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

Alice Ryhl
2025-04-23T08:55:37Z

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?

Alice