[PATCH v19 8/8] rust: page: add `from_raw()`

[Andreas Hindborg <a.hindborg@kernel.org>]

From: Andreas Hindborg <a.hindborg@samsung.com>

Add a method to `Page` that allows construction of an instance from `struct
page` pointer.

Signed-off-by: Andreas Hindborg <a.hindborg@samsung.com>
Reviewed-by: Onur Özkan <work@onurozkan.dev>
---
 rust/kernel/page.rs | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/rust/kernel/page.rs b/rust/kernel/page.rs
index 6dc1c2395acaf..c88fda09ead5a 100644
--- a/rust/kernel/page.rs
+++ b/rust/kernel/page.rs
@@ -143,6 +143,20 @@ pub fn nid(&self) -> i32 {
         unsafe { bindings::page_to_nid(self.as_ptr()) }
     }
 
+    /// Create a `&Page` from a raw `struct page` pointer.
+    ///
+    /// # Safety
+    ///
+    /// `ptr` must be convertible to a shared reference with a lifetime of `'a`.
+    #[inline]
+    pub unsafe fn from_raw<'a>(ptr: *const bindings::page) -> &'a Self {
+        // INVARIANT: By the function safety requirements, `ptr` refers to a valid `struct page`, so
+        // the returned reference upholds the type invariant of `Page`.
+        // SAFETY: By function safety requirements, `ptr` is not null and is convertible to a shared
+        // reference.
+        unsafe { &*ptr.cast() }
+    }
+
     /// Runs a piece of code with this page mapped to an address.
     ///
     /// The page is unmapped when this call returns.

-- 
2.51.2