atomic_bitmap: support enlarging the bitmap

This patch adds the support the enlarge the atomic bitmap.
Some use cases in cloud-Hypervisor needs to enlarge the bitmap
on-demand.

Signed-off-by: Muminul Islam <[email protected]>

Author: russell-islam

src/bitmap/backend/atomic_bitmap.rs

@@ -37,6 +37,15 @@ impl AtomicBitmap {
         }
     }
 
+    /// Enlarge the vector with additionsl byte size, with one bit per page
+    /// Reserve the existing bits and filling out the new space with default.
+    pub fn enlarge(&mut self, additional_size: usize) {
+        let num_pages = additional_size.div_ceil(self.page_size.get());
+        self.size += num_pages;
+        let map_size = self.size.div_ceil(u64::BITS as usize);
+        self.map.resize_with(map_size, Default::default);
+    }
+
     /// Is bit `n` set? Bits outside the range of the bitmap are always unset.
     pub fn is_bit_set(&self, index: usize) -> bool {
         if index < self.size {