dotcloud/docker

//go:build linux

package overlayutils // import "github.com/docker/docker/daemon/graphdriver/overlayutils"

import (
    "context"
    "fmt"
    "os"
    "path"
    "path/filepath"

    "github.com/containerd/log"
    "github.com/docker/docker/daemon/graphdriver"
    "github.com/moby/sys/userns"
    "github.com/pkg/errors"
    "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 {
            log.G(context.TODO()).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), 0o755); 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 {
        log.G(context.TODO()).Warnf("Failed to unmount check directory %v: %v", mnt, err)
    }
    return nil
}

// GetOverlayXattr combines the overlay module's xattr class with the named
// xattr -- `user` when mounted inside a user namespace, and `trusted` when
// mounted in the 'root' namespace.
func GetOverlayXattr(name string) string {
    class := "trusted"
    if userns.RunningInUserNS() {
        class = "user"
    }
    return fmt.Sprintf("%s.overlay.%s", class, name)
}