Allow applying devicetree overlays from Rust.

The overlay is removed on Drop.

Signed-off-by: Ayush Singh <ayush@beagleboard.org>
---
 rust/kernel/of.rs | 34 ++++++++++++++++++++++++++++++++++
 1 file changed, 34 insertions(+)

diff --git a/rust/kernel/of.rs b/rust/kernel/of.rs
index 74d42dce06f0e9f67a0e5bd1287117b4966d4af9..646148cc959fd5414271f9cf9023ef5d77a2ac2c 100644
--- a/rust/kernel/of.rs
+++ b/rust/kernel/of.rs
@@ -75,3 +75,37 @@ pub fn as_raw(&self) -> *mut bindings::device_node {
         self.0.get()
     }
 }
+
+/// Devicetree overlay present in livetree.
+///
+/// The overlay is removed on Drop
+pub struct OvcsId(kernel::ffi::c_int);
+
+impl OvcsId {
+    /// Create and apply an overlay changeset to the live tree.
+    pub fn of_overlay_fdt_apply(overlay: &[u8], base: &DeviceNode) -> Result<Self> {
+        let mut ovcs_id: kernel::ffi::c_int = 0;
+
+        // Ensure that overlay length fits in u32
+        let Ok(overlay_len) = overlay.len().try_into() else {
+            return Err(crate::error::code::E2BIG);
+        };
+
+        crate::error::to_result(unsafe {
+            bindings::of_overlay_fdt_apply(
+                overlay.as_ptr().cast(),
+                overlay_len,
+                &mut ovcs_id,
+                base.as_raw(),
+            )
+        })?;
+
+        Ok(Self(ovcs_id))
+    }
+}
+
+impl Drop for OvcsId {
+    fn drop(&mut self) {
+        unsafe { bindings::of_overlay_remove(&mut self.0) };
+    }
+}

-- 
2.50.1

Hi Ayush,

kernel test robot noticed the following build errors:

[auto build test ERROR on 931e46dcbc7e6035a90e9c4a27a84b660e083f0a]

url:    https://github.com/intel-lab-lkp/linux/commits/Ayush-Singh/rust-kernel-of-Add-DeviceNode-abstraction/20250816-140122
base:   931e46dcbc7e6035a90e9c4a27a84b660e083f0a
patch link:    https://lore.kernel.org/r/20250816-rust-overlay-abs-v2-2-48a2c8921df2%40beagleboard.org
patch subject: [PATCH v2 2/2] rust: kernel: of: Add overlay id abstraction
config: x86_64-rhel-9.4-rust (https://download.01.org/0day-ci/archive/20250817/202508171342.vNfvpebZ-lkp@intel.com/config)
compiler: clang version 20.1.8 (https://github.com/llvm/llvm-project 87f0227cb60147a26a1eeb4fb06e3b505e9c7261)
rustc: rustc 1.88.0 (6b00bc388 2025-06-23)
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20250817/202508171342.vNfvpebZ-lkp@intel.com/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202508171342.vNfvpebZ-lkp@intel.com/

All errors (new ones prefixed by >>):

>> error[E0425]: cannot find function `of_overlay_fdt_apply` in crate `bindings`
   --> rust/kernel/of.rs:95:23
   |
   95 |             bindings::of_overlay_fdt_apply(
   |                       ^^^^^^^^^^^^^^^^^^^^ not found in `bindings`
--
>> error[E0425]: cannot find function `of_overlay_remove` in crate `bindings`
   --> rust/kernel/of.rs:109:28
   |
   109 |         unsafe { bindings::of_overlay_remove(&mut self.0) };
   |                            ^^^^^^^^^^^^^^^^^ not found in `bindings`

-- 
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki