bcachefs-tools isn't handling userspace mount options

[jpsollie]

When we specify in bcachefs kernel code that unknown options cause a mount failure (instead of gracefully ignoring them), all mounts which are performed by the bcachefs helper and have a userspace attribute set in /etc/fstab will fail.
I dug through the util-linux code and found this particular function:
https://github.com/util-linux/util-linux/blob/master/libmount/src/optmap.c#L214C28-L214C51
so, somehow, we should use it to validate whether the options specified are userspace options (and in case we don't deal with it in the userspace helper, we ignore them), or pass them to the kernel mount syscall.
I'm opening a ticket here, because it's clearly something that is a major issue when the git commit for failing on unknown mount options is pulled and userspace mount options have not yet been implemented.
Any suggestions?