[PATCH 3/5] rust: serdev: Simplify callbacks

[Markus Probst <markus.probst@posteo.de>]

Initialize the driver's private data directly on `PrivateData`.

Introduce `OpenGuard` for resource cleanup.

Signed-off-by: Markus Probst <markus.probst@posteo.de>
---
 rust/kernel/serdev.rs | 130 ++++++++++++++++++++------------------------------
 1 file changed, 51 insertions(+), 79 deletions(-)

diff --git a/rust/kernel/serdev.rs b/rust/kernel/serdev.rs
index c16d6593a8d2..66543108ec2f 100644
--- a/rust/kernel/serdev.rs
+++ b/rust/kernel/serdev.rs
@@ -17,16 +17,12 @@
     prelude::*,
     sync::aref::AlwaysRefCounted,
     time::Jiffies,
-    types::{
-        Opaque,
-        ScopeGuard, //
-    }, //
+    types::Opaque, //
 };
 
 use core::{
-    cell::UnsafeCell,
     marker::PhantomData,
-    mem::{offset_of, MaybeUninit},
+    mem::offset_of,
     ptr::NonNull, //
 };
 
@@ -92,24 +88,35 @@ unsafe fn unregister(sdrv: &Opaque<Self::DriverType>) {
     }
 }
 
+struct OpenGuard<'bound> {
+    sdev: &'bound Device<device::Bound>,
+}
+
+impl Drop for OpenGuard<'_> {
+    fn drop(&mut self) {
+        // SAFETY:
+        // - `self.sdev.as_raw()` is guaranteed to be a pointer to a valid
+        //   `struct serdev_device`.
+        // - The existence of self proves that the device is open.
+        unsafe { bindings::serdev_device_close(self.sdev.as_raw()) };
+    }
+}
+
 #[doc(hidden)]
-#[pin_data(PinnedDrop)]
+#[pin_data]
 pub struct PrivateData<'bound, T: Driver> {
-    sdev: &'bound Device<device::Bound>,
     #[pin]
-    driver: UnsafeCell<MaybeUninit<T::Data<'bound>>>,
-    open: UnsafeCell<bool>,
+    driver: T::Data<'bound>,
+    open: OpenGuard<'bound>,
 }
 
-#[pinned_drop]
-impl<T: Driver> PinnedDrop for PrivateData<'_, T> {
-    fn drop(self: Pin<&mut Self>) {
-        // SAFETY: We have exclusive access to `self.open`.
-        if unsafe { *self.open.get() } {
-            // SAFETY: `self.sdev.as_raw()` is guaranteed to be a pointer to a valid
-            // `struct serdev_device`.
-            unsafe { bindings::serdev_device_close(self.sdev.as_raw()) };
-        }
+impl<'bound, T: Driver> PrivateData<'bound, T> {
+    fn driver_data(self: Pin<&Self>) -> Pin<&T::Data<'bound>> {
+        // SAFETY: We treat the result as pinned.
+        let inner = unsafe { Pin::into_inner_unchecked(self) };
+
+        // SAFETY: `self.driver` is pinned.
+        unsafe { Pin::new_unchecked(&inner.driver) }
     }
 }
 
@@ -134,46 +141,30 @@ extern "C" fn probe_callback(sdev: *mut bindings::serdev_device) -> kernel::ffi:
 
         from_result(|| {
             sdev.as_ref().set_drvdata(try_pin_init!(PrivateData::<T> {
-                sdev: &**sdev,
-                driver: MaybeUninit::<T::Data<'_>>::zeroed().into(),
-                open: false.into(),
+                open: {
+                    // SAFETY:
+                    // - `sdev.as_raw()` is guaranteed to be a valid pointer to
+                    //   `serdev_device`.
+                    // - It is safe to call before open.
+                    unsafe { bindings::serdev_device_set_client_ops(sdev.as_raw(), Self::OPS) };
+
+                    // SAFETY: `sdev.as_raw()` is guaranteed to be a valid pointer to
+                    // `serdev_device`.
+                    unsafe { bindings::serdev_device_pause_rx(sdev.as_raw()) };
+
+                    // SAFETY: `sdev.as_raw()` is guaranteed to be a valid pointer to
+                    // `serdev_device`.
+                    to_result(unsafe { bindings::serdev_device_open(sdev.as_raw()) })?;
+
+                    OpenGuard { sdev }
+                },
+                driver <- T::probe(sdev, info),
             }))?;
-            // SAFETY: We just set drvdata to `PrivateData<'_, T>`.
-            let private_data = unsafe { sdev.as_ref().drvdata_borrow::<PrivateData<'_, T>>() };
-            let private_data = ScopeGuard::new_with_data(private_data, |_| {
-                // SAFETY: We just set drvdata to `PrivateData<'_, T>`.
-                drop(unsafe { sdev.as_ref().drvdata_obtain::<PrivateData<'_, T>>() });
-            });
-            // SAFETY: `sdev.as_raw()` is guaranteed to be a valid pointer to `serdev_device`.
-            unsafe { bindings::serdev_device_set_client_ops(sdev.as_raw(), Self::OPS) };
 
             // SAFETY: `sdev.as_raw()` is guaranteed to be a valid pointer to `serdev_device`.
-            unsafe { bindings::serdev_device_pause_rx(sdev.as_raw()) };
-
-            // SAFETY: The serial device bus only ever calls the probe callback with a valid pointer
-            // to a `serdev_device`.
-            to_result(unsafe { bindings::serdev_device_open(sdev.as_raw()) })?;
-
-            // SAFETY: We have exclusive access to `private_data.open`.
-            unsafe { *private_data.open.get() = true };
-
-            let data = T::probe(sdev, info);
+            unsafe { bindings::serdev_device_resume_rx(sdev.as_raw()) };
 
-            // SAFETY: We have exclusive access to `private_data.driver`.
-            let driver = unsafe { &mut *private_data.driver.get() };
-            // SAFETY:
-            // - `driver.as_mut_ptr()` is a valid pointer to uninitialized data.
-            // - `private_data.driver` is pinned.
-            let result = unsafe { pin_init::raw_try_init(driver.as_mut_ptr(), data) };
-
-            result.map(|()| {
-                private_data.dismiss();
-
-                // SAFETY: `sdev.as_raw()` is guaranteed to be a valid pointer to `serdev_device`.
-                unsafe { bindings::serdev_device_resume_rx(sdev.as_raw()) };
-
-                0
-            })
+            Ok(0)
         })
     }
 
@@ -189,21 +180,10 @@ extern "C" fn remove_callback(sdev: *mut bindings::serdev_device) {
         // and stored a `Pin<KBox<PrivateData<'_, T>>>`.
         let private_data = unsafe { sdev.as_ref().drvdata_borrow::<PrivateData<'_, T>>() };
 
-        // SAFETY: No one has exclusive access to `private_data.driver`.
-        let data = unsafe { &*private_data.driver.get() };
-        // SAFETY:
-        // - `private_data.driver` is pinned.
-        // - `remove_callback` is only ever called after a successful call to `probe_callback`,
-        //   hence it's guaranteed that `private_data.driver` was initialized.
-        let data_pinned = unsafe { Pin::new_unchecked(data.assume_init_ref()) };
-
-        T::unbind(sdev, data_pinned);
+        T::unbind(sdev, private_data.driver_data());
 
         // SAFETY: `sdev.as_raw()` is guaranteed to be a valid pointer to `serdev_device`.
         unsafe { bindings::serdev_device_pause_rx(sdev.as_raw()) };
-
-        // SAFETY: We already established that `data` is guaranteed to be initialized.
-        unsafe { data.assume_init_drop() };
     }
 
     extern "C" fn receive_buf_callback(
@@ -211,6 +191,9 @@ extern "C" fn receive_buf_callback(
         buf: *const u8,
         length: usize,
     ) -> usize {
+        // SAFETY: `buf` is guaranteed to be non-null and has the size of `length`.
+        let buf = unsafe { core::slice::from_raw_parts(buf, length) };
+
         // SAFETY: The serial device bus only ever calls the receive buf callback with a valid
         // pointer to a `struct serdev_device`.
         //
@@ -222,18 +205,7 @@ extern "C" fn receive_buf_callback(
         // and stored a `Pin<KBox<PrivateData<'_, T>>>`.
         let private_data = unsafe { sdev.as_ref().drvdata_borrow::<PrivateData<'_, T>>() };
 
-        // SAFETY: No one has exclusive access to `private_data.driver`.
-        let data = unsafe { &*private_data.driver.get() };
-        // SAFETY:
-        // - `private_data.driver` is pinned.
-        // - `receive_buf_callback` is only ever called after a successful call to `probe_callback`,
-        //   hence it's guaranteed that `private_data.driver` was initialized.
-        let data_pinned = unsafe { Pin::new_unchecked(data.assume_init_ref()) };
-
-        // SAFETY: `buf` is guaranteed to be non-null and has the size of `length`.
-        let buf = unsafe { core::slice::from_raw_parts(buf, length) };
-
-        T::receive(sdev, data_pinned, buf)
+        T::receive(sdev, private_data.driver_data(), buf)
     }
 }
 

-- 
2.55.0