Well, at least O_APPEND, O_EXCL, O_SYNC, and flock() aren't guaranteed to work (although they can with recent versions as I understand it).

UID mapping causing read() to return -EACCES after open() succeeds breaks a lot of userland code.

Just ran into this one recently trying to replace Docker w/ Podman for a CICD runner. Before anyone protests we have very strong, abnormal requirements on my project preventing most saner architectures. It wasn’t the root cause but the failure behavior was weird due to the behavior you just described.

Lack of inotify support is one that has annoyed me in the past. It not only breaks some desktop software, but it also should be possible for NFS to support (after all, the server sees the changes and could notify clients).

Thanks for this, it's helpful. Totally heard about O_APPEND and read() returning -EACCESS. The other ones, I agree, should be fixed in later versions of the Linux kernel/NFS client.