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;
 	};
 
 }

kernel/kernel/Memory/FileBackedRegion.cpp

@@ -9,9 +9,6 @@ namespace Kernel
 	{
 		ASSERT(inode->mode().ifreg());
 
-		if (type != Type::PRIVATE)
-			return BAN::Error::from_errno(ENOTSUP);
-
 		if (offset < 0 || offset % PAGE_SIZE || size == 0)
 			return BAN::Error::from_errno(EINVAL);
 		if (size > (size_t)inode->size() || (size_t)offset > (size_t)inode->size() - size)
@@ -24,6 +21,21 @@ namespace Kernel
 
 		TRY(region->initialize(address_range));
 
+		if (type == Type::SHARED)
+		{
+			LockGuard _(inode->m_lock);
+			if (inode->m_shared_region.valid())
+				region->m_shared_data = inode->m_shared_region.lock();
+			else
+			{
+				auto shared_data = TRY(BAN::RefPtr<SharedFileData>::create());
+				TRY(shared_data->pages.resize(BAN::Math::div_round_up<size_t>(inode->size(), PAGE_SIZE)));
+				shared_data->inode = inode;
+				inode->m_shared_region = TRY(shared_data->get_weak_ptr());
+				region->m_shared_data = BAN::move(shared_data);
+			}
+		}
+
 		return region;
 	}
 
@@ -39,7 +51,8 @@ namespace Kernel
 		if (m_vaddr == 0)
 			return;
 
-		ASSERT(m_type == Type::PRIVATE);
+		if (m_type == Type::SHARED)
+			return;
 
 		size_t needed_pages = BAN::Math::div_round_up<size_t>(m_size, PAGE_SIZE);
 		for (size_t i = 0; i < needed_pages; i++)
@@ -50,10 +63,30 @@ namespace Kernel
 		}
 	}
 
+	SharedFileData::~SharedFileData()
+	{
+		for (size_t i = 0; i < pages.size(); i++)
+		{
+			if (pages[i] == 0)
+				continue;
+			
+			{
+				auto& page_table = PageTable::current();
+				LockGuard _(page_table);
+				ASSERT(page_table.is_page_free(0));
+
+				page_table.map_page_at(pages[i], 0, PageTable::Flags::Present);
+				memcpy(page_buffer, (void*)0, PAGE_SIZE);
+				page_table.unmap_page(0);
+			}
+
+			if (auto ret = inode->write(i * PAGE_SIZE, page_buffer, PAGE_SIZE); ret.is_error())
+				dwarnln("{}", ret.error());
+		}
+	}
+
 	BAN::ErrorOr<bool> FileBackedRegion::allocate_page_containing(vaddr_t address)
 	{
-		ASSERT(m_type == Type::PRIVATE);
-
 		ASSERT(contains(address));
 
 		// Check if address is already mapped
@@ -61,6 +94,8 @@ namespace Kernel
 		if (m_page_table.physical_address_of(vaddr) != 0)
 			return false;
 
+		if (m_type == Type::PRIVATE)
+		{
 			// Map new physcial page to address
 			paddr_t paddr = Heap::get().take_free_page();
 			if (paddr == 0)
@@ -77,13 +112,15 @@ namespace Kernel
 				read_ret = m_inode->read(file_offset, (void*)vaddr, bytes);
 			else
 			{
-			LockGuard _(PageTable::current());
-			ASSERT(PageTable::current().is_page_free(0));
+				auto& page_table = PageTable::current();
 
-			PageTable::current().map_page_at(paddr, 0, PageTable::Flags::ReadWrite | PageTable::Flags::Present);
+				LockGuard _(page_table);
+				ASSERT(page_table.is_page_free(0));
+
+				page_table.map_page_at(paddr, 0, PageTable::Flags::ReadWrite | PageTable::Flags::Present);
 				read_ret = m_inode->read(file_offset, (void*)0, bytes);
 				memset((void*)0, 0x00, PAGE_SIZE);
-			PageTable::current().unmap_page(0);
+				page_table.unmap_page(0);
 			}
 
 			if (read_ret.is_error())
@@ -100,6 +137,47 @@ namespace Kernel
 				m_page_table.unmap_page(vaddr);
 				return BAN::Error::from_errno(EIO);
 			}
+		}
+		else if	(m_type == Type::SHARED)
+		{
+			LockGuard _(m_inode->m_lock);
+			ASSERT(m_inode->m_shared_region.valid());
+			ASSERT(m_shared_data->pages.size() == BAN::Math::div_round_up<size_t>(m_inode->size(), PAGE_SIZE));
+
+			auto& pages = m_shared_data->pages;
+			size_t page_index = (vaddr - m_vaddr) / PAGE_SIZE;
+
+			if (pages[page_index] == 0)
+			{
+				pages[page_index] = Heap::get().take_free_page();
+				if (pages[page_index] == 0)
+					return BAN::Error::from_errno(ENOMEM);
+
+				size_t offset = vaddr - m_vaddr;
+				size_t bytes = BAN::Math::min<size_t>(m_size - offset, PAGE_SIZE);
+
+				TRY(m_inode->read(offset, m_shared_data->page_buffer, bytes));
+
+				auto& page_table = PageTable::current();
+
+				// TODO: check if this can cause deadlock?
+				LockGuard page_table_lock(page_table);
+				ASSERT(page_table.is_page_free(0));
+
+				page_table.map_page_at(pages[page_index], 0, PageTable::Flags::ReadWrite | PageTable::Flags::Present);
+				memcpy((void*)0, m_shared_data->page_buffer, PAGE_SIZE);
+				page_table.unmap_page(0);
+			}
+
+			paddr_t paddr = pages[page_index];
+			ASSERT(paddr);
+
+			m_page_table.map_page_at(paddr, vaddr, m_flags);
+		}
+		else
+		{
+			ASSERT_NOT_REACHED();
+		}
 
 		return true;
 	}

kernel/kernel/Process.cpp

@@ -863,7 +863,7 @@ namespace Kernel
 			if (!(inode_flags & O_RDONLY))
 				return BAN::Error::from_errno(EACCES);
 			if (region_type == MemoryRegion::Type::SHARED)
-				if (!(args->prot & PROT_WRITE) || !(inode_flags & O_WRONLY))
+				if ((args->prot & PROT_WRITE) && !(inode_flags & O_WRONLY))
 					return BAN::Error::from_errno(EACCES);
 			
 			auto region = TRY(FileBackedRegion::create(