UBUNTU: SAUCE: Allow mounting datasets more than once (LP: #1759848)

BugLink: https://bugs.launchpad.net/bugs/1759848

Currently mounting an already mounted zfs dataset results in an
error, whereas it is typically allowed with other filesystems.
This causes some bad interactions with mount namespaces. Take
this sequence for example:

 - Create a dataset
 - Create a snapshot of the dataset
 - Create a clone of the snapshot
 - Create a new mount namespace
 - Rename the original dataset

The rename results in unmounting and remounting the clone in the
original mount namespace, however the remount fails because the
dataset is still mounted in the new mount namespace. (Note that
this means the mount in the new mount namespace is never being
unmounted, so perhaps the unmount/remount of the clone isn't
actually necessary.)

The problem here is a result of the way mounting is implemented
in the kernel module. Since it is not mounting block devices it
uses mount_nodev() instead of the usual mount_bdev(). However,
mount_nodev() is written for filesystems for which each mount is
a new instance (i.e. a new super block), and zfs should be able
to detect when a mount request can be satisfied using an existing
super block.

Change zpl_mount() to call sget() directly with it's own test
callback. Passing the objset_t object as the fs data allows
checking if a superblock already exists for the dataset, and in
that case we just need to return a new reference for the sb's
root dentry.

[ Sync'd from zfsutils-linux, from a patch by Seth Forshee and
  backported to zfs 0.6.5.6. Note that this also contains
  some zfstutils changes between 0.6.5.6-0ubuntu20 and
  0.6.5.6-0ubuntu24 which go also sync'd into this fix, which
  is expected part of the zfs sync'ing ]
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Acked-by: Seth Forshee <seth.forshee@canonical.com>
Acked-by: Stefan Bader <stefan.bader@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>

zfs/META

@@ -2,7 +2,7 @@ Meta:         1
 Name:         zfs
 Branch:       1.0
 Version:      0.6.5.6
-Release:      0ubuntu20
+Release:      0ubuntu24
 Release-Tags: relext
 License:      CDDL
 Author:       OpenZFS on Linux

zfs/Makefile.in

@@ -140,6 +140,7 @@ am__aclocal_m4_deps = $(top_srcdir)/config/always-no-bool-compare.m4 \
 	$(top_srcdir)/config/kernel-file-inode.m4 \
 	$(top_srcdir)/config/kernel-fmode-t.m4 \
 	$(top_srcdir)/config/kernel-follow-down-one.m4 \
+	$(top_srcdir)/config/kernel-fst-mount.m4 \
 	$(top_srcdir)/config/kernel-fsync.m4 \
 	$(top_srcdir)/config/kernel-generic_io_acct.m4 \
 	$(top_srcdir)/config/kernel-get-disk-ro.m4 \
@@ -155,7 +156,6 @@ am__aclocal_m4_deps = $(top_srcdir)/config/always-no-bool-compare.m4 \
 	$(top_srcdir)/config/kernel-lseek-execute.m4 \
 	$(top_srcdir)/config/kernel-mk-request-fn.m4 \
 	$(top_srcdir)/config/kernel-mkdir-umode-t.m4 \
-	$(top_srcdir)/config/kernel-mount-nodev.m4 \
 	$(top_srcdir)/config/kernel-open-bdev-exclusive.m4 \
 	$(top_srcdir)/config/kernel-put-link.m4 \
 	$(top_srcdir)/config/kernel-security-inode-init.m4 \

zfs/aclocal.m4

@@ -1245,6 +1245,7 @@ m4_include([config/kernel-fallocate.m4])
 m4_include([config/kernel-file-inode.m4])
 m4_include([config/kernel-fmode-t.m4])
 m4_include([config/kernel-follow-down-one.m4])
+m4_include([config/kernel-fst-mount.m4])
 m4_include([config/kernel-fsync.m4])
 m4_include([config/kernel-generic_io_acct.m4])
 m4_include([config/kernel-get-disk-ro.m4])
@@ -1260,7 +1261,6 @@ m4_include([config/kernel-lookup-nameidata.m4])
 m4_include([config/kernel-lseek-execute.m4])
 m4_include([config/kernel-mk-request-fn.m4])
 m4_include([config/kernel-mkdir-umode-t.m4])
-m4_include([config/kernel-mount-nodev.m4])
 m4_include([config/kernel-open-bdev-exclusive.m4])
 m4_include([config/kernel-put-link.m4])
 m4_include([config/kernel-security-inode-init.m4])

zfs/config/kernel-fst-mount.m4

+dnl #
+dnl # 2.6.38 API change
+dnl # The .get_sb callback has been replaced by a .mount callback
+dnl # in the file_system_type structure.
+dnl #
+AC_DEFUN([ZFS_AC_KERNEL_FST_MOUNT], [
+        AC_MSG_CHECKING([whether fst->mount() exists])
+        ZFS_LINUX_TRY_COMPILE([
+                #include <linux/fs.h>
+
+                static struct dentry *
+                mount(struct file_system_type *fs_type, int flags,
+                    const char *osname, void *data) {
+                        struct dentry *d = NULL;
+                        return (d);
+                }
+
+                static struct file_system_type fst __attribute__ ((unused)) = {
+                        .mount = mount,
+                };
+        ],[
+        ],[
+                AC_MSG_RESULT(yes)
+                AC_DEFINE(HAVE_FST_MOUNT, 1, [fst->mount() exists])
+        ],[
+                AC_MSG_RESULT(no)
+        ])
+])

zfs/config/kernel-mount-nodev.m4

-dnl #
-dnl # 2.6.39 API change
-dnl # The .get_sb callback has been replaced by a .mount callback
-dnl # in the file_system_type structure.  When using the new
-dnl # interface the caller must now use the mount_nodev() helper.
-dnl # This updated callback and helper no longer pass the vfsmount.
-dnl #
-AC_DEFUN([ZFS_AC_KERNEL_MOUNT_NODEV],
-	[AC_MSG_CHECKING([whether mount_nodev() is available])
-	ZFS_LINUX_TRY_COMPILE_SYMBOL([
-		#include <linux/fs.h>
-	], [
-		mount_nodev(NULL, 0, NULL, NULL);
-	], [mount_nodev], [fs/super.c], [
-		AC_MSG_RESULT(yes)
-		AC_DEFINE(HAVE_MOUNT_NODEV, 1, [mount_nodev() is available])
-	], [
-		AC_MSG_RESULT(no)
-	])
-])

zfs/config/kernel.m4

@@ -77,7 +77,7 @@ AC_DEFUN([ZFS_AC_CONFIG_KERNEL], [
 	ZFS_AC_KERNEL_TRUNCATE_SETSIZE
 	ZFS_AC_KERNEL_6ARGS_SECURITY_INODE_INIT_SECURITY
 	ZFS_AC_KERNEL_CALLBACK_SECURITY_INODE_INIT_SECURITY
-	ZFS_AC_KERNEL_MOUNT_NODEV
+	ZFS_AC_KERNEL_FST_MOUNT
 	ZFS_AC_KERNEL_SHRINK
 	ZFS_AC_KERNEL_SHRINK_CONTROL_HAS_NID
 	ZFS_AC_KERNEL_S_INSTANCES_LIST_HEAD

zfs/configure

@@ -21202,9 +21202,9 @@ fi
 
 
 
-	{ $as_echo "$as_me:${as_lineno-$LINENO}: checking whether mount_nodev() is available" >&5
-$as_echo_n "checking whether mount_nodev() is available... " >&6; }
 
+        { $as_echo "$as_me:${as_lineno-$LINENO}: checking whether fst->mount() exists" >&5
+$as_echo_n "checking whether fst->mount() exists... " >&6; }
 
 
 cat confdefs.h - <<_ACEOF >conftest.c
@@ -21212,11 +21212,21 @@ cat confdefs.h - <<_ACEOF >conftest.c
 
                 #include <linux/fs.h>
 
+                static struct dentry *
+                mount(struct file_system_type *fs_type, int flags,
+                    const char *osname, void *data) {
+                        struct dentry *d = NULL;
+                        return (d);
+                }
+
+                static struct file_system_type fst __attribute__ ((unused)) = {
+                        .mount = mount,
+                };
+
 int
 main (void)
 {
 
-		mount_nodev(NULL, 0, NULL, NULL);
 
   ;
   return 0;
@@ -21246,64 +21256,25 @@ _ACEOF
   ac_status=$?
   $as_echo "$as_me:${as_lineno-$LINENO}: \$? = $ac_status" >&5
   test $ac_status = 0; }; }; then :
-  rc=0
-else
-  $as_echo "$as_me: failed program was:" >&5
-sed 's/^/| /' conftest.$ac_ext >&5
- rc=1
-
-
-fi
-	rm -Rf build
-
 
-	if test $rc -ne 0; then :
+                { $as_echo "$as_me:${as_lineno-$LINENO}: result: yes" >&5
+$as_echo "yes" >&6; }
 
-		{ $as_echo "$as_me:${as_lineno-$LINENO}: result: no" >&5
-$as_echo "no" >&6; }
+$as_echo "#define HAVE_FST_MOUNT 1" >>confdefs.h
 
-	else
-		if test "x$enable_linux_builtin" != xyes; then
-
-	grep -q -E '[[:space:]]mount_nodev[[:space:]]' \
-		$LINUX_OBJ/$LINUX_SYMBOLS 2>/dev/null
-	rc=$?
-	if test $rc -ne 0; then
-		export=0
-		for file in fs/super.c; do
-			grep -q -E "EXPORT_SYMBOL.*(mount_nodev)" \
-				"$LINUX/$file" 2>/dev/null
-			rc=$?
-			if test $rc -eq 0; then
-				export=1
-				break;
-			fi
-		done
-		if test $export -eq 0; then :
-			rc=1
-		else :
-			rc=0
-		fi
-	else :
-		rc=0
-	fi
 
-		fi
-		if test $rc -ne 0; then :
+else
+  $as_echo "$as_me: failed program was:" >&5
+sed 's/^/| /' conftest.$ac_ext >&5
 
                 { $as_echo "$as_me:${as_lineno-$LINENO}: result: no" >&5
 $as_echo "no" >&6; }
 
-		else :
 
-		{ $as_echo "$as_me:${as_lineno-$LINENO}: result: yes" >&5
-$as_echo "yes" >&6; }
-
-$as_echo "#define HAVE_MOUNT_NODEV 1" >>confdefs.h
 
+fi
+	rm -Rf build
 
-		fi
-	fi
 
 
 
@@ -30596,9 +30567,9 @@ fi
 
 
 
-	{ $as_echo "$as_me:${as_lineno-$LINENO}: checking whether mount_nodev() is available" >&5
-$as_echo_n "checking whether mount_nodev() is available... " >&6; }
 
+        { $as_echo "$as_me:${as_lineno-$LINENO}: checking whether fst->mount() exists" >&5
+$as_echo_n "checking whether fst->mount() exists... " >&6; }
 
 
 cat confdefs.h - <<_ACEOF >conftest.c
@@ -30606,11 +30577,21 @@ cat confdefs.h - <<_ACEOF >conftest.c
 
                 #include <linux/fs.h>
 
+                static struct dentry *
+                mount(struct file_system_type *fs_type, int flags,
+                    const char *osname, void *data) {
+                        struct dentry *d = NULL;
+                        return (d);
+                }
+
+                static struct file_system_type fst __attribute__ ((unused)) = {
+                        .mount = mount,
+                };
+
 int
 main (void)
 {
 
-		mount_nodev(NULL, 0, NULL, NULL);
 
   ;
   return 0;
@@ -30640,64 +30621,25 @@ _ACEOF
   ac_status=$?
   $as_echo "$as_me:${as_lineno-$LINENO}: \$? = $ac_status" >&5
   test $ac_status = 0; }; }; then :
-  rc=0
-else
-  $as_echo "$as_me: failed program was:" >&5
-sed 's/^/| /' conftest.$ac_ext >&5
- rc=1
-
-
-fi
-	rm -Rf build
-
 
-	if test $rc -ne 0; then :
+                { $as_echo "$as_me:${as_lineno-$LINENO}: result: yes" >&5
+$as_echo "yes" >&6; }
 
-		{ $as_echo "$as_me:${as_lineno-$LINENO}: result: no" >&5
-$as_echo "no" >&6; }
+$as_echo "#define HAVE_FST_MOUNT 1" >>confdefs.h
 
-	else
-		if test "x$enable_linux_builtin" != xyes; then
-
-	grep -q -E '[[:space:]]mount_nodev[[:space:]]' \
-		$LINUX_OBJ/$LINUX_SYMBOLS 2>/dev/null
-	rc=$?
-	if test $rc -ne 0; then
-		export=0
-		for file in fs/super.c; do
-			grep -q -E "EXPORT_SYMBOL.*(mount_nodev)" \
-				"$LINUX/$file" 2>/dev/null
-			rc=$?
-			if test $rc -eq 0; then
-				export=1
-				break;
-			fi
-		done
-		if test $export -eq 0; then :
-			rc=1
-		else :
-			rc=0
-		fi
-	else :
-		rc=0
-	fi
 
-		fi
-		if test $rc -ne 0; then :
+else
+  $as_echo "$as_me: failed program was:" >&5
+sed 's/^/| /' conftest.$ac_ext >&5
 
                 { $as_echo "$as_me:${as_lineno-$LINENO}: result: no" >&5
 $as_echo "no" >&6; }
 
-		else :
 
-		{ $as_echo "$as_me:${as_lineno-$LINENO}: result: yes" >&5
-$as_echo "yes" >&6; }
-
-$as_echo "#define HAVE_MOUNT_NODEV 1" >>confdefs.h
 
+fi
+	rm -Rf build
 
-		fi
-	fi
 
 
 

zfs/contrib/Makefile.in

@@ -129,6 +129,7 @@ am__aclocal_m4_deps = $(top_srcdir)/config/always-no-bool-compare.m4 \
 	$(top_srcdir)/config/kernel-file-inode.m4 \
 	$(top_srcdir)/config/kernel-fmode-t.m4 \
 	$(top_srcdir)/config/kernel-follow-down-one.m4 \
+	$(top_srcdir)/config/kernel-fst-mount.m4 \
 	$(top_srcdir)/config/kernel-fsync.m4 \
 	$(top_srcdir)/config/kernel-generic_io_acct.m4 \
 	$(top_srcdir)/config/kernel-get-disk-ro.m4 \
@@ -144,7 +145,6 @@ am__aclocal_m4_deps = $(top_srcdir)/config/always-no-bool-compare.m4 \
 	$(top_srcdir)/config/kernel-lseek-execute.m4 \
 	$(top_srcdir)/config/kernel-mk-request-fn.m4 \
 	$(top_srcdir)/config/kernel-mkdir-umode-t.m4 \
-	$(top_srcdir)/config/kernel-mount-nodev.m4 \
 	$(top_srcdir)/config/kernel-open-bdev-exclusive.m4 \
 	$(top_srcdir)/config/kernel-put-link.m4 \
 	$(top_srcdir)/config/kernel-security-inode-init.m4 \

zfs/contrib/bash_completion.d/Makefile.in

@@ -130,6 +130,7 @@ am__aclocal_m4_deps = $(top_srcdir)/config/always-no-bool-compare.m4 \
 	$(top_srcdir)/config/kernel-file-inode.m4 \
 	$(top_srcdir)/config/kernel-fmode-t.m4 \
 	$(top_srcdir)/config/kernel-follow-down-one.m4 \
+	$(top_srcdir)/config/kernel-fst-mount.m4 \
 	$(top_srcdir)/config/kernel-fsync.m4 \
 	$(top_srcdir)/config/kernel-generic_io_acct.m4 \
 	$(top_srcdir)/config/kernel-get-disk-ro.m4 \
@@ -145,7 +146,6 @@ am__aclocal_m4_deps = $(top_srcdir)/config/always-no-bool-compare.m4 \
 	$(top_srcdir)/config/kernel-lseek-execute.m4 \
 	$(top_srcdir)/config/kernel-mk-request-fn.m4 \
 	$(top_srcdir)/config/kernel-mkdir-umode-t.m4 \
-	$(top_srcdir)/config/kernel-mount-nodev.m4 \
 	$(top_srcdir)/config/kernel-open-bdev-exclusive.m4 \
 	$(top_srcdir)/config/kernel-put-link.m4 \
 	$(top_srcdir)/config/kernel-security-inode-init.m4 \

zfs/contrib/dracut/90zfs/Makefile.in

@@ -130,6 +130,7 @@ am__aclocal_m4_deps = $(top_srcdir)/config/always-no-bool-compare.m4 \
 	$(top_srcdir)/config/kernel-file-inode.m4 \
 	$(top_srcdir)/config/kernel-fmode-t.m4 \
 	$(top_srcdir)/config/kernel-follow-down-one.m4 \
+	$(top_srcdir)/config/kernel-fst-mount.m4 \
 	$(top_srcdir)/config/kernel-fsync.m4 \
 	$(top_srcdir)/config/kernel-generic_io_acct.m4 \
 	$(top_srcdir)/config/kernel-get-disk-ro.m4 \
@@ -145,7 +146,6 @@ am__aclocal_m4_deps = $(top_srcdir)/config/always-no-bool-compare.m4 \
 	$(top_srcdir)/config/kernel-lseek-execute.m4 \
 	$(top_srcdir)/config/kernel-mk-request-fn.m4 \
 	$(top_srcdir)/config/kernel-mkdir-umode-t.m4 \
-	$(top_srcdir)/config/kernel-mount-nodev.m4 \
 	$(top_srcdir)/config/kernel-open-bdev-exclusive.m4 \
 	$(top_srcdir)/config/kernel-put-link.m4 \
 	$(top_srcdir)/config/kernel-security-inode-init.m4 \

zfs/contrib/dracut/Makefile.in

@@ -129,6 +129,7 @@ am__aclocal_m4_deps = $(top_srcdir)/config/always-no-bool-compare.m4 \
 	$(top_srcdir)/config/kernel-file-inode.m4 \
 	$(top_srcdir)/config/kernel-fmode-t.m4 \
 	$(top_srcdir)/config/kernel-follow-down-one.m4 \
+	$(top_srcdir)/config/kernel-fst-mount.m4 \
 	$(top_srcdir)/config/kernel-fsync.m4 \
 	$(top_srcdir)/config/kernel-generic_io_acct.m4 \
 	$(top_srcdir)/config/kernel-get-disk-ro.m4 \
@@ -144,7 +145,6 @@ am__aclocal_m4_deps = $(top_srcdir)/config/always-no-bool-compare.m4 \
 	$(top_srcdir)/config/kernel-lseek-execute.m4 \
 	$(top_srcdir)/config/kernel-mk-request-fn.m4 \
 	$(top_srcdir)/config/kernel-mkdir-umode-t.m4 \
-	$(top_srcdir)/config/kernel-mount-nodev.m4 \
 	$(top_srcdir)/config/kernel-open-bdev-exclusive.m4 \
 	$(top_srcdir)/config/kernel-put-link.m4 \
 	$(top_srcdir)/config/kernel-security-inode-init.m4 \

zfs/contrib/initramfs/Makefile.in

@@ -130,6 +130,7 @@ am__aclocal_m4_deps = $(top_srcdir)/config/always-no-bool-compare.m4 \
 	$(top_srcdir)/config/kernel-file-inode.m4 \
 	$(top_srcdir)/config/kernel-fmode-t.m4 \
 	$(top_srcdir)/config/kernel-follow-down-one.m4 \
+	$(top_srcdir)/config/kernel-fst-mount.m4 \
 	$(top_srcdir)/config/kernel-fsync.m4 \
 	$(top_srcdir)/config/kernel-generic_io_acct.m4 \
 	$(top_srcdir)/config/kernel-get-disk-ro.m4 \
@@ -145,7 +146,6 @@ am__aclocal_m4_deps = $(top_srcdir)/config/always-no-bool-compare.m4 \
 	$(top_srcdir)/config/kernel-lseek-execute.m4 \
 	$(top_srcdir)/config/kernel-mk-request-fn.m4 \
 	$(top_srcdir)/config/kernel-mkdir-umode-t.m4 \
-	$(top_srcdir)/config/kernel-mount-nodev.m4 \
 	$(top_srcdir)/config/kernel-open-bdev-exclusive.m4 \
 	$(top_srcdir)/config/kernel-put-link.m4 \
 	$(top_srcdir)/config/kernel-security-inode-init.m4 \

zfs/include/Makefile.in

@@ -130,6 +130,7 @@ am__aclocal_m4_deps = $(top_srcdir)/config/always-no-bool-compare.m4 \
 	$(top_srcdir)/config/kernel-file-inode.m4 \
 	$(top_srcdir)/config/kernel-fmode-t.m4 \
 	$(top_srcdir)/config/kernel-follow-down-one.m4 \
+	$(top_srcdir)/config/kernel-fst-mount.m4 \
 	$(top_srcdir)/config/kernel-fsync.m4 \
 	$(top_srcdir)/config/kernel-generic_io_acct.m4 \
 	$(top_srcdir)/config/kernel-get-disk-ro.m4 \
@@ -145,7 +146,6 @@ am__aclocal_m4_deps = $(top_srcdir)/config/always-no-bool-compare.m4 \
 	$(top_srcdir)/config/kernel-lseek-execute.m4 \
 	$(top_srcdir)/config/kernel-mk-request-fn.m4 \
 	$(top_srcdir)/config/kernel-mkdir-umode-t.m4 \
-	$(top_srcdir)/config/kernel-mount-nodev.m4 \
 	$(top_srcdir)/config/kernel-open-bdev-exclusive.m4 \
 	$(top_srcdir)/config/kernel-put-link.m4 \
 	$(top_srcdir)/config/kernel-security-inode-init.m4 \

zfs/include/linux/Makefile.in

@@ -130,6 +130,7 @@ am__aclocal_m4_deps = $(top_srcdir)/config/always-no-bool-compare.m4 \
 	$(top_srcdir)/config/kernel-file-inode.m4 \
 	$(top_srcdir)/config/kernel-fmode-t.m4 \
 	$(top_srcdir)/config/kernel-follow-down-one.m4 \
+	$(top_srcdir)/config/kernel-fst-mount.m4 \
 	$(top_srcdir)/config/kernel-fsync.m4 \
 	$(top_srcdir)/config/kernel-generic_io_acct.m4 \
 	$(top_srcdir)/config/kernel-get-disk-ro.m4 \
@@ -145,7 +146,6 @@ am__aclocal_m4_deps = $(top_srcdir)/config/always-no-bool-compare.m4 \
 	$(top_srcdir)/config/kernel-lseek-execute.m4 \
 	$(top_srcdir)/config/kernel-mk-request-fn.m4 \
 	$(top_srcdir)/config/kernel-mkdir-umode-t.m4 \
-	$(top_srcdir)/config/kernel-mount-nodev.m4 \
 	$(top_srcdir)/config/kernel-open-bdev-exclusive.m4 \
 	$(top_srcdir)/config/kernel-put-link.m4 \
 	$(top_srcdir)/config/kernel-security-inode-init.m4 \

zfs/include/linux/vfs_compat.h

@@ -111,6 +111,30 @@ zpl_bdi_setup_and_register(struct backing_dev_info *bdi, char *name)
 }
 #endif
 
+/*
+ * 4.14 adds SB_* flag definitions, define them to MS_* equivalents
+ * if not set.
+ */
+#ifndef		SB_RDONLY
+#define		SB_RDONLY	MS_RDONLY
+#endif
+
+#ifndef		SB_SILENT
+#define		SB_SILENT	MS_SILENT
+#endif
+
+#ifndef		SB_ACTIVE
+#define		SB_ACTIVE	MS_ACTIVE
+#endif
+
+#ifndef		SB_POSIXACL
+#define		SB_POSIXACL	MS_POSIXACL
+#endif
+
+#ifndef		SB_MANDLOCK
+#define		SB_MANDLOCK	MS_MANDLOCK
+#endif
+
 /*
  * 2.6.38 API change,
  * LOOKUP_RCU flag introduced to distinguish rcu-walk from ref-walk cases.

zfs/include/sys/Makefile.in

@@ -130,6 +130,7 @@ am__aclocal_m4_deps = $(top_srcdir)/config/always-no-bool-compare.m4 \
 	$(top_srcdir)/config/kernel-file-inode.m4 \
 	$(top_srcdir)/config/kernel-fmode-t.m4 \
 	$(top_srcdir)/config/kernel-follow-down-one.m4 \
+	$(top_srcdir)/config/kernel-fst-mount.m4 \
 	$(top_srcdir)/config/kernel-fsync.m4 \
 	$(top_srcdir)/config/kernel-generic_io_acct.m4 \
 	$(top_srcdir)/config/kernel-get-disk-ro.m4 \
@@ -145,7 +146,6 @@ am__aclocal_m4_deps = $(top_srcdir)/config/always-no-bool-compare.m4 \
 	$(top_srcdir)/config/kernel-lseek-execute.m4 \
 	$(top_srcdir)/config/kernel-mk-request-fn.m4 \
 	$(top_srcdir)/config/kernel-mkdir-umode-t.m4 \
-	$(top_srcdir)/config/kernel-mount-nodev.m4 \
 	$(top_srcdir)/config/kernel-open-bdev-exclusive.m4 \
 	$(top_srcdir)/config/kernel-put-link.m4 \
 	$(top_srcdir)/config/kernel-security-inode-init.m4 \

zfs/include/sys/fm/Makefile.in

@@ -130,6 +130,7 @@ am__aclocal_m4_deps = $(top_srcdir)/config/always-no-bool-compare.m4 \
 	$(top_srcdir)/config/kernel-file-inode.m4 \
 	$(top_srcdir)/config/kernel-fmode-t.m4 \
 	$(top_srcdir)/config/kernel-follow-down-one.m4 \
+	$(top_srcdir)/config/kernel-fst-mount.m4 \
 	$(top_srcdir)/config/kernel-fsync.m4 \
 	$(top_srcdir)/config/kernel-generic_io_acct.m4 \
 	$(top_srcdir)/config/kernel-get-disk-ro.m4 \
@@ -145,7 +146,6 @@ am__aclocal_m4_deps = $(top_srcdir)/config/always-no-bool-compare.m4 \
 	$(top_srcdir)/config/kernel-lseek-execute.m4 \
 	$(top_srcdir)/config/kernel-mk-request-fn.m4 \
 	$(top_srcdir)/config/kernel-mkdir-umode-t.m4 \
-	$(top_srcdir)/config/kernel-mount-nodev.m4 \
 	$(top_srcdir)/config/kernel-open-bdev-exclusive.m4 \
 	$(top_srcdir)/config/kernel-put-link.m4 \
 	$(top_srcdir)/config/kernel-security-inode-init.m4 \

zfs/include/sys/fm/fs/Makefile.in

@@ -130,6 +130,7 @@ am__aclocal_m4_deps = $(top_srcdir)/config/always-no-bool-compare.m4 \
 	$(top_srcdir)/config/kernel-file-inode.m4 \
 	$(top_srcdir)/config/kernel-fmode-t.m4 \
 	$(top_srcdir)/config/kernel-follow-down-one.m4 \
+	$(top_srcdir)/config/kernel-fst-mount.m4 \
 	$(top_srcdir)/config/kernel-fsync.m4 \
 	$(top_srcdir)/config/kernel-generic_io_acct.m4 \
 	$(top_srcdir)/config/kernel-get-disk-ro.m4 \
@@ -145,7 +146,6 @@ am__aclocal_m4_deps = $(top_srcdir)/config/always-no-bool-compare.m4 \
 	$(top_srcdir)/config/kernel-lseek-execute.m4 \
 	$(top_srcdir)/config/kernel-mk-request-fn.m4 \
 	$(top_srcdir)/config/kernel-mkdir-umode-t.m4 \
-	$(top_srcdir)/config/kernel-mount-nodev.m4 \
 	$(top_srcdir)/config/kernel-open-bdev-exclusive.m4 \
 	$(top_srcdir)/config/kernel-put-link.m4 \
 	$(top_srcdir)/config/kernel-security-inode-init.m4 \

zfs/include/sys/fs/Makefile.in

@@ -130,6 +130,7 @@ am__aclocal_m4_deps = $(top_srcdir)/config/always-no-bool-compare.m4 \
 	$(top_srcdir)/config/kernel-file-inode.m4 \
 	$(top_srcdir)/config/kernel-fmode-t.m4 \
 	$(top_srcdir)/config/kernel-follow-down-one.m4 \
+	$(top_srcdir)/config/kernel-fst-mount.m4 \
 	$(top_srcdir)/config/kernel-fsync.m4 \
 	$(top_srcdir)/config/kernel-generic_io_acct.m4 \
 	$(top_srcdir)/config/kernel-get-disk-ro.m4 \
@@ -145,7 +146,6 @@ am__aclocal_m4_deps = $(top_srcdir)/config/always-no-bool-compare.m4 \
 	$(top_srcdir)/config/kernel-lseek-execute.m4 \
 	$(top_srcdir)/config/kernel-mk-request-fn.m4 \
 	$(top_srcdir)/config/kernel-mkdir-umode-t.m4 \
-	$(top_srcdir)/config/kernel-mount-nodev.m4 \
 	$(top_srcdir)/config/kernel-open-bdev-exclusive.m4 \
 	$(top_srcdir)/config/kernel-put-link.m4 \
 	$(top_srcdir)/config/kernel-security-inode-init.m4 \

zfs/module/zfs/zpl_super.c

@@ -443,12 +443,56 @@ zpl_fill_super(struct super_block *sb, void *data, int silent)
 	return (error);
 }
 
-#ifdef HAVE_MOUNT_NODEV
+static int
+zpl_test_super(struct super_block *s, void *data)
+{
+	zfs_sb_t *zsb = s->s_fs_info;
+
+	objset_t *os = data;
+
+	if (zsb == NULL)
+		return (0);
+
+	return (os == zsb->z_os);
+}
+
+static struct super_block *
+zpl_mount_impl(struct file_system_type *fs_type, int flags, zfs_mntopts_t *zmo)
+{
+	struct super_block *s;
+	objset_t *os;
+	int err;
+
+	err = dmu_objset_hold(zmo->z_osname, FTAG, &os);
+	if (err)
+		return (ERR_PTR(-err));
+
+	s = zpl_sget(fs_type, zpl_test_super, set_anon_super, flags, os);
+	dmu_objset_rele(os, FTAG);
+	if (IS_ERR(s))
+		return (ERR_CAST(s));
+
+	if (s->s_root == NULL) {
+		err = zpl_fill_super(s, zmo, flags & SB_SILENT ? 1 : 0);
+		if (err) {
+			deactivate_locked_super(s);
+			return (ERR_PTR(err));
+		}
+		s->s_flags |= SB_ACTIVE;
+	} else if ((flags ^ s->s_flags) & SB_RDONLY) {
+		deactivate_locked_super(s);
+		return (ERR_PTR(-EBUSY));
+	}
+
+	return (s);
+}
+#ifdef HAVE_FST_MOUNT
 static struct dentry *
 zpl_mount(struct file_system_type *fs_type, int flags,
     const char *osname, void *data)
 {
 	zfs_mntopts_t *zmo = zfs_mntopts_alloc();
+	struct super_block *sb;
 	int error;
 
 	error = zpl_parse_options((char *)osname, (char *)data, zmo, B_FALSE);
@@ -456,8 +500,11 @@ zpl_mount(struct file_system_type *fs_type, int flags,
 		zfs_mntopts_free(zmo);
 		return (ERR_PTR(error));
 	}
+	sb = zpl_mount_impl(fs_type, flags, zmo);
+	if (IS_ERR(sb))
+		return (ERR_CAST(sb));
 
-	return (mount_nodev(fs_type, flags, zmo, zpl_fill_super));
+	return (dget(sb->s_root));
 }
 #else
 static int
@@ -465,6 +512,7 @@ zpl_get_sb(struct file_system_type *fs_type, int flags,
     const char *osname, void *data, struct vfsmount *mnt)
 {
 	zfs_mntopts_t *zmo = zfs_mntopts_alloc();
+	struct super_block *sb;
 	int error;
 
 	error = zpl_parse_options((char *)osname, (char *)data, zmo, B_FALSE);
@@ -472,10 +520,15 @@ zpl_get_sb(struct file_system_type *fs_type, int flags,
 		zfs_mntopts_free(zmo);
 		return (error);
 	}
+	sb = zpl_mount_impl(fs_type, flags, zmo);
+	if (IS_ERR(sb))
+		return (ERR_CAST(sb));
+
+	(void) simple_set_mnt(mnt, sb);
 
-	return (get_sb_nodev(fs_type, flags, zmo, zpl_fill_super, mnt));
+	return (0);
 }
-#endif /* HAVE_MOUNT_NODEV */
+#endif /* HAVE_FST_MOUNT */
 
 static void
 zpl_kill_sb(struct super_block *sb)
@@ -542,10 +595,10 @@ const struct super_operations zpl_super_operations = {
 struct file_system_type zpl_fs_type = {
 	.owner			= THIS_MODULE,
 	.name			= ZFS_DRIVER,
-#ifdef HAVE_MOUNT_NODEV
+#ifdef HAVE_FST_MOUNT
 	.mount			= zpl_mount,
 #else
 	.get_sb			= zpl_get_sb,
-#endif /* HAVE_MOUNT_NODEV */
+#endif /* HAVE_FST_MOUNT */
 	.kill_sb		= zpl_kill_sb,
 };

zfs/zfs_config.h.in

@@ -162,6 +162,9 @@
 /* sops->free_cached_objects() exists */
 #undef HAVE_FREE_CACHED_OBJECTS
 
+/* fst->mount() exists */
+#undef HAVE_FST_MOUNT
+
 /* fops->fsync() with range */
 #undef HAVE_FSYNC_RANGE
 
@@ -252,9 +255,6 @@
 /* Define to 1 if you have the `mlockall' function. */
 #undef HAVE_MLOCKALL
 
-/* mount_nodev() is available */
-#undef HAVE_MOUNT_NODEV
-
 /* sops->nr_cached_objects() exists */
 #undef HAVE_NR_CACHED_OBJECTS