Kernel: Implement MAP_SHARED for regular files

Every inode holds a weak pointer to shared file data. This contains
physical addresses of pages for inode file data. Physical addresses
are allocated and read on demand.

When last shared mapping is unmapped. The inodes shared data is freed
and written to the inode.

kernel/include/kernel/FS/Inode.h

@@ -3,6 +3,7 @@
 #include <BAN/RefPtr.h>
 #include <BAN/String.h>
 #include <BAN/StringView.h>
+#include <BAN/WeakPtr.h>
 #include <BAN/Vector.h>
 
 #include <kernel/API/DirectoryEntry.h>
@@ -17,6 +18,9 @@ namespace Kernel
 
 	using namespace API;
 
+	class FileBackedRegion;
+	class SharedFileData;
+
 	class Inode : public BAN::RefCounted<Inode>
 	{
 	public:
@@ -112,6 +116,9 @@ namespace Kernel
 
 	private:
 		mutable RecursiveSpinLock m_lock;
+
+		BAN::WeakPtr<SharedFileData> m_shared_region;
+		friend class FileBackedRegion;
 	};
 
 }

kernel/include/kernel/Memory/FileBackedRegion.h

@@ -6,6 +6,17 @@
 namespace Kernel
 {
 
+	struct SharedFileData : public BAN::RefCounted<SharedFileData>, public BAN::Weakable<SharedFileData>
+	{
+		~SharedFileData();
+
+		// FIXME: this should probably be ordered tree like map
+		//        for fast lookup and less memory usage
+		BAN::Vector<paddr_t> pages;
+		BAN::RefPtr<Inode> inode;
+		uint8_t page_buffer[PAGE_SIZE];
+	};
+
 	class FileBackedRegion final : public MemoryRegion
 	{
 		BAN_NON_COPYABLE(FileBackedRegion);
@@ -25,6 +36,8 @@ namespace Kernel
 	private:
 		BAN::RefPtr<Inode> m_inode;
 		const off_t m_offset;
+
+		BAN::RefPtr<SharedFileData> m_shared_data;
 	};
 
 }