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 

1 files changed, 8 insertions, 6 deletions

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 .