code: func ToRootless(spec *specs.Spec) error {
  	// Remove /sys mount because we can't mount /sys when the daemon netns
  	// is not unshared from the host.
  	//
  	// Instead, we could bind-mount /sys from the host, however, `rbind, ro`
  	// does not make /sys/fs/cgroup read-only (and we can't bind-mount /sys
  	// without rbind)
  	//
  	// PR for making /sys/fs/cgroup read-only is proposed, but it is very
  	// complicated: https://github.com/opencontainers/runc/pull/1869
  	//
  	// For buildkit usecase, we suppose we don't need to provide /sys to
  	// containers and remove /sys mount as a workaround.
  	var mounts []specs.Mount
  	for _, mount := range spec.Mounts {
  		if strings.HasPrefix(mount.Destination, "/sys") {
  			continue
  		}
  		mounts = append(mounts, mount)
  	}
  	spec.Mounts = mounts
  
  	// Remove cgroups so as to avoid `container_linux.go:337: starting container process caused "process_linux.go:280: applying cgroup configuration for process caused \"mkdir /sys/fs/cgroup/cpuset/buildkit: permission denied\""`
  	spec.Linux.Resources = nil
  	spec.Linux.CgroupsPath = ""
  	return nil
  }
docs: // ToRootless converts spec to be compatible with "rootless" runc.
  // * Remove /sys mount
  // * Remove cgroups
  //
  // See docs/rootless.md for the supported runc revision.