rust: alloc: Add realloc and alloc_zeroed to the GlobalAlloc impl

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: Rust-for-Linux#68
Signed-off-by: Björn Roy Baron <bjorn3_gh@protonmail.com>

Author: bjorn3

rust/kernel/allocator.rs

@@ -21,6 +21,26 @@ unsafe impl GlobalAlloc for KernelAllocator {
             bindings::kfree(ptr as *const core::ffi::c_void);
         }
     }
+
+    unsafe fn realloc(&self, ptr: *mut u8, _layout: Layout, new_size: usize) -> *mut u8 {
+        unsafe {
+            bindings::krealloc(
+                ptr as *const core::ffi::c_void,
+                new_size,
+                bindings::GFP_KERNEL,
+            ) as *mut u8
+        }
+    }
+
+    unsafe fn alloc_zeroed(&self, layout: Layout) -> *mut u8 {
+        unsafe {
+            bindings::krealloc(
+                core::ptr::null(),
+                layout.size(),
+                bindings::GFP_KERNEL | bindings::__GFP_ZERO,
+            ) as *mut u8
+        }
+    }
 }
 
 #[global_allocator]