Kernel: add basic support for symlinks

kernel/include/kernel/FS/Ext2.h

@@ -141,10 +141,13 @@ namespace Kernel
 
 		virtual BAN::StringView name() const override { return m_name; }
 
-		virtual BAN::ErrorOr<size_t> read(size_t, void*, size_t) override;
+		virtual BAN::ErrorOr<BAN::String> link_target() override;
+		
 		virtual BAN::ErrorOr<BAN::Vector<BAN::String>> read_directory_entries(size_t) override;
 		virtual BAN::ErrorOr<BAN::RefPtr<Inode>> read_directory_inode(BAN::StringView) override;
 
+		virtual BAN::ErrorOr<size_t> read(size_t, void*, size_t) override;
+
 		virtual BAN::ErrorOr<void> create_file(BAN::StringView, mode_t) override;
 
 	private:

kernel/include/kernel/FS/Inode.h

@@ -78,6 +78,8 @@ namespace Kernel
 
 		virtual BAN::StringView name() const = 0;
 
+		virtual BAN::ErrorOr<BAN::String> link_target() { ASSERT_NOT_REACHED(); }
+
 		virtual BAN::ErrorOr<BAN::RefPtr<Inode>> read_directory_inode(BAN::StringView) { if (!mode().ifdir()) return BAN::Error::from_errno(ENOTDIR); ASSERT_NOT_REACHED(); }
 		virtual BAN::ErrorOr<BAN::Vector<BAN::String>> read_directory_entries(size_t)  { if (!mode().ifdir()) return BAN::Error::from_errno(ENOTDIR); ASSERT_NOT_REACHED(); }
 

kernel/include/kernel/FS/VirtualFileSystem.h

@@ -25,7 +25,7 @@ namespace Kernel
 			BAN::RefPtr<Inode> inode;
 			BAN::String canonical_path;
 		};
-		BAN::ErrorOr<File> file_from_absolute_path(BAN::StringView);
+		BAN::ErrorOr<File> file_from_absolute_path(BAN::StringView, bool follow_links);
 
 	private:
 		VirtualFileSystem() = default;
@@ -39,7 +39,7 @@ namespace Kernel
 		MountPoint* mount_from_root_inode(BAN::RefPtr<Inode>);
 
 	private:
-		SpinLock						m_lock;
+		RecursiveSpinLock				m_lock;
 		FileSystem*						m_root_fs = nullptr;
 		BAN::Vector<MountPoint>			m_mount_points;
 	};

kernel/kernel/FS/Ext2.cpp

@@ -247,6 +247,14 @@ namespace Kernel
 		ASSERT_NOT_REACHED();
 	}
 	
+	BAN::ErrorOr<BAN::String> Ext2Inode::link_target()
+	{
+		ASSERT(mode().iflnk());
+		if (m_inode.size < sizeof(m_inode.block))
+			return BAN::String((const char*)m_inode.block);
+		ASSERT_NOT_REACHED();
+	}
+
 	BAN::ErrorOr<size_t> Ext2Inode::read(size_t offset, void* buffer, size_t count)
 	{
 		// FIXME: update atime if needed

kernel/kernel/FS/VirtualFileSystem.cpp

@@ -40,7 +40,7 @@ namespace Kernel
 
 	BAN::ErrorOr<void> VirtualFileSystem::mount(BAN::StringView partition, BAN::StringView target)
 	{
-		auto partition_file = TRY(file_from_absolute_path(partition));
+		auto partition_file = TRY(file_from_absolute_path(partition, true));
 		if (partition_file.inode->inode_type() != Inode::InodeType::Device)
 			return BAN::Error::from_errno(ENOTBLK);
 
@@ -54,7 +54,7 @@ namespace Kernel
 
 	BAN::ErrorOr<void> VirtualFileSystem::mount(FileSystem* file_system, BAN::StringView path)
 	{
-		auto file = TRY(file_from_absolute_path(path));
+		auto file = TRY(file_from_absolute_path(path, true));
 		if (!file.inode->mode().ifdir())
 			return BAN::Error::from_errno(ENOTDIR);
 
@@ -82,7 +82,7 @@ namespace Kernel
 		return nullptr;
 	}
 
-	BAN::ErrorOr<VirtualFileSystem::File> VirtualFileSystem::file_from_absolute_path(BAN::StringView path)
+	BAN::ErrorOr<VirtualFileSystem::File> VirtualFileSystem::file_from_absolute_path(BAN::StringView path, bool follow_links)
 	{
 		LockGuard _(m_lock);
 
@@ -124,6 +124,28 @@ namespace Kernel
 
 				if (auto* mount_point = mount_from_host_inode(inode))
 					inode = mount_point->target->root_inode();
+
+				if (follow_links && inode->mode().iflnk())
+				{
+					auto target = TRY(inode->link_target());
+					if (target.empty())
+						return BAN::Error::from_errno(ENOENT);
+					if (target.front() == '/')
+					{
+						File file = TRY(file_from_absolute_path(target, follow_links));
+						inode = file.inode;
+						canonical_path = BAN::move(file.canonical_path);
+					}
+					else
+					{
+						while (canonical_path.back() != '/')
+							canonical_path.pop_back();
+						TRY(canonical_path.append(target));
+						File file = TRY(file_from_absolute_path(canonical_path, follow_links));
+						inode = file.inode;
+						canonical_path = BAN::move(file.canonical_path);
+					}
+				}
 			}
 		}
 

kernel/kernel/Process.cpp

@@ -301,7 +301,7 @@ namespace Kernel
 
 		BAN::String absolute_path = TRY(absolute_path_of(path));
 
-		auto file = TRY(VirtualFileSystem::get().file_from_absolute_path(absolute_path));
+		auto file = TRY(VirtualFileSystem::get().file_from_absolute_path(absolute_path, !(flags & O_NOFOLLOW)));
 
 		LockGuard _(m_lock);
 		int fd = TRY(get_free_fd());
@@ -421,7 +421,7 @@ namespace Kernel
 		auto directory = absolute_path.sv().substring(0, index);
 		auto file_name = absolute_path.sv().substring(index);
 
-		auto parent_file = TRY(VirtualFileSystem::get().file_from_absolute_path(directory));
+		auto parent_file = TRY(VirtualFileSystem::get().file_from_absolute_path(directory, true));
 		TRY(parent_file.inode->create_file(file_name, mode));
 
 		return {};
@@ -510,7 +510,7 @@ namespace Kernel
 	{
 		BAN::String absolute_path = TRY(absolute_path_of(path));
 
-		auto file = TRY(VirtualFileSystem::get().file_from_absolute_path(absolute_path));
+		auto file = TRY(VirtualFileSystem::get().file_from_absolute_path(absolute_path, true));
 		if (!file.inode->mode().ifdir())
 			return BAN::Error::from_errno(ENOTDIR);