linux-kernel - [PATCH v2 10/12] rust: Add dma

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Message-ID: <20250521204654.1610607-11-lyude@redhat.com>
Date: Wed, 21 May 2025 16:29:17 -0400
From: Lyude Paul <lyude@...hat.com>
To: dri-devel@...ts.freedesktop.org,
	rust-for-linux@...r.kernel.org,
	linux-kernel@...r.kernel.org
Cc: Miguel Ojeda <ojeda@...nel.org>,
	Alex Gaynor <alex.gaynor@...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 <a.hindborg@...nel.org>,
	Alice Ryhl <aliceryhl@...gle.com>,
	Trevor Gross <tmgross@...ch.edu>,
	Danilo Krummrich <dakr@...nel.org>,
	Sumit Semwal <sumit.semwal@...aro.org>,
	Christian König <christian.koenig@....com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Wedson Almeida Filho <wedsonaf@...il.com>,
	Xiangfei Ding <dingxiangfei2009@...il.com>,
	linux-media@...r.kernel.org (open list:DMA BUFFER SHARING FRAMEWORK:Keyword:\bdma_(?:buf|fence|resv)\b),
	linaro-mm-sig@...ts.linaro.org (moderated list:DMA BUFFER SHARING FRAMEWORK:Keyword:\bdma_(?:buf|fence|resv)\b)
Subject: [PATCH v2 10/12] rust: Add dma_buf stub bindings

In order to implement the gem export callback, we need a type to represent
struct dma_buf. So - this commit introduces a set of stub bindings for
dma_buf. These bindings provide a ref-counted DmaBuf object, but don't
currently implement any functionality for using the DmaBuf.

Signed-off-by: Lyude Paul <lyude@...hat.com>
---
 rust/kernel/dma_buf.rs | 39 +++++++++++++++++++++++++++++++++++++++
 rust/kernel/lib.rs     |  1 +
 2 files changed, 40 insertions(+)
 create mode 100644 rust/kernel/dma_buf.rs

diff --git a/rust/kernel/dma_buf.rs b/rust/kernel/dma_buf.rs
new file mode 100644
index 0000000000000..318518ff0b28f
--- /dev/null
+++ b/rust/kernel/dma_buf.rs
@@ -0,0 +1,39 @@
+// SPDX-License-Identifier: GPL-2.0
+
+//! DMA buffer API
+//!
+//! C header: [`include/linux/dma-buf.h`](srctree/include/linux/dma-buf.h)
+
+use bindings;
+use kernel::types::*;
+
+/// A DMA buffer object.
+///
+/// # Invariants
+///
+/// The data layout of this type is equivalent to that of `struct dma_buf`.
+#[repr(transparent)]
+pub struct DmaBuf(Opaque<bindings::dma_buf>);
+
+// SAFETY: `struct dma_buf` is thread-safe
+unsafe impl Send for DmaBuf {}
+// SAFETY: `struct dma_buf` is thread-safe
+unsafe impl Sync for DmaBuf {}
+
+impl DmaBuf {
+    /// Convert from a `*mut bindings::dma_buf` to a [`DmaBuf`].
+    ///
+    /// # Safety
+    ///
+    /// The caller guarantees that `self_ptr` points to a valid initialized `struct dma_buf` for the
+    /// duration of the lifetime of `'a`, and promises to not violate rust's data aliasing rules
+    /// using the reference provided by this function.
+    pub(crate) unsafe fn as_ref<'a>(self_ptr: *mut bindings::dma_buf) -> &'a Self {
+        // SAFETY: Our data layout is equivalent to `dma_buf` .
+        unsafe { &*self_ptr.cast() }
+    }
+
+    pub(crate) fn as_raw(&self) -> *mut bindings::dma_buf {
+        self.0.get()
+    }
+}
diff --git a/rust/kernel/lib.rs b/rust/kernel/lib.rs
index cbacedfe54434..02d4311bb080c 100644
--- a/rust/kernel/lib.rs
+++ b/rust/kernel/lib.rs
@@ -49,6 +49,7 @@
 pub mod device_id;
 pub mod devres;
 pub mod dma;
+pub mod dma_buf;
 pub mod driver;
 #[cfg(CONFIG_DRM = "y")]
 pub mod drm;
-- 
2.49.0