// reference

Extended attributes (xattr)

You put a small note (xattr) on file over the mount. Note shows on the mount and in session. Original file has no note.

Linux uses setfattr / getfattr (package attr). macOS uses xattr.

Linux

setfattr -n user.comment -v testdata ~/pfs-mnt/hello.txt
getfattr -n user.comment ~/pfs-mnt/hello.txt
getfattr -n user.comment ~/pfs-session/hello.txt
getfattr -n user.comment ~/pfs-base/hello.txt
setfattr -x user.comment ~/pfs-mnt/hello.txt

macOS

xattr -w comment testdata ~/pfs-mnt/hello.txt
xattr -p comment ~/pfs-mnt/hello.txt
xattr -p comment ~/pfs-session/hello.txt
xattr -p comment ~/pfs-base/hello.txt
xattr -d comment ~/pfs-mnt/hello.txt

Mount and session print testdata. Base has no such attribute (xattr: ... No such xattr: comment on macOS, or getfattr error on Linux).

Unmount before next check:

On macOS:

umount ~/pfs-mnt

On Linux:

fusermount3 -u ~/pfs-mnt