Create a Mutex<T> type backed by the kernel mutex type

Signed-off-by: Finn Behrens <[email protected]>

Author: kloenk

drivers/char/rust_example/src/lib.rs

@@ -4,6 +4,7 @@
 #![feature(global_asm)]
 
 use kernel::prelude::*;
+use kernel::sync::Mutex;
 
 module! {
     type: RustExample,
@@ -36,6 +37,14 @@ impl KernelModule for RustExample {
         println!("Parameters:");
         println!("  my_bool:  {}", my_bool.read());
         println!("  my_i32:   {}", my_i32.read());
+
+        let mutex = Mutex::new(1, "mutex");
+        println!("mutex: {:?}", mutex);
+        unsafe {
+            let guard = mutex.lock();
+            println!("data: {}", guard);
+        }
+
         Ok(RustExample {
             message: "on the heap!".to_owned(),
         })

rust/kernel/src/lib.rs

@@ -3,7 +3,7 @@
 //! The `kernel` crate
 
 #![no_std]
-#![feature(allocator_api, alloc_error_handler)]
+#![feature(allocator_api, alloc_error_handler, negative_impls)]
 
 // Ensure conditional compilation based on the kernel configuration works;
 // otherwise we may silently break things like initcall handling.
@@ -24,6 +24,8 @@ pub mod prelude;
 pub mod printk;
 pub mod random;
 
+pub mod sync;
+
 #[cfg(CONFIG_SYSCTL)]
 pub mod sysctl;
 

rust/kernel/src/sync.rs

@@ -0,0 +1,145 @@
+// SPDX-License-Identifier: GPL-2.0
+
+use core::cell::UnsafeCell;
+use core::fmt;
+use core::ops::{Deref, DerefMut};
+
+use crate::bindings;
+
+pub struct Mutex<T: ?Sized> {
+    lock: bindings::mutex,
+    data: UnsafeCell<T>,
+}
+
+impl<T> Mutex<T> {
+    /// Create a new Mutex
+    pub fn new(data: T, _name: &'static str) -> Self {
+        let lock = bindings::mutex::default();
+        // TODO: write mutex debug traces like .magic.
+        // TODO: use name in the debug version
+
+        Self {
+            data: UnsafeCell::new(data),
+            lock,
+        }
+    }
+}
+
+impl<T: ?Sized> Mutex<T> {
+    /// acquire a lock on the mutex
+    /// # unsafe
+    /// This is unsafe, as it returns a second lock if one is already help by the current process
+    // with CONFIG_DEBUG_LOCK_ALLOW mutex_lock is a macro, which calls mutex_lock_nested(&mutex, 0)
+    #[cfg(CONFIG_DEBUG_LOCK_ALLOC)]
+    pub unsafe fn lock<'a>(&'a self) -> MutexGuard<'a, T> {
+        unsafe {
+            bindings::mutex_lock_nested(
+                &self.lock as *const bindings::mutex as *mut bindings::mutex,
+                0,
+            );
+        }
+        MutexGuard { inner: &self }
+    }
+
+    /// acquire a lock on the mutex
+    /// # unsafe
+    /// This is unsafe, as it returns a second lock if one is already help by the current process
+    #[cfg(not(CONFIG_DEBUG_LOCK_ALLOC))]
+    pub unsafe fn lock<'a>(&'a self) -> MutexGuard<'a, T> {
+        unsafe {
+            bindings::mutex_lock(&self.lock as *const bindings::mutex as *mut bindings::mutex);
+        }
+        MutexGuard { inner: &self }
+    }
+
+    /// try to acquire the lock, returns none on failure
+    /// # unsafe
+    /// This is unsafe, as it returns a second lock if one is already help by the current process
+    pub unsafe fn trylock<'a>(&'a self) -> Option<MutexGuard<'a, T>> {
+        let ret = unsafe {
+            bindings::mutex_trylock(&self.lock as *const bindings::mutex as *mut bindings::mutex)
+        };
+        if ret == 1 {
+            Some(MutexGuard { inner: &self })
+        } else {
+            None
+        }
+    }
+
+    /// test if the mutex is locked
+    pub fn is_locked(&self) -> bool {
+        unsafe {
+            bindings::mutex_is_locked(&self.lock as *const bindings::mutex as *mut bindings::mutex)
+        }
+    }
+
+    fn unlock(&self) {
+        unsafe {
+            bindings::mutex_unlock(&self.lock as *const bindings::mutex as *mut bindings::mutex);
+        }
+    }
+}
+
+unsafe impl<T: ?Sized> Send for Mutex<T> {}
+unsafe impl<T: ?Sized + Send> Sync for Mutex<T> {}
+
+impl<T: ?Sized + fmt::Debug> fmt::Debug for Mutex<T> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        // kindly borrowed from std::sync::Mutex
+        match unsafe { self.trylock() } {
+            Some(guard) => f.debug_struct("Mutex").field("data", &guard).finish(),
+            None => {
+                struct LockedPlaceholder;
+                impl fmt::Debug for LockedPlaceholder {
+                    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+                        f.write_str("<locked>")
+                    }
+                }
+
+                f.debug_struct("Mutex")
+                    .field("data", &LockedPlaceholder)
+                    .finish()
+            }
+        }
+    }
+}
+
+#[must_use]
+pub struct MutexGuard<'a, T: ?Sized> {
+    inner: &'a Mutex<T>,
+}
+
+impl<'a, T: ?Sized> !Send for MutexGuard<'a, T> {}
+unsafe impl<'a, T: ?Sized> Sync for MutexGuard<'a, T> {}
+
+impl<'a, T: ?Sized> Deref for MutexGuard<'a, T> {
+    type Target = T;
+
+    fn deref(&self) -> &Self::Target {
+        unsafe { &*self.inner.data.get() }
+    }
+}
+
+impl<'a, T: ?Sized> DerefMut for MutexGuard<'a, T> {
+    fn deref_mut(&mut self) -> &mut Self::Target {
+        unsafe { &mut *self.inner.data.get() }
+    }
+}
+
+impl<'a, T: ?Sized + fmt::Debug> fmt::Debug for MutexGuard<'a, T> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        fmt::Debug::fmt(self.deref(), f)
+    }
+}
+
+impl<'a, T: ?Sized + fmt::Display> fmt::Display for MutexGuard<'a, T> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        fmt::Display::fmt(self.deref(), f)
+    }
+}
+
+impl<'a, T: ?Sized> Drop for MutexGuard<'a, T> {
+    fn drop(&mut self) {
+        self.inner.unlock();
+    }
+}