linux-kernel - [PATCH 4/5] rust: alloc: add Vec::clear

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Message-ID: <20250311-iov-iter-v1-4-f6c9134ea824@google.com>
Date: Tue, 11 Mar 2025 14:25:15 +0000
From: Alice Ryhl <aliceryhl@...gle.com>
To: Greg Kroah-Hartman <gregkh@...uxfoundation.org>, Alexander Viro <viro@...iv.linux.org.uk>, 
	Arnd Bergmann <arnd@...db.de>, Miguel Ojeda <ojeda@...nel.org>
Cc: Boqun Feng <boqun.feng@...il.com>, Gary Guo <gary@...yguo.net>, 
	"Björn Roy Baron" <bjorn3_gh@...tonmail.com>, Benno Lossin <benno.lossin@...ton.me>, 
	Andreas Hindborg <a.hindborg@...nel.org>, Trevor Gross <tmgross@...ch.edu>, 
	Danilo Krummrich <dakr@...nel.org>, Matthew Maurer <mmaurer@...gle.com>, Lee Jones <lee@...nel.org>, 
	linux-kernel@...r.kernel.org, rust-for-linux@...r.kernel.org, 
	Alice Ryhl <aliceryhl@...gle.com>
Subject: [PATCH 4/5] rust: alloc: add Vec::clear

Our custom Vec type is missing the stdlib method `clear`, thus add it.
It will be used in the miscdevice sample.

Signed-off-by: Alice Ryhl <aliceryhl@...gle.com>
---
 rust/kernel/alloc/kvec.rs | 27 +++++++++++++++++++++++++++
 1 file changed, 27 insertions(+)

diff --git a/rust/kernel/alloc/kvec.rs b/rust/kernel/alloc/kvec.rs
index ae9d072741cedbb34bed0be0c20cc75472aa53be..2d213ede2873cef87116a5527e8e24008c970a58 100644
--- a/rust/kernel/alloc/kvec.rs
+++ b/rust/kernel/alloc/kvec.rs
@@ -395,6 +395,33 @@ pub fn into_raw_parts(self) -> (*mut T, usize, usize) {
         (ptr, len, capacity)
     }
 
+    /// Clears the vector, removing all values.
+    ///
+    /// Note that this method has no effect on the allocated capacity
+    /// of the vector.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// let mut v = kernel::kvec![1, 2, 3]?;
+    ///
+    /// v.clear();
+    ///
+    /// assert!(v.is_empty());
+    /// # Ok::<(), Error>(())
+    /// ```
+    #[inline]
+    pub fn clear(&mut self) {
+        let elems: *mut [T] = self.as_mut_slice();
+
+        // INVARIANT: This call changes the number of elements to zero.
+        self.len = 0;
+
+        // SAFETY: The values being dropped are valid values of type `T` by the type invariants.
+        // It's okay to invalidate them as we just changed the length to zero.
+        unsafe { ptr::drop_in_place(elems) };
+    }
+
     /// Ensures that the capacity exceeds the length by at least `additional` elements.
     ///
     /// # Examples

-- 
2.49.0.rc0.332.g42c0ae87b1-goog