rust/faux: Add missing parent argument to Registration::new()

A little late in the review of the faux device interface, we added the
ability to specify a parent device when creating new faux devices - but
this never got ported over to the rust bindings. So, let's add the missing
argument now so we don't have to convert other users later down the line.

Signed-off-by: Lyude Paul <lyude@redhat.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Link: https://lore.kernel.org/r/20250227193522.198344-1-lyude@redhat.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Author: Lyude

rust/kernel/faux.rs

@@ -23,11 +23,20 @@ pub struct Registration(NonNull<bindings::faux_device>);
 
 impl Registration {
     /// Create and register a new faux device with the given name.
-    pub fn new(name: &CStr) -> Result<Self> {
+    pub fn new(name: &CStr, parent: Option<&device::Device>) -> Result<Self> {
         // SAFETY:
         // - `name` is copied by this function into its own storage
         // - `faux_ops` is safe to leave NULL according to the C API
-        let dev = unsafe { bindings::faux_device_create(name.as_char_ptr(), null_mut(), null()) };
+        // - `parent` can be either NULL or a pointer to a `struct device`, and `faux_device_create`
+        //   will take a reference to `parent` using `device_add` - ensuring that it remains valid
+        //   for the lifetime of the faux device.
+        let dev = unsafe {
+            bindings::faux_device_create(
+                name.as_char_ptr(),
+                parent.map_or(null_mut(), |p| p.as_raw()),
+                null(),
+            )
+        };
 
         // The above function will return either a valid device, or NULL on failure
         // INVARIANT: The device will remain registered until faux_device_destroy() is called, which

samples/rust/rust_driver_faux.rs

@@ -20,7 +20,7 @@ impl Module for SampleModule {
     fn init(_module: &'static ThisModule) -> Result<Self> {
         pr_info!("Initialising Rust Faux Device Sample\n");
 
-        let reg = faux::Registration::new(c_str!("rust-faux-sample-device"))?;
+        let reg = faux::Registration::new(c_str!("rust-faux-sample-device"), None)?;
 
         dev_info!(reg.as_ref(), "Hello from faux device!\n");