linux-kernel - Re: [PATCH v3 3/7] rust: alloc: add Vec::push_within

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Message-ID: <aAirBuiNdraU4ty3@google.com>
Date: Wed, 23 Apr 2025 08:55:34 +0000
From: Alice Ryhl <aliceryhl@...gle.com>
To: Boqun Feng <boqun.feng@...il.com>
Cc: Danilo Krummrich <dakr@...nel.org>, Matthew Maurer <mmaurer@...gle.com>, rust-for-linux@...r.kernel.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 3/7] rust: alloc: add Vec::push_within_capacity

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@...gle.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