Re: [PATCH v4 7/7] rust: alloc: add Vec::insert_within_capacity

[Alice Ryhl <aliceryhl@google.com>]

On Tue, Apr 29, 2025 at 05:30:06PM +0200, Greg KH wrote:
> On Tue, Apr 29, 2025 at 02:44:27PM +0000, Alice Ryhl wrote:
> > This adds a variant of Vec::insert that does not allocate memory. This
> > makes it safe to use this function while holding a spinlock. Rust Binder
> > uses it for the range allocator fast path.
> > 
> > Signed-off-by: Alice Ryhl <aliceryhl@google.com>
> > ---
> >  rust/kernel/alloc/kvec.rs | 39 +++++++++++++++++++++++++++++++++++++++
> >  1 file changed, 39 insertions(+)
> > 
> > diff --git a/rust/kernel/alloc/kvec.rs b/rust/kernel/alloc/kvec.rs
> > index 0682108951675cbee05faa130e5a9ce72fc343ba..998afdcde47bec94b2c9d990ba3afbb3488ea99e 100644
> > --- a/rust/kernel/alloc/kvec.rs
> > +++ b/rust/kernel/alloc/kvec.rs
> > @@ -355,6 +355,45 @@ pub unsafe fn push_within_capacity_unchecked(&mut self, v: T) {
> >          unsafe { self.inc_len(1) };
> >      }
> >  
> > +    /// Inserts an element at the given index in the [`Vec`] instance.
> > +    ///
> > +    /// Fails if the vector does not have capacity for the new element. Panics if the index is out
> > +    /// of bounds.
> 
> Why panic and why not just return an error instead?

It's for consistency with stdlib. Illegal use is panic, expected error
conditions are errors.

Alice