summaryrefslogtreecommitdiff
path: root/lib/backupclient/BackupStoreFileDiff.cpp
blob: 3699eb499bea726b74cf8250a80ef86e0641f670 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
// --------------------------------------------------------------------------
//
// File
//		Name:    BackupStoreFileDiff.cpp
//		Purpose: Functions relating to diffing BackupStoreFiles
//		Created: 12/1/04
//
// --------------------------------------------------------------------------

#include "Box.h"

#include <new>
#include <map>
#include <signal.h>
#include <sys/time.h>

#include "BackupStoreFile.h"
#include "BackupStoreFileWire.h"
#include "BackupStoreFileCryptVar.h"
#include "BackupStoreObjectMagic.h"
#include "BackupStoreException.h"
#include "BackupStoreFileEncodeStream.h"
#include "BackupStoreConstants.h"
#include "FileStream.h"
#include "RollingChecksum.h"
#include "MD5Digest.h"
#include "CommonException.h"

#include "MemLeakFindOn.h"

using namespace BackupStoreFileCryptVar;
using namespace BackupStoreFileCreation;

// By default, don't trace out details of the diff as we go along -- would fill up logs significantly.
// But it's useful for the test.
#ifndef NDEBUG
	bool BackupStoreFile::TraceDetailsOfDiffProcess = false;
#endif

static void LoadIndex(IOStream &rBlockIndex, int64_t ThisID, BlocksAvailableEntry **ppIndex, int64_t &rNumBlocksOut, int Timeout, bool &rCanDiffFromThis);
static void FindMostUsedSizes(BlocksAvailableEntry *pIndex, int64_t NumBlocks, int32_t Sizes[BACKUP_FILE_DIFF_MAX_BLOCK_SIZES]);
static void SearchForMatchingBlocks(IOStream &rFile, std::map<int64_t, int64_t> &rFoundBlocks, BlocksAvailableEntry *pIndex, int64_t NumBlocks, int32_t Sizes[BACKUP_FILE_DIFF_MAX_BLOCK_SIZES]);
static void SetupHashTable(BlocksAvailableEntry *pIndex, int64_t NumBlocks, int32_t BlockSize, BlocksAvailableEntry **pHashTable);
static bool SecondStageMatch(BlocksAvailableEntry *pFirstInHashList, RollingChecksum &fastSum, uint8_t *pBeginnings, uint8_t *pEndings, int Offset, int32_t BlockSize, int64_t FileBlockNumber,
BlocksAvailableEntry *pIndex, std::map<int64_t, int64_t> &rFoundBlocks);
static void GenerateRecipe(BackupStoreFileEncodeStream::Recipe &rRecipe, BlocksAvailableEntry *pIndex, int64_t NumBlocks, std::map<int64_t, int64_t> &rFoundBlocks, int64_t SizeOfInputFile);

// Avoid running on too long with diffs
static int sMaximumDiffTime = 600;		// maximum time to spend diffing
static bool sDiffTimedOut = false;
static bool sSetTimerSignelHandler = false;
static void TimerSignalHandler(int signal);
static void StartDiffTimer();


// --------------------------------------------------------------------------
//
// Function
//		Name:    BackupStoreFile::SetMaximumDiffingTime(int)
//		Purpose: Sets the maximum time to spend diffing, in seconds. Time is
//				 process virutal time.
//		Created: 19/3/04
//
// --------------------------------------------------------------------------
void BackupStoreFile::SetMaximumDiffingTime(int Seconds)
{
	sMaximumDiffTime = Seconds;
	TRACE1("Set maximum diffing time to %d seconds\n", Seconds);
}


// --------------------------------------------------------------------------
//
// Function
//		Name:    BackupStoreFile::MoveStreamPositionToBlockIndex(IOStream &)
//		Purpose: Move the file pointer in this stream to just before the block index.
//				 Assumes that the stream is at the beginning, seekable, and
//				 reading from the stream is OK.
//		Created: 12/1/04
//
// --------------------------------------------------------------------------
void BackupStoreFile::MoveStreamPositionToBlockIndex(IOStream &rStream)
{
	// Size of file
	int64_t fileSize = rStream.BytesLeftToRead();

	// Get header
	file_StreamFormat hdr;

	// Read the header
	if(!rStream.ReadFullBuffer(&hdr, sizeof(hdr), 0 /* not interested in bytes read if this fails */, IOStream::TimeOutInfinite))
	{
		// Couldn't read header
		THROW_EXCEPTION(BackupStoreException, CouldntReadEntireStructureFromStream)
	}

	// Check magic number
	if(ntohl(hdr.mMagicValue) != OBJECTMAGIC_FILE_MAGIC_VALUE_V1
#ifndef BOX_DISABLE_BACKWARDS_COMPATIBILITY_BACKUPSTOREFILE
		&& ntohl(hdr.mMagicValue) != OBJECTMAGIC_FILE_MAGIC_VALUE_V0
#endif
		)
	{
		THROW_EXCEPTION(BackupStoreException, BadBackupStoreFile)
	}
	
	// Work out where the index is
	int64_t numBlocks = box_ntoh64(hdr.mNumBlocks);
	int64_t blockHeaderPosFromEnd = ((numBlocks * sizeof(file_BlockIndexEntry)) + sizeof(file_BlockIndexHeader));
	
	// Sanity check
	if(blockHeaderPosFromEnd > static_cast<int64_t>(fileSize - sizeof(file_StreamFormat)))
	{
		THROW_EXCEPTION(BackupStoreException, BadBackupStoreFile)
	}
	
	// Seek to that position
	rStream.Seek(0 - blockHeaderPosFromEnd, IOStream::SeekType_End);
	
	// Done. Stream now in right position (as long as the file is formatted correctly)
}


// --------------------------------------------------------------------------
//
// Function
//		Name:    BackupStoreFile::EncodeFileDiff(const char *, int64_t, const BackupStoreFilename &, int64_t, IOStream &, int64_t *)
//		Purpose: Similar to EncodeFile, but takes the object ID of the file it's
//				 diffing from, and the index of the blocks in a stream. It'll then
//				 calculate which blocks can be reused from that old file.
//				 The timeout is the timeout value for reading the diff block index.
//				 If pIsCompletelyDifferent != 0, it will be set to true if the
//				 the two files are completely different (do not share any block), false otherwise.
//				 
//		Created: 12/1/04
//
// --------------------------------------------------------------------------
std::auto_ptr<IOStream> BackupStoreFile::EncodeFileDiff(const char *Filename, int64_t ContainerID,
	const BackupStoreFilename &rStoreFilename, int64_t DiffFromObjectID, IOStream &rDiffFromBlockIndex,
	int Timeout, int64_t *pModificationTime, bool *pIsCompletelyDifferent)
{
	// Is it a symlink?
	{
		struct stat st;
		if(::lstat(Filename, &st) != 0)
		{
			THROW_EXCEPTION(CommonException, OSFileError)
		}
		if((st.st_mode & S_IFLNK) == S_IFLNK)
		{
			// Don't do diffs for symlinks
			if(pIsCompletelyDifferent != 0)
			{
				*pIsCompletelyDifferent = true;
			}
			return EncodeFile(Filename, ContainerID, rStoreFilename, pModificationTime);
		}
	}

	// Load in the blocks
	BlocksAvailableEntry *pindex = 0;
	int64_t blocksInIndex = 0;
	bool canDiffFromThis = false;
	LoadIndex(rDiffFromBlockIndex, DiffFromObjectID, &pindex, blocksInIndex, Timeout, canDiffFromThis);
	//TRACE1("Diff: Blocks in index: %lld\n", blocksInIndex);
	
	if(!canDiffFromThis)
	{
		// Don't do diffing...
		if(pIsCompletelyDifferent != 0)
		{
			*pIsCompletelyDifferent = true;
		}
		return EncodeFile(Filename, ContainerID, rStoreFilename, pModificationTime);
	}
	
	// Pointer to recipe we're going to create
	BackupStoreFileEncodeStream::Recipe *precipe = 0;

	// Start the timeout timer, so that the operation doesn't continue for ever
	StartDiffTimer();
	
	try
	{
		// Find which sizes should be scanned
		int32_t sizesToScan[BACKUP_FILE_DIFF_MAX_BLOCK_SIZES];
		FindMostUsedSizes(pindex, blocksInIndex, sizesToScan);
		
		// Flag for reporting to the user
		bool completelyDifferent;
			
		// BLOCK
		{
			// Search the file to find matching blocks
			std::map<int64_t, int64_t> foundBlocks; // map of offset in file to index in block index
			int64_t sizeOfInputFile = 0;
			// BLOCK
			{
				FileStream file(Filename);
				// Get size of file
				sizeOfInputFile = file.BytesLeftToRead();
				// Find all those lovely matching blocks
				SearchForMatchingBlocks(file, foundBlocks, pindex, blocksInIndex, sizesToScan);
				
				// Is it completely different?
				completelyDifferent = (foundBlocks.size() == 0);
			}
			
			// Create a recipe -- if the two files are completely different, don't put the from file ID in the recipe.
			precipe = new BackupStoreFileEncodeStream::Recipe(pindex, blocksInIndex, completelyDifferent?(0):(DiffFromObjectID));
			BlocksAvailableEntry *pindexKeptRef = pindex;	// we need this later, but must set pindex == 0 now, because of exceptions
			pindex = 0;		// Recipe now has ownership
			
			// Fill it in
			GenerateRecipe(*precipe, pindexKeptRef, blocksInIndex, foundBlocks, sizeOfInputFile);
		}
		// foundBlocks no longer required
		
		// Create the stream
		std::auto_ptr<IOStream> stream(new BackupStoreFileEncodeStream);
	
		// Do the initial setup
		((BackupStoreFileEncodeStream*)stream.get())->Setup(Filename, precipe, ContainerID, rStoreFilename, pModificationTime);
		precipe = 0;	// Stream has taken ownership of this
		
		// Tell user about completely different status?
		if(pIsCompletelyDifferent != 0)
		{
			*pIsCompletelyDifferent = completelyDifferent;
		}
	
		// Return the stream for the caller
		return stream;
	}
	catch(...)
	{
		// cleanup
		if(pindex != 0)
		{
			::free(pindex);
			pindex = 0;
		}
		if(precipe != 0)
		{
			delete precipe;
			precipe = 0;
		}
		throw;
	}
}

// --------------------------------------------------------------------------
//
// Function
//		Name:    static LoadIndex(IOStream &, int64_t, BlocksAvailableEntry **, int64_t, bool &)
//		Purpose: Read in an index, and decrypt, and store in the in memory block format.
//				 rCanDiffFromThis is set to false if the version of the from file is too old.
//		Created: 12/1/04
//
// --------------------------------------------------------------------------
static void LoadIndex(IOStream &rBlockIndex, int64_t ThisID, BlocksAvailableEntry **ppIndex, int64_t &rNumBlocksOut, int Timeout, bool &rCanDiffFromThis)
{
	// Reset
	rNumBlocksOut = 0;
	rCanDiffFromThis = false;
	
	// Read header
	file_BlockIndexHeader hdr;
	if(!rBlockIndex.ReadFullBuffer(&hdr, sizeof(hdr), 0 /* not interested in bytes read if this fails */, Timeout))
	{
		// Couldn't read header
		THROW_EXCEPTION(BackupStoreException, CouldntReadEntireStructureFromStream)
	}

#ifndef BOX_DISABLE_BACKWARDS_COMPATIBILITY_BACKUPSTOREFILE
	// Check against backwards comptaibility stuff
	if(hdr.mMagicValue == (int32_t)htonl(OBJECTMAGIC_FILE_BLOCKS_MAGIC_VALUE_V0))
	{
		// Won't diff against old version
		
		// Absorb rest of stream
		char buffer[2048];
		while(rBlockIndex.StreamDataLeft())
		{
			rBlockIndex.Read(buffer, sizeof(buffer), 1000 /* 1 sec timeout */);
		}
		
		// Tell caller
		rCanDiffFromThis = false;
		return;
	}
#endif

	// Check magic
	if(hdr.mMagicValue != (int32_t)htonl(OBJECTMAGIC_FILE_BLOCKS_MAGIC_VALUE_V1))
	{
		THROW_EXCEPTION(BackupStoreException, BadBackupStoreFile)
	}
	
	// Check that we're not trying to diff against a file which references blocks from another file
	if(((int64_t)box_ntoh64(hdr.mOtherFileID)) != 0)
	{
		THROW_EXCEPTION(BackupStoreException, CannotDiffAnIncompleteStoreFile)
	}

	// Mark as an acceptable diff.
	rCanDiffFromThis = true;

	// Get basic information
	int64_t numBlocks = box_ntoh64(hdr.mNumBlocks);
	uint64_t entryIVBase = box_ntoh64(hdr.mEntryIVBase);
	
	//TODO: Verify that these sizes look reasonable
	
	// Allocate space for the index
	BlocksAvailableEntry *pindex = (BlocksAvailableEntry*)::malloc(sizeof(BlocksAvailableEntry) * numBlocks);
	if(pindex == 0)
	{
		throw std::bad_alloc();
	}
	
	try
	{	
		for(int64_t b = 0; b < numBlocks; ++b)
		{
			// Read an entry from the stream
			file_BlockIndexEntry entry;
			if(!rBlockIndex.ReadFullBuffer(&entry, sizeof(entry), 0 /* not interested in bytes read if this fails */, Timeout))
			{
				// Couldn't read entry
				THROW_EXCEPTION(BackupStoreException, CouldntReadEntireStructureFromStream)
			}	
		
			// Calculate IV for this entry
			uint64_t iv = entryIVBase;
			iv += b;
			// Network byte order
			iv = box_hton64(iv);
			sBlowfishDecryptBlockEntry.SetIV(&iv);			
			
			// Decrypt the encrypted section
			file_BlockIndexEntryEnc entryEnc;
			int sectionSize = sBlowfishDecryptBlockEntry.TransformBlock(&entryEnc, sizeof(entryEnc),
					entry.mEnEnc, sizeof(entry.mEnEnc));
			if(sectionSize != sizeof(entryEnc))
			{
				THROW_EXCEPTION(BackupStoreException, BlockEntryEncodingDidntGiveExpectedLength)
			}

			// Check that we're not trying to diff against a file which references blocks from another file
			if(((int64_t)box_ntoh64(entry.mEncodedSize)) <= 0)
			{
				THROW_EXCEPTION(BackupStoreException, CannotDiffAnIncompleteStoreFile)
			}
			
			// Store all the required information
			pindex[b].mpNextInHashList = 0;	// hash list not set up yet
			pindex[b].mSize = ntohl(entryEnc.mSize);
			pindex[b].mWeakChecksum = ntohl(entryEnc.mWeakChecksum);
			::memcpy(pindex[b].mStrongChecksum, entryEnc.mStrongChecksum, sizeof(pindex[b].mStrongChecksum));
		}
		
		// Store index pointer for called
		ASSERT(ppIndex != 0);
		*ppIndex = pindex;

		// Store number of blocks for caller
		rNumBlocksOut = numBlocks;	

	}
	catch(...)
	{
		// clean up and send the exception along its way
		::free(pindex);
		throw;
	}
}


// --------------------------------------------------------------------------
//
// Function
//		Name:    static FindMostUsedSizes(BlocksAvailableEntry *, int64_t, int32_t[BACKUP_FILE_DIFF_MAX_BLOCK_SIZES])
//		Purpose: Finds the most commonly used block sizes in the index
//		Created: 12/1/04
//
// --------------------------------------------------------------------------
static void FindMostUsedSizes(BlocksAvailableEntry *pIndex, int64_t NumBlocks, int32_t Sizes[BACKUP_FILE_DIFF_MAX_BLOCK_SIZES])
{
	// Array for lengths
	int64_t sizeCounts[BACKUP_FILE_DIFF_MAX_BLOCK_SIZES];

	// Set arrays to lots of zeros (= unused entries)
	for(int l = 0; l < BACKUP_FILE_DIFF_MAX_BLOCK_SIZES; ++l)
	{
		Sizes[l] = 0;
		sizeCounts[l] = 0;
	}

	// Array for collecting sizes
	std::map<int32_t, int64_t> foundSizes;
	
	// Run through blocks and make a count of the entries
	for(int64_t b = 0; b < NumBlocks; ++b)
	{
		// Only if the block size is bigger than the minimum size we'll scan for
		if(pIndex[b].mSize > BACKUP_FILE_DIFF_MIN_BLOCK_SIZE)
		{
			// Find entry?
			std::map<int32_t, int64_t>::const_iterator f(foundSizes.find(pIndex[b].mSize));
			if(f != foundSizes.end())
			{
				// Increment existing entry
				foundSizes[pIndex[b].mSize] = foundSizes[pIndex[b].mSize] + 1;
			}
			else
			{
				// New entry
				foundSizes[pIndex[b].mSize] = 1;
			}
		}
	}
	
	// Make the block sizes
	for(std::map<int32_t, int64_t>::const_iterator i(foundSizes.begin()); i != foundSizes.end(); ++i)
	{
		// Find the position of the size in the array
		for(int t = 0; t < BACKUP_FILE_DIFF_MAX_BLOCK_SIZES; ++t)
		{
			// Instead of sorting on the raw count of blocks,
			// take the file area covered by this block size.
			if(i->second * i->first > sizeCounts[t] * Sizes[t])
			{
				// Then this size belong before this entry -- shuffle them up
				for(int s = (BACKUP_FILE_DIFF_MAX_BLOCK_SIZES - 1); s >= t; --s)
				{
					Sizes[s] = Sizes[s-1];
					sizeCounts[s] = sizeCounts[s-1];
				}
				
				// Insert this size
				Sizes[t] = i->first;
				sizeCounts[t] = i->second;
				
				// Shouldn't do any more searching
				break;
			}
		}
	}
	
	// trace the size table in debug builds
#ifndef NDEBUG
	if(BackupStoreFile::TraceDetailsOfDiffProcess)
	{
		for(int t = 0; t < BACKUP_FILE_DIFF_MAX_BLOCK_SIZES; ++t)
		{
			TRACE3("Diff block size %d: %d (count = %lld)\n", t, Sizes[t], sizeCounts[t]);
		}
	}
#endif
}



// --------------------------------------------------------------------------
//
// Function
//		Name:    static SearchForMatchingBlocks(IOStream &, std::map<int64_t, int64_t> &, BlocksAvailableEntry *, int64_t, int32_t[BACKUP_FILE_DIFF_MAX_BLOCK_SIZES])
//		Purpose: Find the matching blocks within the file.
//		Created: 12/1/04
//
// --------------------------------------------------------------------------
static void SearchForMatchingBlocks(IOStream &rFile, std::map<int64_t, int64_t> &rFoundBlocks,
	BlocksAvailableEntry *pIndex, int64_t NumBlocks, int32_t Sizes[BACKUP_FILE_DIFF_MAX_BLOCK_SIZES])
{
	std::map<int64_t, int32_t> goodnessOfFit;

	// Allocate the hash lookup table
	BlocksAvailableEntry **phashTable = (BlocksAvailableEntry **)::malloc(sizeof(BlocksAvailableEntry *) * (64*1024));

	// Choose a size for the buffer, just a little bit more than the maximum block size
	int32_t bufSize = Sizes[0];
	for(int z = 1; z < BACKUP_FILE_DIFF_MAX_BLOCK_SIZES; ++z)
	{
		if(Sizes[z] > bufSize) bufSize = Sizes[z];
	}
	bufSize += 4;
	ASSERT(bufSize > Sizes[0]);
	ASSERT(bufSize > 0);
	if(bufSize > (BACKUP_FILE_MAX_BLOCK_SIZE + 1024))
	{
		THROW_EXCEPTION(BackupStoreException, BadBackupStoreFile)
	}
	
	// TODO: Use buffered file class
	// Because we read in the file a scanned block size at a time, it is likely to be
	// inefficient. Probably will be much better to use a buffering IOStream class which
	// reads data in at the size of the filesystem block size.

	// Allocate the buffers.
	uint8_t *pbuffer0 = (uint8_t *)::malloc(bufSize);
	uint8_t *pbuffer1 = (uint8_t *)::malloc(bufSize);
	try
	{
		// Check buffer allocation
		if(pbuffer0 == 0 || pbuffer1 == 0 || phashTable == 0)
		{
			// If a buffer got allocated, it will be cleaned up in the catch block
			throw std::bad_alloc();
		}
		
		// Flag to abort the run, if too many blocks are found -- avoid using
		// huge amounts of processor time when files contain many similar blocks.
		bool abortSearch = false;
		
		// Search for each block size in turn
		// NOTE: Do the smallest size first, so that the scheme for adding
		// entries in the found list works as expected and replaces smallers block
		// with larger blocks when it finds matches at the same offset in the file.
		for(int s = BACKUP_FILE_DIFF_MAX_BLOCK_SIZES - 1; s >= 0; --s)
		{
			ASSERT(Sizes[s] <= bufSize);
			//TRACE2("Diff pass %d, for block size %d\n", s, Sizes[s]);
			
			// Check we haven't finished
			if(Sizes[s] == 0)
			{
				// empty entry, try next size
				continue;
			}
			
			// Set up the hash table entries
			SetupHashTable(pIndex, NumBlocks, Sizes[s], phashTable);
		
			// Shift file position to beginning
			rFile.Seek(0, IOStream::SeekType_Absolute);
			
			// Read first block
			if(rFile.Read(pbuffer0, Sizes[s]) != Sizes[s])
			{
				// Size of file too short to match -- do next size
				continue;
			}
			
			// Setup block pointers
			uint8_t *beginnings = pbuffer0;
			uint8_t *endings = pbuffer1;
			int offset = 0;
			
			// Calculate the first checksum, ready for rolling
			RollingChecksum rolling(beginnings, Sizes[s]);
			
			// Then roll, until the file is exhausted
			int64_t fileBlockNumber = 0;
			int64_t fileOffset = 0;
			int rollOverInitialBytes = 0;
			while(true)
			{
				// Load in another block of data, and record how big it is
				int bytesInEndings = rFile.Read(endings, Sizes[s]);
				int tmp;

				// Skip any bytes from a previous matched block
				if(rollOverInitialBytes > 0 && offset < bytesInEndings)
				{
					int spaceLeft = bytesInEndings - offset;
					int thisRoll = (rollOverInitialBytes > spaceLeft) ? spaceLeft : rollOverInitialBytes;

					rolling.RollForwardSeveral(beginnings+offset, endings+offset, Sizes[s], thisRoll);

					offset += thisRoll;
					fileOffset += thisRoll;
					rollOverInitialBytes -= thisRoll;

					if(rollOverInitialBytes)
					{
						goto refresh;
					}
				}

				if(goodnessOfFit.count(fileOffset))
				{
					tmp = goodnessOfFit[fileOffset];
				}
				else
				{
					tmp = 0;
				}

				if(tmp >= Sizes[s])
				{
					// Skip over bigger ready-matched blocks completely
					rollOverInitialBytes = tmp;
					int spaceLeft = bytesInEndings - offset;
					int thisRoll = (rollOverInitialBytes > spaceLeft) ? spaceLeft : rollOverInitialBytes;

					rolling.RollForwardSeveral(beginnings+offset, endings+offset, Sizes[s], thisRoll);

					offset += thisRoll;
					fileOffset += thisRoll;
					rollOverInitialBytes -= thisRoll;

					if(rollOverInitialBytes)
					{
						goto refresh;
					}
				}

				while(offset < bytesInEndings)
				{
					// Is current checksum in hash list?
					uint16_t hash = rolling.GetComponentForHashing();
					if(phashTable[hash] != 0 && (goodnessOfFit.count(fileOffset) == 0 || goodnessOfFit[fileOffset] < Sizes[s]))
					{
						if(SecondStageMatch(phashTable[hash], rolling, beginnings, endings, offset, Sizes[s], fileBlockNumber, pIndex, rFoundBlocks))
						{
							goodnessOfFit[fileOffset] = Sizes[s];

							// Block matched, roll the checksum forward to the next block without doing
							// any more comparisons, because these are pointless (as any more matches will be ignored when
							// the receipe is generated) and just take up valuable processor time. Edge cases are
							// especially nasty, using huge amounts of time and memory.
							int skip = Sizes[s];
							if(offset < bytesInEndings && skip > 0)
							{
								int spaceLeft = bytesInEndings - offset;
								int thisRoll = (skip > spaceLeft) ? spaceLeft : skip;

								rolling.RollForwardSeveral(beginnings+offset, endings+offset, Sizes[s], thisRoll);

								offset += thisRoll;
								fileOffset += thisRoll;
								skip -= thisRoll;
							}
							// Not all the bytes necessary will have been skipped, so get them
							// skipped after the next block is loaded.
							rollOverInitialBytes = skip;
							
							// End this loop, so the final byte isn't used again
							break;
						}
						
						if(static_cast<int64_t>(rFoundBlocks.size()) > (NumBlocks * BACKUP_FILE_DIFF_MAX_BLOCK_FIND_MULTIPLE) || sDiffTimedOut)
						{
							abortSearch = true;
							break;
						}
					}
					
					// Roll checksum forward
					rolling.RollForward(beginnings[offset], endings[offset], Sizes[s]);
				
					// Increment offsets
					++offset;
					++fileOffset;
				}
				
				if(abortSearch) break;
				
			refresh:
				// Finished?
				if(bytesInEndings != Sizes[s])
				{
					// No more data in file -- check the final block
					// (Do a copy and paste of 5 lines of code instead of introducing a comparison for
					// each byte of the file)
					uint16_t hash = rolling.GetComponentForHashing();
					if(phashTable[hash] != 0 && (goodnessOfFit.count(fileOffset) == 0 || goodnessOfFit[fileOffset] < Sizes[s]))
					{
						if(SecondStageMatch(phashTable[hash], rolling, beginnings, endings, offset, Sizes[s], fileBlockNumber, pIndex, rFoundBlocks))
						{
							goodnessOfFit[fileOffset] = Sizes[s];
						}
					}

					// finish
					break;
				}
				
				// Switch buffers, reset offset
				beginnings = endings;
				endings = (beginnings == pbuffer0)?(pbuffer1):(pbuffer0);	// ie the other buffer
				offset = 0;

				// And count the blocks which have been done
				++fileBlockNumber;
			}

			if(abortSearch) break;
		}
		
		// Free buffers and hash table
		::free(pbuffer1);
		pbuffer1 = 0;
		::free(pbuffer0);
		pbuffer0 = 0;
		::free(phashTable);
		phashTable = 0;
	}
	catch(...)
	{
		// Cleanup and throw
		if(pbuffer1 != 0) ::free(pbuffer1);
		if(pbuffer0 != 0) ::free(pbuffer0);
		if(phashTable != 0) ::free(phashTable);
		throw;
	}
	
#ifndef NDEBUG
	if(BackupStoreFile::TraceDetailsOfDiffProcess)
	{
		// Trace out the found blocks in debug mode
		TRACE0("Diff: list of found blocks\n======== ======== ======== ========\n  Offset   BlkIdx     Size Movement\n");
		for(std::map<int64_t, int64_t>::const_iterator i(rFoundBlocks.begin()); i != rFoundBlocks.end(); ++i)
		{
			int64_t orgLoc = 0;
			for(int64_t b = 0; b < i->second; ++b)
			{
				orgLoc += pIndex[b].mSize;
			}
			TRACE4("%8lld %8lld %8lld %8lld\n", i->first, i->second,
				(int64_t)(pIndex[i->second].mSize), i->first - orgLoc);
		}
		TRACE0("======== ======== ======== ========\n");
	}
#endif
}


// --------------------------------------------------------------------------
//
// Function
//		Name:    static SetupHashTable(BlocksAvailableEntry *, int64_t, in32_t, BlocksAvailableEntry **)
//		Purpose: Set up the hash table ready for a scan
//		Created: 14/1/04
//
// --------------------------------------------------------------------------
static void SetupHashTable(BlocksAvailableEntry *pIndex, int64_t NumBlocks, int32_t BlockSize, BlocksAvailableEntry **pHashTable)
{
	// Set all entries in the hash table to zero
	::memset(pHashTable, 0, (sizeof(BlocksAvailableEntry *) * (64*1024)));

	// Scan through the blocks, building the hash table
	for(int64_t b = 0; b < NumBlocks; ++b)
	{
		// Only look at the required block size
		if(pIndex[b].mSize == BlockSize)
		{
			// Get the value under which to hash this entry
			uint16_t hash = RollingChecksum::ExtractHashingComponent(pIndex[b].mWeakChecksum);
			
			// Already present in table?
			if(pHashTable[hash] != 0)
			{
				//TRACE1("Another hash entry for %d found\n", hash);
				// Yes -- need to set the pointer in this entry to the current entry to build the linked list
				pIndex[b].mpNextInHashList = pHashTable[hash];
			}

			// Put a pointer to this entry in the hash table
			pHashTable[hash] = pIndex + b;
		}
	}
}


// --------------------------------------------------------------------------
//
// Function
//		Name:    static bool SecondStageMatch(xxx)
//		Purpose: When a match in the hash table is found, scan for second stage match using strong checksum.
//		Created: 14/1/04
//
// --------------------------------------------------------------------------
static bool SecondStageMatch(BlocksAvailableEntry *pFirstInHashList, RollingChecksum &fastSum, uint8_t *pBeginnings, uint8_t *pEndings,
	int Offset, int32_t BlockSize, int64_t FileBlockNumber, BlocksAvailableEntry *pIndex, std::map<int64_t, int64_t> &rFoundBlocks)
{
	// Check parameters
	ASSERT(pBeginnings != 0);
	ASSERT(pEndings != 0);
	ASSERT(Offset >= 0);
	ASSERT(BlockSize > 0);
	ASSERT(pFirstInHashList != 0);
	ASSERT(pIndex != 0);

	uint16_t Hash = fastSum.GetComponentForHashing();
	uint32_t Checksum = fastSum.GetChecksum();

	// Before we go to the expense of the MD5, make sure it's a darn good match on the checksum we already know.
	BlocksAvailableEntry *scan = pFirstInHashList;
	bool found=false;
	while(scan != 0)
	{
		if(scan->mWeakChecksum == Checksum)
		{
			found = true;
			break;
		}
		scan = scan->mpNextInHashList;
	}
	if(!found)
	{
		return false;
	}

	// Calculate the strong MD5 digest for this block
	MD5Digest strong;
	// Add the data from the beginnings
	strong.Add(pBeginnings + Offset, BlockSize - Offset);
	// Add any data from the endings
	if(Offset > 0)
	{
		strong.Add(pEndings, Offset);
	}
	strong.Finish();
	
	// Then go through the entries in the hash list, comparing with the strong digest calculated
	scan = pFirstInHashList;
	//TRACE0("second stage match\n");
	while(scan != 0)
	{
		//TRACE3("scan size %d, block size %d, hash %d\n", scan->mSize, BlockSize, Hash);
		ASSERT(scan->mSize == BlockSize);
		ASSERT(RollingChecksum::ExtractHashingComponent(scan->mWeakChecksum) == Hash);
	
		// Compare?
		if(strong.DigestMatches(scan->mStrongChecksum))
		{
			//TRACE0("Match!\n");
			// Found! Add to list of found blocks...
			int64_t fileOffset = (FileBlockNumber * BlockSize) + Offset;
			int64_t blockIndex = (scan - pIndex);	// pointer arthmitic is frowned upon. But most efficient way of doing it here -- alternative is to use more memory
			
			// We do NOT search for smallest blocks first, as this code originally assumed.
			// To prevent this from potentially overwriting a better match, the caller must determine
			// the relative "goodness" of any existing match and this one, and avoid the call if it
			// could be detrimental.
			rFoundBlocks[fileOffset] = blockIndex;
			
			// No point in searching further, report success
			return true;
		}
	
		// Next
		scan = scan->mpNextInHashList;
	}
	
	// Not matched
	return false;
}


// --------------------------------------------------------------------------
//
// Function
//		Name:    static GenerateRecipe(BackupStoreFileEncodeStream::Recipe &, BlocksAvailableEntry *, int64_t, std::map<int64_t, int64_t> &)
//		Purpose: Fills in the recipe from the found block list
//		Created: 15/1/04
//
// --------------------------------------------------------------------------
static void GenerateRecipe(BackupStoreFileEncodeStream::Recipe &rRecipe, BlocksAvailableEntry *pIndex,
		int64_t NumBlocks, std::map<int64_t, int64_t> &rFoundBlocks, int64_t SizeOfInputFile)
{
	// NOTE: This function could be a lot more sophisiticated. For example, if
	// a small block overlaps a big block like this
	//   ****
	//      *******************************
	// then the small block will be used, not the big one. But it'd be better to
	// just ignore the small block and keep the big one. However, some stats should
	// be gathered about real world files before writing complex code which might
	// go wrong.

	// Initialise a blank instruction
	BackupStoreFileEncodeStream::RecipeInstruction instruction;
	#define RESET_INSTRUCTION			\
	instruction.mSpaceBefore = 0;		\
	instruction.mBlocks = 0;			\
	instruction.mpStartBlock = 0;
	RESET_INSTRUCTION

	// First, a special case for when there are no found blocks
	if(rFoundBlocks.size() == 0)
	{
		// No blocks, just a load of space
		instruction.mSpaceBefore = SizeOfInputFile;
		rRecipe.push_back(instruction);	
	
		#ifndef NDEBUG
		if(BackupStoreFile::TraceDetailsOfDiffProcess)
		{
			TRACE1("Diff: Default recipe generated, %lld bytes of file\n", SizeOfInputFile);
		}
		#endif
		
		// Don't do anything
		return;
	}

	// Current location
	int64_t loc = 0;

	// Then iterate through the list, generating the recipe
	std::map<int64_t, int64_t>::const_iterator i(rFoundBlocks.begin());
	ASSERT(i != rFoundBlocks.end());	// check logic

	// Counting for debug tracing
#ifndef NDEBUG
	int64_t debug_NewBytesFound = 0;
	int64_t debug_OldBlocksUsed = 0;
#endif
	
	for(; i != rFoundBlocks.end(); ++i)
	{
		// Remember... map is (position in file) -> (index of block in pIndex)
		
		if(i->first < loc)
		{
			// This block overlaps the last one
			continue;
		}
		else if(i->first > loc)
		{
			// There's a gap between the end of the last thing and this block.
			// If there's an instruction waiting, push it onto the list
			if(instruction.mSpaceBefore != 0 || instruction.mpStartBlock != 0)
			{
				rRecipe.push_back(instruction);
			}
			// Start a new instruction, with the gap ready
			RESET_INSTRUCTION
			instruction.mSpaceBefore = i->first - loc;
			// Move location forward to match
			loc += instruction.mSpaceBefore;
#ifndef NDEBUG
			debug_NewBytesFound += instruction.mSpaceBefore;
#endif
		}
		
		// First, does the current instruction need pushing back, because this block is not
		// sequential to the last one?
		if(instruction.mpStartBlock != 0 && (pIndex + i->second) != (instruction.mpStartBlock + instruction.mBlocks))
		{
			rRecipe.push_back(instruction);
			RESET_INSTRUCTION
		}
		
		// Add in this block
		if(instruction.mpStartBlock == 0)
		{
			// This block starts a new instruction
			instruction.mpStartBlock = pIndex + i->second;
			instruction.mBlocks = 1;
		}
		else
		{
			// It continues the previous section of blocks
			instruction.mBlocks += 1;
		}

#ifndef NDEBUG
		debug_OldBlocksUsed++;
#endif

		// Move location forward
		loc += pIndex[i->second].mSize;
	}
	
	// Push the last instruction generated
	rRecipe.push_back(instruction);
	
	// Is there any space left at the end which needs sending?
	if(loc != SizeOfInputFile)
	{
		RESET_INSTRUCTION
		instruction.mSpaceBefore = SizeOfInputFile - loc;
#ifndef NDEBUG
		debug_NewBytesFound += instruction.mSpaceBefore;
#endif
		rRecipe.push_back(instruction);		
	}
	
	// dump out the recipe
#ifndef NDEBUG
	TRACE2("Diff: %lld new bytes found, %lld old blocks used\n", debug_NewBytesFound, debug_OldBlocksUsed);
	if(BackupStoreFile::TraceDetailsOfDiffProcess)
	{
		TRACE1("Diff: Recipe generated (size %d)\n======== ========= ========\nSpace b4 FirstBlk  NumBlks\n", rRecipe.size());
		{
			for(unsigned int e = 0; e < rRecipe.size(); ++e)
			{
				char b[64];
				sprintf(b, "%8lld", (int64_t)(rRecipe[e].mpStartBlock - pIndex));
				TRACE3("%8lld %s %8lld\n", rRecipe[e].mSpaceBefore, (rRecipe[e].mpStartBlock == 0)?"       -":b, (int64_t)rRecipe[e].mBlocks);
			}
		}
		TRACE0("======== ========= ========\n");
	}
#endif
}


// --------------------------------------------------------------------------
//
// Function
//		Name:    static TimerSignalHandler(int)
//		Purpose: Signal handler
//		Created: 19/3/04
//
// --------------------------------------------------------------------------
void TimerSignalHandler(int signal)
{
	sDiffTimedOut = true;
}


// --------------------------------------------------------------------------
//
// Function
//		Name:    static StartDiffTimer()
//		Purpose: Starts the diff timeout timer
//		Created: 19/3/04
//
// --------------------------------------------------------------------------
void StartDiffTimer()
{
	// Set timer signal handler
	if(!sSetTimerSignelHandler)
	{
		::signal(SIGVTALRM, TimerSignalHandler);
		sSetTimerSignelHandler = true;
	}

	struct itimerval timeout;
	// Don't want this to repeat
	timeout.it_interval.tv_sec = 0;
	timeout.it_interval.tv_usec = 0;
	// Single timeout after the specified number of seconds
	timeout.it_value.tv_sec = sMaximumDiffTime;
	timeout.it_value.tv_usec = 0;
	// Set timer
	if(::setitimer(ITIMER_VIRTUAL, &timeout, NULL) != 0)
	{
		TRACE0("WARNING: couldn't set diff timeout\n");
	}
	
	// Unset flag (last thing)
	sDiffTimedOut = false;
}