moby/vendor/github.com/containerd/containerd/fs/diff_unix.go

// +build !windows

package fs

import (
	"bytes"
	"os"
	"syscall"

	"github.com/containerd/continuity/sysx"
	"github.com/pkg/errors"
)

// detectDirDiff returns diff dir options if a directory could
// be found in the mount info for upper which is the direct
// diff with the provided lower directory
func detectDirDiff(upper, lower string) *diffDirOptions {
	// TODO: get mount options for upper
	// TODO: detect AUFS
	// TODO: detect overlay
	return nil
}

// compareSysStat returns whether the stats are equivalent,
// whether the files are considered the same file, and
// an error
func compareSysStat(s1, s2 interface{}) (bool, error) {
	ls1, ok := s1.(*syscall.Stat_t)
	if !ok {
		return false, nil
	}
	ls2, ok := s2.(*syscall.Stat_t)
	if !ok {
		return false, nil
	}

	return ls1.Mode == ls2.Mode && ls1.Uid == ls2.Uid && ls1.Gid == ls2.Gid && ls1.Rdev == ls2.Rdev, nil
}

func compareCapabilities(p1, p2 string) (bool, error) {
	c1, err := sysx.LGetxattr(p1, "security.capability")
	if err != nil && err != sysx.ENODATA {
		return false, errors.Wrapf(err, "failed to get xattr for %s", p1)
	}
	c2, err := sysx.LGetxattr(p2, "security.capability")
	if err != nil && err != sysx.ENODATA {
		return false, errors.Wrapf(err, "failed to get xattr for %s", p2)
	}
	return bytes.Equal(c1, c2), nil
}

func isLinked(f os.FileInfo) bool {
	s, ok := f.Sys().(*syscall.Stat_t)
	if !ok {
		return false
	}
	return !f.IsDir() && s.Nlink > 1
}