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package archive
import (
"archive/tar"
"fmt"
"os"
"path/filepath"
"strings"
"github.com/moby/sys/userns"
"golang.org/x/sys/unix"
)
func getWhiteoutConverter(format WhiteoutFormat) tarWhiteoutConverter {
if format == OverlayWhiteoutFormat {
return overlayWhiteoutConverter{}
}
return nil
}
type overlayWhiteoutConverter struct{}
func (overlayWhiteoutConverter) ConvertWrite(hdr *tar.Header, path string, fi os.FileInfo) (wo *tar.Header, _ error) {
// convert whiteouts to AUFS format
if fi.Mode()&os.ModeCharDevice != 0 && hdr.Devmajor == 0 && hdr.Devminor == 0 {
// we just rename the file and make it normal
dir, filename := filepath.Split(hdr.Name)
hdr.Name = filepath.Join(dir, WhiteoutPrefix+filename)
hdr.Mode = 0o600
hdr.Typeflag = tar.TypeReg
hdr.Size = 0
}
if fi.Mode()&os.ModeDir == 0 {
// FIXME(thaJeztah): return a sentinel error instead of nil, nil
return nil, nil
}
opaqueXattrName := "trusted.overlay.opaque"
if userns.RunningInUserNS() {
opaqueXattrName = "user.overlay.opaque"
}
// convert opaque dirs to AUFS format by writing an empty file with the prefix
opaque, err := lgetxattr(path, opaqueXattrName)
if err != nil {
return nil, err
}
if len(opaque) != 1 || opaque[0] != 'y' {
// FIXME(thaJeztah): return a sentinel error instead of nil, nil
return nil, nil
}
delete(hdr.PAXRecords, paxSchilyXattr+opaqueXattrName)
// create a header for the whiteout file
// it should inherit some properties from the parent, but be a regular file
return &tar.Header{
Typeflag: tar.TypeReg,
Mode: hdr.Mode & int64(os.ModePerm),
Name: filepath.Join(hdr.Name, WhiteoutOpaqueDir), // #nosec G305 -- An archive is being created, not extracted.
Size: 0,
Uid: hdr.Uid,
Uname: hdr.Uname,
Gid: hdr.Gid,
Gname: hdr.Gname,
AccessTime: hdr.AccessTime,
ChangeTime: hdr.ChangeTime,
}, nil
}
func (c overlayWhiteoutConverter) ConvertRead(hdr *tar.Header, path string) (bool, error) {
base := filepath.Base(path)
dir := filepath.Dir(path)
// if a directory is marked as opaque by the AUFS special file, we need to translate that to overlay
if base == WhiteoutOpaqueDir {
opaqueXattrName := "trusted.overlay.opaque"
if userns.RunningInUserNS() {
opaqueXattrName = "user.overlay.opaque"
}
err := unix.Setxattr(dir, opaqueXattrName, []byte{'y'}, 0)
if err != nil {
return false, fmt.Errorf("setxattr('%s', %s=y): %w", dir, opaqueXattrName, err)
}
// don't write the file itself
return false, err
}
// if a file was deleted and we are using overlay, we need to create a character device
if strings.HasPrefix(base, WhiteoutPrefix) {
originalBase := base[len(WhiteoutPrefix):]
originalPath := filepath.Join(dir, originalBase)
if err := unix.Mknod(originalPath, unix.S_IFCHR, 0); err != nil {
return false, fmt.Errorf("failed to mknod('%s', S_IFCHR, 0): %w", originalPath, err)
}
if err := os.Chown(originalPath, hdr.Uid, hdr.Gid); err != nil {
return false, err
}
// don't write the file itself
return false, nil
}
return true, nil
}
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