Re: [PATCH WIP 3/8] rust: alloc: implement AllocatorWithFlags trait

[Benno Lossin <benno.lossin@proton.me>]

On 29.04.24 22:11, Danilo Krummrich wrote:
> Signed-off-by: Danilo Krummrich <dakr@redhat.com>
> ---
>  rust/kernel/alloc.rs | 21 +++++++++++++++++++++
>  1 file changed, 21 insertions(+)
> 
> diff --git a/rust/kernel/alloc.rs b/rust/kernel/alloc.rs
> index 9bc1b48b5641..ec45ba8f77ce 100644
> --- a/rust/kernel/alloc.rs
> +++ b/rust/kernel/alloc.rs
> @@ -8,6 +8,14 @@
>  pub mod box_ext;
>  pub mod vec_ext;
> 
> +use core::{
> +    alloc::{Allocator, AllocError, Layout},
> +    ptr,
> +    ptr::NonNull,
> +};
> +
> +use flags::*;
> +
>  /// Flags to be used when allocating memory.
>  ///
>  /// They can be combined with the operators `|`, `&`, and `!`.
> @@ -68,3 +76,16 @@ pub mod flags {
>      /// small allocations.
>      pub const GFP_NOWAIT: Flags = Flags(bindings::GFP_NOWAIT);
>  }
> +
> +pub unsafe trait AllocatorWithFlags: Allocator {
> +    unsafe fn alloc_flags(&self, layout: Layout, flags: Flags) -> Result<NonNull<[u8]>, AllocError>;
> +    unsafe fn realloc_flags(&self, ptr: *mut u8, old_size: usize, layout: Layout, flags: Flags) -> Result<NonNull<[u8]>, AllocError>;

Please use `rustfmt`, there exists a make target that does it for you.

Also why are these functions `unsafe`? You haven't specified a `Safety`
section, which means nobody knows what the requirements are.

> +
> +    fn default_allocate(&self, layout: Layout) -> Result<NonNull<[u8]>, AllocError> {
> +        unsafe { self.realloc_flags(ptr::null_mut(), 0, layout, GFP_KERNEL) }
> +    }

Why do we want to have these functions? I think that it would make sense
to forbid all other ways of allocating memory. So only allow allocation
where the flags are explicitly passed.

-- 
Cheers,
Benno

> +
> +    fn default_allocate_zeroed(&self, layout: Layout) -> Result<NonNull<[u8]>, AllocError> {
> +        unsafe { self.realloc_flags(ptr::null_mut(), 0, layout, GFP_KERNEL | __GFP_ZERO) }
> +    }
> +}
> --
> 2.44.0
>