On Wed, Aug 14, 2024 at 05:01:34PM +0000, Benno Lossin wrote: > On 12.08.24 20:22, Danilo Krummrich wrote: > > +/// The kernel's [`Box`] type - a heap allocation for a single value of type `T`. > > +/// > > +/// This is the kernel's version of the Rust stdlib's `Box`. There are a couple of differences, > > +/// for example no `noalias` attribute is emitted and partially moving out of a `Box` is not > > +/// supported. > > I would add "But otherwise it works the same." (I don't know if there is > a comma needed after the "otherwise"). There are more differences we don't list here, and probably don't need to. Hence, saying that it otherwise works the same isn't correct. > Also I remember that there was one more difference with a custom box > compared to the stdlib, but I forgot what that was, does someone else > remember? We should also put that here. Obviously, there are also quite some API differences. For instance, `Box` generally requires two generics, value type and allocator, we take page flags and return a `Result`, where std just panics on failure. > > > +/// > > +/// `Box` works with any of the kernel's allocators, e.g. [`super::allocator::Kmalloc`], > > +/// [`super::allocator::Vmalloc`] or [`super::allocator::KVmalloc`]. There are aliases for `Box` > > +/// with these allocators ([`KBox`], [`VBox`], [`KVBox`]). > > +/// > > +/// When dropping a [`Box`], the value is also dropped and the heap memory is automatically freed. > > +/// > > +/// # Examples > > +/// > > +/// ``` > > +/// let b = KBox::<u64>::new(24_u64, GFP_KERNEL)?; > > +/// > > +/// assert_eq!(*b, 24_u64); > > +/// > > +/// # Ok::<(), Error>(()) > > +/// ``` > > +/// > > +/// ``` > > +/// # use kernel::bindings; > > +/// > > +/// const SIZE: usize = bindings::KMALLOC_MAX_SIZE as usize + 1; > > +/// struct Huge([u8; SIZE]); > > +/// > > +/// assert!(KBox::<Huge>::new_uninit(GFP_KERNEL | __GFP_NOWARN).is_err()); > > +/// ``` > > +/// > > +/// ``` > > +/// # use kernel::bindings; > > +/// > > +/// const SIZE: usize = bindings::KMALLOC_MAX_SIZE as usize + 1; > > +/// struct Huge([u8; SIZE]); > > +/// > > +/// assert!(KVBox::<Huge>::new_uninit(GFP_KERNEL).is_ok()); > > +/// ``` > > +/// > > +/// # Invariants > > +/// > > +/// The [`Box`]' pointer always properly aligned and either points to memory allocated with `A` or, > > "pointer always properly" -> "pointer is properly" > > > +/// for zero-sized types, is a dangling pointer. > > I think this section would look nicer, if it were formatted using bullet > points (that way the bracketing of the "or" is also unambiguous). > > Additionally, this is missing that the pointer is valid for reads and > writes. > > > +pub struct Box<T: ?Sized, A: Allocator>(NonNull<T>, PhantomData<A>); > > Why no `repr(transparent)`? I wasn't entirely sure whether that's OK with the additional `PhantomData`, but I think it is, gonna add it. > > > + > > +/// Type alias for `Box` with a `Kmalloc` allocator. > > I think we should add that this is only designed for small values. I don't want duplicate the existing documentation around kmalloc and friends [1]. Maybe we can refer to the existing documentation somehow. [1] https://www.kernel.org/doc/html/latest/core-api/memory-allocation.html > > > +/// > > +/// # Examples > > +/// > > +/// ``` > > +/// let b = KBox::new(24_u64, GFP_KERNEL)?; > > +/// > > +/// assert_eq!(*b, 24_u64); > > +/// > > +/// # Ok::<(), Error>(()) > > +/// ``` > > +pub type KBox<T> = Box<T, super::allocator::Kmalloc>; > > + > > +/// Type alias for `Box` with a `Vmalloc` allocator. > > Same here, add that this is supposed to be used for big values (or is > this also a general-purpose allocator, just not guaranteeing that the > memory is physically contiguous? in that case I would document it > here and also on `Vmalloc`). Same as above, I'd rather not duplicate that. But I'm happy to link things in, just not sure what's the best way doing it.
