[PATCH 4/8] rust: debugfs: Allow subdir creation in builder interface

[Matthew Maurer <mmaurer@google.com>]

Allows creating subdirectories in the builder intended to be cleaned up
by `debugfs_remove` at the same time as the root.

Signed-off-by: Matthew Maurer <mmaurer@google.com>
---
 rust/kernel/debugfs.rs | 26 ++++++++++++++++++++++++++
 1 file changed, 26 insertions(+)

diff --git a/rust/kernel/debugfs.rs b/rust/kernel/debugfs.rs
index f6240fd056f8598d5ef06bdaf61c5c33eab5b734..6c7cf7e97741b98d2c0654d01fca3de0d8047e97 100644
--- a/rust/kernel/debugfs.rs
+++ b/rust/kernel/debugfs.rs
@@ -347,6 +347,32 @@ pub fn display_file<T: Display + Sized>(&self, name: &CStr, data: &'a T) -> Resu
         core::mem::forget(unsafe { self.inner.display_file_raw(name, data)? });
         Ok(())
     }
+
+    /// Creates a nested directory that may live as long as its parent
+    ///
+    /// # Example
+    ///
+    /// ```
+    /// # use kernel::c_str;
+    /// # use kernel::debugfs::{Dir, Values};
+    /// let dir = Dir::new(c_str!("foo"), None)?;
+    /// let foo = KBox::pin_init(Values::attach(0, dir), GFP_KERNEL)?;
+    /// foo.as_ref().build(|_value, builder| {
+    ///   builder.dir(c_str!("bar"))?;
+    ///   Ok::<(), Error>(())
+    /// })?;
+    /// // foo/bar will still exist at this point in DebugFS
+    /// # Ok::<(), Error>(())
+    /// ```
+    pub fn dir(&self, name: &CStr) -> Result<Builder<'a>> {
+        let dir = Dir::new(name, Some(self))?;
+        // SAFETY: We're suppressing the drop of the ARef we received, so we know it will live
+        // until its parent is `debugfs_remove`'d. The lifetime of the parent is 'a, so we can
+        // convert it to a similarly lived reference.
+        let dir: &'a Dir = unsafe { ARef::into_raw(dir).as_ref() };
+        // SAFETY: Since 'a is a builder lifetime, we can propagate our invariants
+        Ok(unsafe { Builder::new(dir) })
+    }
 }
 
 impl<'a> Deref for Builder<'a> {

-- 
2.49.0.901.g37484f566f-goog