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From: mattgilbride@google.com
To: "Miguel Ojeda" <ojeda@kernel.org>,
	"Alex Gaynor" <alex.gaynor@gmail.com>,
	"Wedson Almeida Filho" <wedsonaf@gmail.com>,
	"Boqun Feng" <boqun.feng@gmail.com>,
	"Gary Guo" <gary@garyguo.net>,
	"Björn Roy Baron" <bjorn3_gh@protonmail.com>,
	"Benno Lossin" <benno.lossin@proton.me>,
	"Andreas Hindborg" <a.hindborg@samsung.com>,
	"Alice Ryhl" <aliceryhl@google.com>,
	"Greg Kroah-Hartman" <gregkh@linuxfoundation.org>,
	"Arve Hjønnevåg" <arve@android.com>,
	"Todd Kjos" <tkjos@android.com>,
	"Martijn Coenen" <maco@android.com>,
	"Joel Fernandes" <joel@joelfernandes.org>,
	"Carlos Llamas" <cmllamas@google.com>,
	"Suren Baghdasaryan" <surenb@google.com>,
	"Christian Brauner" <brauner@kernel.org>
Cc: Rob Landley <rob@landley.net>,
	Davidlohr Bueso <dave@stgolabs.net>,
	 Michel Lespinasse <michel@lespinasse.org>,
	rust-for-linux@vger.kernel.org,  linux-kernel@vger.kernel.org,
	Matt Gilbride <mattgilbride@google.com>
Subject: [PATCH 1/6] rust: add `container_of!` macro
Date: Mon, 05 Feb 2024 15:50:01 +0000	[thread overview]
Message-ID: <20240205-b4-rbtree-v1-1-995e3eee38c0@google.com> (raw)
In-Reply-To: <20240205-b4-rbtree-v1-0-995e3eee38c0@google.com>

From: Wedson Almeida Filho <wedsonaf@gmail.com>

This macro is used to obtain a pointer to an entire struct
when given a pointer to a field in that struct.

Signed-off-by: Wedson Almeida Filho <wedsonaf@gmail.com>
Signed-off-by: Matt Gilbride <mattgilbride@google.com>
---
 rust/kernel/lib.rs | 32 ++++++++++++++++++++++++++++++++
 1 file changed, 32 insertions(+)

diff --git a/rust/kernel/lib.rs b/rust/kernel/lib.rs
index 7ac39874aeac..c7963efd1318 100644
--- a/rust/kernel/lib.rs
+++ b/rust/kernel/lib.rs
@@ -102,3 +102,35 @@ fn panic(info: &core::panic::PanicInfo<'_>) -> ! {
     // SAFETY: FFI call.
     unsafe { bindings::BUG() };
 }
+
+/// Produces a pointer to an object from a pointer to one of its fields.
+///
+/// # Safety
+///
+/// The pointer passed to this macro, and the pointer returned by this macro, must both be in
+/// bounds of the same allocation.
+///
+/// # Examples
+///
+/// ```
+/// # use kernel::container_of;
+/// struct Test {
+///     a: u64,
+///     b: u32,
+/// }
+///
+/// let test = Test { a: 10, b: 20 };
+/// let b_ptr = &test.b;
+/// // SAFETY: The pointer points at the `b` field of a `Test`, so the resulting pointer will be
+/// // in-bounds of the same allocation as `b_ptr`.
+/// let test_alias = unsafe { container_of!(b_ptr, Test, b) };
+/// assert!(core::ptr::eq(&test, test_alias));
+/// ```
+#[macro_export]
+macro_rules! container_of {
+    ($ptr:expr, $type:ty, $($f:tt)*) => {{
+        let ptr = $ptr as *const _ as *const u8;
+        let offset: usize = ::core::mem::offset_of!($type, $($f)*);
+        ptr.sub(offset) as *const $type
+    }}
+}

-- 
2.43.0.594.gd9cf4e227d-goog


  reply	other threads:[~2024-02-05 15:50 UTC|newest]

Thread overview: 15+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2024-02-05 15:50 [PATCH 0/6] Red-black tree abstraction needed by Rust Binder mattgilbride
2024-02-05 15:50 ` mattgilbride [this message]
2024-02-09 13:10   ` [PATCH 1/6] rust: add `container_of!` macro Alice Ryhl
2024-02-10  8:05   ` Trevor Gross
2024-02-12  9:56     ` Alice Ryhl
2024-02-05 15:50 ` [PATCH 2/6] rust: rbtree: add red-black tree implementation backed by the C version mattgilbride
2024-02-09 13:04   ` Alice Ryhl
2024-02-05 15:50 ` [PATCH 3/6] rust: rbtree: add `RBTreeIterator` mattgilbride
2024-02-09 13:06   ` Alice Ryhl
2024-02-05 15:50 ` [PATCH 4/6] rust: rbtree: add `RBTreeIteratorMut` mattgilbride
2024-02-09 13:06   ` Alice Ryhl
2024-02-05 15:50 ` [PATCH 5/6] rust: rbtree: add `RBTreeCursor` mattgilbride
2024-02-09 13:06   ` Alice Ryhl
2024-02-05 15:50 ` [PATCH 6/6] rust: rbtree: add `RBTree::entry` mattgilbride
2024-02-09 13:07   ` Alice Ryhl

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