[PATCH v4 01/27] rust: alloc: remove `'static` bound on `ForeignOwnable`

[Danilo Krummrich <dakr@kernel.org>]

From: Gary Guo <gary@garyguo.net>

The `'static` bound is currently necessary because there's no
restriction on the lifetime of the GAT. Add a `Self: 'a` bound to
restrict possible lifetimes on `Borrowed` and `BorrowedMut`, and lift
the `'static` requirement.

Reviewed-by: Alexandre Courbot <acourbot@nvidia.com>
Signed-off-by: Gary Guo <gary@garyguo.net>
Signed-off-by: Danilo Krummrich <dakr@kernel.org>
---
 rust/kernel/alloc/kbox.rs | 24 ++++++++++++++++++------
 rust/kernel/types.rs      |  8 ++++++--
 2 files changed, 24 insertions(+), 8 deletions(-)

diff --git a/rust/kernel/alloc/kbox.rs b/rust/kernel/alloc/kbox.rs
index c824ed6e1523..2f8c16473c2c 100644
--- a/rust/kernel/alloc/kbox.rs
+++ b/rust/kernel/alloc/kbox.rs
@@ -477,7 +477,7 @@ fn try_init<E>(init: impl Init<T, E>, flags: Flags) -> Result<Self, E>
 
 // SAFETY: The pointer returned by `into_foreign` comes from a well aligned
 // pointer to `T` allocated by `A`.
-unsafe impl<T: 'static, A> ForeignOwnable for Box<T, A>
+unsafe impl<T, A> ForeignOwnable for Box<T, A>
 where
     A: Allocator,
 {
@@ -487,8 +487,14 @@ unsafe impl<T: 'static, A> ForeignOwnable for Box<T, A>
         core::mem::align_of::<T>()
     };
 
-    type Borrowed<'a> = &'a T;
-    type BorrowedMut<'a> = &'a mut T;
+    type Borrowed<'a>
+        = &'a T
+    where
+        Self: 'a;
+    type BorrowedMut<'a>
+        = &'a mut T
+    where
+        Self: 'a;
 
     fn into_foreign(self) -> *mut c_void {
         Box::into_raw(self).cast()
@@ -516,13 +522,19 @@ unsafe fn borrow_mut<'a>(ptr: *mut c_void) -> &'a mut T {
 
 // SAFETY: The pointer returned by `into_foreign` comes from a well aligned
 // pointer to `T` allocated by `A`.
-unsafe impl<T: 'static, A> ForeignOwnable for Pin<Box<T, A>>
+unsafe impl<T, A> ForeignOwnable for Pin<Box<T, A>>
 where
     A: Allocator,
 {
     const FOREIGN_ALIGN: usize = <Box<T, A> as ForeignOwnable>::FOREIGN_ALIGN;
-    type Borrowed<'a> = Pin<&'a T>;
-    type BorrowedMut<'a> = Pin<&'a mut T>;
+    type Borrowed<'a>
+        = Pin<&'a T>
+    where
+        Self: 'a;
+    type BorrowedMut<'a>
+        = Pin<&'a mut T>
+    where
+        Self: 'a;
 
     fn into_foreign(self) -> *mut c_void {
         // SAFETY: We are still treating the box as pinned.
diff --git a/rust/kernel/types.rs b/rust/kernel/types.rs
index 4329d3c2c2e5..9cf9f869d195 100644
--- a/rust/kernel/types.rs
+++ b/rust/kernel/types.rs
@@ -27,10 +27,14 @@ pub unsafe trait ForeignOwnable: Sized {
     const FOREIGN_ALIGN: usize;
 
     /// Type used to immutably borrow a value that is currently foreign-owned.
-    type Borrowed<'a>;
+    type Borrowed<'a>
+    where
+        Self: 'a;
 
     /// Type used to mutably borrow a value that is currently foreign-owned.
-    type BorrowedMut<'a>;
+    type BorrowedMut<'a>
+    where
+        Self: 'a;
 
     /// Converts a Rust-owned object to a foreign-owned one.
     ///
-- 
2.54.0