Blacklist zfs with overlay

Docker-DCO-1.1-Signed-off-by: Jessica Frazelle <jess@docker.com> (github: jfrazelle)

daemon/graphdriver/driver.go

@@ -25,6 +25,7 @@ const (
 	FsMagicReiserFs    = FsMagic(0x52654973)
 	FsMagicSmbFs       = FsMagic(0x0000517B)
 	FsMagicJffs2Fs     = FsMagic(0x000072b6)
+	FsMagicZfs         = FsMagic(0x2fc12fc1)
 	FsMagicUnsupported = FsMagic(0x00000000)
 )
 
@@ -58,6 +59,7 @@ var (
 		FsMagicReiserFs:    "reiserfs",
 		FsMagicSmbFs:       "smb",
 		FsMagicJffs2Fs:     "jffs2",
+		FsMagicZfs:         "zfs",
 		FsMagicUnsupported: "unsupported",
 	}
 )

daemon/graphdriver/overlay/overlay.go

@@ -118,6 +118,9 @@ func Init(home string, options []string) (graphdriver.Driver, error) {
 	case graphdriver.FsMagicAufs:
 		log.Error("'overlay' is not supported over aufs.")
 		return nil, graphdriver.ErrIncompatibleFS
+	case graphdriver.FsMagicZfs:
+		log.Error("'overlay' is not supported over zfs.")
+		return nil, graphdriver.ErrIncompatibleFS
 	}
 
 	// Create the driver home dir