[nfsv4] GETATTR within an Absent File System in 5661

[Tom Haynes <[e-mail]>]

      11.3. Getting Attributes for an Absent File System


   When a file system is absent, most attributes are not available, but
   it is necessary to allow the client access to the small set of
   attributes that are available, and most particularly those that give
   information about the correct current locations for this file system:
   fs_locations and fs_locations_info.


        11.3.1. GETATTR within an Absent File System


   As mentioned above, an exception is made for GETATTR in that
   attributes may be obtained for a filehandle within an absent file
   system.  This exception only applies if the attribute mask contains
   at least one attribute bit that indicates the client is interested in
   a result regarding an absent file system: fs_locations,
   fs_locations_info, or fs_status.  If none of these attributes is
   requested, GETATTR will result in an NFS4ERR_MOVED error.



I can see two other attributes which we might want to allow the client
access to in order to determine if a file system was migrated:

1) fsid

PUTFH {fileid} GETATTR {fsid}

Allows the client to determine that a filesystem boundary was crossed.

If the client isn't allowed to detect this, then it might have problems
mangling the paths.

2) mounted_on_fileid

And the client might want to check where to mount the new filesystem.

Hmm, 2) is not as strong a need as 1).