Re: [PATCH v3 1/3] rust: maple_tree: add MapleTree

[Alice Ryhl <aliceryhl@google.com>]

On Tue, Sep 02, 2025 at 11:01:19AM +0200, Danilo Krummrich wrote:
> On Tue Sep 2, 2025 at 10:35 AM CEST, Alice Ryhl wrote:
> > The maple tree will be used in the Tyr driver to allocate and keep track
> > of GPU allocations created internally (i.e. not by userspace). It will
> > likely also be used in the Nova driver eventually.
> >
> > This adds the simplest methods for additional and removal that do not
> > require any special care with respect to concurrency.
> >
> > This implementation is based on the RFC by Andrew but with significant
> > changes to simplify the implementation.
> >
> > Co-developed-by: Andrew Ballance <andrewjballance@gmail.com>
> > Signed-off-by: Andrew Ballance <andrewjballance@gmail.com>
> > Signed-off-by: Alice Ryhl <aliceryhl@google.com>
> 
> One nit below, otherwise:
> 
> 	Reviewed-by: Danilo Krummrich <dakr@kernel.org>

Thanks!

> > +    pub fn insert_range<R>(&self, range: R, value: T, gfp: Flags) -> Result<(), InsertError<T>>
> > +    where
> > +        R: RangeBounds<usize>,
> > +    {
> > +        let Some((first, last)) = to_maple_range(range) else {
> > +            return Err(InsertError {
> > +                value,
> > +                cause: InsertErrorKind::InvalidRequest,
> > +            });
> > +        };
> > +
> > +        let ptr = T::into_foreign(value);
> > +
> > +        // SAFETY: The tree is valid, and we are passing a pointer to an owned instance of `T`.
> > +        let res = to_result(unsafe {
> > +            bindings::mtree_insert_range(self.tree.get(), first, last, ptr, gfp.as_raw())
> > +        });
> > +
> > +        if let Err(err) = res {
> > +            // SAFETY: As `mtree_insert_range` failed, it is safe to take back ownership.
> > +            let value = unsafe { T::from_foreign(ptr) };
> > +
> > +            let cause = if err == ENOMEM {
> > +                InsertErrorKind::AllocError(kernel::alloc::AllocError)
> > +            } else if err == EEXIST {
> > +                InsertErrorKind::Occupied
> > +            } else {
> > +                InsertErrorKind::InvalidRequest
> > +            };
> > +            Err(InsertError { value, cause })
> > +        } else {
> > +            Ok(())
> > +        }
> > +    }
> 
> 	// SAFETY: The tree is valid, and we are passing a pointer to an owned instance of `T`.
> 	to_result(unsafe {
> 	    bindings::mtree_insert_range(self.tree.get(), first, last, ptr, gfp.as_raw())
> 	}).map_err(|err| {
> 	    // SAFETY: As `mtree_insert_range` failed, it is safe to take back ownership.
> 	    let value = unsafe { T::from_foreign(ptr) };
> 	
> 	    let cause = if err == ENOMEM {
> 	        InsertErrorKind::AllocError(kernel::alloc::AllocError)
> 	    } else if err == EEXIST {
> 	        InsertErrorKind::Occupied
> 	    } else {
> 	        InsertErrorKind::InvalidRequest
> 	    };
> 	    Err(InsertError { value, cause })
> 	})
> 
> I think that's a bit cleaner than the above (not compile tested).

I don't love it. How about a match instead of if/else?

Alice