Jeff Layton wrote:
> When remounting an NFS or NFS4 filesystem, the new NFS options are not
> respected, yet the remount will still return success. This patch adds
> a remount_fs sb op for NFS that checks any new nfs mount options against
> the existing ones and fails the mount if any have changed.
> 
> This is only implemented for string-based mount options since doing
> this with binary options isn't really feasible.

It might be feasible if mount.nfs were smart enough to read /etc/mtab 
and merge the old mount options with the remount options.