pkg/archive: use mount pkg

It makes sense to use mount package here because
 - it no longer requires /proc to be mounted
 - it provides verbose errors so the caller doesn't have to

Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>

pkg/archive/archive_linux.go

@@ -10,6 +10,7 @@ import (
 	"syscall"
 
 	"github.com/containerd/continuity/fs"
+	"github.com/docker/docker/pkg/mount"
 	"github.com/docker/docker/pkg/system"
 	"github.com/pkg/errors"
 	"golang.org/x/sys/unix"
@@ -152,9 +153,8 @@ func mknodChar0Overlay(cleansedOriginalPath string) error {
 		return errors.Wrapf(err, "failed to create a dummy lower file %s", lowerDummy)
 	}
 	mOpts := fmt.Sprintf("lowerdir=%s,upperdir=%s,workdir=%s", lower, upper, work)
-	// docker/pkg/mount.Mount() requires procfs to be mounted. So we use syscall.Mount() directly instead.
-	if err := syscall.Mount("overlay", merged, "overlay", uintptr(0), mOpts); err != nil {
-		return errors.Wrapf(err, "failed to mount overlay (%s) on %s", mOpts, merged)
+	if err := mount.Mount("overlay", merged, "overlay", mOpts); err != nil {
+		return err
 	}
 	mergedDummy := filepath.Join(merged, dummyBase)
 	if err := os.Remove(mergedDummy); err != nil {
@@ -237,9 +237,8 @@ func createDirWithOverlayOpaque(tmp string) (string, error) {
 		return "", errors.Wrapf(err, "failed to create a dummy lower directory %s", lowerDummy)
 	}
 	mOpts := fmt.Sprintf("lowerdir=%s,upperdir=%s,workdir=%s", lower, upper, work)
-	// docker/pkg/mount.Mount() requires procfs to be mounted. So we use syscall.Mount() directly instead.
-	if err := syscall.Mount("overlay", merged, "overlay", uintptr(0), mOpts); err != nil {
-		return "", errors.Wrapf(err, "failed to mount overlay (%s) on %s", mOpts, merged)
+	if err := mount.Mount("overlay", merged, "overlay", mOpts); err != nil {
+		return "", err
 	}
 	mergedDummy := filepath.Join(merged, dummyBase)
 	if err := os.Remove(mergedDummy); err != nil {

pkg/archive/archive_linux_test.go

@@ -9,6 +9,7 @@ import (
 	"syscall"
 	"testing"
 
+	"github.com/docker/docker/pkg/mount"
 	"github.com/docker/docker/pkg/reexec"
 	"github.com/docker/docker/pkg/system"
 	rsystem "github.com/opencontainers/runc/libcontainer/system"
@@ -204,11 +205,11 @@ func supportsOverlay(dir string) error {
 		}
 	}
 	mOpts := fmt.Sprintf("lowerdir=%s,upperdir=%s,workdir=%s", lower, upper, work)
-	if err := syscall.Mount("overlay", merged, "overlay", uintptr(0), mOpts); err != nil {
-		return errors.Wrapf(err, "failed to mount overlay (%s) on %s", mOpts, merged)
+	if err := mount.Mount("overlay", merged, "overlay", mOpts); err != nil {
+		return err
 	}
-	if err := syscall.Unmount(merged, 0); err != nil {
-		return errors.Wrapf(err, "failed to unmount %s", merged)
+	if err := mount.Unmount(merged); err != nil {
+		return err
 	}
 	return nil
 }

pkg/mount/mount.go

@@ -105,7 +105,7 @@ func Mount(device, target, mType, options string) error {
 	return mount(device, target, mType, uintptr(flag), data)
 }
 
-// Mount will mount filesystem according to the specified configuration.
+// ForceMount will mount filesystem according to the specified configuration.
 // Options must be specified like the mount or fstab unix commands:
 // "opt1=val1,opt2=val2". See flags.go for supported option flags.
 //