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Fix remounting snapshots read-write

It's not enough to preserve/restore MS_RDONLY on the superblock flags
to avoid remounting a snapshot read-write: be explicit about our
intentions to the VFS layer so the readonly bit is updated correctly
in do_remount_sb().

Reviewed-by: Chunwei Chen <tuxoko@gmail.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: loli10K <ezomori.nozomu@gmail.com>
Closes #6510
Closes #6515
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loli10K authored and tonyhutter committed Aug 17, 2017
1 parent fb3f1fd commit 3468fdbd347c39db5c3c73a6bcaea69871a66fe9
@@ -1761,8 +1761,15 @@ zfs_remount(struct super_block *sb, int *flags, zfs_mnt_t *zm)
{
zfsvfs_t *zfsvfs = sb->s_fs_info;
vfs_t *vfsp;
boolean_t issnap = dmu_objset_is_snapshot(zfsvfs->z_os);
int error;

if ((issnap || !spa_writeable(dmu_objset_spa(zfsvfs->z_os))) &&
!(*flags & MS_RDONLY)) {
*flags |= MS_RDONLY;
return (EROFS);
}

error = zfsvfs_parse_options(zm->mnt_data, &vfsp);
if (error)
return (error);
@@ -1772,7 +1779,8 @@ zfs_remount(struct super_block *sb, int *flags, zfs_mnt_t *zm)

vfsp->vfs_data = zfsvfs;
zfsvfs->z_vfs = vfsp;
(void) zfs_register_callbacks(vfsp);
if (!issnap)
(void) zfs_register_callbacks(vfsp);

return (error);
}
@@ -108,7 +108,8 @@ tests = ['zfs_inherit_001_neg', 'zfs_inherit_002_neg', 'zfs_inherit_003_pos']
tests = ['zfs_mount_001_pos', 'zfs_mount_002_pos', 'zfs_mount_003_pos',
'zfs_mount_004_pos', 'zfs_mount_005_pos', 'zfs_mount_007_pos',
'zfs_mount_008_pos', 'zfs_mount_009_neg', 'zfs_mount_010_neg',
'zfs_mount_011_neg', 'zfs_mount_012_neg', 'zfs_mount_all_001_pos']
'zfs_mount_011_neg', 'zfs_mount_012_neg', 'zfs_mount_all_001_pos',
'zfs_mount_remount']

[tests/functional/cli_root/zfs_promote]
tests = ['zfs_promote_001_pos', 'zfs_promote_002_pos', 'zfs_promote_003_pos',
@@ -16,4 +16,5 @@ dist_pkgdata_SCRIPTS = \
zfs_mount_010_neg.ksh \
zfs_mount_011_neg.ksh \
zfs_mount_012_neg.ksh \
zfs_mount_all_001_pos.ksh
zfs_mount_all_001_pos.ksh \
zfs_mount_remount.ksh
@@ -0,0 +1,144 @@
#!/bin/ksh -p
#
# CDDL HEADER START
#
# The contents of this file are subject to the terms of the
# Common Development and Distribution License (the "License").
# You may not use this file except in compliance with the License.
#
# You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
# or http://www.opensolaris.org/os/licensing.
# See the License for the specific language governing permissions
# and limitations under the License.
#
# When distributing Covered Code, include this CDDL HEADER in each
# file and include the License file at usr/src/OPENSOLARIS.LICENSE.
# If applicable, add the following below this CDDL HEADER, with the
# fields enclosed by brackets "[]" replaced with your own identifying
# information: Portions Copyright [yyyy] [name of copyright owner]
#
# CDDL HEADER END
#

#
# Copyright 2017, loli10K <ezomori.nozomu@gmail.com>. All rights reserved.
#

. $STF_SUITE/include/libtest.shlib
. $STF_SUITE/tests/functional/cli_root/zfs_mount/zfs_mount.kshlib

#
# DESCRIPTION:
# Verify remount functionality, expecially on readonly objects.
#
# STRATEGY:
# 1. Prepare a filesystem and a snapshot
# 2. Verify we can (re)mount the dataset readonly/read-write
# 3. Verify we can mount the snapshot and it's mounted readonly
# 4. Verify we can't remount it read-write
# 5. Re-import the pool readonly
# 6. Verify we can't remount its filesystem read-write
#

verify_runnable "both"

function cleanup
{
log_must zpool export $TESTPOOL
log_must zpool import $TESTPOOL
snapexists $TESTSNAP && log_must zfs destroy $TESTSNAP
[[ -d $MNTPSNAP ]] && log_must rmdir $MNTPSNAP
return 0
}

#
# Verify the $filesystem is mounted readonly
# This is preferred over "log_mustnot touch $fs" because we actually want to
# verify the error returned is EROFS
#
function readonlyfs # filesystem
{
typeset filesystem="$1"

file_write -o create -f $filesystem/file.dat
ret=$?
if [[ $ret != 30 ]]; then
log_fail "Writing to $filesystem did not return EROFS ($ret)."
fi
}

#
# Verify $dataset is mounted with $option
#
function checkmount # dataset option
{
typeset dataset="$1"
typeset option="$2"

options="$(awk -v ds="$dataset" '$1 == ds { print $4 }' /proc/mounts)"
if [[ "$options" == '' ]]; then
log_fail "Dataset $dataset is not mounted"
elif [[ ! -z "${options##*$option*}" ]]; then
log_fail "Dataset $dataset is not mounted with expected "\
"option $option ($options)"
else
log_note "Dataset $dataset is mounted with option $option"
fi
}

log_assert "Verify remount functionality on both filesystem and snapshots"

log_onexit cleanup

# 1. Prepare a filesystem and a snapshot
TESTFS=$TESTPOOL/$TESTFS
TESTSNAP="$TESTFS@snap"
datasetexists $TESTFS || log_must zfs create $TESTFS
snapexists $TESTSNAP || log_must zfs snapshot $TESTSNAP
log_must zfs set readonly=off $TESTFS
MNTPFS="$(get_prop mountpoint $TESTFS)"
MNTPSNAP="$TESTDIR/zfs_snap_mount"
log_must mkdir -p $MNTPSNAP

# 2. Verify we can (re)mount the dataset readonly/read-write
log_must touch $MNTPFS/file.dat
checkmount $TESTFS 'rw'
log_must mount -o remount,ro $TESTFS $MNTPFS
readonlyfs $MNTPFS
checkmount $TESTFS 'ro'
log_must mount -o remount,rw $TESTFS $MNTPFS
log_must touch $MNTPFS/file.dat
checkmount $TESTFS 'rw'

# 3. Verify we can (re)mount the snapshot readonly
log_must mount -t zfs $TESTSNAP $MNTPSNAP
readonlyfs $MNTPSNAP
checkmount $TESTSNAP 'ro'
log_must mount -o remount,ro $TESTSNAP $MNTPSNAP
readonlyfs $MNTPSNAP
checkmount $TESTSNAP 'ro'
log_must umount $MNTPSNAP

# 4. Verify we can't remount a snapshot read-write
# The "mount -o rw" command will succeed but the snapshot is mounted readonly.
# The "mount -o remount,rw" command must fail with an explicit error.
log_must mount -t zfs -o rw $TESTSNAP $MNTPSNAP
readonlyfs $MNTPSNAP
checkmount $TESTSNAP 'ro'
log_mustnot mount -o remount,rw $TESTSNAP $MNTPSNAP
readonlyfs $MNTPSNAP
checkmount $TESTSNAP 'ro'
log_must umount $MNTPSNAP

# 5. Re-import the pool readonly
log_must zpool export $TESTPOOL
log_must zpool import -o readonly=on $TESTPOOL

# 6. Verify we can't remount its filesystem read-write
readonlyfs $MNTPFS
checkmount $TESTFS 'ro'
log_mustnot mount -o remount,rw $MNTPFS
readonlyfs $MNTPFS
checkmount $TESTFS 'ro'

log_pass "Both filesystem and snapshots can be remounted correctly."

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