Improve zfs init log message for zfs

Signed-off-by: Drew Hubl <drew.hubl@gmail.com>
Signed-off-by: Brian Goff <cpuguy83@gmail.com>
Upstream-commit: 27b002f4a02e2d9f6eded9004b82cb81f121264f
Component: engine

components/engine/daemon/graphdriver/zfs/zfs_linux.go

@@ -1,21 +1,22 @@
 package zfs
 
 import (
-	"fmt"
-
 	"github.com/docker/docker/daemon/graphdriver"
 	"github.com/sirupsen/logrus"
-	"golang.org/x/sys/unix"
 )
 
-func checkRootdirFs(rootdir string) error {
-	var buf unix.Statfs_t
-	if err := unix.Statfs(rootdir, &buf); err != nil {
-		return fmt.Errorf("Failed to access '%s': %s", rootdir, err)
+func checkRootdirFs(rootDir string) error {
+	fsMagic, err := graphdriver.GetFSMagic(rootDir)
+	if err != nil {
+		return err
+	}
+	backingFS := "unknown"
+	if fsName, ok := graphdriver.FsNames[fsMagic]; ok {
+		backingFS = fsName
 	}
 
-	if graphdriver.FsMagic(buf.Type) != graphdriver.FsMagicZfs {
-		logrus.Debugf("[zfs] no zfs dataset found for rootdir '%s'", rootdir)
+	if fsMagic != graphdriver.FsMagicZfs {
+		logrus.WithField("root", rootDir).WithField("backingFS", backingFS).WithField("driver", "zfs").Error("No zfs dataset found for root")
 		return graphdriver.ErrPrerequisites
 	}