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moby--moby/daemon/graphdriver/overlay2/check.go

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// +build linux
package overlay2
import (
"fmt"
"io/ioutil"
"os"
"path"
"path/filepath"
"syscall"
"github.com/Sirupsen/logrus"
"github.com/docker/docker/pkg/system"
"github.com/pkg/errors"
)
// hasOpaqueCopyUpBug checks whether the filesystem has a bug
// which copies up the opaque flag when copying up an opaque
// directory. When this bug exists naive diff should be used.
func hasOpaqueCopyUpBug(d string) error {
td, err := ioutil.TempDir(d, "opaque-bug-check")
if err != nil {
return err
}
defer func() {
if err := os.RemoveAll(td); err != nil {
logrus.Warnf("Failed to remove check directory %v: %v", td, err)
}
}()
// Make directories l1/d, l2/d, l3, work, merged
if err := os.MkdirAll(filepath.Join(td, "l1", "d"), 0755); err != nil {
return err
}
if err := os.MkdirAll(filepath.Join(td, "l2", "d"), 0755); err != nil {
return err
}
if err := os.Mkdir(filepath.Join(td, "l3"), 0755); err != nil {
return err
}
if err := os.Mkdir(filepath.Join(td, "work"), 0755); err != nil {
return err
}
if err := os.Mkdir(filepath.Join(td, "merged"), 0755); err != nil {
return err
}
// Mark l2/d as opaque
if err := system.Lsetxattr(filepath.Join(td, "l2", "d"), "trusted.overlay.opaque", []byte("y"), 0); err != nil {
return errors.Wrap(err, "failed to set opaque flag on middle layer")
}
opts := fmt.Sprintf("lowerdir=%s:%s,upperdir=%s,workdir=%s", path.Join(td, "l2"), path.Join(td, "l1"), path.Join(td, "l3"), path.Join(td, "work"))
if err := syscall.Mount("overlay", filepath.Join(td, "merged"), "overlay", 0, opts); err != nil {
return errors.Wrap(err, "failed to mount overlay")
}
defer func() {
if err := syscall.Unmount(filepath.Join(td, "merged"), 0); err != nil {
logrus.Warnf("Failed to unmount check directory %v: %v", filepath.Join(td, "merged"), err)
}
}()
// Touch file in d to force copy up of opaque directory "d" from "l2" to "l3"
if err := ioutil.WriteFile(filepath.Join(td, "merged", "d", "f"), []byte{}, 0644); err != nil {
return errors.Wrap(err, "failed to write to merged directory")
}
// Check l3/d does not have opaque flag
xattrOpaque, err := system.Lgetxattr(filepath.Join(td, "l3", "d"), "trusted.overlay.opaque")
if err != nil {
return errors.Wrap(err, "failed to read opaque flag on upper layer")
}
if string(xattrOpaque) == "y" {
return errors.New("opaque flag erroneously copied up, consider update to kernel 4.8 or later to fix")
}
return nil
}