Change default to overlay=on

Filesystems allow overlay mounts by default on FreeBSD and Linux.

Respect the native convention by switching the default to overlay=on,
while retaining the option to turn the property off for compatibility
with other operating systems' conventions.

Update documentation and tests accordingly.

Reviewed-by: Richard Laager <[email protected]>
Reviewed-by: Brian Behlendorf <[email protected]>
Signed-off-by: Ryan Moeller <[email protected]>
Closes #10030 

9 files changed, 53 insertions, 64 deletions

diff --git a/lib/libzfs/libzfs_mount.c b/lib/libzfs/libzfs_mount.c
index c3fe97d55..4d4b49753 100644
--- a/lib/libzfs/libzfs_mount.c
+++ b/lib/libzfs/libzfs_mount.c
@@ -474,8 +474,8 @@ zfs_mount_at(zfs_handle_t *zhp, const char *options, int flags,
 	}
 
 	/*
-	 * Overlay mounts are disabled by default but may be enabled
-	 * via the 'overlay' property or the 'zfs mount -O' option.
+	 * Overlay mounts are enabled by default but may be disabled
+	 * via the 'overlay' property. The -O flag remains for compatibility.
 	 */
 	if (!(flags & MS_OVERLAY)) {
 		if (zfs_prop_get(zhp, ZFS_PROP_OVERLAY, overlay,
@@ -489,7 +489,7 @@ zfs_mount_at(zfs_handle_t *zhp, const char *options, int flags,
 	/*
 	 * Determine if the mountpoint is empty.  If so, refuse to perform the
 	 * mount.  We don't perform this check if 'remount' is
-	 * specified or if overlay option(-O) is given
+	 * specified or if overlay option (-O) is given
 	 */
 	if ((flags & MS_OVERLAY) == 0 && !remount &&
 	    !dir_is_empty(mountpoint)) {
diff --git a/man/man8/zfsprops.8 b/man/man8/zfsprops.8
index a0a0c46ac..b87e3e608 100644
--- a/man/man8/zfsprops.8
+++ b/man/man8/zfsprops.8
@@ -1157,14 +1157,16 @@ See
 for more information on
 .Sy nbmand
 mounts. This property is not used on Linux.
-.It Sy overlay Ns = Ns Sy off Ns | Ns Sy on
+.It Sy overlay Ns = Ns Sy on Ns | Ns Sy off
 Allow mounting on a busy directory or a directory which already contains
-files or directories. This is the default mount behavior for Linux file systems.
-For consistency with OpenZFS on other platforms overlay mounts are
-.Sy off
-by default. Set to
+files or directories.
+This is the default mount behavior for Linux and FreeBSD file systems.
+On these platforms the property is
 .Sy on
-to enable overlay mounts.
+by default.
+Set to
+.Sy off
+to disable overlay mounts for consistency with OpenZFS on other platforms.
 .It Sy primarycache Ns = Ns Sy all Ns | Ns Sy none Ns | Ns Sy metadata
 Controls what is cached in the primary cache
 .Pq ARC .
diff --git a/module/zcommon/zfs_prop.c b/module/zcommon/zfs_prop.c
index 8dfadfaaf..3ba3b8a84 100644
--- a/module/zcommon/zfs_prop.c
+++ b/module/zcommon/zfs_prop.c
@@ -406,7 +406,7 @@ zfs_prop_init(void)
 	zprop_register_index(ZFS_PROP_NBMAND, "nbmand", 0, PROP_INHERIT,
 	    ZFS_TYPE_FILESYSTEM | ZFS_TYPE_SNAPSHOT, "on | off", "NBMAND",
 	    boolean_table);
-	zprop_register_index(ZFS_PROP_OVERLAY, "overlay", 0, PROP_INHERIT,
+	zprop_register_index(ZFS_PROP_OVERLAY, "overlay", 1, PROP_INHERIT,
 	    ZFS_TYPE_FILESYSTEM, "on | off", "OVERLAY", boolean_table);
 
 	/* default index properties */
diff --git a/tests/runfiles/common.run b/tests/runfiles/common.run
index ea26a3ae3..f2107f47b 100644
--- a/tests/runfiles/common.run
+++ b/tests/runfiles/common.run
@@ -181,7 +181,7 @@ tags = ['functional', 'cli_root', 'zfs_load-key']
 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_009_neg', 'zfs_mount_010_neg', 'zfs_mount_011_neg',
-    'zfs_mount_012_neg', 'zfs_mount_all_001_pos', 'zfs_mount_encrypted',
+    'zfs_mount_012_pos', 'zfs_mount_all_001_pos', 'zfs_mount_encrypted',
     'zfs_mount_remount', 'zfs_mount_all_fail', 'zfs_mount_all_mountpoints',
     'zfs_mount_test_race']
 tags = ['functional', 'cli_root', 'zfs_mount']
diff --git a/tests/zfs-tests/tests/functional/cli_root/zfs_mount/Makefile.am b/tests/zfs-tests/tests/functional/cli_root/zfs_mount/Makefile.am
index 8a137b830..37c094238 100644
--- a/tests/zfs-tests/tests/functional/cli_root/zfs_mount/Makefile.am
+++ b/tests/zfs-tests/tests/functional/cli_root/zfs_mount/Makefile.am
@@ -13,7 +13,7 @@ dist_pkgdata_SCRIPTS = \
 	zfs_mount_009_neg.ksh \
 	zfs_mount_010_neg.ksh \
 	zfs_mount_011_neg.ksh \
-	zfs_mount_012_neg.ksh \
+	zfs_mount_012_pos.ksh \
 	zfs_mount_all_001_pos.ksh \
 	zfs_mount_all_fail.ksh \
 	zfs_mount_all_mountpoints.ksh \
diff --git a/tests/zfs-tests/tests/functional/cli_root/zfs_mount/zfs_mount_006_pos.ksh b/tests/zfs-tests/tests/functional/cli_root/zfs_mount/zfs_mount_006_pos.ksh
index 5c954354d..5edce35c7 100755
--- a/tests/zfs-tests/tests/functional/cli_root/zfs_mount/zfs_mount_006_pos.ksh
+++ b/tests/zfs-tests/tests/functional/cli_root/zfs_mount/zfs_mount_006_pos.ksh
@@ -35,22 +35,20 @@
 
 #
 # DESCRIPTION:
-#	Invoke "zfs mount <filesystem>" with a filesystem
-#	mountpoint that is identical to an existing one.
-#	It will fail with a return code of 1.  For Linux,
-#	place a file in the directory to ensure the failure.
-#	Also for Linux, test overlay=off (default) in which case
-#	the mount will fail, and overlay=on, where the mount
-#	will succeed.
+#	Invoke "zfs mount <filesystem>" with a filesystem mountpoint that is
+#	identical to an existing one.  It will fail with a return code of 1
+#	when overlay=off.  Place a file in the directory to ensure the failure.
+#	Also test overlay=on (default) in which case the mount will not fail.
 #
 # STRATEGY:
 #	1. Prepare an existing mounted filesystem.
-#	2. Setup a new filesystem and make sure that it is unmounted.
-#	3. For Linux, place a file in the mount point folder.
-#       4. Mount the new filesystem using the various combinations
-#		- zfs set mountpoint=<identical path> <filesystem>
-#		- zfs set mountpoint=<top path> <filesystem>
-#       5. Verify that mount failed with return code of 1.
+#	2. Setup a new filesystem with overlay=off and make sure that it is
+#	   unmounted.
+#	3. Place a file in the mount point folder.
+#	4. Mount the new filesystem using the various combinations
+#	   - zfs set mountpoint=<identical path> <filesystem>
+#	   - zfs set mountpoint=<top path> <filesystem>
+#	5. Verify that mount failed with return code of 1.
 #	6. For Linux, also set overlay=on and verify the mount is
 #	   allowed.
 #
@@ -76,7 +74,7 @@ typeset -i ret=0
 
 log_assert "Verify that 'zfs $mountcmd <filesystem>'" \
 	"where the mountpoint is identical or on top of an existing one" \
-	"will fail with return code 1."
+	"will fail with return code 1 when overlay=off."
 
 log_onexit cleanup
 
@@ -98,8 +96,8 @@ done
 log_must zfs set mountpoint=$mtpt $TESTPOOL/$TESTFS
 log_must zfs $mountcmd $TESTPOOL/$TESTFS
 
-if is_linux; then
-	log_must zfs set overlay=off $TESTPOOL/$TESTFS
+log_must zfs set overlay=off $TESTPOOL/$TESTFS
+if ! is_illumos; then
 	touch $mtpt/file.1
 	log_must ls -l $mtpt | grep file
 fi
@@ -107,7 +105,7 @@ fi
 mounted $TESTPOOL/$TESTFS || \
 	log_unresolved "Filesystem $TESTPOOL/$TESTFS is unmounted"
 
-log_must zfs create $TESTPOOL/$TESTFS1
+log_must zfs create -o overlay=off $TESTPOOL/$TESTFS1
 
 unmounted $TESTPOOL/$TESTFS1 || \
 	log_must force_unmount $TESTPOOL/$TESTFS1
@@ -123,9 +121,9 @@ while [[ $depth -gt 0 ]] ; do
 
 	log_mustnot zfs $mountcmd $TESTPOOL/$TESTFS1
 
-	# For Linux, test the overlay=on feature which allows
-	# mounting of non-empty directory.
-	if is_linux; then
+	if ! is_illumos; then
+		# Test the overlay=on feature which allows
+		# mounting of non-empty directory.
 		log_must zfs set overlay=on $TESTPOOL/$TESTFS1
 		log_must zfs $mountcmd $TESTPOOL/$TESTFS1
 		log_must force_unmount $TESTPOOL/$TESTFS1
diff --git a/tests/zfs-tests/tests/functional/cli_root/zfs_mount/zfs_mount_008_pos.ksh b/tests/zfs-tests/tests/functional/cli_root/zfs_mount/zfs_mount_008_pos.ksh
index 84835a0d6..4b3bf40bc 100755
--- a/tests/zfs-tests/tests/functional/cli_root/zfs_mount/zfs_mount_008_pos.ksh
+++ b/tests/zfs-tests/tests/functional/cli_root/zfs_mount/zfs_mount_008_pos.ksh
@@ -73,7 +73,8 @@ log_must mkfile 1M $testfile $testfile1
 
 log_must zfs unmount $fs1
 log_must zfs set mountpoint=$mntpnt $fs1
-log_mustnot zfs mount $fs1
+log_must zfs mount $fs1
+log_must zfs unmount $fs1
 log_must zfs mount -O $fs1
 
 # Create new file in override mountpoint
diff --git a/tests/zfs-tests/tests/functional/cli_root/zfs_mount/zfs_mount_012_neg.ksh b/tests/zfs-tests/tests/functional/cli_root/zfs_mount/zfs_mount_012_pos.ksh
index 3e6799aa0..5ff094d2c 100755
--- a/tests/zfs-tests/tests/functional/cli_root/zfs_mount/zfs_mount_012_neg.ksh
+++ b/tests/zfs-tests/tests/functional/cli_root/zfs_mount/zfs_mount_012_pos.ksh
@@ -18,9 +18,6 @@
 
 #
 # DESCRIPTION:
-#  Linux:
-#   Verify that zfs mount fails with a non-empty directory
-#  FreeSD:
 #   Verify that zfs mount succeeds with a non-empty directory
 #
 
@@ -34,18 +31,12 @@
 # 6. Unmount the dataset
 # 7. Create a file in the directory created in step 2
 # 8. Attempt to mount the dataset
-# 9. Verify the mount fails
+# 9. Verify the mount succeeds
 #
 
 verify_runnable "both"
 
-if is_linux; then
-	behaves="fails"
-else
-	behaves="succeeds"
-fi
-
-log_assert "zfs mount $behaves with non-empty directory"
+log_assert "zfs mount succeeds with non-empty directory"
 
 fs=$TESTPOOL/$TESTFS
 
@@ -55,12 +46,8 @@ log_must zfs set mountpoint=$TESTDIR $fs
 log_must zfs mount $fs
 log_must zfs umount $fs
 log_must touch $TESTDIR/testfile.$$
-if is_linux; then
-	log_mustnot zfs mount $fs
-else
-	log_must zfs mount $fs
-	log_must zfs umount $fs
-fi
+log_must zfs mount $fs
+log_must zfs umount $fs
 log_must rm -rf $TESTDIR
 
-log_pass "zfs mount $behaves with non-empty directory as expected."
+log_pass "zfs mount succeeds with non-empty directory as expected."
diff --git a/tests/zfs-tests/tests/functional/cli_root/zfs_mount/zfs_mount_all_fail.ksh b/tests/zfs-tests/tests/functional/cli_root/zfs_mount/zfs_mount_all_fail.ksh
index 93a47d7d6..d1103bddc 100755
--- a/tests/zfs-tests/tests/functional/cli_root/zfs_mount/zfs_mount_all_fail.ksh
+++ b/tests/zfs-tests/tests/functional/cli_root/zfs_mount/zfs_mount_all_fail.ksh
@@ -30,8 +30,8 @@
 #       1. Create zfs filesystems
 #       2. Unmount a leaf filesystem
 #       3. Create a file in the above filesystem's mountpoint
-#       4. Verify that 'zfs mount -a' fails to mount the above if on Linux
-#          or succeeds if on FreeBSD
+#       4. Verify that 'zfs mount -a' succeeds if overlay=on and
+#          fails to mount the above if overlay=off
 #       5. Verify that all other filesystems were mounted
 #
 
@@ -83,17 +83,18 @@ done
 # Create a stray file in one filesystem's mountpoint
 touch $path/0/strayfile
 
-# Verify that zfs mount -a fails on Linux or succeeds on FreeBSD
 export __ZFS_POOL_RESTRICT="$TESTPOOL"
-if is_linux; then
-	log_mustnot zfs $mountall
-	log_mustnot mounted "$TESTPOOL/0"
-	typeset behaved="failed"
-else
-	log_must zfs $mountall
-	log_must mounted "$TESTPOOL/0"
-	typeset behaved="succeeded"
-fi
+
+# Verify that zfs mount -a succeeds with overlay=on (default)
+log_must zfs $mountall
+log_must mounted "$TESTPOOL/0"
+log_must zfs $unmountall
+
+# Verify that zfs mount -a succeeds with overlay=off
+log_must zfs set overlay=off "$TESTPOOL/0"
+log_mustnot zfs $mountall
+log_mustnot mounted "$TESTPOOL/0"
+
 unset __ZFS_POOL_RESTRICT
 
 # All other filesystems should be mounted
@@ -101,4 +102,4 @@ for ((i=1; i<$fscount; i++)); do
 	log_must mounted "$TESTPOOL/$i"
 done
 
-log_pass "'zfs $mountall' $behaved as expected."
+log_pass "'zfs $mountall' behaves as expected."