[issue1537] null mount does not accept -o update

[Matthew Dillon]

:Antonio Huete Jimenez <tuxillo at quantumachine.net> added the comment:
:
:Simon,
:
:I've checked FBSD and NBSD. The former can only do update mounts for NFS ex=
:ports
:it seems, and the latter can't at all.
:
:Any hit for doing this?
:
:Cheers,
:Antonio Huete
:
:----------
:status: unread -> chatting

    hit -> hint I assume.  Yes, you should be able to imlement the
    MNT_UPDATE stuff for null mounts.  MNT_UPDATE implementations only
    allow certain flags to be changed out from under the mounted filesystem.
    For null mounts basically the only thing you can update is read-only
    vs read-write operation.

    You can see how other VFSs handle MNT_UPDATE.  It is fairly
    straightforward.
    
					-Matt
					Matthew Dillon 
					<dillon at backplane.com>