Use MNT_FORCE as an approximate equivalent to MNT_DETACH

Also, we don't need to truncate the path name for zfs mount points.
FreeBSD versions prior to 12.0 had a limitation of 88 characters
for mount points but this has been increased to 1024.

Signed-off-by: Doug Rabson <dfr@rabson.org>

drivers/zfs/zfs_freebsd.go

@@ -2,7 +2,6 @@ package zfs
 
 import (
 	"fmt"
-	"strings"
 
 	"github.com/containers/storage/drivers"
 	"github.com/pkg/errors"
@@ -26,19 +25,10 @@ func checkRootdirFs(rootdir string) error {
 }
 
 func getMountpoint(id string) string {
-	maxlen := 12
-
-	// we need to preserve filesystem suffix
-	suffix := strings.SplitN(id, "-", 2)
-
-	if len(suffix) > 1 {
-		return id[:maxlen] + "-" + suffix[1]
-	}
-
-	return id[:maxlen]
+	return id
 }
 
 func detachUnmount(mountpoint string) error {
-	// FreeBSD doesn't have an equivalent to MNT_DETACH
-	return unix.Unmount(mountpoint, 0)
+	// FreeBSD's MNT_FORCE is roughly equivalent to MNT_DETACH
+	return unix.Unmount(mountpoint, unix.MNT_FORCE)
 }

pkg/mount/flags_freebsd.go

@@ -27,6 +27,8 @@ const (
 	// NOATIME will not update the file access time when reading from a file.
 	NOATIME = unix.MNT_NOATIME
 
+	mntDetach = unix.MNT_FORCE
+
 	NODIRATIME  = 0
 	NODEV       = 0
 	DIRSYNC     = 0
@@ -43,5 +45,4 @@ const (
 	RSHARED     = 0
 	RELATIME    = 0
 	STRICTATIME = 0
-	mntDetach   = 0
 )