[Bug-tar] request for info page change

[Erik Bryer]

I have found that, without using either automout or LVM, the device numbers of 
NFS mount points will change. (Linux Kernel=2.6.18, GNU tar 1.22.) I think the 
info page & manual ought to be updated to reflect that `--no-check-device' is 
suggested for any NFS mount.

The info page states, "...NFS devices have undependable values when an 
automounter gets in the picture" and "device numbers can cause spurious 
redumping of unmodified files... when archiving LVM snapshot volumes."
I'm not using automout or LVM on any of my systems, but device numbers do 
change, causing a redump.

It may have been the change from devfs (in-kernel) to udev (user-space) that 
did this, but device numbers on Linux are now "cookies" (L. Torvalds) and not 
dependably assigned to the same physical device or NFS mount point. (Udev sorts 
out the device-number to device-name translation for physical devices in /dev 
but does not seem to help NFS.) Therefore, NFS device numbers are not 
dependable on Linux. An important point. It took me quite a while to figure out 
how all this works and satisfy myself that it is true, so I thought I would 
share it. Maybe it will save someone some time later. I'm going with the 
`--no-check-device' option.