Re: [PATCH v6 09/26] rust: alloc: implement kernel `Box`

[Boqun Feng <boqun.feng@gmail.com>]

On Tue, Aug 20, 2024 at 05:26:22PM +0200, Danilo Krummrich wrote:
> On Tue, Aug 20, 2024 at 11:47:45AM +0200, Alice Ryhl wrote:
> > On Fri, Aug 16, 2024 at 2:13 AM Danilo Krummrich <dakr@kernel.org> wrote:
> > >
> > > `Box` provides the simplest way to allocate memory for a generic type
> > > with one of the kernel's allocators, e.g. `Kmalloc`, `Vmalloc` or
> > > `KVmalloc`.
> > >
> > > In contrast to Rust's `Box` type, the kernel `Box` type considers the
> > > kernel's GFP flags for all appropriate functions, always reports
> > > allocation failures through `Result<_, AllocError>` and remains
> > > independent from unstable features.
> > >
> > > Signed-off-by: Danilo Krummrich <dakr@kernel.org>
> > 
> > Overall looks good to me, but I have a question:
> > 
> > > +impl<T: 'static, A> ForeignOwnable for Box<T, A>
> > > +where
> > > +    A: Allocator,
> > > +{
> > > +    type Borrowed<'a> = &'a T;
> > > +    type BorrowedMut<'a> = &'a mut T;
> > > [..]
> > > +    unsafe fn borrow_mut<'a>(ptr: *const core::ffi::c_void) -> &'a mut T {
> > > +        // SAFETY: The safety requirements of this method ensure that the pointer is valid and that
> > > +        // nothing else will access the value for the duration of 'a.
> > > +        unsafe { &mut *ptr.cast_mut().cast() }
> > > +    }
> > 
> > Where does this come from? It looks like you've based the series on
> > top of [1], but I dropped that patch a long time ago, and I don't see
> > it in rust-dev anymore.
> 
> I comes from me rebasing onto rust-dev. When Boqun asked me to resolve the merge
> conflicts a few days ago, this patch was in rust-dev. I think it disappeared two
> days ago or so.
> 
> @Bonqun: Need to me to rebase again?
> 

No need to rebase for this. I've already applied your series on
rust-dev. The background of carrying `borrow_mut` is because it was
simple to do, and so I carried it as the best effort, now with more
`ForeignOwnable` ipmls, I think it's better if we just drop it, and
re-introduce if needed.

Sorry for a bit out-of-sync on this one.

Regards,
Boqun

> - Danilo
> 
> > 
> > Alice
> > 
> > [1]: https://lore.kernel.org/all/20230710074642.683831-1-aliceryhl@google.com/
> >