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Date:   Sat, 29 Jul 2023 09:10:22 +0000
To:     Miguel Ojeda <ojeda@kernel.org>,
        Wedson Almeida Filho <wedsonaf@gmail.com>,
        Alex Gaynor <alex.gaynor@gmail.com>
From:   Benno Lossin <benno.lossin@proton.me>
Cc:     Boqun Feng <boqun.feng@gmail.com>, Gary Guo <gary@garyguo.net>,
        =?utf-8?Q?Bj=C3=B6rn_Roy_Baron?= <bjorn3_gh@protonmail.com>,
        Benno Lossin <benno.lossin@proton.me>,
        Alice Ryhl <aliceryhl@google.com>,
        Andreas Hindborg <nmi@metaspace.dk>,
        rust-for-linux@vger.kernel.org, linux-kernel@vger.kernel.org,
        Martin Rodriguez Reboredo <yakoyoku@gmail.com>
Subject: [PATCH v3 11/13] rust: init: make `PinInit<T, E>` a supertrait of `Init<T, E>`
Message-ID: <20230729090838.225225-12-benno.lossin@proton.me>
In-Reply-To: <20230729090838.225225-1-benno.lossin@proton.me>
References: <20230729090838.225225-1-benno.lossin@proton.me>
Feedback-ID: 71780778:user:proton
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Precedence: bulk

Remove the blanket implementation of `PinInit<T, E> for I where I:
Init<T, E>`. This blanket implementation prevented custom types that
implement `PinInit`.

Reviewed-by: Martin Rodriguez Reboredo <yakoyoku@gmail.com>
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Signed-off-by: Benno Lossin <benno.lossin@proton.me>
---
v2 -> v3:
- add blank missing line,
- added Reviewed-by's from Martin and Alice.

 rust/kernel/init.rs            | 21 ++++++++-------------
 rust/kernel/init/__internal.rs | 12 ++++++++++++
 2 files changed, 20 insertions(+), 13 deletions(-)

diff --git a/rust/kernel/init.rs b/rust/kernel/init.rs
index 06ecab4901f2..040dc9a5f9fd 100644
--- a/rust/kernel/init.rs
+++ b/rust/kernel/init.rs
@@ -807,7 +807,7 @@ pub unsafe trait PinInit<T: ?Sized, E =3D Infallible>: =
Sized {
 ///
 /// [`Arc<T>`]: crate::sync::Arc
 #[must_use =3D "An initializer must be used in order to create its value."=
]
-pub unsafe trait Init<T: ?Sized, E =3D Infallible>: Sized {
+pub unsafe trait Init<T: ?Sized, E =3D Infallible>: PinInit<T, E> {
     /// Initializes `slot`.
     ///
     /// # Safety
@@ -818,18 +818,6 @@ pub unsafe trait Init<T: ?Sized, E =3D Infallible>: Si=
zed {
     unsafe fn __init(self, slot: *mut T) -> Result<(), E>;
 }
=20
-// SAFETY: Every in-place initializer can also be used as a pin-initialize=
r.
-unsafe impl<T: ?Sized, E, I> PinInit<T, E> for I
-where
-    I: Init<T, E>,
-{
-    unsafe fn __pinned_init(self, slot: *mut T) -> Result<(), E> {
-        // SAFETY: `__init` meets the same requirements as `__pinned_init`=
, except that it does not
-        // require `slot` to not move after init.
-        unsafe { self.__init(slot) }
-    }
-}
-
 /// Creates a new [`PinInit<T, E>`] from the given closure.
 ///
 /// # Safety
@@ -971,6 +959,13 @@ unsafe fn __init(self, slot: *mut T) -> Result<(), E> =
{
     }
 }
=20
+// SAFETY: Every type can be initialized by-value. `__pinned_init` calls `=
__init`.
+unsafe impl<T, E> PinInit<T, E> for T {
+    unsafe fn __pinned_init(self, slot: *mut T) -> Result<(), E> {
+        unsafe { self.__init(slot) }
+    }
+}
+
 /// Smart pointer that can initialize memory in-place.
 pub trait InPlaceInit<T>: Sized {
     /// Use the given pin-initializer to pin-initialize a `T` inside of a =
new smart pointer of this
diff --git a/rust/kernel/init/__internal.rs b/rust/kernel/init/__internal.r=
s
index 7abd1fb65e41..12e195061525 100644
--- a/rust/kernel/init/__internal.rs
+++ b/rust/kernel/init/__internal.rs
@@ -32,6 +32,18 @@ unsafe fn __init(self, slot: *mut T) -> Result<(), E> {
     }
 }
=20
+// SAFETY: While constructing the `InitClosure`, the user promised that it=
 upholds the
+// `__pinned_init` invariants.
+unsafe impl<T: ?Sized, F, E> PinInit<T, E> for InitClosure<F, T, E>
+where
+    F: FnOnce(*mut T) -> Result<(), E>,
+{
+    #[inline]
+    unsafe fn __pinned_init(self, slot: *mut T) -> Result<(), E> {
+        (self.0)(slot)
+    }
+}
+
 /// This trait is only implemented via the `#[pin_data]` proc-macro. It is=
 used to facilitate
 /// the pin projections within the initializers.
 ///
--=20
2.41.0