[PATCH] rust: misc: add OWNER field to the `MiscDevice` trait

[Alexandru Radovici <alexandru.radovici@wyliodrin.com>]

Add `OWNER` constant to the `MiscDevice` trait to allow modules
to prevent unloading while the device is in use.

Set the `OWNER` field in the `rust_misc_device` example.

Signed-off-by: Alexandru Radovici <alexandru.radovici@wyliodrin.com>
---
This patch exposes the `owner` field of `file_operations` to the
Rust API `MiscDevice` trait. It allows users to prevent the
unloading of their loadable modules written in Rust
while their `MiscDevice` is still in use.

Without this ability, writing a misc loadable module and running
the following commands will Oops the kernel.

   # insmod misc_module.ko
   # sleep 10 > /dev/misc_device
   # rmmod misc_module

   ... after the sleep, the kernel Oops

I added the `OWNER` field to the `rust_misc_device` example.
---
 rust/kernel/miscdevice.rs        | 13 ++++++++++++-
 samples/rust/rust_misc_device.rs |  4 ++++
 2 files changed, 16 insertions(+), 1 deletion(-)

diff --git a/rust/kernel/miscdevice.rs b/rust/kernel/miscdevice.rs
index 83ce50def5ac..21c5d88c5dc4 100644
--- a/rust/kernel/miscdevice.rs
+++ b/rust/kernel/miscdevice.rs
@@ -31,7 +31,7 @@
         Opaque, //
     },
 };
-use core::marker::PhantomData;
+use core::{marker::PhantomData, ptr};
 
 /// Options for creating a misc device.
 #[derive(Copy, Clone)]
@@ -126,6 +126,12 @@ pub trait MiscDevice: Sized {
     /// What kind of pointer should `Self` be wrapped in.
     type Ptr: ForeignOwnable + Send + Sync;
 
+    /// Set the owner of this `MiscDevice` instance.
+    ///
+    /// In case this is compiled as a module, setting this prevents
+    /// the module unloading while the device is still in use.
+    const OWNER: Option<&'static ThisModule> = None;
+
     /// Called when the misc device is opened.
     ///
     /// The returned pointer will be stored as the private data for the file.
@@ -430,6 +436,11 @@ impl<T: MiscDevice> MiscdeviceVTable<T> {
         } else {
             None
         },
+        #[cfg(CONFIG_MODULES)]
+        owner: match T::OWNER {
+            Some(module) => module.as_ptr(),
+            None => ptr::null_mut(),
+        },
         ..pin_init::zeroed()
     };
 
diff --git a/samples/rust/rust_misc_device.rs b/samples/rust/rust_misc_device.rs
index 41e26c825060..bf8801ea3cb2 100644
--- a/samples/rust/rust_misc_device.rs
+++ b/samples/rust/rust_misc_device.rs
@@ -177,6 +177,10 @@ struct RustMiscDevice {
 impl MiscDevice for RustMiscDevice {
     type Ptr = Pin<KBox<Self>>;
 
+    // Set the OWNER constant to the current module to prevent the unloading
+    // of this module while this device is in use.
+    const OWNER: Option<&'static ThisModule> = Some(&crate::THIS_MODULE);
+
     fn open(_file: &File, misc: &MiscDeviceRegistration<Self>) -> Result<Pin<KBox<Self>>> {
         let dev = ARef::from(misc.device());
 

---
base-commit: c21bb4193868a8de71fc4693fa741e195fdf5d86
change-id: 20260805-rust_tmp-095994661956

Best regards,
-- 
Alexandru Radovici <alexandru.radovici@wyliodrin.com>