github.com/Prakhar-Agarwal-byte/moby@v0.0.0-20231027092010-a14e3e8ab87e/daemon/graphdriver/overlayutils/overlayutils.go (about)

     1  //go:build linux
     2  
     3  package overlayutils // import "github.com/Prakhar-Agarwal-byte/moby/daemon/graphdriver/overlayutils"
     4  
     5  import (
     6  	"context"
     7  	"fmt"
     8  	"os"
     9  	"path"
    10  	"path/filepath"
    11  
    12  	"github.com/containerd/containerd/pkg/userns"
    13  	"github.com/containerd/log"
    14  	"github.com/Prakhar-Agarwal-byte/moby/daemon/graphdriver"
    15  	"github.com/pkg/errors"
    16  	"golang.org/x/sys/unix"
    17  )
    18  
    19  // ErrDTypeNotSupported denotes that the backing filesystem doesn't support d_type.
    20  func ErrDTypeNotSupported(driver, backingFs string) error {
    21  	msg := fmt.Sprintf("%s: the backing %s filesystem is formatted without d_type support, which leads to incorrect behavior.", driver, backingFs)
    22  	if backingFs == "xfs" {
    23  		msg += " Reformat the filesystem with ftype=1 to enable d_type support."
    24  	}
    25  
    26  	if backingFs == "extfs" {
    27  		msg += " Reformat the filesystem (or use tune2fs) with -O filetype flag to enable d_type support."
    28  	}
    29  
    30  	msg += " Backing filesystems without d_type support are not supported."
    31  
    32  	return graphdriver.NotSupportedError(msg)
    33  }
    34  
    35  // SupportsOverlay checks if the system supports overlay filesystem
    36  // by performing an actual overlay mount.
    37  //
    38  // checkMultipleLowers parameter enables check for multiple lowerdirs,
    39  // which is required for the overlay2 driver.
    40  func SupportsOverlay(d string, checkMultipleLowers bool) error {
    41  	// We can't rely on go-selinux.GetEnabled() to detect whether SELinux is enabled,
    42  	// because RootlessKit doesn't mount /sys/fs/selinux in the child: https://github.com/rootless-containers/rootlesskit/issues/94
    43  	// So we check $_DOCKERD_ROOTLESS_SELINUX, which is set by dockerd-rootless.sh .
    44  	if os.Getenv("_DOCKERD_ROOTLESS_SELINUX") == "1" {
    45  		// Kernel 5.11 introduced support for rootless overlayfs, but incompatible with SELinux,
    46  		// so fallback to fuse-overlayfs.
    47  		// https://github.com/moby/moby/issues/42333
    48  		return errors.New("overlay is not supported for Rootless with SELinux")
    49  	}
    50  
    51  	td, err := os.MkdirTemp(d, "check-overlayfs-support")
    52  	if err != nil {
    53  		return err
    54  	}
    55  	defer func() {
    56  		if err := os.RemoveAll(td); err != nil {
    57  			log.G(context.TODO()).Warnf("Failed to remove check directory %v: %v", td, err)
    58  		}
    59  	}()
    60  
    61  	for _, dir := range []string{"lower1", "lower2", "upper", "work", "merged"} {
    62  		if err := os.Mkdir(filepath.Join(td, dir), 0o755); err != nil {
    63  			return err
    64  		}
    65  	}
    66  
    67  	mnt := filepath.Join(td, "merged")
    68  	lowerDir := path.Join(td, "lower2")
    69  	if checkMultipleLowers {
    70  		lowerDir += ":" + path.Join(td, "lower1")
    71  	}
    72  	opts := fmt.Sprintf("lowerdir=%s,upperdir=%s,workdir=%s", lowerDir, path.Join(td, "upper"), path.Join(td, "work"))
    73  	if err := unix.Mount("overlay", mnt, "overlay", 0, opts); err != nil {
    74  		return errors.Wrap(err, "failed to mount overlay")
    75  	}
    76  	if err := unix.Unmount(mnt, 0); err != nil {
    77  		log.G(context.TODO()).Warnf("Failed to unmount check directory %v: %v", mnt, err)
    78  	}
    79  	return nil
    80  }
    81  
    82  // GetOverlayXattr combines the overlay module's xattr class with the named
    83  // xattr -- `user` when mounted inside a user namespace, and `trusted` when
    84  // mounted in the 'root' namespace.
    85  func GetOverlayXattr(name string) string {
    86  	class := "trusted"
    87  	if userns.RunningInUserNS() {
    88  		class = "user"
    89  	}
    90  	return fmt.Sprintf("%s.overlay.%s", class, name)
    91  }