> > Why change it twice?  It seems like it's actually less work to do the
> > heavy-lifting-in-mountd scheme, because it doesn't require you to
> > implement fsctl(2).
> 
> The thing is that I have no idea about how to do this at the moment.
> Do we have any example in the kernel on how to cummunicate it
> with an userland process so that the latter has to return a value to
> the former?  Maybe the userfs SoC project has a decent way to
> do this?  What happens if the kernel requests a mount export entry
> to mountd and mountd crashes/locks?

a blocking system call to wait requests should be enough.
we have similar structure in nfsd for kerberos.
check rick's nfsv4 code as well.

YAMAMOTO Takashi