Whilst trying to understand the problem I looked at the source of nfsmount in klibc. Nfsmount has a switch statement in which it checks the value of nfsvers and only proceeds if it is 2 or 3. Given that my version of nfsmount, compiled with klcc, can indeed mount using NFSv4 I suspect that in libc's version the switch statement only needs to be extended with the cases 4, 4.0, 4.1 and 4.2. It's not entirely trivial, but it's hard to understand why it hasn't been done sometime during the last 15 years.
I may take a closer look when I've fixed my next bug.
Whilst trying to understand the problem I looked at the source of nfsmount in klibc. Nfsmount has a switch statement in which it checks the value of nfsvers and only proceeds if it is 2 or 3. Given that my version of nfsmount, compiled with klcc, can indeed mount using NFSv4 I suspect that in libc's version the switch statement only needs to be extended with the cases 4, 4.0, 4.1 and 4.2. It's not entirely trivial, but it's hard to understand why it hasn't been done sometime during the last 15 years.
I may take a closer look when I've fixed my next bug.