| // +build linux |
| |
| package overlay2 |
| |
| import ( |
| "fmt" |
| "io/ioutil" |
| "os" |
| "path" |
| "path/filepath" |
| "syscall" |
| |
| "github.com/docker/docker/pkg/system" |
| "github.com/pkg/errors" |
| "github.com/sirupsen/logrus" |
| "golang.org/x/sys/unix" |
| ) |
| |
| // doesSupportNativeDiff checks whether the filesystem has a bug |
| // which copies up the opaque flag when copying up an opaque |
| // directory or the kernel enable CONFIG_OVERLAY_FS_REDIRECT_DIR. |
| // When these exist naive diff should be used. |
| func doesSupportNativeDiff(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, l1/d1, 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, "l1", "d1"), 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 := unix.Mount("overlay", filepath.Join(td, "merged"), "overlay", 0, opts); err != nil { |
| return errors.Wrap(err, "failed to mount overlay") |
| } |
| defer func() { |
| if err := unix.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") |
| } |
| |
| // rename "d1" to "d2" |
| if err := os.Rename(filepath.Join(td, "merged", "d1"), filepath.Join(td, "merged", "d2")); err != nil { |
| // if rename failed with syscall.EXDEV, the kernel doesn't have CONFIG_OVERLAY_FS_REDIRECT_DIR enabled |
| if err.(*os.LinkError).Err == syscall.EXDEV { |
| return nil |
| } |
| return errors.Wrap(err, "failed to rename dir in merged directory") |
| } |
| // get the xattr of "d2" |
| xattrRedirect, err := system.Lgetxattr(filepath.Join(td, "l3", "d2"), "trusted.overlay.redirect") |
| if err != nil { |
| return errors.Wrap(err, "failed to read redirect flag on upper layer") |
| } |
| |
| if string(xattrRedirect) == "d1" { |
| return errors.New("kernel has CONFIG_OVERLAY_FS_REDIRECT_DIR enabled") |
| } |
| |
| return nil |
| } |