro Yamada <masahiroy@...nel.org>, 
 Nathan Chancellor <nathan@...nel.org>, Nicolas Schier <nicolas@...sle.eu>, 
 Luis Chamberlain <mcgrof@...nel.org>
Cc: Trevor Gross <tmgross@...ch.edu>, 
 Adam Bratschi-Kaye <ark.email@...il.com>, rust-for-linux@...r.kernel.org, 
 linux-kernel@...r.kernel.org, linux-kbuild@...r.kernel.org, 
 Petr Pavlu <petr.pavlu@...e.com>, Sami Tolvanen <samitolvanen@...gle.com>, 
 Daniel Gomez <da.gomez@...sung.com>, Simona Vetter <simona.vetter@...ll.ch>, 
 Greg KH <gregkh@...uxfoundation.org>, linux-modules@...r.kernel.org, 
 Andreas Hindborg <a.hindborg@...nel.org>
Subject: [PATCH v4 2/4] rust: str: implement `strip_prefix` for `BStr`

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

Signed-off-by: Andreas Hindborg <a.hindborg@...nel.org>

---

It is also possible to get this method by implementing
`core::slice::SlicePattern` for `BStr`. `SlicePattern` is unstable, so this
seems more reasonable.
---
 rust/kernel/str.rs | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/rust/kernel/str.rs b/rust/kernel/str.rs
index c441acf76ebd1f14919b6d233edffbbbbf944619..9c446ff1ad7adba7ca09a5ae9df00fd369a32899 100644
--- a/rust/kernel/str.rs
+++ b/rust/kernel/str.rs
@@ -31,6 +31,22 @@ pub const fn from_bytes(bytes: &[u8]) -> &Self {
         // SAFETY: `BStr` is transparent to `[u8]`.
         unsafe { &*(bytes as *const [u8] as *const BStr) }
     }
+
+    /// Strip a prefix from `self`. Delegates to [`slice::strip_prefix`].
+    ///
+    /// # Example
+    /// ```
+    /// 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: &Self) -> Option<&BStr> {
+        self.deref()
+            .strip_prefix(pattern.deref())
+            .map(Self::from_bytes)
+    }
 }
 
 impl fmt::Display for BStr {

-- 
2.47.0