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Sergey Poznyakoff
58
doc/tar-snapshot-edit.texi
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58
doc/tar-snapshot-edit.texi
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@c This is part of the paxutils manual.
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@c Copyright (C) 2007 Free Software Foundation, Inc.
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@c This file is distributed under GFDL 1.1 or any later version
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@c published by the Free Software Foundation.
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@cindex Device numbers, changing
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@cindex snapshot files, editing
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@cindex snapshot files, fixing device numbers
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Sometimes device numbers can change after upgrading your kernel
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version or recofiguring the harvare. Reportedly this is the case with
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some newer @i{Linux} kernels, when using @acronym{LVM}. In majority of
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cases this change is unnoticed by the users. However, it influences
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@command{tar} incremental backups: the device number is stored in tar
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snapshot files (@pxref{Snapshot Files}) and is used to determine whether
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the file has changed since the last backup. If the device numbers
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change for some reason, the next backup you run will be a full backup.
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@pindex tar-snapshot-edit
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To minimize the impact in these cases, GNU @command{tar} comes with
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the @command{tar-snapshot-edit} utility for inspecting and updating
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device numbers in snapshot files. The utility, written by
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Dustin J.@: Mitchell, is available from
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@uref{http://www.gnu.org/@/software/@/tar/@/utils/@/tar-snapshot-edit.html,
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@GNUTAR{} home page}.
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To obtain the device numbers used in the snapshot file, run
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@smallexample
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$ @kbd{tar-snapshot-edit @var{snapfile}}
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@end smallexample
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@noindent
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where @var{snapfile} is the name of the snapshot file (you can supply as many
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files as you wish in a single command line ).
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To update all occurrences of the given device number in the file, use
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@option{-r} option. It takes a single argument of the form
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@samp{@var{olddev}-@var{newdev}}, where @var{olddev} is the device number
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used in the snapshot file, and @var{newdev} is the corresponding new device
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number. Both numbers may be specified in hex (e.g., @samp{0xfe01}),
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decimal (e.g., @samp{65025}), or as a major:minor number pair (e.g.,
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@samp{254:1}). To change several device numbers at once, specify them
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in a single comma-separated list, as in
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@option{-r 0x3060-0x4500,0x307-0x4600}.
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Before updating the snapshot file, it is a good idea to create a backup
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copy of it. This is accomplished by @samp{-b} option. The name of the
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backup file is obtained by appending @samp{~} to the original file name.
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An example session:
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@smallexample
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$ @kbd{tar-snapshot-edit /var/backup/snap.a}
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file version 2
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/tmp/snap: Device 0x0306 occurs 634 times.
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$ @kbd{tar-snapshot-edit -b -r 0x0306-0x4500 /var/backup/snap.a}
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file version 2
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@end smallexample
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328
scripts/tar-snapshot-edit
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328
scripts/tar-snapshot-edit
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#! /usr/bin/perl -w
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# Display and edit the 'dev' field in tar's snapshots
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# Copyright (C) 2007 Free Software Foundation, Inc.
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#
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# This program is free software; you can redistribute it and/or modify
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# it under the terms of the GNU General Public License as published by
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# the Free Software Foundation; either version 2, or (at your option)
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# any later version.
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#
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# This program is distributed in the hope that it will be useful,
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# but WITHOUT ANY WARRANTY; without even the implied warranty of
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# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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# GNU General Public License for more details.
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#
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# You should have received a copy of the GNU General Public License
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# along with this program; if not, write to the Free Software
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# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
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# 02110-1301, USA.
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#
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# Author: Dustin J. Mitchell <dustin@zmanda.com>
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#
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# This script is capable of replacing values in the 'dev' field of an
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# incremental backup 'snapshot' file. This is useful when the device
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# used to store files in a tar archive changes, without the files
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# themselves changing. This may happen when, for example, a device
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# driver changes major or minor numbers.
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use Getopt::Std;
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## reading
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sub read_incr_db ($) {
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my $filename = shift;
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open(my $file, "<$filename") || die "Could not open '$filename' for reading";
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my $header_str = <$file>;
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my $file_version;
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if ($header_str =~ /^GNU tar-[^-]*-([0-9]+)\n$/) {
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$file_version = $1+0;
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} else {
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$file_version = 0;
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}
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print "file version $file_version\n";
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if ($file_version == 0) {
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return read_incr_db_0($file, $header_str);
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} elsif ($file_version == 1) {
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return read_incr_db_1($file);
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} elsif ($file_version == 2) {
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return read_incr_db_2($file);
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} else {
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die "Unrecognized snapshot version in header '$header_str'";
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}
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}
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sub read_incr_db_0 ($$) {
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my $file = shift;
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my $header_str = shift;
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my $hdr_timestamp_sec = $header_str;
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chop $hdr_timestamp_sec;
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my $hdr_timestamp_nsec = ''; # not present in file format 0
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my @dirs;
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while (<$file>) {
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/^([0-9]*) ([0-9]*) (.*)\n$/ || die("Bad snapshot line $_");
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push @dirs, { dev=>$1,
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ino=>$2,
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name=>$3 };
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}
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close($file);
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# file version, timestamp, timestamp, dir list
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return [ 0, $hdr_timestamp_sec, $hdr_timestamp_nsec, \@dirs ];
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}
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sub read_incr_db_1 ($) {
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my $file = shift;
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my $timestamp = <$file>; # "sec nsec"
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my ($hdr_timestamp_sec, $hdr_timestamp_nsec) = ($timestamp =~ /([0-9]*) ([0-9]*)/);
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my @dirs;
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while (<$file>) {
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/^([0-9]*) ([0-9]*) ([0-9]*) ([0-9]*) (.*)\n$/ || die("Bad snapshot line $_");
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push @dirs, { timestamp_sec=>$1,
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timestamp_nsec=>$2,
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dev=>$3,
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ino=>$4,
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name=>$5 };
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}
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close($file);
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# file version, timestamp, timestamp, dir list
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return [ 1, $hdr_timestamp_sec, $hdr_timestamp_nsec, \@dirs ];
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}
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sub read_incr_db_2 ($) {
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my $file = shift;
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$/="\0"; # $INPUT_RECORD_SEPARATOR
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my $hdr_timestamp_sec = <$file>;
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chop $hdr_timestamp_sec;
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my $hdr_timestamp_nsec = <$file>;
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chop $hdr_timestamp_nsec;
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my @dirs;
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while (1) {
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last if eof($file);
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my $nfs = <$file>;
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my $timestamp_sec = <$file>;
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my $timestamp_nsec = <$file>;
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my $dev = <$file>;
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my $ino = <$file>;
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my $name = <$file>;
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# get rid of trailing NULs
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chop $nfs;
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chop $timestamp_sec;
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chop $timestamp_nsec;
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chop $dev;
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chop $ino;
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chop $name;
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my @dirents;
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while (my $dirent = <$file>) {
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chop $dirent;
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push @dirents, $dirent;
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last if ($dirent eq "");
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}
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die "missing terminator" unless (<$file> eq "\0");
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push @dirs, { nfs=>$nfs,
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timestamp_sec=>$timestamp_sec,
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timestamp_nsec=>$timestamp_nsec,
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dev=>$dev,
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ino=>$ino,
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name=>$name,
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dirents=>\@dirents };
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}
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close($file);
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$/ = "\n"; # reset to normal
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# file version, timestamp, timestamp, dir list
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return [ 2, $hdr_timestamp_sec, $hdr_timestamp_nsec, \@dirs ];
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}
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## display
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sub show_device_counts ($$) {
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my $info = shift;
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my $filename = shift;
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my %devices;
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foreach my $dir (@{${@$info}[3]}) {
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my $dev = ${%$dir}{'dev'};
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$devices{$dev}++;
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}
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foreach $dev (sort keys %devices) {
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printf "$filename: Device 0x%04x occurs $devices{$dev} times.\n", $dev;
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}
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}
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## editing
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sub replace_device_number ($@) {
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my $info = shift(@_);
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my @repl = @_;
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foreach my $dir (@{${@$info}[3]}) {
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foreach $x (@repl) {
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if (${%$dir}{'dev'} eq $$x[0]) {
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${%$dir}{'dev'} = $$x[1];
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last;
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}
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}
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}
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}
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## writing
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sub write_incr_db ($$) {
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my $info = shift;
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my $filename = shift;
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my $file_version = $$info[0];
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open($file, ">$filename") || die "Could not open '$filename' for writing";
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if ($file_version == 0) {
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write_incr_db_0($info, $file);
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} elsif ($file_version == 1) {
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write_incr_db_1($info, $file);
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} elsif ($file_version == 2) {
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write_incr_db_2($info, $file);
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} else {
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die "Unknown file version $file_version.";
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}
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close($file);
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}
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sub write_incr_db_0 ($$) {
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my $info = shift;
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my $file = shift;
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my $timestamp_sec = $info->[1];
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print $file "$timestamp_sec\n";
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foreach my $dir (@{${@$info}[3]}) {
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print $file "${%$dir}{'dev'} ";
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print $file "${%$dir}{'ino'} ";
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print $file "${%$dir}{'name'}\n";
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}
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}
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sub write_incr_db_1 ($$) {
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my $info = shift;
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my $file = shift;
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print $file "GNU tar-1.15-1\n";
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my $timestamp_sec = $info->[1];
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my $timestamp_nsec = $info->[2];
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print $file "$timestamp_sec $timestamp_nsec\n";
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foreach my $dir (@{${@$info}[3]}) {
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print $file "${%$dir}{'timestamp_sec'} ";
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print $file "${%$dir}{'timestamp_nsec'} ";
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print $file "${%$dir}{'dev'} ";
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print $file "${%$dir}{'ino'} ";
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print $file "${%$dir}{'name'}\n";
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}
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}
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sub write_incr_db_2 ($$) {
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my $info = shift;
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my $file = shift;
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print $file "GNU tar-1.16-2\n";
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my $timestamp_sec = $info->[1];
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my $timestamp_nsec = $info->[2];
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print $file $timestamp_sec . "\0";
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print $file $timestamp_nsec . "\0";
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foreach my $dir (@{${@$info}[3]}) {
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print $file ${%$dir}{'nfs'} . "\0";
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print $file ${%$dir}{'timestamp_sec'} . "\0";
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print $file ${%$dir}{'timestamp_nsec'} . "\0";
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print $file ${%$dir}{'dev'} . "\0";
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print $file ${%$dir}{'ino'} . "\0";
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print $file ${%$dir}{'name'} . "\0";
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foreach my $dirent (@{${%$dir}{'dirents'}}) {
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print $file $dirent . "\0";
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}
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print $file "\0";
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}
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}
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## main
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sub main {
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our ($opt_b, $opt_r, $opt_h);
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getopts('br:h');
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HELP_MESSAGE() if ($opt_h || $#ARGV == -1 || ($opt_b && !$opt_r));
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my @repl;
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if ($opt_r) {
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foreach my $spec (split(/,/, $opt_r)) {
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($spec =~ /^([^-]+)-([^-]+)/) || die "Invalid replacement specification '$opt_r'";
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push @repl, [interpret_dev($1), interpret_dev($2)];
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}
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}
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foreach my $snapfile (@ARGV) {
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my $info = read_incr_db($snapfile);
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if ($opt_r ) {
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if ($opt_b) {
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rename($snapfile, $snapfile . "~") || die "Could not rename '$snapfile' to backup";
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}
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replace_device_number($info, @repl);
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write_incr_db($info, $snapfile);
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} else {
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show_device_counts($info, $snapfile);
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}
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}
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}
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sub HELP_MESSAGE {
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print "Usage: tar-snapshot-edit.pl [-r 'DEV1-DEV2[,DEV3-DEV4...]' [-b]] SNAPFILE [SNAPFILE [..]]\n";
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print "\n";
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print " Without -r, summarize the 'device' values in each SNAPFILE.\n";
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print "\n";
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print " With -r, replace occurrences of DEV1 with DEV2 in each SNAPFILE.\n";
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print " DEV1 and DEV2 may be specified in hex (e.g., 0xfe01), decimal (e.g.,\n";
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print " 65025), or MAJ:MIN (e.g., 254:1). To replace multiple occurrences,\n";
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print " separate them with commas. If -b is also specified, backup\n";
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print " files (ending with '~') will be created.\n";
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exit 1;
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}
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sub interpret_dev ($) {
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my $dev = shift;
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if ($dev =~ /^([0-9]+):([0-9]+)$/) {
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return $1 * 256 + $2;
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} elsif ($dev =~ /^0x[0-9a-fA-F]+$/) {
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return oct $dev;
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} elsif ($dev =~ /^[0-9]+$/) {
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return $dev+0;
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} else {
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die "Invalid device specification '$dev'";
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}
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}
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main
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Reference in New Issue
Block a user