Description of problem:
Running "exportfs -av" or "exportfs -rv" does not synchronize /var/lib/nfs/xtab
with /etc/exports as it should according to the man page of exportfs.

The xtab remains always empty.

Version-Release number of selected component (if applicable):
$ rpm -qa | grep nfs
nfs-utils-lib-1.0.8-8.fc7
nfs-utils-1.0.12-4.fc7

How reproducible:

Steps to Reproduce:
1. export directory (/etc/export)
2. mount direcotry (other machine)
3. run exportfs
  
Actual results:
$ cat /etc/exports 
/M_EXPORT *(rw,sync,root_squash)
$ /etc/init.d/nfs restart
Shutting down NFS mountd:                                  [  OK  ]
Shutting down NFS daemon:                                  [  OK  ]
Shutting down NFS quotas:                                  [  OK  ]
Shutting down NFS services:                                [  OK  ]
Starting NFS services:                                     [  OK  ]
Starting NFS quotas:                                       [  OK  ]
Starting NFS daemon:                                       [  OK  ]
Starting NFS mountd:                                       [  OK  ]
$ exportfs -rv
exporting *:/M_EXPORT
$ echo $?
0
$ cat /var/lib/nfs/xtab
$

xtab is empty ..

Expected results:
cat /var/lib/nfs/xtab
... some conent about exported nfs directories

Additional info:
I red the man page of exportfs. From this I would expect some content for the
xtab file. Is this file simply not used anymore? If so, then a change of the
man page would be needed.

I searched also for other bugzillas about this problem, and I found only one ... 
that mentioned this behavior at one comment. See bugzilla #165346 Comment #6.