Index: head/usr.sbin/fstyp/Makefile
===================================================================
--- head/usr.sbin/fstyp/Makefile	(revision 287936)
+++ head/usr.sbin/fstyp/Makefile	(revision 287937)
@@ -1,47 +1,47 @@
 # $FreeBSD$
 
 .include <src.opts.mk>
 
 PROG=	fstyp
 SRCS=	cd9660.c ext2fs.c fstyp.c geli.c msdosfs.c ntfs.c ufs.c
 
 .if ${MK_ZFS} != "no"
 SRCS +=	zfs.c
 .endif
 
 MAN=	fstyp.8
 
-WARNS?=	0
+WARNS?=	2
 
 .include <src.opts.mk>
 
 .if ${MK_TESTS} != "no"
 SUBDIR+=	tests
 .endif
 
 .if ${MK_ZFS} != "no"
 IGNORE_PRAGMA=  YES
 
 CFLAGS+= -DNEED_SOLARIS_BOOLEAN -DHAVE_ZFS
 CFLAGS+= -I${.CURDIR}/../../sys/cddl/compat/opensolaris
 CFLAGS+= -I${.CURDIR}/../../cddl/compat/opensolaris/include
 CFLAGS+= -I${.CURDIR}/../../cddl/compat/opensolaris/lib/libumem
 CFLAGS+= -I${.CURDIR}/../../cddl/contrib/opensolaris/lib/libnvpair
 CFLAGS+= -I${.CURDIR}/../../cddl/contrib/opensolaris/lib/libzpool/common
 CFLAGS+= -I${.CURDIR}/../../sys/cddl/contrib/opensolaris/uts/common/fs/zfs
 CFLAGS+= -I${.CURDIR}/../../sys/cddl/contrib/opensolaris/uts/common
 CFLAGS+= -I${.CURDIR}/../../sys/cddl/contrib/opensolaris/uts/common/sys
 CFLAGS+= -I${.CURDIR}/../../cddl/contrib/opensolaris/head
 .endif
 
 CFLAGS+=-I${.CURDIR}/../../sys
 
 DPADD=   ${LIBGEOM} ${LIBMD}
 LDADD=   -lgeom -lmd
 
 .if ${MK_ZFS} != "no"
 DPADD += ${LIBNVPAIR} ${LIBZFS}
 LDADD += -lnvpair -lzfs
 .endif
 
 .include <bsd.prog.mk>
Index: head/usr.sbin/fstyp/zfs.c
===================================================================
--- head/usr.sbin/fstyp/zfs.c	(revision 287936)
+++ head/usr.sbin/fstyp/zfs.c	(revision 287937)
@@ -1,70 +1,75 @@
 /*-
  * Copyright (c) 2015 Allan Jude <allanjude@FreeBSD.org>
+ * Copyright (c) 2015 Xin LI <delphij@FreeBSD.org>
  * All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
  *    documentation and/or other materials provided with the distribution.
  *
  * THIS SOFTWARE IS PROVIDED BY THE AUTHORS AND CONTRIBUTORS ``AS IS'' AND
  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHORS OR CONTRIBUTORS BE LIABLE
  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  * SUCH DAMAGE.
  */
 
 #include <sys/cdefs.h>
 __FBSDID("$FreeBSD$");
 
 #include <sys/types.h>
 #include <stdint.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
 #include <unistd.h>
 
 #include <libnvpair.h>
 #include <sys/vdev_impl.h>
 
 #include "fstyp.h"
 
 int
 fstyp_zfs(FILE *fp, char *label, size_t labelsize)
 {
-	vdev_label_t *zpool_ptr = NULL;
-	vdev_label_t zpool_label;
-	char *buf = zpool_label.vl_vdev_phys.vp_nvlist;
+	vdev_label_t *vdev_label = NULL;
+	vdev_phys_t *vdev_phys;
 	char *zpool_name = NULL;
-	size_t buflen = sizeof (zpool_label.vl_vdev_phys.vp_nvlist);
 	nvlist_t *config = NULL;
+	int err = 0;
 
-	zpool_ptr = (vdev_label_t *)read_buf(fp, 0, sizeof(zpool_label));
-	if (zpool_ptr == NULL)
+	/*
+	 * Read in the first ZFS vdev label ("L0"), located at the beginning
+	 * of the vdev and extract the pool name from it.
+	 *
+	 * TODO: the checksum of label should be validated.
+	 */
+	vdev_label = (vdev_label_t *)read_buf(fp, 0, sizeof(*vdev_label));
+	if (vdev_label == NULL)
 		return (1);
-	zpool_label = *zpool_ptr;
-	if (nvlist_unpack(buf, buflen, &config, 0) != 0)
-		goto zfserr;
-	if (nvlist_lookup_string(config, "name", &zpool_name) != 0)
-		goto zfserr;
-	strlcpy(label, zpool_name, labelsize);
-	nvlist_free(config);
-	free(zpool_ptr);
-	return (0);
 
-zfserr:
+	vdev_phys = &(vdev_label->vl_vdev_phys);
+
+	if ((nvlist_unpack(vdev_phys->vp_nvlist, sizeof(vdev_phys->vp_nvlist),
+	    &config, 0)) == 0 &&
+	    (nvlist_lookup_string(config, "name", &zpool_name) == 0)) {
+		strlcpy(label, zpool_name, labelsize);
+	} else
+		err = 1;
+
 	nvlist_free(config);
-	free(zpool_ptr);
+	free(vdev_label);
 
-	return (1);
+	return (err);
 }