github.com/demonoid81/moby@v0.0.0-20200517203328-62dd8e17c460/daemon/graphdriver/overlay2/check.go (about)

     1  // +build linux
     2  
     3  package overlay2 // import "github.com/demonoid81/moby/daemon/graphdriver/overlay2"
     4  
     5  import (
     6  	"fmt"
     7  	"io/ioutil"
     8  	"os"
     9  	"path"
    10  	"path/filepath"
    11  	"syscall"
    12  
    13  	"github.com/demonoid81/moby/pkg/system"
    14  	"github.com/pkg/errors"
    15  	"golang.org/x/sys/unix"
    16  )
    17  
    18  // doesSupportNativeDiff checks whether the filesystem has a bug
    19  // which copies up the opaque flag when copying up an opaque
    20  // directory or the kernel enable CONFIG_OVERLAY_FS_REDIRECT_DIR.
    21  // When these exist naive diff should be used.
    22  func doesSupportNativeDiff(d string) error {
    23  	td, err := ioutil.TempDir(d, "opaque-bug-check")
    24  	if err != nil {
    25  		return err
    26  	}
    27  	defer func() {
    28  		if err := os.RemoveAll(td); err != nil {
    29  			logger.Warnf("Failed to remove check directory %v: %v", td, err)
    30  		}
    31  	}()
    32  
    33  	// Make directories l1/d, l1/d1, l2/d, l3, work, merged
    34  	if err := os.MkdirAll(filepath.Join(td, "l1", "d"), 0755); err != nil {
    35  		return err
    36  	}
    37  	if err := os.MkdirAll(filepath.Join(td, "l1", "d1"), 0755); err != nil {
    38  		return err
    39  	}
    40  	if err := os.MkdirAll(filepath.Join(td, "l2", "d"), 0755); err != nil {
    41  		return err
    42  	}
    43  	if err := os.Mkdir(filepath.Join(td, "l3"), 0755); err != nil {
    44  		return err
    45  	}
    46  	if err := os.Mkdir(filepath.Join(td, workDirName), 0755); err != nil {
    47  		return err
    48  	}
    49  	if err := os.Mkdir(filepath.Join(td, mergedDirName), 0755); err != nil {
    50  		return err
    51  	}
    52  
    53  	// Mark l2/d as opaque
    54  	if err := system.Lsetxattr(filepath.Join(td, "l2", "d"), "trusted.overlay.opaque", []byte("y"), 0); err != nil {
    55  		return errors.Wrap(err, "failed to set opaque flag on middle layer")
    56  	}
    57  
    58  	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, workDirName))
    59  	if err := unix.Mount("overlay", filepath.Join(td, mergedDirName), "overlay", 0, opts); err != nil {
    60  		return errors.Wrap(err, "failed to mount overlay")
    61  	}
    62  	defer func() {
    63  		if err := unix.Unmount(filepath.Join(td, mergedDirName), 0); err != nil {
    64  			logger.Warnf("Failed to unmount check directory %v: %v", filepath.Join(td, mergedDirName), err)
    65  		}
    66  	}()
    67  
    68  	// Touch file in d to force copy up of opaque directory "d" from "l2" to "l3"
    69  	if err := ioutil.WriteFile(filepath.Join(td, mergedDirName, "d", "f"), []byte{}, 0644); err != nil {
    70  		return errors.Wrap(err, "failed to write to merged directory")
    71  	}
    72  
    73  	// Check l3/d does not have opaque flag
    74  	xattrOpaque, err := system.Lgetxattr(filepath.Join(td, "l3", "d"), "trusted.overlay.opaque")
    75  	if err != nil {
    76  		return errors.Wrap(err, "failed to read opaque flag on upper layer")
    77  	}
    78  	if string(xattrOpaque) == "y" {
    79  		return errors.New("opaque flag erroneously copied up, consider update to kernel 4.8 or later to fix")
    80  	}
    81  
    82  	// rename "d1" to "d2"
    83  	if err := os.Rename(filepath.Join(td, mergedDirName, "d1"), filepath.Join(td, mergedDirName, "d2")); err != nil {
    84  		// if rename failed with syscall.EXDEV, the kernel doesn't have CONFIG_OVERLAY_FS_REDIRECT_DIR enabled
    85  		if err.(*os.LinkError).Err == syscall.EXDEV {
    86  			return nil
    87  		}
    88  		return errors.Wrap(err, "failed to rename dir in merged directory")
    89  	}
    90  	// get the xattr of "d2"
    91  	xattrRedirect, err := system.Lgetxattr(filepath.Join(td, "l3", "d2"), "trusted.overlay.redirect")
    92  	if err != nil {
    93  		return errors.Wrap(err, "failed to read redirect flag on upper layer")
    94  	}
    95  
    96  	if string(xattrRedirect) == "d1" {
    97  		return errors.New("kernel has CONFIG_OVERLAY_FS_REDIRECT_DIR enabled")
    98  	}
    99  
   100  	return nil
   101  }