[SRC,XENIAL] UBUNTU: SAUCE: Allow mounting datasets more than once (LP: #1759848)

From: Colin Ian King <colin.king@canonical.com>

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>
---
 zfs/META                                  |   2 +-
 zfs/Makefile.in                           |   2 +-
 zfs/aclocal.m4                            |   2 +-
 zfs/config/kernel-fst-mount.m4            |  28 ++++++
 zfs/config/kernel-mount-nodev.m4          |  20 ----
 zfs/config/kernel.m4                      |   2 +-
 zfs/configure                             | 150 +++++++++---------------------
 zfs/contrib/Makefile.in                   |   2 +-
 zfs/contrib/bash_completion.d/Makefile.in |   2 +-
 zfs/contrib/dracut/90zfs/Makefile.in      |   2 +-
 zfs/contrib/dracut/Makefile.in            |   2 +-
 zfs/contrib/initramfs/Makefile.in         |   2 +-
 zfs/include/Makefile.in                   |   2 +-
 zfs/include/linux/Makefile.in             |   2 +-
 zfs/include/linux/vfs_compat.h            |  24 +++++
 zfs/include/sys/Makefile.in               |   2 +-
 zfs/include/sys/fm/Makefile.in            |   2 +-
 zfs/include/sys/fm/fs/Makefile.in         |   2 +-
 zfs/include/sys/fs/Makefile.in            |   2 +-
 zfs/module/zfs/zpl_super.c                |  65 +++++++++++--
 zfs/zfs_config.h.in                       |   6 +-
 21 files changed, 175 insertions(+), 148 deletions(-)
 create mode 100644 zfs/config/kernel-fst-mount.m4
 delete mode 100644 zfs/config/kernel-mount-nodev.m4

On Mon, Jun 25, 2018 at 08:36:41PM +0100, Colin King wrote:
> From: Colin Ian King <colin.king@canonical.com>
> 
> 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>

Backport looks good.

Acked-by: Seth Forshee <seth.forshee@canonical.com>

On 25/06/18 20:36, Colin King wrote:
> From: Colin Ian King <colin.king@canonical.com>
> 
> 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>
> ---
>  zfs/META                                  |   2 +-
>  zfs/Makefile.in                           |   2 +-
>  zfs/aclocal.m4                            |   2 +-
>  zfs/config/kernel-fst-mount.m4            |  28 ++++++
>  zfs/config/kernel-mount-nodev.m4          |  20 ----
>  zfs/config/kernel.m4                      |   2 +-
>  zfs/configure                             | 150 +++++++++---------------------
>  zfs/contrib/Makefile.in                   |   2 +-
>  zfs/contrib/bash_completion.d/Makefile.in |   2 +-
>  zfs/contrib/dracut/90zfs/Makefile.in      |   2 +-
>  zfs/contrib/dracut/Makefile.in            |   2 +-
>  zfs/contrib/initramfs/Makefile.in         |   2 +-
>  zfs/include/Makefile.in                   |   2 +-
>  zfs/include/linux/Makefile.in             |   2 +-
>  zfs/include/linux/vfs_compat.h            |  24 +++++
>  zfs/include/sys/Makefile.in               |   2 +-
>  zfs/include/sys/fm/Makefile.in            |   2 +-
>  zfs/include/sys/fm/fs/Makefile.in         |   2 +-
>  zfs/include/sys/fs/Makefile.in            |   2 +-
>  zfs/module/zfs/zpl_super.c                |  65 +++++++++++--
>  zfs/zfs_config.h.in                       |   6 +-
>  21 files changed, 175 insertions(+), 148 deletions(-)
>  create mode 100644 zfs/config/kernel-fst-mount.m4
>  delete mode 100644 zfs/config/kernel-mount-nodev.m4
> 
> diff --git a/zfs/META b/zfs/META
> index 6c7026c..6837592 100644
> --- a/zfs/META
> +++ b/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
> diff --git a/zfs/Makefile.in b/zfs/Makefile.in
> index 8f68539..f9b0f69 100644
> --- a/zfs/Makefile.in
> +++ b/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 \
> diff --git a/zfs/aclocal.m4 b/zfs/aclocal.m4
> index 391fd54..75a4bfe 100644
> --- a/zfs/aclocal.m4
> +++ b/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])
> diff --git a/zfs/config/kernel-fst-mount.m4 b/zfs/config/kernel-fst-mount.m4
> new file mode 100644
> index 0000000..a8ac50b
> --- /dev/null
> +++ b/zfs/config/kernel-fst-mount.m4
> @@ -0,0 +1,28 @@
> +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)
> +        ])
> +])
> diff --git a/zfs/config/kernel-mount-nodev.m4 b/zfs/config/kernel-mount-nodev.m4
> deleted file mode 100644
> index 28a4515..0000000
> --- a/zfs/config/kernel-mount-nodev.m4
> +++ /dev/null
> @@ -1,20 +0,0 @@
> -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)
> -	])
> -])
> diff --git a/zfs/config/kernel.m4 b/zfs/config/kernel.m4
> index 0eddc2f..0ba5f07d 100644
> --- a/zfs/config/kernel.m4
> +++ b/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
> diff --git a/zfs/configure b/zfs/configure
> index 8d61725..502dec9 100755
> --- a/zfs/configure
> +++ b/zfs/configure
> @@ -21202,21 +21202,31 @@ 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
> +$as_echo_n "checking whether fst->mount() exists... " >&6; }
>  
>  
>  cat confdefs.h - <<_ACEOF >conftest.c
>  
>  
> -		#include <linux/fs.h>
> +                #include <linux/fs.h>
> +
> +                static struct dentry *
> +                mount(struct file_system_type *fs_type, int flags,
> +                    const char *osname, void *data) {
> +                        struct dentry *d = NULL;
> +                        return (d);
> +                }
> +
> +                static struct file_system_type fst __attribute__ ((unused)) = {
> +                        .mount = mount,
> +                };
>  
>  int
>  main (void)
>  {
>  
> -		mount_nodev(NULL, 0, NULL, NULL);
>  
>    ;
>    return 0;
> @@ -21246,64 +21256,25 @@ _ACEOF
>    ac_status=$?
>    $as_echo "$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
> +                { $as_echo "$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
>  
>  
>  
> @@ -30596,21 +30567,31 @@ 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
> +$as_echo_n "checking whether fst->mount() exists... " >&6; }
>  
>  
>  cat confdefs.h - <<_ACEOF >conftest.c
>  
>  
> -		#include <linux/fs.h>
> +                #include <linux/fs.h>
> +
> +                static struct dentry *
> +                mount(struct file_system_type *fs_type, int flags,
> +                    const char *osname, void *data) {
> +                        struct dentry *d = NULL;
> +                        return (d);
> +                }
> +
> +                static struct file_system_type fst __attribute__ ((unused)) = {
> +                        .mount = mount,
> +                };
>  
>  int
>  main (void)
>  {
>  
> -		mount_nodev(NULL, 0, NULL, NULL);
>  
>    ;
>    return 0;
> @@ -30640,64 +30621,25 @@ _ACEOF
>    ac_status=$?
>    $as_echo "$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
> +                { $as_echo "$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
>  
>  
>  
> diff --git a/zfs/contrib/Makefile.in b/zfs/contrib/Makefile.in
> index 1ced2ca..c1204cd 100644
> --- a/zfs/contrib/Makefile.in
> +++ b/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 \
> diff --git a/zfs/contrib/bash_completion.d/Makefile.in b/zfs/contrib/bash_completion.d/Makefile.in
> index a848010..f29d5cc 100644
> --- a/zfs/contrib/bash_completion.d/Makefile.in
> +++ b/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 \
> diff --git a/zfs/contrib/dracut/90zfs/Makefile.in b/zfs/contrib/dracut/90zfs/Makefile.in
> index 80f3262..63da6ed 100644
> --- a/zfs/contrib/dracut/90zfs/Makefile.in
> +++ b/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 \
> diff --git a/zfs/contrib/dracut/Makefile.in b/zfs/contrib/dracut/Makefile.in
> index 5136e7f..eed070a 100644
> --- a/zfs/contrib/dracut/Makefile.in
> +++ b/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 \
> diff --git a/zfs/contrib/initramfs/Makefile.in b/zfs/contrib/initramfs/Makefile.in
> index 5bf9c44..7a567be 100644
> --- a/zfs/contrib/initramfs/Makefile.in
> +++ b/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 \
> diff --git a/zfs/include/Makefile.in b/zfs/include/Makefile.in
> index 5dcbe26..be50bca 100644
> --- a/zfs/include/Makefile.in
> +++ b/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 \
> diff --git a/zfs/include/linux/Makefile.in b/zfs/include/linux/Makefile.in
> index 52deade..70974df 100644
> --- a/zfs/include/linux/Makefile.in
> +++ b/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 \
> diff --git a/zfs/include/linux/vfs_compat.h b/zfs/include/linux/vfs_compat.h
> index 8037055..f440f36 100644
> --- a/zfs/include/linux/vfs_compat.h
> +++ b/zfs/include/linux/vfs_compat.h
> @@ -112,6 +112,30 @@ 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.
>   */
> diff --git a/zfs/include/sys/Makefile.in b/zfs/include/sys/Makefile.in
> index 20f498f..c0a0c2d 100644
> --- a/zfs/include/sys/Makefile.in
> +++ b/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 \
> diff --git a/zfs/include/sys/fm/Makefile.in b/zfs/include/sys/fm/Makefile.in
> index d8d132f..b6f5397 100644
> --- a/zfs/include/sys/fm/Makefile.in
> +++ b/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 \
> diff --git a/zfs/include/sys/fm/fs/Makefile.in b/zfs/include/sys/fm/fs/Makefile.in
> index 2c61a5e..a1216fb 100644
> --- a/zfs/include/sys/fm/fs/Makefile.in
> +++ b/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 \
> diff --git a/zfs/include/sys/fs/Makefile.in b/zfs/include/sys/fs/Makefile.in
> index 95d7b62..4715b29 100644
> --- a/zfs/include/sys/fs/Makefile.in
> +++ b/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 \
> diff --git a/zfs/module/zfs/zpl_super.c b/zfs/module/zfs/zpl_super.c
> index bcdbbd6..f75a0d8 100644
> --- a/zfs/module/zfs/zpl_super.c
> +++ b/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,
>  };
> diff --git a/zfs/zfs_config.h.in b/zfs/zfs_config.h.in
> index c5026c8..60cf471 100644
> --- a/zfs/zfs_config.h.in
> +++ b/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
>  
> 

Did this get a 2nd ACK and applied?

Note. Subject should be [PATCH][SRU][XENUAL]...



On 26/06/18 14:11, Seth Forshee wrote:
> On Mon, Jun 25, 2018 at 08:36:41PM +0100, Colin King wrote:
>> From: Colin Ian King <colin.king@canonical.com>
>>
>> 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>
> 
> Backport looks good.
> 
> Acked-by: Seth Forshee <seth.forshee@canonical.com>
>

On 25.06.2018 21:36, Colin King wrote:
> From: Colin Ian King <colin.king@canonical.com>
> 
> 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: Stefan Bader <stefan.bader@canonical.com>
> ---

Had not had a 2nd ack and therefor not, yet applied. But might be now.

-Stefan

>  zfs/META                                  |   2 +-
>  zfs/Makefile.in                           |   2 +-
>  zfs/aclocal.m4                            |   2 +-
>  zfs/config/kernel-fst-mount.m4            |  28 ++++++
>  zfs/config/kernel-mount-nodev.m4          |  20 ----
>  zfs/config/kernel.m4                      |   2 +-
>  zfs/configure                             | 150 +++++++++---------------------
>  zfs/contrib/Makefile.in                   |   2 +-
>  zfs/contrib/bash_completion.d/Makefile.in |   2 +-
>  zfs/contrib/dracut/90zfs/Makefile.in      |   2 +-
>  zfs/contrib/dracut/Makefile.in            |   2 +-
>  zfs/contrib/initramfs/Makefile.in         |   2 +-
>  zfs/include/Makefile.in                   |   2 +-
>  zfs/include/linux/Makefile.in             |   2 +-
>  zfs/include/linux/vfs_compat.h            |  24 +++++
>  zfs/include/sys/Makefile.in               |   2 +-
>  zfs/include/sys/fm/Makefile.in            |   2 +-
>  zfs/include/sys/fm/fs/Makefile.in         |   2 +-
>  zfs/include/sys/fs/Makefile.in            |   2 +-
>  zfs/module/zfs/zpl_super.c                |  65 +++++++++++--
>  zfs/zfs_config.h.in                       |   6 +-
>  21 files changed, 175 insertions(+), 148 deletions(-)
>  create mode 100644 zfs/config/kernel-fst-mount.m4
>  delete mode 100644 zfs/config/kernel-mount-nodev.m4
> 
> diff --git a/zfs/META b/zfs/META
> index 6c7026c..6837592 100644
> --- a/zfs/META
> +++ b/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
> diff --git a/zfs/Makefile.in b/zfs/Makefile.in
> index 8f68539..f9b0f69 100644
> --- a/zfs/Makefile.in
> +++ b/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 \
> diff --git a/zfs/aclocal.m4 b/zfs/aclocal.m4
> index 391fd54..75a4bfe 100644
> --- a/zfs/aclocal.m4
> +++ b/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])
> diff --git a/zfs/config/kernel-fst-mount.m4 b/zfs/config/kernel-fst-mount.m4
> new file mode 100644
> index 0000000..a8ac50b
> --- /dev/null
> +++ b/zfs/config/kernel-fst-mount.m4
> @@ -0,0 +1,28 @@
> +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)
> +        ])
> +])
> diff --git a/zfs/config/kernel-mount-nodev.m4 b/zfs/config/kernel-mount-nodev.m4
> deleted file mode 100644
> index 28a4515..0000000
> --- a/zfs/config/kernel-mount-nodev.m4
> +++ /dev/null
> @@ -1,20 +0,0 @@
> -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)
> -	])
> -])
> diff --git a/zfs/config/kernel.m4 b/zfs/config/kernel.m4
> index 0eddc2f..0ba5f07d 100644
> --- a/zfs/config/kernel.m4
> +++ b/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
> diff --git a/zfs/configure b/zfs/configure
> index 8d61725..502dec9 100755
> --- a/zfs/configure
> +++ b/zfs/configure
> @@ -21202,21 +21202,31 @@ 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
> +$as_echo_n "checking whether fst->mount() exists... " >&6; }
>  
>  
>  cat confdefs.h - <<_ACEOF >conftest.c
>  
>  
> -		#include <linux/fs.h>
> +                #include <linux/fs.h>
> +
> +                static struct dentry *
> +                mount(struct file_system_type *fs_type, int flags,
> +                    const char *osname, void *data) {
> +                        struct dentry *d = NULL;
> +                        return (d);
> +                }
> +
> +                static struct file_system_type fst __attribute__ ((unused)) = {
> +                        .mount = mount,
> +                };
>  
>  int
>  main (void)
>  {
>  
> -		mount_nodev(NULL, 0, NULL, NULL);
>  
>    ;
>    return 0;
> @@ -21246,64 +21256,25 @@ _ACEOF
>    ac_status=$?
>    $as_echo "$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
> +                { $as_echo "$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
>  
>  
>  
> @@ -30596,21 +30567,31 @@ 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
> +$as_echo_n "checking whether fst->mount() exists... " >&6; }
>  
>  
>  cat confdefs.h - <<_ACEOF >conftest.c
>  
>  
> -		#include <linux/fs.h>
> +                #include <linux/fs.h>
> +
> +                static struct dentry *
> +                mount(struct file_system_type *fs_type, int flags,
> +                    const char *osname, void *data) {
> +                        struct dentry *d = NULL;
> +                        return (d);
> +                }
> +
> +                static struct file_system_type fst __attribute__ ((unused)) = {
> +                        .mount = mount,
> +                };
>  
>  int
>  main (void)
>  {
>  
> -		mount_nodev(NULL, 0, NULL, NULL);
>  
>    ;
>    return 0;
> @@ -30640,64 +30621,25 @@ _ACEOF
>    ac_status=$?
>    $as_echo "$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
> +                { $as_echo "$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
>  
>  
>  
> diff --git a/zfs/contrib/Makefile.in b/zfs/contrib/Makefile.in
> index 1ced2ca..c1204cd 100644
> --- a/zfs/contrib/Makefile.in
> +++ b/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 \
> diff --git a/zfs/contrib/bash_completion.d/Makefile.in b/zfs/contrib/bash_completion.d/Makefile.in
> index a848010..f29d5cc 100644
> --- a/zfs/contrib/bash_completion.d/Makefile.in
> +++ b/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 \
> diff --git a/zfs/contrib/dracut/90zfs/Makefile.in b/zfs/contrib/dracut/90zfs/Makefile.in
> index 80f3262..63da6ed 100644
> --- a/zfs/contrib/dracut/90zfs/Makefile.in
> +++ b/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 \
> diff --git a/zfs/contrib/dracut/Makefile.in b/zfs/contrib/dracut/Makefile.in
> index 5136e7f..eed070a 100644
> --- a/zfs/contrib/dracut/Makefile.in
> +++ b/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 \
> diff --git a/zfs/contrib/initramfs/Makefile.in b/zfs/contrib/initramfs/Makefile.in
> index 5bf9c44..7a567be 100644
> --- a/zfs/contrib/initramfs/Makefile.in
> +++ b/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 \
> diff --git a/zfs/include/Makefile.in b/zfs/include/Makefile.in
> index 5dcbe26..be50bca 100644
> --- a/zfs/include/Makefile.in
> +++ b/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 \
> diff --git a/zfs/include/linux/Makefile.in b/zfs/include/linux/Makefile.in
> index 52deade..70974df 100644
> --- a/zfs/include/linux/Makefile.in
> +++ b/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 \
> diff --git a/zfs/include/linux/vfs_compat.h b/zfs/include/linux/vfs_compat.h
> index 8037055..f440f36 100644
> --- a/zfs/include/linux/vfs_compat.h
> +++ b/zfs/include/linux/vfs_compat.h
> @@ -112,6 +112,30 @@ 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.
>   */
> diff --git a/zfs/include/sys/Makefile.in b/zfs/include/sys/Makefile.in
> index 20f498f..c0a0c2d 100644
> --- a/zfs/include/sys/Makefile.in
> +++ b/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 \
> diff --git a/zfs/include/sys/fm/Makefile.in b/zfs/include/sys/fm/Makefile.in
> index d8d132f..b6f5397 100644
> --- a/zfs/include/sys/fm/Makefile.in
> +++ b/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 \
> diff --git a/zfs/include/sys/fm/fs/Makefile.in b/zfs/include/sys/fm/fs/Makefile.in
> index 2c61a5e..a1216fb 100644
> --- a/zfs/include/sys/fm/fs/Makefile.in
> +++ b/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 \
> diff --git a/zfs/include/sys/fs/Makefile.in b/zfs/include/sys/fs/Makefile.in
> index 95d7b62..4715b29 100644
> --- a/zfs/include/sys/fs/Makefile.in
> +++ b/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 \
> diff --git a/zfs/module/zfs/zpl_super.c b/zfs/module/zfs/zpl_super.c
> index bcdbbd6..f75a0d8 100644
> --- a/zfs/module/zfs/zpl_super.c
> +++ b/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,
>  };
> diff --git a/zfs/zfs_config.h.in b/zfs/zfs_config.h.in
> index c5026c8..60cf471 100644
> --- a/zfs/zfs_config.h.in
> +++ b/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
>  
>

On 06/25/18 21:36, Colin King wrote:
> From: Colin Ian King <colin.king@canonical.com>
> 
> 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>
> ---
>  zfs/META                                  |   2 +-
>  zfs/Makefile.in                           |   2 +-
>  zfs/aclocal.m4                            |   2 +-
>  zfs/config/kernel-fst-mount.m4            |  28 ++++++
>  zfs/config/kernel-mount-nodev.m4          |  20 ----
>  zfs/config/kernel.m4                      |   2 +-
>  zfs/configure                             | 150 +++++++++---------------------
>  zfs/contrib/Makefile.in                   |   2 +-
>  zfs/contrib/bash_completion.d/Makefile.in |   2 +-
>  zfs/contrib/dracut/90zfs/Makefile.in      |   2 +-
>  zfs/contrib/dracut/Makefile.in            |   2 +-
>  zfs/contrib/initramfs/Makefile.in         |   2 +-
>  zfs/include/Makefile.in                   |   2 +-
>  zfs/include/linux/Makefile.in             |   2 +-
>  zfs/include/linux/vfs_compat.h            |  24 +++++
>  zfs/include/sys/Makefile.in               |   2 +-
>  zfs/include/sys/fm/Makefile.in            |   2 +-
>  zfs/include/sys/fm/fs/Makefile.in         |   2 +-
>  zfs/include/sys/fs/Makefile.in            |   2 +-
>  zfs/module/zfs/zpl_super.c                |  65 +++++++++++--
>  zfs/zfs_config.h.in                       |   6 +-
>  21 files changed, 175 insertions(+), 148 deletions(-)
>  create mode 100644 zfs/config/kernel-fst-mount.m4
>  delete mode 100644 zfs/config/kernel-mount-nodev.m4
> 
> diff --git a/zfs/META b/zfs/META
> index 6c7026c..6837592 100644
> --- a/zfs/META
> +++ b/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
> diff --git a/zfs/Makefile.in b/zfs/Makefile.in
> index 8f68539..f9b0f69 100644
> --- a/zfs/Makefile.in
> +++ b/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 \
> diff --git a/zfs/aclocal.m4 b/zfs/aclocal.m4
> index 391fd54..75a4bfe 100644
> --- a/zfs/aclocal.m4
> +++ b/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])
> diff --git a/zfs/config/kernel-fst-mount.m4 b/zfs/config/kernel-fst-mount.m4
> new file mode 100644
> index 0000000..a8ac50b
> --- /dev/null
> +++ b/zfs/config/kernel-fst-mount.m4
> @@ -0,0 +1,28 @@
> +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)
> +        ])
> +])
> diff --git a/zfs/config/kernel-mount-nodev.m4 b/zfs/config/kernel-mount-nodev.m4
> deleted file mode 100644
> index 28a4515..0000000
> --- a/zfs/config/kernel-mount-nodev.m4
> +++ /dev/null
> @@ -1,20 +0,0 @@
> -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)
> -	])
> -])
> diff --git a/zfs/config/kernel.m4 b/zfs/config/kernel.m4
> index 0eddc2f..0ba5f07d 100644
> --- a/zfs/config/kernel.m4
> +++ b/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
> diff --git a/zfs/configure b/zfs/configure
> index 8d61725..502dec9 100755
> --- a/zfs/configure
> +++ b/zfs/configure
> @@ -21202,21 +21202,31 @@ 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
> +$as_echo_n "checking whether fst->mount() exists... " >&6; }
>  
>  
>  cat confdefs.h - <<_ACEOF >conftest.c
>  
>  
> -		#include <linux/fs.h>
> +                #include <linux/fs.h>
> +
> +                static struct dentry *
> +                mount(struct file_system_type *fs_type, int flags,
> +                    const char *osname, void *data) {
> +                        struct dentry *d = NULL;
> +                        return (d);
> +                }
> +
> +                static struct file_system_type fst __attribute__ ((unused)) = {
> +                        .mount = mount,
> +                };
>  
>  int
>  main (void)
>  {
>  
> -		mount_nodev(NULL, 0, NULL, NULL);
>  
>    ;
>    return 0;
> @@ -21246,64 +21256,25 @@ _ACEOF
>    ac_status=$?
>    $as_echo "$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
> +                { $as_echo "$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
>  
>  
>  
> @@ -30596,21 +30567,31 @@ 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
> +$as_echo_n "checking whether fst->mount() exists... " >&6; }
>  
>  
>  cat confdefs.h - <<_ACEOF >conftest.c
>  
>  
> -		#include <linux/fs.h>
> +                #include <linux/fs.h>
> +
> +                static struct dentry *
> +                mount(struct file_system_type *fs_type, int flags,
> +                    const char *osname, void *data) {
> +                        struct dentry *d = NULL;
> +                        return (d);
> +                }
> +
> +                static struct file_system_type fst __attribute__ ((unused)) = {
> +                        .mount = mount,
> +                };
>  
>  int
>  main (void)
>  {
>  
> -		mount_nodev(NULL, 0, NULL, NULL);
>  
>    ;
>    return 0;
> @@ -30640,64 +30621,25 @@ _ACEOF
>    ac_status=$?
>    $as_echo "$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
> +                { $as_echo "$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
>  
>  
>  
> diff --git a/zfs/contrib/Makefile.in b/zfs/contrib/Makefile.in
> index 1ced2ca..c1204cd 100644
> --- a/zfs/contrib/Makefile.in
> +++ b/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 \
> diff --git a/zfs/contrib/bash_completion.d/Makefile.in b/zfs/contrib/bash_completion.d/Makefile.in
> index a848010..f29d5cc 100644
> --- a/zfs/contrib/bash_completion.d/Makefile.in
> +++ b/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 \
> diff --git a/zfs/contrib/dracut/90zfs/Makefile.in b/zfs/contrib/dracut/90zfs/Makefile.in
> index 80f3262..63da6ed 100644
> --- a/zfs/contrib/dracut/90zfs/Makefile.in
> +++ b/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 \
> diff --git a/zfs/contrib/dracut/Makefile.in b/zfs/contrib/dracut/Makefile.in
> index 5136e7f..eed070a 100644
> --- a/zfs/contrib/dracut/Makefile.in
> +++ b/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 \
> diff --git a/zfs/contrib/initramfs/Makefile.in b/zfs/contrib/initramfs/Makefile.in
> index 5bf9c44..7a567be 100644
> --- a/zfs/contrib/initramfs/Makefile.in
> +++ b/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 \
> diff --git a/zfs/include/Makefile.in b/zfs/include/Makefile.in
> index 5dcbe26..be50bca 100644
> --- a/zfs/include/Makefile.in
> +++ b/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 \
> diff --git a/zfs/include/linux/Makefile.in b/zfs/include/linux/Makefile.in
> index 52deade..70974df 100644
> --- a/zfs/include/linux/Makefile.in
> +++ b/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 \
> diff --git a/zfs/include/linux/vfs_compat.h b/zfs/include/linux/vfs_compat.h
> index 8037055..f440f36 100644
> --- a/zfs/include/linux/vfs_compat.h
> +++ b/zfs/include/linux/vfs_compat.h
> @@ -112,6 +112,30 @@ 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.
>   */
> diff --git a/zfs/include/sys/Makefile.in b/zfs/include/sys/Makefile.in
> index 20f498f..c0a0c2d 100644
> --- a/zfs/include/sys/Makefile.in
> +++ b/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 \
> diff --git a/zfs/include/sys/fm/Makefile.in b/zfs/include/sys/fm/Makefile.in
> index d8d132f..b6f5397 100644
> --- a/zfs/include/sys/fm/Makefile.in
> +++ b/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 \
> diff --git a/zfs/include/sys/fm/fs/Makefile.in b/zfs/include/sys/fm/fs/Makefile.in
> index 2c61a5e..a1216fb 100644
> --- a/zfs/include/sys/fm/fs/Makefile.in
> +++ b/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 \
> diff --git a/zfs/include/sys/fs/Makefile.in b/zfs/include/sys/fs/Makefile.in
> index 95d7b62..4715b29 100644
> --- a/zfs/include/sys/fs/Makefile.in
> +++ b/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 \
> diff --git a/zfs/module/zfs/zpl_super.c b/zfs/module/zfs/zpl_super.c
> index bcdbbd6..f75a0d8 100644
> --- a/zfs/module/zfs/zpl_super.c
> +++ b/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,
>  };
> diff --git a/zfs/zfs_config.h.in b/zfs/zfs_config.h.in
> index c5026c8..60cf471 100644
> --- a/zfs/zfs_config.h.in
> +++ b/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
>  
> 

Applied to xenial/master-next branch.

Thanks,
Kleber