[PATCH 3/3] rust: alloc: Add realloc and alloc_zeroed to the GlobalAlloc impl

[Boqun Feng]

From: Björn Roy Baron <bjorn3_gh@xxxxxxxxxxxxxx>

While there are default impls for these methods, using the respective C
api's is faster. Currently neither the existing nor these new
GlobalAlloc method implementations are actually called. Instead the
__rust_* function defined below the GlobalAlloc impl are used. With
rustc 1.71 these functions will be gone and all allocation calls will go
through the GlobalAlloc implementation.

Link: https://github.com/Rust-for-Linux/linux/issues/68
Signed-off-by: Björn Roy Baron <bjorn3_gh@xxxxxxxxxxxxxx>
[boqun: add size adjustment for alignment requirement]
Signed-off-by: Boqun Feng <boqun.feng@xxxxxxxxx>
---
 rust/kernel/allocator.rs | 27 +++++++++++++++++++++++++++
 1 file changed, 27 insertions(+)

diff --git a/rust/kernel/allocator.rs b/rust/kernel/allocator.rs
index 1aec688cf0e0..6f1f50465ab3 100644
--- a/rust/kernel/allocator.rs
+++ b/rust/kernel/allocator.rs
@@ -51,6 +51,33 @@ unsafe fn dealloc(&self, ptr: *mut u8, _layout: Layout) {
             bindings::kfree(ptr as *const core::ffi::c_void);
         }
     }
+
+    unsafe fn realloc(&self, ptr: *mut u8, layout: Layout, new_size: usize) -> *mut u8 {
+        // SAFETY:
+        // - `new_size`, when rounded up to the nearest multiple of `layout.align()`, will not
+        //   overflow `isize` by the function safety requirement.
+        // - `layout.align()` is a proper alignment (i.e. not zero and must be a power of two).
+        let layout = unsafe { Layout::from_size_align_unchecked(new_size, layout.align()) };
+
+        // SAFETY:
+        // - `ptr` is either null or a pointer allocated by this allocator by the function safety
+        //   requirement.
+        // - the size of `layout` is not zero because `new_size` is not zero by the function safety
+        //   requirement.
+        unsafe { krealloc_aligned(ptr, layout, bindings::GFP_KERNEL) }
+    }
+
+    unsafe fn alloc_zeroed(&self, layout: Layout) -> *mut u8 {
+        // SAFETY: `ptr::null_mut()` is null and `layout` has a non-zero size by the function safety
+        // requirement.
+        unsafe {
+            krealloc_aligned(
+                ptr::null_mut(),
+                layout,
+                bindings::GFP_KERNEL | bindings::__GFP_ZERO,
+            )
+        }
+    }
 }
 
 #[global_allocator]
-- 
2.41.0