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//go:build linux
// +build linux
package overlayutils // import "github.com/docker/docker/daemon/graphdriver/overlayutils"
import (
"fmt"
"os"
"path"
"path/filepath"
"github.com/docker/docker/daemon/graphdriver"
"github.com/pkg/errors"
"github.com/sirupsen/logrus"
"golang.org/x/sys/unix"
)
// ErrDTypeNotSupported denotes that the backing filesystem doesn't support d_type.
func ErrDTypeNotSupported(driver, backingFs string) error {
msg := fmt.Sprintf("%s: the backing %s filesystem is formatted without d_type support, which leads to incorrect behavior.", driver, backingFs)
if backingFs == "xfs" {
msg += " Reformat the filesystem with ftype=1 to enable d_type support."
}
if backingFs == "extfs" {
msg += " Reformat the filesystem (or use tune2fs) with -O filetype flag to enable d_type support."
}
msg += " Backing filesystems without d_type support are not supported."
return graphdriver.NotSupportedError(msg)
}
// SupportsOverlay checks if the system supports overlay filesystem
// by performing an actual overlay mount.
//
// checkMultipleLowers parameter enables check for multiple lowerdirs,
// which is required for the overlay2 driver.
func SupportsOverlay(d string, checkMultipleLowers bool) error {
// We can't rely on go-selinux.GetEnabled() to detect whether SELinux is enabled,
// because RootlessKit doesn't mount /sys/fs/selinux in the child: https://github.com/rootless-containers/rootlesskit/issues/94
// So we check $_DOCKERD_ROOTLESS_SELINUX, which is set by dockerd-rootless.sh .
if os.Getenv("_DOCKERD_ROOTLESS_SELINUX") == "1" {
// Kernel 5.11 introduced support for rootless overlayfs, but incompatible with SELinux,
// so fallback to fuse-overlayfs.
// https://github.com/moby/moby/issues/42333
return errors.New("overlay is not supported for Rootless with SELinux")
}
td, err := os.MkdirTemp(d, "check-overlayfs-support")
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)
}
}()
for _, dir := range []string{"lower1", "lower2", "upper", "work", "merged"} {
if err := os.Mkdir(filepath.Join(td, dir), 0755); err != nil {
return err
}
}
mnt := filepath.Join(td, "merged")
lowerDir := path.Join(td, "lower2")
if checkMultipleLowers {
lowerDir += ":" + path.Join(td, "lower1")
}
opts := fmt.Sprintf("lowerdir=%s,upperdir=%s,workdir=%s", lowerDir, path.Join(td, "upper"), path.Join(td, "work"))
if err := unix.Mount("overlay", mnt, "overlay", 0, opts); err != nil {
return errors.Wrap(err, "failed to mount overlay")
}
if err := unix.Unmount(mnt, 0); err != nil {
logrus.Warnf("Failed to unmount check directory %v: %v", mnt, err)
}
return nil
}
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