Re: [PATCH v5 13/26] rust: alloc: implement kernel `Vec` type

[Danilo Krummrich]

On Wed, Aug 14, 2024 at 10:42:28AM +0200, Alice Ryhl wrote:
> > +#[macro_export]
> > +macro_rules! kvec {
> > +    () => (
> > +        {
> > +            $crate::alloc::KVec::new()
> > +        }
> > +    );
> > +    ($elem:expr; $n:expr) => (
> > +        {
> > +            $crate::alloc::KVec::from_elem($elem, $n, GFP_KERNEL)
> > +        }
> > +    );
> > +    ($($x:expr),+ $(,)?) => (
> > +        {
> > +            match $crate::alloc::KBox::new([$($x),+], GFP_KERNEL) {
> > +                Ok(b) => Ok($crate::alloc::KBox::into_vec(b)),
> > +                Err(e) => Err(e),
> 
> Hmm. This currently generates code that:
> 
> 1. Creates the array.
> 2. Allocates the memory.
> 3. Moves the array into the box.
> 
> Whereas the stdlib macro swaps step 1 and 2.

Isn't stdlib [1] doing the same thing I do?

[1] https://doc.rust-lang.org/1.80.1/src/alloc/macros.rs.html#49

> You can do the same by utilizing new_uninit. A sketch:
> 
> match KBox::<[_; _]>::new_uninit(GFP_KERNEL) {

How do we get the size here? `#![feature(generic_arg_infer)]` seems to be
unstable.

>     Ok(b) => Ok(KVec::from(KBox::write(b, [$($x),+]))),
>     Err(e) => Err(e),
> }