[BUG] Is casefold unreported in /proc/mounts?

[Daniel Tang]

Upon successfully mounting via `sudo mount -t tmpfs -o casefold test /mnt`, I
cannot find a read-only way to determine whether this option is enabled.
`mount`, `cat /proc/mounts`, and `cat /proc/mountinfo` only display "rw",
"relatime", and "inode64", never "casefold" for both with and without
`-o casefold`. The only way on 7.0.0-34-generic to test I found is
`mkdir test ; chattr +F test ; echo $?`, but that isn't atomic. Which command
can determine, without writing anything, whether someone or some program
specified `-o casefold`? If absent, I suggest adding the missing info to
`/proc/mounts`, likely `mm/shmem.c:shmem_show_options`.

Link: https://lore.kernel.org/r/20241021-tonyk-tmpfs-v8-6-f443d5814194@xxxxxxxxxx