Getting "encryption not enabled" on an ext4 filesystem

[alexandracristea09]

I keep getting this error when trying to encrypt a directory:

"fscrypt encrypt /var/opencloud/test_fscrypt/
[ERROR] fscrypt encrypt: encryption not enabled on filesystem /var/opencloud (/dev/sdc1).
To enable encryption support on this filesystem, run:
     sudo tune2fs -O encrypt "/dev/sdc1"
Also ensure that your kernel has CONFIG_FS_ENCRYPTION=y. See the documentation for more details."

The kernel configuration contains the encryption enablement:

grep FS_ENCRYPTION /boot/config-$(uname -r)
CONFIG_FS_ENCRYPTION=y
CONFIG_FS_ENCRYPTION_ALGS=m

Also the 'encrypt' feature flag appears:

sudo tune2fs -l /dev/sdc1 | grep 'Filesystem features'
Filesystem features:      has_journal ext_attr resize_inode dir_index filetype needs_recovery extent 64bit flex_bg encrypt sparse_super large_file huge_file dir_nlink extra_isize metadata_csum

I've tried unmounting and remounting the filesystem, rebooting, running 'tune2fs -O encrypt /dev/device', but nothing seems to work.
I mention that the machine is running on Linux 9.7, kernel version is 5.14.0-570.37.1.el9_6.x86_64.

[ebiggers]

This happens when the kernel returns -EOPNOTSUPP from the fscrypt ioctls on the filesystem. From reading through the kernel code, the only other case I can find where that is a possibility (besides the two that fscrypt is already aware of) is the case where the filesystem is mounted with -o dax. Was that perhaps the case here? Encryption and DAX (Direct Access) are not compatible.