+++ /dev/null
-#!/usr/bin/perl -w
-#
-# Proof-of-concept/reference decoder for LBS-format backup snapshots.
-#
-# This decoder aims to decompress an LBS snapshot. It is not meant to be
-# particularly efficient, but should be a small and portable tool for doing so
-# (important for recovering from data loss). It is also meant to serve as a
-# check on the snapshot tool and data format itself, and serve as documentation
-# for the format.
-#
-# This decoder does not understand TAR archives; it assumes that all segments
-# in the snapshot have already been decompressed, and that objects are
-# available simply as files in the filesystem. This simplifies the design.
-#
-# Limitations: Since this code is probably using 32-bit arithmetic, files
-# larger than 2-4 GB may not be properly handled.
-#
-# Copyright (C) 2007 Michael Vrable
-
-use strict;
-use Digest::SHA1;
-use File::Basename;
-
-my $OBJECT_DIR; # Where are the unpacked objects available?
-my $DEST_DIR = "."; # Where should restored files should be placed?
-my $RECURSION_LIMIT = 3; # Bound on recursive object references
-
-my $VERBOSE = 0; # Set to 1 to enable debugging messages
-
-############################ CHECKSUM VERIFICATION ############################
-# A very simple layer for verifying checksums. Checksums may be used on object
-# references directly, and can also be used to verify entire reconstructed
-# files.
-#
-# A checksum to verify is given in the form "algorithm=hexdigest". Given such
-# a string, we can construct a "verifier" object. Bytes can be incrementally
-# added to the verifier, and at the end a test can be made to see if the
-# checksum matches. The caller need not know what algorithm is used. However,
-# at the moment we only support SHA-1 for computing digest (algorith name
-# "sha1").
-sub verifier_create {
- my $checksum = shift;
-
- if ($checksum !~ m/^(\w+)=([0-9a-f]+)$/) {
- die "Malformed checksum: $checksum";
- }
- my ($algorithm, $hash) = ($1, $2);
- if ($algorithm ne 'sha1') {
- die "Unsupported checksum algorithm: $algorithm";
- }
-
- my %verifier = (
- ALGORITHM => $algorithm,
- HASH => $hash,
- DIGESTER => new Digest::SHA1
- );
-
- return \%verifier;
-}
-
-sub verifier_add_bytes {
- my $verifier = shift;
- my $digester = $verifier->{DIGESTER};
- my $data = shift;
-
- $digester->add($data);
-}
-
-sub verifier_check {
- my $verifier = shift;
- my $digester = $verifier->{DIGESTER};
-
- my $newhash = $digester->hexdigest();
- if ($VERBOSE && $verifier->{HASH} ne $newhash) {
- print STDERR "Verification failure: ",
- $newhash, " != ", $verifier->{HASH}, "\n";
- }
- return ($verifier->{HASH} eq $newhash);
-}
-
-################################ OBJECT ACCESS ################################
-# The base of the decompressor is the object reference layer. See ref.h for a
-# description of the format for object references. These functions will parse
-# an object reference, locate the object data from the filesystem, perform any
-# necessary integrity checks (if a checksum is included), and return the object
-# data.
-sub load_ref {
- # First, try to parse the object reference string into constituent pieces.
- # The format is segment/object(checksum)[range]. Both the checksum and
- # range are optional.
- my $ref_str = shift;
-
- if ($ref_str !~ m/^([-0-9a-f]+)\/([0-9a-f]+)(\(\S+\))?(\[\S+\])?$/) {
- die "Malformed object reference: $ref_str";
- }
-
- my ($segment, $object, $checksum, $range) = ($1, $2, $3, $4);
-
- # Next, use the segment/object components to locate and read the object
- # contents from disk.
- open OBJECT, "<", "$OBJECT_DIR/$segment/$object"
- or die "Unable to open object $OBJECT_DIR/$segment/$object: $!";
- my $contents = join '', <OBJECT>;
- close OBJECT;
-
- # If a checksum was specified in the object reference, verify the object
- # integrity by computing a checksum of the read data and comparing.
- if ($checksum) {
- $checksum =~ m/^\((\S+)\)$/;
- my $verifier = verifier_create($1);
- verifier_add_bytes($verifier, $contents);
- if (!verifier_check($verifier)) {
- die "Integrity check for object $ref_str failed";
- }
- }
-
- # If a range was specified, then only a subset of the bytes of the object
- # are desired. Extract just the desired bytes.
- if ($range) {
- if ($range !~ m/^\[(\d+)\+(\d+)\]$/) {
- die "Malformed object range: $range";
- }
-
- my $object_size = length $contents;
- my ($start, $length) = ($1 + 0, $2 + 0);
- if ($start >= $object_size || $start + $length > $object_size) {
- die "Object range $range falls outside object bounds "
- . "(actual size $object_size)";
- }
-
- $contents = substr $contents, $start, $length;
- }
-
- return $contents;
-}
-
-############################### FILE PROCESSING ###############################
-# Process the metadata for a single file. process_file is the main entry
-# point; it should be given a list of file metadata key/value pairs.
-# iterate_objects is a helper function used to iterate over the set of object
-# references that contain the file data for a regular file.
-
-sub parse_int {
- my $str = shift;
- if ($str =~ /^0/) {
- return oct($str);
- } else {
- return $str + 0;
- }
-}
-
-sub uri_decode {
- my $str = shift;
- $str =~ s/%([0-9a-f]{2})/chr(hex($1))/ge;
- return $str;
-}
-
-sub iterate_objects {
- my $callback = shift; # Function to be called for each reference
- my $arg = shift; # Argument passed to callback
- my $text = shift; # Whitespace-separate list of object references
-
- # Simple limit to guard against cycles in the object references
- my $recursion_level = shift || 0;
- if ($recursion_level >= $RECURSION_LIMIT) {
- die "Recursion limit reached";
- }
-
- # Split the provided text at whitespace boundaries to produce the list of
- # object references. If any of these start with "@", then we have an
- # indirect reference, and must look up that object and call iterate_objects
- # with the contents.
- my $obj;
- foreach $obj (split /\s+/, $text) {
- next if $obj eq "";
- if ($obj =~ /^@(\S+)$/) {
- my $indirect = load_ref($1);
- iterate_objects($callback, $arg, $indirect, $recursion_level + 1);
- } else {
- &$callback($arg, $obj);
- }
- }
-}
-
-sub obj_callback {
- my $state = shift;
- my $obj = shift;
- my $data = load_ref($obj);
- print FILE $data
- or die "Error writing file data: $!";
- verifier_add_bytes($state->{VERIFIER}, $data);
- $state->{BYTES} += length($data);
-}
-
-# Extract the contents of a regular file by concatenating all the objects that
-# comprise it.
-sub unpack_file {
- my $name = shift;
- my %info = @_;
- my %state = ();
-
- if (!defined $info{data}) {
- die "File contents not specified for $name";
- }
- if (!defined $info{checksum} || !defined $info{size}) {
- die "File $name is missing checksum or size";
- }
-
- $info{size} = parse_int($info{size});
-
- # Open the file to be recreated. The data will be written out by the call
- # to iterate_objects.
- open FILE, ">", "$DEST_DIR/$name"
- or die "Cannot write file $name: $!";
-
- # Set up state so that we can incrementally compute the checksum and length
- # of the reconstructed data. Then iterate over all objects in the file.
- $state{VERIFIER} = verifier_create($info{checksum});
- $state{BYTES} = 0;
- iterate_objects(\&obj_callback, \%state, $info{data});
-
- close FILE;
-
- # Verify that the reconstructed object matches the size/checksum we were
- # given.
- if (!verifier_check($state{VERIFIER}) || $state{BYTES} != $info{size}) {
- die "File reconstruction failed for $name: size or checksum differs";
- }
-}
-
-sub process_file {
- my %info = @_;
-
- if (!defined($info{name})) {
- die "Filename not specified in metadata block";
- }
-
- my $type = $info{type};
-
- my $filename = uri_decode($info{name});
- print "$filename\n" if $VERBOSE;
-
- # Restore the specified file. How to do so depends upon the file type, so
- # dispatch based on that.
- my $dest = "$DEST_DIR/$filename";
- if ($type eq '-') {
- # Regular file
- unpack_file($filename, %info);
- } elsif ($type eq 'd') {
- # Directory
- if ($filename ne '.') {
- mkdir $dest or die "Cannot create directory $filename: $!";
- }
- } elsif ($type eq 'l') {
- # Symlink
- if (!defined($info{contents})) {
- die "Symlink $filename has no value specified";
- }
- my $contents = uri_decode($info{contents});
- symlink $contents, $dest
- or die "Cannot create symlink $filename: $!";
-
- # TODO: We can't properly restore all metadata for symbolic links
- # (attempts to do so below will change metadata for the pointed-to
- # file). This should be later fixed, but for now we simply return
- # before getting to the restore metadata step below.
- return;
- } elsif ($type eq 'p' || $type eq 's' || $type eq 'c' || $type eq 'b') {
- # Pipe, socket, character device, block device.
- # TODO: Handle these cases.
- print STDERR "Ignoring special file $filename of type $type\n";
- return;
- } else {
- die "Unknown file type '$type' for file $filename";
- }
-
- # Restore mode, ownership, and any other metadata for the file. This is
- # split out from the code above since the code is the same regardless of
- # file type.
- my $mtime = $info{mtime} || time();
- utime time(), $mtime, $dest
- or warn "Unable to update mtime for $dest";
-
- my $uid = -1;
- my $gid = -1;
- if (defined $info{user}) {
- my @items = split /\s/, $info{user};
- $uid = parse_int($items[0]) if exists $items[0];
- }
- if (defined $info{group}) {
- my @items = split /\s/, $info{group};
- $gid = parse_int($items[0]) if exists $items[0];
- }
- chown $uid, $gid, $dest
- or warn "Unable to change ownership for $dest";
-
- if (defined $info{mode}) {
- my $mode = parse_int($info{mode});
- chmod $mode, $dest
- or warn "Unable to change permissions for $dest";
- }
-}
-
-########################### METADATA LIST PROCESSING ##########################
-# Process the file metadata listing provided, and as information for each file
-# is extracted, pass it to process_file. This will recursively follow indirect
-# references to other metadata objects.
-sub process_metadata {
- my ($metadata, $recursion_level) = @_;
-
- # Check recursion; this will prevent us from infinitely recursing on an
- # indirect reference which loops back to itself.
- $recursion_level ||= 0;
- if ($recursion_level >= $RECURSION_LIMIT) {
- die "Recursion limit reached";
- }
-
- # Split the metadata into lines, then start processing each line. There
- # are two primary cases:
- # - Lines starting with "@" are indirect references to other metadata
- # objects. Recursively process that object before continuing.
- # - Other lines should come in groups separated by a blank line; these
- # contain metadata for a single file that should be passed to
- # process_file.
- # Note that blocks of metadata about a file cannot span a boundary between
- # metadata objects.
- my %info = ();
- my $line;
- my $last_key;
- foreach $line (split /\n/, $metadata) {
- # If we find a blank line or a reference to another block, process any
- # data for the previous file first.
- if ($line eq '' || $line =~ m/^@/) {
- process_file(%info) if %info;
- %info = ();
- undef $last_key;
- next if $line eq '';
- }
-
- # Recursively handle indirect metadata blocks.
- if ($line =~ m/^@(\S+)$/) {
- print "Indirect: $1\n" if $VERBOSE;
- my $indirect = load_ref($1);
- process_metadata($indirect, $recursion_level + 1);
- next;
- }
-
- # Try to parse the data as "key: value" pairs of file metadata. Also
- # handle continuation lines, which start with whitespace and continue
- # the previous "key: value" pair.
- if ($line =~ m/^(\w+):\s*(.*)$/) {
- $info{$1} = $2;
- $last_key = $1;
- } elsif ($line =~/^\s/ && defined $last_key) {
- $info{$last_key} .= $line;
- } else {
- print STDERR "Junk in file metadata section: $line\n";
- }
- }
-
- # Process any last file metadata which has not already been processed.
- process_file(%info) if %info;
-}
-
-############################### MAIN ENTRY POINT ##############################
-# Program start. We expect to be called with a single argument, which is the
-# name of the backup descriptor file written by a backup pass. This will name
-# the root object in the snapshot, from which we can reach all other data we
-# need.
-
-# Parse command-line arguments. The first (required) is the name of the
-# snapshot descriptor file. The backup objects are assumed to be stored in the
-# same directory as the descriptor. The second (optional) argument is the
-# directory where the restored files should be written; it defaults to ".";
-my $descriptor = $ARGV[0];
-unless (defined($descriptor) && -r $descriptor) {
- print STDERR "Usage: $0 <snapshot file>\n";
- exit 1;
-}
-
-if (defined($ARGV[1])) {
- $DEST_DIR = $ARGV[1];
-}
-
-$OBJECT_DIR = dirname($descriptor);
-print "Source directory: $OBJECT_DIR\n" if $VERBOSE;
-
-# Read the snapshot descriptor to find the root object. Parse it to get a set
-# of key/value pairs.
-open DESCRIPTOR, "<", $descriptor
- or die "Cannot open backup descriptor file $descriptor: $!";
-my %descriptor = ();
-my ($line, $last_key);
-while (defined($line = <DESCRIPTOR>)) {
- # Any lines of the form "key: value" should be inserted into the
- # %descriptor dictionary. Any continuation line (a line starting with
- # whitespace) will append text to the previous key's value. Ignore other
- # lines.
- chomp $line;
-
- if ($line =~ m/^(\w+):\s*(.*)$/) {
- $descriptor{$1} = $2;
- $last_key = $1;
- } elsif ($line =~/^\s/ && defined $last_key) {
- $descriptor{$last_key} .= $line;
- } else {
- undef $last_key;
- print STDERR "Ignoring line in backup descriptor: $line\n";
- }
-}
-
-# A valid backup descriptor should at the very least specify the root metadata
-# object.
-if (!exists $descriptor{Root}) {
- die "Expected 'Root:' specification in backup descriptor file";
-}
-my $root = $descriptor{Root};
-close DESCRIPTOR;
-
-# Set the umask to something restrictive. As we unpack files, we'll originally
-# write the files/directories without setting the permissions, so be
-# conservative and ensure that they can't be read. Afterwards, we'll properly
-# fix up permissions.
-umask 077;
-
-# Start processing metadata stored in the root to recreate the files.
-print "Root object: $root\n" if $VERBOSE;
-my $contents = load_ref($root);
-process_metadata($contents);
projects / cumulus.git / blobdiff