nfs4 filesystem mounted via the "bind" option reports wrong fstype

[Gabriel Barazer <gabriel@oxeva.fr>]

Hi,

A nfs4 filesystem, mounted elsewhere via the "bind" option (the usual 
way to do with nfsv4 and its pseudofs), reports wrong fstype "nfs" 
instead of "nfs4" filesystem.
An example is much easier to understand :
Server-side :
- /exports is the pseudo root filesystem (fsid=0 option in /etc/exports)
- /exports/data is a mountpoint for another filesystem (not the same 
device-id as /exports). This condition seems to be what triggers the bug
- /exports/data must be exported with the "nohide" option (again, the 
usual way to do se with nfsv4)

Client-side :
- mount server:/  on /imports
- mount "bind" /imports/data on /home/data
(this magically shows a second nfs mount in /proc/mounts)
And here is the bug : this second mount is of fstype "nfs" instead of 
"nfs4" although the options field contains "vers=4".

This is like a cosmetic bug, but this becomes a problem when some apps 
need to differentiate nfs and nfs4 fstype (e.g. linuxquota uses it to 
know how to handle the nfs source-path)

Gabriel
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