[Bug-tar] Heuristic for NFS filesystems don't always work

[Göran Uddeborg]

I'm using tar to create backups.  According to the documentation,
listed-incremental mode should consider all NFS file systems as equal,
but that doesn't work for me.  If an NFS filesystem gets a new device
number than last time, tar wants to rebackup the whole tree.

I took a look in the code, and if I understand it correctly, the
heuristic is that if the most significant bit of the device number is
set, then it is an NFS file system.  On my Fedora Linux system,
however, NFS file systems gets very low numbers, with the major number
equal to zero and the minor number being around 20.  (It appears to be
the "next free number".  But I haven't investigated in detail where it
starts counting and if there are other conditions involved.)

See an example of doing "stat" on my home directory on a machine where
it is NFS mounted:

freddi$ env LANG=C stat ~
  File: `/home/g\303\266ran'
  Size: 12288           Blocks: 32         IO Block: 262144 directory
Device: 13h/19d Inode: 3852847     Links: 146
Access: (2755/drwxr-sr-x)  Uid: (  503/  göran)   Gid: (  503/  göran)
Access: 2009-02-03 11:04:16.000000000 +0100
Modify: 2009-02-03 10:39:51.000000000 +0100
Change: 2009-02-03 10:39:51.000000000 +0100