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

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Message-ID: <Z9EyKgrlMVwBagfu@google.com>
Date: Wed, 12 Mar 2025 07:05:14 +0000
From: Alice Ryhl <aliceryhl@...gle.com>
To: Danilo Krummrich <dakr@...nel.org>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>, Alexander Viro <viro@...iv.linux.org.uk>, 
	Arnd Bergmann <arnd@...db.de>, Miguel Ojeda <ojeda@...nel.org>, 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>, 
	Matthew Maurer <mmaurer@...gle.com>, Lee Jones <lee@...nel.org>, linux-kernel@...r.kernel.org, 
	rust-for-linux@...r.kernel.org
Subject: Re: [PATCH 4/5] rust: alloc: add Vec::clear

On Tue, Mar 11, 2025 at 03:40:51PM +0100, Danilo Krummrich wrote:
> On Tue, Mar 11, 2025 at 02:25:15PM +0000, Alice Ryhl wrote:
> > 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;
> 
> Please use self.set_len() instead, such that we have to cover all safety
> requirements enforced by self.set_len().

Will do.

> With that,
> 
> 	Acked-by: Danilo Krummrich <dakr@...nel.org> # for char-misc
> 
> in case you want to take it through the char-misc tree.
> 
> Ironically, self.set_len() lacks your invariant comment and corresponding safety
> requirement, I will send a patch to fix this up, unless you want to. :-)

Go for it.

Alice