> Perhaps something like an fsctl() would be a good approach.
> Quotactl() is very close. Things like quotactl() could be
> folded into an fsctl(). Changing between r/w and r/o would
> be really easy. Freezing/unfreezing would too which is needed
> for LVM-based snapshots and in certain replication scenarios.

I hasten to add: resizing an online volume is another
likely use of fsctl().

For some things I'm doing I overload quotactl() to do
fsctl() operations.

Regards,
	-gww