github.com/wozhu6104/docker@v20.10.10+incompatible/daemon/graphdriver/overlayutils/overlayutils.go (about)

     1  // +build linux
     2  
     3  package overlayutils // import "github.com/docker/docker/daemon/graphdriver/overlayutils"
     4  
     5  import (
     6  	"fmt"
     7  	"io/ioutil"
     8  	"os"
     9  	"path"
    10  	"path/filepath"
    11  
    12  	"github.com/docker/docker/daemon/graphdriver"
    13  	"github.com/pkg/errors"
    14  	"github.com/sirupsen/logrus"
    15  	"golang.org/x/sys/unix"
    16  )
    17  
    18  // ErrDTypeNotSupported denotes that the backing filesystem doesn't support d_type.
    19  func ErrDTypeNotSupported(driver, backingFs string) error {
    20  	msg := fmt.Sprintf("%s: the backing %s filesystem is formatted without d_type support, which leads to incorrect behavior.", driver, backingFs)
    21  	if backingFs == "xfs" {
    22  		msg += " Reformat the filesystem with ftype=1 to enable d_type support."
    23  	}
    24  
    25  	if backingFs == "extfs" {
    26  		msg += " Reformat the filesystem (or use tune2fs) with -O filetype flag to enable d_type support."
    27  	}
    28  
    29  	msg += " Backing filesystems without d_type support are not supported."
    30  
    31  	return graphdriver.NotSupportedError(msg)
    32  }
    33  
    34  // SupportsOverlay checks if the system supports overlay filesystem
    35  // by performing an actual overlay mount.
    36  //
    37  // checkMultipleLowers parameter enables check for multiple lowerdirs,
    38  // which is required for the overlay2 driver.
    39  func SupportsOverlay(d string, checkMultipleLowers bool) error {
    40  	// We can't rely on go-selinux.GetEnabled() to detect whether SELinux is enabled,
    41  	// because RootlessKit doesn't mount /sys/fs/selinux in the child: https://github.com/rootless-containers/rootlesskit/issues/94
    42  	// So we check $_DOCKERD_ROOTLESS_SELINUX, which is set by dockerd-rootless.sh .
    43  	if os.Getenv("_DOCKERD_ROOTLESS_SELINUX") == "1" {
    44  		// Kernel 5.11 introduced support for rootless overlayfs, but incompatible with SELinux,
    45  		// so fallback to fuse-overlayfs.
    46  		// https://github.com/moby/moby/issues/42333
    47  		return errors.New("overlay is not supported for Rootless with SELinux")
    48  	}
    49  
    50  	td, err := ioutil.TempDir(d, "check-overlayfs-support")
    51  	if err != nil {
    52  		return err
    53  	}
    54  	defer func() {
    55  		if err := os.RemoveAll(td); err != nil {
    56  			logrus.Warnf("Failed to remove check directory %v: %v", td, err)
    57  		}
    58  	}()
    59  
    60  	for _, dir := range []string{"lower1", "lower2", "upper", "work", "merged"} {
    61  		if err := os.Mkdir(filepath.Join(td, dir), 0755); err != nil {
    62  			return err
    63  		}
    64  	}
    65  
    66  	mnt := filepath.Join(td, "merged")
    67  	lowerDir := path.Join(td, "lower2")
    68  	if checkMultipleLowers {
    69  		lowerDir += ":" + path.Join(td, "lower1")
    70  	}
    71  	opts := fmt.Sprintf("lowerdir=%s,upperdir=%s,workdir=%s", lowerDir, path.Join(td, "upper"), path.Join(td, "work"))
    72  	if err := unix.Mount("overlay", mnt, "overlay", 0, opts); err != nil {
    73  		return errors.Wrap(err, "failed to mount overlay")
    74  	}
    75  	if err := unix.Unmount(mnt, 0); err != nil {
    76  		logrus.Warnf("Failed to unmount check directory %v: %v", mnt, err)
    77  	}
    78  	return nil
    79  }