linux-kernel - [RFC PATCH 09/11] RUST: implement `ForeignOwnable` for `Pin`

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Message-Id: <20230503090708.2524310-10-nmi@metaspace.dk>
Date:   Wed,  3 May 2023 11:07:06 +0200
From:   Andreas Hindborg <nmi@...aspace.dk>
To:     Jens Axboe <axboe@...nel.dk>, Christoph Hellwig <hch@....de>,
        Keith Busch <kbusch@...nel.org>,
        Damien Le Moal <Damien.LeMoal@....com>,
        Hannes Reinecke <hare@...e.de>,
        lsf-pc@...ts.linux-foundation.org, rust-for-linux@...r.kernel.org,
        linux-block@...r.kernel.org
Cc:     Andreas Hindborg <a.hindborg@...sung.com>,
        Matthew Wilcox <willy@...radead.org>,
        Miguel Ojeda <ojeda@...nel.org>,
        Alex Gaynor <alex.gaynor@...il.com>,
        Wedson Almeida Filho <wedsonaf@...il.com>,
        Boqun Feng <boqun.feng@...il.com>, Gary Guo <gary@...yguo.net>,
        Björn Roy Baron <bjorn3_gh@...tonmail.com>,
        Benno Lossin <benno.lossin@...ton.me>,
        Andreas Hindborg <nmi@...aspace.dk>,
        linux-kernel@...r.kernel.org (open list), gost.dev@...sung.com
Subject: [RFC PATCH 09/11] RUST: implement `ForeignOwnable` for `Pin`

From: Andreas Hindborg <a.hindborg@...sung.com>

Implement `ForeignOwnable for Pin<T> where T: ForeignOwnable + Deref`.

Imported from rust tree [1]

[1] https://github.com/Rust-for-Linux/linux/tree/bc22545f38d74473cfef3e9fd65432733435b79f

Cc: Wedson Almeida Filho <wedsonaf@...il.com>
---
 rust/kernel/types.rs | 24 ++++++++++++++++++++++++
 1 file changed, 24 insertions(+)

diff --git a/rust/kernel/types.rs b/rust/kernel/types.rs
index 29db59d6119a..98e71e96a7fc 100644
--- a/rust/kernel/types.rs
+++ b/rust/kernel/types.rs
@@ -9,6 +9,7 @@ use core::{
     marker::PhantomData,
     mem::MaybeUninit,
     ops::{Deref, DerefMut},
+    pin::Pin,
     ptr::NonNull,
 };
 
@@ -100,6 +101,29 @@ impl ForeignOwnable for () {
     unsafe fn from_foreign(_: *const core::ffi::c_void) -> Self {}
 }
 
+impl<T: ForeignOwnable + Deref> ForeignOwnable for Pin<T> {
+    type Borrowed<'a> = T::Borrowed<'a>;
+
+    fn into_foreign(self) -> *const core::ffi::c_void {
+        // SAFETY: We continue to treat the pointer as pinned by returning just a pointer to it to
+        // the caller.
+        let inner = unsafe { Pin::into_inner_unchecked(self) };
+        inner.into_foreign()
+    }
+
+    unsafe fn borrow<'a>(ptr: *const core::ffi::c_void) -> Self::Borrowed<'a> {
+        // SAFETY: The safety requirements for this function are the same as the ones for
+        // `T::borrow`.
+        unsafe { T::borrow(ptr) }
+    }
+
+    unsafe fn from_foreign(p: *const core::ffi::c_void) -> Self {
+        // SAFETY: The object was originally pinned.
+        // The passed pointer comes from a previous call to `T::into_foreign`.
+        unsafe { Pin::new_unchecked(T::from_foreign(p)) }
+    }
+}
+
 /// Runs a cleanup function/closure when dropped.
 ///
 /// The [`ScopeGuard::dismiss`] function prevents the cleanup function from running.
-- 
2.40.0