Message-ID: <20250207004049.178049-1-lyude@redhat.com>
Date: Thu,  6 Feb 2025 19:40:45 -0500
From: Lyude Paul <lyude@...hat.com>
To: rust-for-linux@...r.kernel.org,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Maíra Canal <mairacanal@...eup.net>
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>,
	"Rafael J. Wysocki" <rafael@...nel.org>,
	Wedson Almeida Filho <wedsonaf@...il.com>,
	Mika Westerberg <mika.westerberg@...ux.intel.com>,
	Xiangfei Ding <dingxiangfei2009@...il.com>,
	linux-kernel@...r.kernel.org (open list)
Subject: [PATCH v2] rust/kernel: Add faux device bindings

This introduces a crate for working with faux devices in rust, along with
adding sample code to show how the API is used. Unlike other types of
devices, we don't provide any hooks for device probe/removal - since these
are optional for the faux API and are unnecessary in rust.

Signed-off-by: Lyude Paul <lyude@...hat.com>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: Maíra Canal <mairacanal@...eup.net>

---
V2:
* Check for NULL on return from device_create(), not a pointer error
* Rename Device to Registration to make its purpose more clear
* Drop platform device comment from crate docstring.
* Update MAINTAINERS

Signed-off-by: Lyude Paul <lyude@...hat.com>
---
 MAINTAINERS                      |  2 ++
 rust/bindings/bindings_helper.h  |  1 +
 rust/kernel/faux.rs              | 60 ++++++++++++++++++++++++++++++++
 rust/kernel/lib.rs               |  1 +
 samples/rust/Kconfig             | 10 ++++++
 samples/rust/Makefile            |  1 +
 samples/rust/rust_driver_faux.rs | 29 +++++++++++++++
 7 files changed, 104 insertions(+)
 create mode 100644 rust/kernel/faux.rs
 create mode 100644 samples/rust/rust_driver_faux.rs

diff --git a/MAINTAINERS b/MAINTAINERS
index 2f0dc98dab5fa..aa81e57b4c25c 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -7119,8 +7119,10 @@ F:	rust/kernel/device.rs
 F:	rust/kernel/device_id.rs
 F:	rust/kernel/devres.rs
 F:	rust/kernel/driver.rs
+F:	rust/kernel/faux.rs
 F:	rust/kernel/platform.rs
 F:	samples/rust/rust_driver_platform.rs
+F:	samples/rust/rust_driver_faux.rs
 
 DRIVERS FOR OMAP ADAPTIVE VOLTAGE SCALING (AVS)
 M:	Nishanth Menon <nm@...com>
diff --git a/rust/bindings/bindings_helper.h b/rust/bindings/bindings_helper.h
index 55354e4dec14e..f46cf3bb70695 100644
--- a/rust/bindings/bindings_helper.h
+++ b/rust/bindings/bindings_helper.h
@@ -11,6 +11,7 @@
 #include <linux/blk_types.h>
 #include <linux/blkdev.h>
 #include <linux/cred.h>
+#include <linux/device/faux.h>
 #include <linux/errname.h>
 #include <linux/ethtool.h>
 #include <linux/file.h>
diff --git a/rust/kernel/faux.rs b/rust/kernel/faux.rs
new file mode 100644
index 0000000000000..6c0a795b27477
--- /dev/null
+++ b/rust/kernel/faux.rs
@@ -0,0 +1,60 @@
+// SPDX-License-Identifier: GPL-2.0-only
+
+//! Abstractions for the faux bus.
+//!
+//! This crate provides bindings for working with faux devices in kernel modules.
+//!
+//! C header: [`include/linux/device/faux.h`]
+use crate::{bindings, device, error::code::*, prelude::*};
+use core::ptr::{addr_of_mut, null, NonNull};
+
+/// The registration of a faux device.
+///
+/// This type represents the registration of a [`struct faux_device`]. When an instance of this type
+/// is dropped, its respective faux device will be unregistered from the system.
+///
+/// # Invariants
+///
+/// `self.0` always holds a valid pointer to an initialized and registered [`struct faux_device`].
+///
+/// [`struct faux_device`]: srctree/include/linux/device/faux.h
+#[repr(transparent)]
+pub struct Registration(NonNull<bindings::faux_device>);
+
+impl Registration {
+    /// Create and register a new faux device with the given name.
+    pub fn new(name: &CStr) -> Result<Self> {
+        // SAFETY:
+        // - `name` is copied by this function into its own storage
+        // - `faux_ops` is safe to leave NULL according to the C API
+        let dev = unsafe { bindings::faux_device_create(name.as_char_ptr(), null()) };
+
+        // The above function will return either a valid device, or NULL on failure
+        Ok(Self(NonNull::new(dev).ok_or(ENOMEM)?))
+    }
+
+    fn as_raw(&self) -> *mut bindings::faux_device {
+        self.0.as_ptr()
+    }
+}
+
+impl AsRef<device::Device> for Registration {
+    fn as_ref(&self) -> &device::Device {
+        // SAFETY: The underlying `device` in `faux_device` is guaranteed by the C API to be
+        // a valid initialized `device`.
+        unsafe { device::Device::as_ref(addr_of_mut!((*self.as_raw()).dev)) }
+    }
+}
+
+impl Drop for Registration {
+    fn drop(&mut self) {
+        // SAFETY: self.0 is a valid registered faux_device via our type invariants.
+        unsafe { bindings::faux_device_destroy(self.as_raw()) }
+    }
+}
+
+// SAFETY: The faux device API is thread-safe
+unsafe impl Send for Registration {}
+
+// SAFETY: The faux device API is thread-safe
+unsafe impl Sync for Registration {}
diff --git a/rust/kernel/lib.rs b/rust/kernel/lib.rs
index 496ed32b0911a..398242f92a961 100644
--- a/rust/kernel/lib.rs
+++ b/rust/kernel/lib.rs
@@ -46,6 +46,7 @@
 pub mod devres;
 pub mod driver;
 pub mod error;
+pub mod faux;
 #[cfg(CONFIG_RUST_FW_LOADER_ABSTRACTIONS)]
 pub mod firmware;
 pub mod fs;
diff --git a/samples/rust/Kconfig b/samples/rust/Kconfig
index 918dbead2c0b4..3b6eae84b2977 100644
--- a/samples/rust/Kconfig
+++ b/samples/rust/Kconfig
@@ -61,6 +61,16 @@ config SAMPLE_RUST_DRIVER_PLATFORM
 
 	  If unsure, say N.
 
+config SAMPLE_RUST_DRIVER_FAUX
+	tristate "Faux Driver"
+	help
+	  This option builds the Rust Faux driver sample.
+
+	  To compile this as a module, choose M here:
+	  the module will be called rust_driver_faux.
+
+	  If unsure, say N.
+
 config SAMPLE_RUST_HOSTPROGS
 	bool "Host programs"
 	help
diff --git a/samples/rust/Makefile b/samples/rust/Makefile
index 5a8ab0df0567c..0dbc6d90f1ef9 100644
--- a/samples/rust/Makefile
+++ b/samples/rust/Makefile
@@ -6,6 +6,7 @@ obj-$(CONFIG_SAMPLE_RUST_MISC_DEVICE)		+= rust_misc_device.o
 obj-$(CONFIG_SAMPLE_RUST_PRINT)			+= rust_print.o
 obj-$(CONFIG_SAMPLE_RUST_DRIVER_PCI)		+= rust_driver_pci.o
 obj-$(CONFIG_SAMPLE_RUST_DRIVER_PLATFORM)	+= rust_driver_platform.o
+obj-$(CONFIG_SAMPLE_RUST_DRIVER_FAUX)		+= rust_driver_faux.o
 
 rust_print-y := rust_print_main.o rust_print_events.o
 
diff --git a/samples/rust/rust_driver_faux.rs b/samples/rust/rust_driver_faux.rs
new file mode 100644
index 0000000000000..81ec465d52651
--- /dev/null
+++ b/samples/rust/rust_driver_faux.rs
@@ -0,0 +1,29 @@
+// SPDX-License-Identifier: GPL-2.0
+
+//! Rust faux device sample.
+
+use kernel::{c_str, faux::*, prelude::*, Module};
+
+module! {
+    type: SampleModule,
+    name: "rust_faux_driver",
+    author: "Lyude Paul",
+    description: "Rust faux device sample",
+    license: "GPL",
+}
+
+struct SampleModule {
+    _dev: Registration,
+}
+
+impl Module for SampleModule {
+    fn init(_module: &'static ThisModule) -> Result<Self> {
+        pr_info!("Initialising Rust Faux Device Sample\n");
+
+        let dev = Registration::new(c_str!("rust-faux-sample-device"))?;
+
+        dev_info!(dev.as_ref(), "Hello from faux device!");
+
+        Ok(Self { _dev: dev })
+    }
+}

base-commit: 808eb958781e4ebb6e9c0962af2e856767e20f45
prerequisite-patch-id: f05ff916822e21eec452f9e5b8d11339c409265a
-- 
2.48.1

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