/etc/exports - a strange restriction

[Norbert Koch]

> I'd like to share some directories hierarchy under /usr file system, but 
>   I don't want to share all /usr at all.
> 
> On these lines in /etc/exports:
> 
> /usr/tinderbox -ro -alldirs -maproot=0:0 localhost
> 
> i get an error message:
> 
> mountd[347]: -alldirs requested but /usr/tinderbox is not a filesystem 
> mountpoint
> 
> Why so strict restriction?

As far as I know, it is a restriction of the nfs specification.
If you only want to export a single directory, you could e.g.
use mount_null/mount_nullfs(8).

Norbert