Pinned module

rust/kernel/lib.rs

@@ -21,6 +21,7 @@
 #![feature(new_uninit)]
 #![feature(pin_macro)]
 #![feature(receiver_trait)]
+#![feature(type_alias_impl_trait)]
 #![feature(unsize)]
 
 // Ensure conditional compilation based on the kernel configuration works;
@@ -59,7 +60,7 @@ const __LOG_PREFIX: &[u8] = b"rust_kernel\0";
 /// The top level entrypoint to implementing a kernel module.
 ///
 /// For any teardown or cleanup operations, your type may implement [`Drop`].
-pub trait Module: Sized + Sync {
+pub trait Module: Sized + Sync + Send {
     /// Called at module initialization time.
     ///
     /// Use this method to perform whatever setup or registration your module
@@ -69,6 +70,34 @@ pub trait Module: Sized + Sync {
     fn init(module: &'static ThisModule) -> error::Result<Self>;
 }
 
+/// A module that is pinned and initialised in-place.
+pub trait InPlaceModule: Sync + Send {
+    /// The type that implements the pinned initialisation of the module.
+    type Init: init::PinInit<Self, error::Error>;
+
+    /// Creates an initialiser for the module.
+    ///
+    /// It is called when the module is loaded.
+    fn init(module: &'static ThisModule) -> error::Result<Self::Init>;
+}
+
+impl<T: Module> InPlaceModule for T {
+    type Init = impl init::PinInit<Self, error::Error>;
+
+    fn init(module: &'static ThisModule) -> error::Result<Self::Init> {
+        let m = <Self as Module>::init(module)?;
+
+        let initer = move |slot: *mut Self| {
+            // SAFETY: `slot` is valid for write per the contract with `pin_init_from_closure`.
+            unsafe { slot.write(m) };
+            Ok(())
+        };
+
+        // SAFETY: On success, `initer` always fully initialises an instance of `Self`.
+        Ok(unsafe { init::pin_init_from_closure(initer) })
+    }
+}
+
 /// Equivalent to `THIS_MODULE` in the C API.
 ///
 /// C header: `include/linux/export.h`

rust/macros/module.rs

@@ -208,7 +208,7 @@ pub(crate) fn module(ts: TokenStream) -> TokenStream {
             #[used]
             static __IS_RUST_MODULE: () = ();
 
-            static mut __MOD: Option<{type_}> = None;
+            static mut __MOD: core::mem::MaybeUninit<{type_}> = core::mem::MaybeUninit::uninit();
 
             // SAFETY: `__this_module` is constructed by the kernel at load time and will not be
             // freed until the module is unloaded.
@@ -270,23 +270,21 @@ pub(crate) fn module(ts: TokenStream) -> TokenStream {
             }}
 
             fn __init() -> core::ffi::c_int {{
-                match <{type_} as kernel::Module>::init(&THIS_MODULE) {{
-                    Ok(m) => {{
-                        unsafe {{
-                            __MOD = Some(m);
-                        }}
-                        return 0;
-                    }}
-                    Err(e) => {{
-                        return e.to_errno();
-                    }}
+                let initer = match <{type_} as kernel::InPlaceModule>::init(&THIS_MODULE) {{
+                    Ok(i) => i,
+                    Err(e) => return e.to_errno(),
+                }};
+
+                match unsafe {{ initer.__pinned_init(__MOD.as_mut_ptr()) }} {{
+                    Ok(m) => 0,
+                    Err(e) => e.to_errno(),
                 }}
             }}
 
             fn __exit() {{
                 unsafe {{
                     // Invokes `drop()` on `__MOD`, which should be used for cleanup.
-                    __MOD = None;
+                    __MOD.assume_init_drop();
                 }}
             }}
 

samples/rust/Kconfig

@@ -20,6 +20,17 @@ config SAMPLE_RUST_MINIMAL
 
 	  If unsure, say N.
 
+config SAMPLE_RUST_INPLACE
+	tristate "Minimal in-place"
+	help
+	  This option builds the Rust minimal module with in-place
+	  initialisation.
+
+	  To compile this as a module, choose M here:
+	  the module will be called rust_inplace.
+
+	  If unsure, say N.
+
 config SAMPLE_RUST_PRINT
 	tristate "Printing macros"
 	help

samples/rust/Makefile

@@ -1,6 +1,7 @@
 # SPDX-License-Identifier: GPL-2.0
 
 obj-$(CONFIG_SAMPLE_RUST_MINIMAL)		+= rust_minimal.o
+obj-$(CONFIG_SAMPLE_RUST_INPLACE)		+= rust_inplace.o
 obj-$(CONFIG_SAMPLE_RUST_PRINT)			+= rust_print.o
 
 subdir-$(CONFIG_SAMPLE_RUST_HOSTPROGS)		+= hostprogs

samples/rust/rust_inplace.rs

@@ -0,0 +1,41 @@
+// SPDX-License-Identifier: GPL-2.0
+
+//! Rust minimal in-place sample.
+
+use kernel::prelude::*;
+
+module! {
+    type: RustInPlace,
+    name: "rust_inplace",
+    author: "Rust for Linux Contributors",
+    description: "Rust minimal in-place sample",
+    license: "GPL",
+}
+
+#[pin_data(PinnedDrop)]
+struct RustInPlace {
+    numbers: Vec<i32>,
+}
+
+impl kernel::InPlaceModule for RustInPlace {
+    type Init = impl PinInit<Self, Error>;
+    fn init(_module: &'static ThisModule) -> Result<Self::Init> {
+        pr_info!("Rust minimal sample (init)\n");
+        pr_info!("Am I built-in? {}\n", !cfg!(MODULE));
+
+        let mut numbers = Vec::new();
+        numbers.try_push(72)?;
+        numbers.try_push(108)?;
+        numbers.try_push(200)?;
+
+        Ok(try_pin_init!(Self { numbers }))
+    }
+}
+
+#[pinned_drop]
+impl PinnedDrop for RustInPlace {
+    fn drop(self: Pin<&mut Self>) {
+        pr_info!("My numbers are {:?}\n", self.numbers);
+        pr_info!("Rust minimal inplace sample (exit)\n");
+    }
+}

scripts/Makefile.build

@@ -277,7 +277,7 @@ $(obj)/%.lst: $(src)/%.c FORCE
 # Compile Rust sources (.rs)
 # ---------------------------------------------------------------------------
 
-rust_allowed_features := core_ffi_c,explicit_generic_args_with_impl_trait,new_uninit,pin_macro
+rust_allowed_features := core_ffi_c,explicit_generic_args_with_impl_trait,new_uninit,pin_macro,type_alias_impl_trait
 
 rust_common_cmd = \
 	RUST_MODFILE=$(modfile) $(RUSTC_OR_CLIPPY) $(rust_flags) \