uefi: add MemoryMap::raw() and MemoryMap::raw_mut()

There are scenarios where users need the raw memory map. For example,
but not limited to, bootloaders that want to embed the EFI memory map in a
Multiboot2 boot information structure.

Author: phip1611

uefi/CHANGELOG.md

@@ -11,6 +11,7 @@
 - Added `table::{set_system_table, system_table_boot, system_table_runtime}`.
   This provides an initial API for global tables that do not require passing
   around a reference.
+- `MemoryMap::raw` and `MemoryMap::raw_mut` 
 
 ## Changed
 - `SystemTable::exit_boot_services` is now `unsafe`. See that method's

uefi/src/table/boot.rs

@@ -1801,6 +1801,43 @@ impl<'buf> MemoryMap<'buf> {
 
         Some(desc)
     }
+
+    /// Returns a reference to the underlying buffer, which is the raw UEFI
+    /// memory map, and the corresponding properties.
+    #[must_use]
+    pub fn raw(
+        &'buf self,
+    ) -> (
+        &'buf [u8],
+        usize, /* desc_size */
+        u32,   /* version */
+    ) {
+        (
+            &self.buf[0..self.map_size],
+            self.desc_size,
+            MemoryDescriptor::VERSION,
+        )
+    }
+
+    /// Mutable version of [`Self::raw`].
+    ///
+    /// # Safety
+    /// Unsafe because changes to the memory map may break it, causing this
+    /// abstraction to produce erroneous behavior.
+    #[must_use]
+    pub unsafe fn raw_mut(
+        &'buf mut self,
+    ) -> (
+        &'buf mut [u8],
+        usize, /* desc_size */
+        u32,   /* version */
+    ) {
+        (
+            &mut self.buf[0..self.map_size],
+            self.desc_size,
+            MemoryDescriptor::VERSION,
+        )
+    }
 }
 
 impl core::ops::Index<usize> for MemoryMap<'_> {