//go:build linux

package host

import "golang.org/x/sys/unix"

// walkNoFollowDir is the one descriptor walk behind consoleDir and the root
// migration's floor repair. It opens base, then each name beneath it in
// turn with O_NOFOLLOW|O_DIRECTORY, so no symlink is followed below base.
// check sees every directory on the way (last false) before anything
// beneath it is opened or made, and the final directory (last true) once it
// is open. A missing name is made only when create(last) allows it: Mkdirat
// 0755 then Fchmodat 0755 beneath its checked parent, the parent fsynced,
// and the name opened again with O_NOFOLLOW. It returns the checked final
// directory's descriptor; errors are the system call's or check's own.
func walkNoFollowDir(base string, names []string, create func(last bool) bool, check func(fd int, last bool) error) (int, error) {
	if len(names) == 0 {
		return -1, unix.EINVAL
	}
	fd, err := unix.Open(base, unix.O_RDONLY|unix.O_DIRECTORY|unix.O_CLOEXEC, 0)
	if err != nil {
		return -1, err
	}
	for i, name := range names {
		last := i == len(names)-1
		if err = check(fd, false); err != nil {
			unix.Close(fd)
			return -1, err
		}
		next, e := unix.Openat(fd, name, unix.O_RDONLY|unix.O_DIRECTORY|unix.O_NOFOLLOW|unix.O_CLOEXEC, 0)
		if e == unix.ENOENT && create(last) {
			e = unix.Mkdirat(fd, name, 0o755)
			if e == nil {
				e = unix.Fchmodat(fd, name, 0o755, 0)
			}
			if e == nil || e == unix.EEXIST {
				if e = unix.Fsync(fd); e == nil {
					next, e = unix.Openat(fd, name, unix.O_RDONLY|unix.O_DIRECTORY|unix.O_NOFOLLOW|unix.O_CLOEXEC, 0)
				}
			}
		}
		unix.Close(fd)
		if e != nil {
			return -1, e
		}
		fd = next
		if last {
			if err = check(fd, true); err != nil {
				unix.Close(fd)
				return -1, err
			}
		}
	}
	return fd, nil
}