Re: [PATCH v3 3/7] rust: alloc: add Vec::push_within_capacity

Boqun Feng
2025-04-23T16:00:00Z

On Wed, Apr 23, 2025 at 08:55:34AM +0000, Alice Ryhl wrote:
> On Tue, Apr 22, 2025 at 02:29:53PM -0700, Boqun Feng wrote:
> > On Tue, Apr 22, 2025 at 09:52:18AM +0000, Alice Ryhl wrote:
> > > This introduces a new method called `push_within_capacity` for appending
> > > to a vector without attempting to allocate if the capacity is full. Rust
> > > Binder will use this in various places to safely push to a vector while
> > > holding a spinlock.
> > >
> > > The implementation is moved to a push_within_capacity_unchecked method.
> > > This is preferred over having push() call push_within_capacity()
> > > followed by an unwrap_unchecked() for simpler unsafe.
> > >
> > > Signed-off-by: Alice Ryhl <aliceryhl@google.com>
> > > ---
> > > rust/kernel/alloc/kvec.rs | 41 ++++++++++++++++++++++++++++++++++++++---
> > > 1 file changed, 38 insertions(+), 3 deletions(-)
> > >
> > > diff --git a/rust/kernel/alloc/kvec.rs b/rust/kernel/alloc/kvec.rs
> > > index ebca0cfd31c67f3ce13c4825d7039e34bb54f4d4..a005a295262cb1e8b7c118125ffa07ae252e257c 100644
> > > --- a/rust/kernel/alloc/kvec.rs
> > > +++ b/rust/kernel/alloc/kvec.rs
> > > @@ -307,17 +307,52 @@ pub fn spare_capacity_mut(&mut self) -> &mut [MaybeUninit<T>] {
> > > /// ```
> > > pub fn push(&mut self, v: T, flags: Flags) -> Result<(), AllocError> {
> > > self.reserve(1, flags)?;
> > > + // SAFETY: The call to `reserve` was successful, so the capacity is at least one greater
> > > + // than the length.
> > > + unsafe { self.push_within_capacity_unchecked(v) };
> > > + Ok(())
> > > + }
> > > +
> > > + /// Appends an element to the back of the [`Vec`] instance without reallocating.
> > > + ///
> > > + /// Fails if the vector does not have capacity for the new element.
> > > + ///
> > > + /// # Examples
> > > + ///
> > > + /// ```
> > > + /// let mut v = KVec::with_capacity(10, GFP_KERNEL);
> >
> > Should be:
> >
> > /// let mut v = KVec::with_capacity(10, GFP_KERNEL)?;
> >
> > , right? I.e. a question mark is missing.
> >
> > The rest looks good to me.
>
> Will be fixed in the next version. Let me know if you want me to add
> your Reviewed-by tag with this fixed?
>

Sure, feel free to add

Reviewed-by: Boqun Feng <boqun.feng@gmail.com>

Regards,
Boqun

> Alice