Re: [Bug-tar] update version of tar-snapshot-edit script

[Nathan Stratton Treadway]

On Wed, Sep 14, 2011 at 18:15:50 -0400, Nathan Stratton Treadway wrote:
> On Sat, Aug 27, 2011 at 14:48:11 -0400, Nathan Stratton Treadway wrote:
> > During a recent discussion on the amanda-users mailing list, we
> > discovered that the tar-snapshot-edit script currently found at
> > 
> >   http://www.gnu.org/software/tar/utils/tar-snapshot-edit
> > 
> > doesn't work with recent versions of Perl.  (It works when I try it with
> > Perl 5.8.8, but not with, for example, Perl 5.10.1 from Ubuntu Lucid.)
> [...]
> > still seems like it might prove useful from time to time. So I'm
> > attaching an updated version of the script which appears to work
> > correctly with both versions of Perl (and presumably later ones as
> > well).
> 
> Let me know if I can provide any other information about these changes
> to the tar-snapshot-edit script.

I realized that the "info" documentation for the script should also be
updated to reflect the new formatting for the output it generates;
here's a patch that does that.

It also takes a stab at updating and expanding a few other parts of that
page (e.g. to mention the --no-check-device option); feel free to tweak
those changes as you see fit...


                                                        Nathan

                                

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--- tar_orig/doc/tar-snapshot-edit.texi 2011-09-17 18:12:04.039667522 -0400
+++ tar/doc/tar-snapshot-edit.texi      2011-09-19 00:38:19.439667098 -0400
@@ -6,24 +6,28 @@
 @cindex Device numbers, changing
 @cindex snapshot files, editing
 @cindex snapshot files, fixing device numbers
-  Sometimes device numbers can change after upgrading your kernel
-version or reconfiguring the hardware.  Reportedly this is the case with
-some newer @i{Linux} kernels, when using @acronym{LVM}.  In majority of
+  Various situations can cause device numbers to change: upgrading your
+kernel version, reconfiguring your hardware, loading kernel modules in a
+different order, using virtual volumes that are assembled dynamically
+(such as with @acronym{LVM} or @acronym{RAID}), hot-plugging drives
+(e.g. external USB or Firewire drives), etc.  In the majority of 
 cases this change is unnoticed by the users.  However, it influences
 @command{tar} incremental backups: the device number is stored in tar
 snapshot files (@pxref{Snapshot Files}) and is used to determine whether
 the file has changed since the last backup.  If the device numbers
-change for some reason, the next backup you run will be a full backup.
+change for some reason, by default the next backup you run will be a
+full backup.
+
 
 @pindex tar-snapshot-edit
   To minimize the impact in these cases, GNU @command{tar} comes with
 the @command{tar-snapshot-edit} utility for inspecting and updating
-device numbers in snapshot files.  The utility, written by
-Dustin J.@: Mitchell, is available from
+device numbers in snapshot files.  (The utility, written by
+Dustin J.@: Mitchell, is also available from the
 @uref{http://www.gnu.org/@/software/@/tar/@/utils/@/tar-snapshot-edit.html,
address@hidden home page}.
address@hidden home page}.)
 
-  To obtain the device numbers used in the snapshot file, run
+  To obtain a summary of the device numbers found in the snapshot file, run
 
 @smallexample
 $ @kbd{tar-snapshot-edit @var{snapfile}}
@@ -31,10 +35,19 @@
 
 @noindent
 where @var{snapfile} is the name of the snapshot file (you can supply as many
-files as you wish in a single command line).
-
-To update all occurrences of the given device number in the file, use
address@hidden option.  It takes a single argument of the form
+files as you wish in a single command line).  You can then compare the 
+numbers across snapshot files, or against those currently in use on the
+live filesystem (using @command{ls -l} or @command{stat}).
+
+  Assuming the device numbers have indeed changed, it's often possible
+to simply tell @GNUTAR{} to ignore the device number when processing the
+incremental snapshot files for these backups, using the
address@hidden option (@pxref{device numbers}).
+
+  Alternatively, you can use the @command{tar-edit-snapshot} script's 
address@hidden option to update all occurrences of the given device
+number in the snapshot file(s).  It takes a single argument
+of the form
 @address@hidden@var{newdev}},  where @var{olddev} is the device number
 used in the snapshot file, and @var{newdev} is the corresponding new device
 number.  Both numbers may be specified in hex (e.g., @samp{0xfe01}),
@@ -49,9 +62,30 @@
 
 An example session:
 @smallexample
-$ @kbd{tar-snapshot-edit /var/backup/snap.a}
-file version 2
-/tmp/snap: Device 0x0306 occurs 634 times.
-$ @kbd{tar-snapshot-edit -b -r 0x0306-0x4500 /var/backup/snap.a}
-file version 2
+$ @kbd{tar-snapshot-edit root_snap.0 boot_snap.0}
+File: root_snap.0
+  Detected snapshot file version: 2
+
+  Device 0x0000 occurs 1 times.
+  Device 0x0003 occurs 1 times.
+  Device 0x0005 occurs 1 times.
+  Device 0x0013 occurs 1 times.
+  Device 0x6801 occurs 1 times.
+  Device 0x6803 occurs 6626 times.
+  Device 0xfb00 occurs 1 times.
+
+File: boot_snap.0
+  Detected snapshot file version: 2
+
+  Device 0x6801 occurs 3 times.
+$ @kbd{tar-snapshot-edit -b -r 0x6801-0x6901,0x6803-0x6903 root_snap.0 
boot_snap.0}
+File: root_snap.0
+  Detected snapshot file version: 2
+
+  Updated 6627 records.
+
+File: boot_snap.0
+  Detected snapshot file version: 2
+
+  Updated 3 records.
 @end smallexample