[PATCH v3 3/3] rust: miscdevice: Provide accessor to pull out miscdevice::this_device

[Alice Ryhl <aliceryhl@xxxxxxxxxx>]

From: Lee Jones <lee@xxxxxxxxxx>

There are situations where a pointer to a `struct device` will become
necessary (e.g. for calling into dev_*() functions).  This accessor
allows callers to pull this out from the `struct miscdevice`.

Signed-off-by: Lee Jones <lee@xxxxxxxxxx>
Signed-off-by: Alice Ryhl <aliceryhl@xxxxxxxxxx>
---
 rust/kernel/miscdevice.rs | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/rust/kernel/miscdevice.rs b/rust/kernel/miscdevice.rs
index 75a9d26c8001..20895e809607 100644
--- a/rust/kernel/miscdevice.rs
+++ b/rust/kernel/miscdevice.rs
@@ -10,6 +10,7 @@
 
 use crate::{
     bindings,
+    device::Device,
     error::{to_result, Error, Result, VTABLE_DEFAULT_ERROR},
     fs::File,
     prelude::*,
@@ -85,6 +86,16 @@ pub fn register(opts: MiscDeviceOptions) -> impl PinInit<Self, Error> {
     pub fn as_raw(&self) -> *mut bindings::miscdevice {
         self.inner.get()
     }
+
+    /// Access the `this_device` field.
+    pub fn device(&self) -> &Device {
+        // SAFETY: This can only be called after a successful register(), which always
+        // initialises `this_device` with a valid device. Furthermore, the signature of this
+        // function tells the borrow-checker that the `&Device` reference must not outlive the
+        // `&MiscDeviceRegistration<T>` used to obtain it, so the last use of the reference must be
+        // before the underlying `struct miscdevice` is destroyed.
+        unsafe { Device::as_ref((*self.as_raw()).this_device) }
+    }
 }
 
 #[pinned_drop]

-- 
2.47.1.613.gc27f4b7a9f-goog