what's needed is a application barrier() call

The problem can be stated simply enough. User land application writers need to be able to do atomic updates, and (orthogonally) for way for information to be sure on disk single way that works across all file systems without special libraries or having to change their code. That means those interfaces must be in POSIX, and with the added complication that all existing file systems we have, and all those we can envisage in the future can implement them efficiently.

Maybe write barriers are just the interface we need, maybe not. What we need is a Paul McKenney to do for this problem what Paul did for a very similar problem in multi CPU memory architectures. He wrote the RCU stuff and in the process became intimately familiar for the problem and all possible solutions. He then worked for years to get a standard set of functions that solved the problem to be added to the C standard library. Where is your white knight in shining armour when you need them? Who knows, maybe our knight will be female for a change.

One thing hasn't changed though, and that is the ability of the female of our special to create work. Now I feel compelled to learn about Featherstich.