Kernel: Invalidate file-backed VMO's when inodes are written.

The current strategy is simply to nuke all physical pages and force
reload them from disk. This is obviously not optimal and should eventually
be optimized. It should be fairly straightforward.

Kernel/MemoryManager.cpp

@@ -492,10 +492,11 @@ void MemoryManager::remap_region_page(Region& region, unsigned page_index_in_reg
 #endif
 }
 
-void MemoryManager::remap_region(Process& process, Region& region)
+void MemoryManager::remap_region(PageDirectory& page_directory, Region& region)
 {
     InterruptDisabler disabler;
-    map_region_at_address(process.page_directory(), region, region.laddr(), true);
+    ASSERT(region.page_directory() == &page_directory);
+    map_region_at_address(page_directory, region, region.laddr(), true);
 }
 
 void MemoryManager::map_region_at_address(PageDirectory& page_directory, Region& region, LinearAddress laddr, bool user_allowed)
@@ -587,7 +588,7 @@ RetainPtr<Region> Region::clone()
     // 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);
-    MM.remap_region(*current, *this);
+    MM.remap_region(current->page_directory(), *this);
     return adopt(*new Region(laddr(), size(), m_vmo->clone(), m_offset_in_vmo, String(m_name), m_readable, m_writable, true));
 }
 
@@ -734,6 +735,91 @@ VMObject::~VMObject()
     MM.unregister_vmo(*this);
 }
 
+template<typename Callback>
+void VMObject::for_each_region(Callback callback)
+{
+    // FIXME: Figure out a better data structure so we don't have to walk every single region every time an inode changes.
+    //        Perhaps VMObject could have a Vector<Region*> with all of his mappers?
+    for (auto* region : MM.m_regions) {
+        if (&region->vmo() == this)
+            callback(*region);
+    }
+}
+
+void VMObject::inode_size_changed(Badge<Inode>, size_t old_size, size_t new_size)
+{
+    InterruptDisabler disabler;
+
+    size_t old_page_count = page_count();
+    m_size = new_size;
+
+    if (page_count() > old_page_count) {
+        // Add null pages and let the fault handler page these in when that day comes.
+        for (size_t i = old_page_count; i < page_count(); ++i)
+            m_physical_pages.append(nullptr);
+    } else {
+        // Prune the no-longer valid pages. I'm not sure this is actually correct behavior.
+        for (size_t i = page_count(); i < old_page_count; ++i)
+            m_physical_pages.take_last();
+    }
+
+    // FIXME: Consolidate with inode_contents_changed() so we only do a single walk.
+    for_each_region([] (Region& region) {
+        ASSERT(region.page_directory());
+        MM.remap_region(*region.page_directory(), region);
+    });
+}
+
+void VMObject::inode_contents_changed(Badge<Inode>, off_t offset, size_t size, const byte* data)
+{
+    InterruptDisabler disabler;
+    ASSERT(offset >= 0);
+
+    // FIXME: Only invalidate the parts that actually changed.
+    for (auto& physical_page : m_physical_pages)
+        physical_page = nullptr;
+
+#if 0
+    size_t current_offset = offset;
+    size_t remaining_bytes = size;
+    const byte* data_ptr = data;
+
+    auto to_page_index = [] (size_t offset) -> size_t {
+        return offset / PAGE_SIZE;
+    };
+
+    if (current_offset & PAGE_MASK) {
+        size_t page_index = to_page_index(current_offset);
+        size_t bytes_to_copy = min(size, PAGE_SIZE - (current_offset & PAGE_MASK));
+        if (m_physical_pages[page_index]) {
+            auto* ptr = MM.quickmap_page(*m_physical_pages[page_index]);
+            memcpy(ptr, data_ptr, bytes_to_copy);
+            MM.unquickmap_page();
+        }
+        current_offset += bytes_to_copy;
+        data += bytes_to_copy;
+        remaining_bytes -= bytes_to_copy;
+    }
+
+    for (size_t page_index = to_page_index(current_offset); page_index < m_physical_pages.size(); ++page_index) {
+        size_t bytes_to_copy = PAGE_SIZE - (current_offset & PAGE_MASK);
+        if (m_physical_pages[page_index]) {
+            auto* ptr = MM.quickmap_page(*m_physical_pages[page_index]);
+            memcpy(ptr, data_ptr, bytes_to_copy);
+            MM.unquickmap_page();
+        }
+        current_offset += bytes_to_copy;
+        data += bytes_to_copy;
+    }
+#endif
+
+    // FIXME: Consolidate with inode_size_changed() so we only do a single walk.
+    for_each_region([] (Region& region) {
+        ASSERT(region.page_directory());
+        MM.remap_region(*region.page_directory(), region);
+    });
+}
+
 int Region::commit()
 {
     InterruptDisabler disabler;