mountd: Junctions inherit parent export's options

mountd: Junctions inherit parent export's options

Attempting to access junctions on a Linux NFS server from an NFS
client connected via an ephemeral source port fails with a "client
insecure" error on the server.  This happens even when the
"insecure" export option is specified on the junction's parent
export.

As a test, via a mountd code change, I added "insecure" to the fixed
export options that mountd sets up for each junction, and the error
disappeared.

It's simple enough for old-school referrals configured directly in
/etc/exports ("refer=") to have the needed options specified there.
Cache entries for junctions, however, are created on the fly by
mountd, and don't ever appear in /etc/exports.  So there's nowhere
obvious that export options for junctions can be specified.

Bruce suggested that in order to specify unique export options for
junctions, they should inherit the export options of their parent
export.  The junction's parent's exportent is duplicated in order
to create an exportent for the junction itself.

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Steve Dickson <steved@redhat.com>