Kernel: Encapsulate the Region's COW map a bit better.

AK/Bitmap.h

@@ -45,15 +45,19 @@ public:
     byte* data() { return m_data; }
     const byte* data() const { return m_data; }
 
+    void fill(bool value)
+    {
+        memset(m_data, value ? 0xff : 0x00, size_in_bytes());
+    }
+
 private:
     explicit Bitmap(int size, bool default_value)
         : m_size(size)
         , m_owned(true)
     {
         ASSERT(m_size != 0);
-        int size_to_allocate = ceil_div(size, 8);
-        m_data = reinterpret_cast<byte*>(kmalloc(size_to_allocate));
-        memset(m_data, default_value ? 0xff : 0x00, size_to_allocate);
+        m_data = reinterpret_cast<byte*>(kmalloc(size_in_bytes()));
+        fill(default_value);
     }
 
     Bitmap(byte* data, int size)
@@ -63,6 +67,8 @@ private:
     {
     }
 
+    int size_in_bytes() const { return ceil_div(m_size, 8); }
+
     byte* m_data { nullptr };
     int m_size { 0 };
     bool m_owned { false };

Kernel/FileSystem/ProcFS.cpp

@@ -279,7 +279,7 @@ ByteBuffer procfs$pid_vmo(InodeIdentifier identifier)
             auto& physical_page = region->vmo().physical_pages()[i];
             builder.appendf("P%x%s(%u) ",
                 physical_page ? physical_page->paddr().get() : 0,
-                region->cow_map().get(i) ? "!" : "",
+                region->should_cow(i) ? "!" : "",
                 physical_page ? physical_page->retain_count() : 0
             );
         }

Kernel/VM/MemoryManager.cpp

@@ -264,7 +264,7 @@ bool MemoryManager::zero_page(Region& region, unsigned page_index_in_region)
 #ifdef PAGE_FAULT_DEBUG
     dbgprintf("      >> ZERO P%x\n", physical_page->paddr().get());
 #endif
-    region.m_cow_map.set(page_index_in_region, false);
+    region.set_should_cow(page_index_in_region, false);
     vmo.physical_pages()[page_index_in_region] = move(physical_page);
     remap_region_page(region, page_index_in_region, true);
     return true;
@@ -278,7 +278,7 @@ bool MemoryManager::copy_on_write(Region& region, unsigned page_index_in_region)
 #ifdef PAGE_FAULT_DEBUG
         dbgprintf("    >> It's a COW page but nobody is sharing it anymore. Remap r/w\n");
 #endif
-        region.m_cow_map.set(page_index_in_region, false);
+        region.set_should_cow(page_index_in_region, false);
         remap_region_page(region, page_index_in_region, true);
         return true;
     }
@@ -296,7 +296,7 @@ bool MemoryManager::copy_on_write(Region& region, unsigned page_index_in_region)
     memcpy(dest_ptr, src_ptr, PAGE_SIZE);
     vmo.physical_pages()[page_index_in_region] = move(physical_page);
     unquickmap_page();
-    region.m_cow_map.set(page_index_in_region, false);
+    region.set_should_cow(page_index_in_region, false);
     remap_region_page(region, page_index_in_region, true);
     return true;
 }
@@ -379,7 +379,7 @@ PageFaultResponse MemoryManager::handle_page_fault(const PageFault& fault)
             return PageFaultResponse::Continue;
         }
     } else if (fault.is_protection_violation()) {
-        if (region->m_cow_map.get(page_index_in_region)) {
+        if (region->should_cow(page_index_in_region)) {
 #ifdef PAGE_FAULT_DEBUG
             dbgprintf("PV(cow) fault in Region{%p}[%u]\n", region, page_index_in_region);
 #endif
@@ -534,7 +534,7 @@ void MemoryManager::remap_region_page(Region& region, unsigned page_index_in_reg
     ASSERT(physical_page);
     pte.set_physical_page_base(physical_page->paddr().get());
     pte.set_present(true); // FIXME: Maybe we should use the is_readable flag here?
-    if (region.m_cow_map.get(page_index_in_region))
+    if (region.should_cow(page_index_in_region))
         pte.set_writable(false);
     else
         pte.set_writable(region.is_writable());
@@ -570,7 +570,7 @@ void MemoryManager::map_region_at_address(PageDirectory& page_directory, Region&
             pte.set_physical_page_base(physical_page->paddr().get());
             pte.set_present(true); // FIXME: Maybe we should use the is_readable flag here?
             // FIXME: It seems wrong that the *region* cow map is essentially using *VMO* relative indices.
-            if (region.m_cow_map.get(region.first_page_index() + i))
+            if (region.should_cow(region.first_page_index() + i))
                 pte.set_writable(false);
             else
                 pte.set_writable(region.is_writable());

Kernel/VM/Region.cpp

@@ -94,8 +94,7 @@ Retained<Region> Region::clone()
               laddr().get());
 #endif
     // Set up a COW region. The parent (this) region becomes COW as well!
-    for (size_t i = 0; i < page_count(); ++i)
-        m_cow_map.set(i, true);
+    m_cow_map.fill(true);
     MM.remap_region(current->process().page_directory(), *this);
     return adopt(*new Region(laddr(), size(), m_vmo->clone(), m_offset_in_vmo, String(m_name), m_readable, m_writable, true));
 }

Kernel/VM/Region.h

@@ -75,7 +75,8 @@ public:
         m_page_directory.clear();
     }
 
-    const Bitmap& cow_map() const { return m_cow_map; }
+    bool should_cow(size_t page_index) const { return m_cow_map.get(page_index); }
+    void set_should_cow(size_t page_index, bool cow) { m_cow_map.set(page_index, cow); }
 
     void set_writable(bool b) { m_writable = b; }