Kernel/LibC: Add support for creating hardlinks

kernel/include/kernel/FS/Ext2/Inode.h

@@ -36,6 +36,7 @@ namespace Kernel
 		virtual BAN::ErrorOr<size_t> list_next_inodes_impl(off_t, struct dirent*, size_t) override;
 		virtual BAN::ErrorOr<void> create_file_impl(BAN::StringView, mode_t, uid_t, gid_t) override;
 		virtual BAN::ErrorOr<void> create_directory_impl(BAN::StringView, mode_t, uid_t, gid_t) override;
+		virtual BAN::ErrorOr<void> link_inode_impl(BAN::StringView, BAN::RefPtr<Inode>) override;
 		virtual BAN::ErrorOr<void> unlink_impl(BAN::StringView) override;
 
 		virtual BAN::ErrorOr<BAN::String> link_target_impl() override;

kernel/include/kernel/FS/Inode.h

@@ -95,6 +95,7 @@ namespace Kernel
 		BAN::ErrorOr<size_t> list_next_inodes(off_t, struct dirent* list, size_t list_size);
 		BAN::ErrorOr<void> create_file(BAN::StringView, mode_t, uid_t, gid_t);
 		BAN::ErrorOr<void> create_directory(BAN::StringView, mode_t, uid_t, gid_t);
+		BAN::ErrorOr<void> link_inode(BAN::StringView, BAN::RefPtr<Inode>);
 		BAN::ErrorOr<void> unlink(BAN::StringView);
 
 		// Link API
@@ -131,6 +132,7 @@ namespace Kernel
 		virtual BAN::ErrorOr<size_t> list_next_inodes_impl(off_t, struct dirent*, size_t)		{ return BAN::Error::from_errno(ENOTSUP); }
 		virtual BAN::ErrorOr<void> create_file_impl(BAN::StringView, mode_t, uid_t, gid_t)		{ return BAN::Error::from_errno(ENOTSUP); }
 		virtual BAN::ErrorOr<void> create_directory_impl(BAN::StringView, mode_t, uid_t, gid_t)	{ return BAN::Error::from_errno(ENOTSUP); }
+		virtual BAN::ErrorOr<void> link_inode_impl(BAN::StringView, BAN::RefPtr<Inode>)			{ return BAN::Error::from_errno(ENOTSUP); }
 		virtual BAN::ErrorOr<void> unlink_impl(BAN::StringView)									{ return BAN::Error::from_errno(ENOTSUP); }
 
 		// Link API

kernel/include/kernel/Process.h

@@ -110,6 +110,7 @@ namespace Kernel
 		BAN::ErrorOr<long> sys_write(int fd, const void* buffer, size_t count);
 		BAN::ErrorOr<long> sys_access(const char* path, int amode);
 		BAN::ErrorOr<long> sys_create_dir(const char*, mode_t);
+		BAN::ErrorOr<long> sys_hardlinkat(int fd1, const char* path1, int fd2, const char* path2, int flag);
 		BAN::ErrorOr<long> sys_unlink(const char*);
 		BAN::ErrorOr<long> sys_readlinkat(int fd, const char* path, char* buffer, size_t bufsize);
 

kernel/kernel/FS/Ext2/Inode.cpp

@@ -518,6 +518,23 @@ done:
 		return {};
 	}
 
+	BAN::ErrorOr<void> Ext2Inode::link_inode_impl(BAN::StringView name, BAN::RefPtr<Inode> inode)
+	{
+		ASSERT(this->mode().ifdir());
+		ASSERT(!inode->mode().ifdir());
+
+		if (&m_fs != inode->filesystem())
+			return BAN::Error::from_errno(EXDEV);
+
+		if (!find_inode_impl(name).is_error())
+			return BAN::Error::from_errno(EEXIST);
+
+		auto ext2_inode = static_cast<Ext2Inode*>(inode.ptr());
+		TRY(link_inode_to_directory(*ext2_inode, name));
+
+		return {};
+	}
+
 	BAN::ErrorOr<void> Ext2Inode::link_inode_to_directory(Ext2Inode& inode, BAN::StringView name)
 	{
 		if (!this->mode().ifdir())

kernel/kernel/FS/Inode.cpp

@@ -93,6 +93,16 @@ namespace Kernel
 		return create_directory_impl(name, mode, uid, gid);
 	}
 
+	BAN::ErrorOr<void> Inode::link_inode(BAN::StringView name, BAN::RefPtr<Inode> inode)
+	{
+		LockGuard _(m_mutex);
+		if (!this->mode().ifdir())
+			return BAN::Error::from_errno(ENOTDIR);
+		if (inode->mode().ifdir())
+			return BAN::Error::from_errno(EINVAL);
+		return link_inode_impl(name, inode);
+	}
+
 	BAN::ErrorOr<void> Inode::unlink(BAN::StringView name)
 	{
 		LockGuard _(m_mutex);

kernel/kernel/Process.cpp

@@ -1042,6 +1042,40 @@ namespace Kernel
 		return 0;
 	}
 
+	BAN::ErrorOr<long> Process::sys_hardlinkat(int fd1, const char* path1, int fd2, const char* path2, int flag)
+	{
+		LockGuard _(m_process_lock);
+		TRY(validate_string_access(path1));
+		TRY(validate_string_access(path2));
+
+		auto inode = TRY(find_file(fd1, path1, flag)).inode;
+		if (inode->mode().ifdir())
+			return BAN::Error::from_errno(EISDIR);
+
+		auto parent = TRY(find_parent(fd2, path2));
+
+		BAN::RefPtr<Inode> parent_inode;
+		BAN::StringView file_name;
+
+		BAN::StringView path2_sv = path2;
+		if (auto index = path2_sv.rfind('/'); index.has_value())
+		{
+			parent_inode = TRY(VirtualFileSystem::get().file_from_relative_path(parent, m_credentials, path2_sv.substring(0, index.value()), O_EXEC | O_WRONLY)).inode;
+			file_name = path2_sv.substring(index.value() + 1);
+		}
+		else
+		{
+			parent_inode = parent.inode;
+			file_name = path2_sv;
+			if (!parent_inode->can_access(m_credentials, O_WRONLY))
+				return BAN::Error::from_errno(EACCES);
+		}
+
+		ASSERT(parent_inode->mode().ifdir());
+		TRY(parent_inode->link_inode(file_name, inode));
+		return 0;
+	}
+
 	BAN::ErrorOr<long> Process::sys_unlink(const char* path)
 	{
 		LockGuard _(m_process_lock);

userspace/libraries/LibC/include/sys/syscall.h

@@ -90,6 +90,7 @@ __BEGIN_DECLS
 	O(SYS_PTSNAME,			ptsname)		\
 	O(SYS_FSYNC,			fsync)			\
 	O(SYS_SYMLINKAT,		symlinkat)		\
+	O(SYS_HARDLINKAT,		hardlinkat)		\
 
 enum Syscall
 {

userspace/libraries/LibC/unistd.cpp

@@ -630,3 +630,13 @@ int symlinkat(const char* path1, int fd, const char* path2)
 {
 	return syscall(SYS_SYMLINKAT, path1, fd, path2);
 }
+
+int link(const char* path1, const char* path2)
+{
+	return linkat(AT_FDCWD, path1, AT_FDCWD, path2, 0);
+}
+
+int linkat(int fd1, const char *path1, int fd2, const char *path2, int flag)
+{
+	return syscall(SYS_HARDLINKAT, fd1, path1, fd2, path2, flag);
+}