courgette/ensemble_create.cc

   1 // Copyright (c) 2011 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 // The main idea in Courgette is to do patching *under a tranformation*.  The
   6 // input is transformed into a new representation, patching occurs in the new
   7 // repesentation, and then the tranform is reversed to get the patched data.
   8 //
   9 // The idea is applied to pieces (or 'elements') of the whole (or 'ensemble').
  10 // Each of the elements has to go through the same set of steps in lock-step.
  11
  12 // This file contains the code to create the patch.
  13
  14
  15 #include "courgette/ensemble.h"
  16
  17 #include <vector>
  18 #include <limits>
  19
  20 #include "base/basictypes.h"
  21 #include "base/logging.h"
  22 #include "base/time.h"
  23
  24 #include "courgette/third_party/bsdiff.h"
  25 #include "courgette/crc.h"
  26 #include "courgette/difference_estimator.h"
  27 #include "courgette/streams.h"
  28 #include "courgette/region.h"
  29 #include "courgette/simple_delta.h"
  30
  31 #include "courgette/patcher_x86_32.h"
  32 #include "courgette/patch_generator_x86_32.h"
  33
  34 namespace courgette {
  35
  36 TransformationPatchGenerator::TransformationPatchGenerator(
  37     Element* old_element,
  38     Element* new_element,
  39     TransformationPatcher* patcher)
  40     : old_element_(old_element),
  41       new_element_(new_element),
  42       patcher_(patcher) {
  43 }
  44
  45 TransformationPatchGenerator::~TransformationPatchGenerator() {
  46   delete patcher_;
  47 }
  48
  49 // The default implementation of PredictTransformParameters delegates to the
  50 // patcher.
  51 Status TransformationPatchGenerator::PredictTransformParameters(
  52     SinkStreamSet* prediction) {
  53   return patcher_->PredictTransformParameters(prediction);
  54 }
  55
  56 // The default implementation of Reform delegates to the patcher.
  57 Status TransformationPatchGenerator::Reform(
  58     SourceStreamSet* transformed_element,
  59     SinkStream* reformed_element) {
  60   return patcher_->Reform(transformed_element, reformed_element);
  61 }
  62
  63 // Makes a TransformationPatchGenerator of the appropriate variety for the
  64 // Element kind.
  65 TransformationPatchGenerator* MakeGenerator(Element* old_element,
  66                                             Element* new_element) {
  67   switch (new_element->kind()) {
  68     case EXE_UNKNOWN:
  69       break;
  70     case EXE_WIN_32_X86: {
  71       TransformationPatchGenerator* generator =
  72           new PatchGeneratorX86_32(
  73               old_element,
  74               new_element,
  75               new PatcherX86_32(old_element->region()),
  76               EXE_WIN_32_X86);
  77       return generator;
  78     }
  79     case EXE_ELF_32_X86: {
  80       TransformationPatchGenerator* generator =
  81           new PatchGeneratorX86_32(
  82               old_element,
  83               new_element,
  84               new PatcherX86_32(old_element->region()),
  85               EXE_ELF_32_X86);
  86       return generator;
  87     }
  88   }
  89
  90   LOG(WARNING) << "Unexpected Element::Kind " << old_element->kind();
  91   return NULL;
  92 }
  93
  94 // Checks to see if the proposed comparison is 'unsafe'.  Sometimes one element
  95 // from 'old' is matched as the closest element to multiple elements from 'new'.
  96 // Each time this happens, the old element is transformed and serialized.  This
  97 // is a problem when the old element is huge compared with the new element
  98 // because the mutliple serialized copies can be much bigger than the size of
  99 // either ensemble.
 100 //
 101 // The right way to avoid this is to ensure any one element from 'old' is
 102 // serialized once, which requires matching code in the patch application.
 103 //
 104 // This is a quick hack to avoid the problem by prohibiting a big difference in
 105 // size between matching elements.
 106 bool UnsafeDifference(Element* old_element, Element* new_element) {
 107   double kMaxBloat = 2.0;
 108   size_t kMinWorrysomeDifference = 2 << 20;  // 2MB
 109   size_t old_size = old_element->region().length();
 110   size_t new_size = new_element->region().length();
 111   size_t low_size = std::min(old_size, new_size);
 112   size_t high_size = std::max(old_size, new_size);
 113   if (high_size - low_size < kMinWorrysomeDifference) return false;
 114   if (high_size < low_size * kMaxBloat) return false;
 115   return true;
 116 }
 117
 118 // FindGenerators finds TransformationPatchGenerators for the elements of
 119 // |new_ensemble|.  For each element of |new_ensemble| we find the closest
 120 // matching element from |old_ensemble| and use that as the basis for
 121 // differential compression.  The elements have to be the same kind so as to
 122 // support transformation into the same kind of 'new representation'.
 123 //
 124 Status FindGenerators(Ensemble* old_ensemble, Ensemble* new_ensemble,
 125                       std::vector<TransformationPatchGenerator*>* generators) {
 126   base::Time start_find_time = base::Time::Now();
 127   old_ensemble->FindEmbeddedElements();
 128   new_ensemble->FindEmbeddedElements();
 129   VLOG(1) << "done FindEmbeddedElements "
 130           << (base::Time::Now() - start_find_time).InSecondsF();
 131
 132   std::vector<Element*> old_elements(old_ensemble->elements());
 133   std::vector<Element*> new_elements(new_ensemble->elements());
 134
 135   VLOG(1) << "old has " << old_elements.size() << " elements";
 136   VLOG(1) << "new has " << new_elements.size() << " elements";
 137
 138   DifferenceEstimator difference_estimator;
 139   std::vector<DifferenceEstimator::Base*> bases;
 140
 141   base::Time start_bases_time = base::Time::Now();
 142   for (size_t i = 0;  i < old_elements.size();  ++i) {
 143     bases.push_back(
 144         difference_estimator.MakeBase(old_elements[i]->region()));
 145   }
 146   VLOG(1) << "done make bases "
 147           << (base::Time::Now() - start_bases_time).InSecondsF() << "s";
 148
 149   for (size_t new_index = 0;  new_index < new_elements.size();  ++new_index) {
 150     Element* new_element = new_elements[new_index];
 151     DifferenceEstimator::Subject* new_subject =
 152         difference_estimator.MakeSubject(new_element->region());
 153
 154     // Search through old elements to find the best match.
 155     //
 156     // TODO(sra): This is O(N x M), i.e. O(N^2) since old_ensemble and
 157     // new_ensemble probably have a very similar structure.  We can make the
 158     // search faster by making the comparison provided by DifferenceEstimator
 159     // more nuanced, returning early if the measured difference is greater than
 160     // the current best.  This will be most effective if we can arrange that the
 161     // first elements we try to match are likely the 'right' ones.  We could
 162     // prioritize elements that are of a similar size or similar position in the
 163     // sequence of elements.
 164     //
 165     Element* best_old_element = NULL;
 166     size_t best_difference = std::numeric_limits<size_t>::max();
 167     for (size_t old_index = 0;  old_index < old_elements.size();  ++old_index) {
 168       Element* old_element = old_elements[old_index];
 169       // Elements of different kinds are incompatible.
 170       if (old_element->kind() != new_element->kind())
 171         continue;
 172
 173       if (UnsafeDifference(old_element, new_element))
 174         continue;
 175
 176       base::Time start_compare = base::Time::Now();
 177       DifferenceEstimator::Base* old_base = bases[old_index];
 178       size_t difference = difference_estimator.Measure(old_base, new_subject);
 179
 180       VLOG(1) << "Compare " << old_element->Name()
 181               << " to " << new_element->Name()
 182               << " --> " << difference
 183               << " in " << (base::Time::Now() - start_compare).InSecondsF()
 184               << "s";
 185       if (difference == 0) {
 186         VLOG(1) << "Skip " << new_element->Name()
 187                 << " - identical to " << old_element->Name();
 188         best_difference = 0;
 189         best_old_element = NULL;
 190         break;
 191       }
 192       if (difference < best_difference) {
 193         best_difference = difference;
 194         best_old_element = old_element;
 195       }
 196     }
 197
 198     if (best_old_element) {
 199       VLOG(1) << "Matched " << best_old_element->Name()
 200               << " to " << new_element->Name()
 201               << " --> " << best_difference;
 202       TransformationPatchGenerator* generator =
 203           MakeGenerator(best_old_element, new_element);
 204       if (generator)
 205         generators->push_back(generator);
 206     }
 207   }
 208
 209   VLOG(1) << "done FindGenerators found " << generators->size()
 210           << " in " << (base::Time::Now() - start_find_time).InSecondsF()
 211           << "s";
 212
 213   return C_OK;
 214 }
 215
 216 void FreeGenerators(std::vector<TransformationPatchGenerator*>* generators) {
 217   for (size_t i = 0;  i < generators->size();  ++i) {
 218     delete (*generators)[i];
 219   }
 220   generators->clear();
 221 }
 222
 223 ////////////////////////////////////////////////////////////////////////////////
 224
 225 Status GenerateEnsemblePatch(SourceStream* base,
 226                              SourceStream* update,
 227                              SinkStream* final_patch) {
 228   VLOG(1) << "start GenerateEnsemblePatch";
 229   base::Time start_time = base::Time::Now();
 230
 231   Region old_region(base->Buffer(), base->Remaining());
 232   Region new_region(update->Buffer(), update->Remaining());
 233   Ensemble old_ensemble(old_region, "old");
 234   Ensemble new_ensemble(new_region, "new");
 235   std::vector<TransformationPatchGenerator*> generators;
 236   Status generators_status = FindGenerators(&old_ensemble, &new_ensemble,
 237                                             &generators);
 238   if (generators_status != C_OK)
 239     return generators_status;
 240
 241   SinkStreamSet patch_streams;
 242
 243   SinkStream* tranformation_descriptions      = patch_streams.stream(0);
 244   SinkStream* parameter_correction            = patch_streams.stream(1);
 245   SinkStream* transformed_elements_correction = patch_streams.stream(2);
 246   SinkStream* ensemble_correction             = patch_streams.stream(3);
 247
 248   size_t number_of_transformations = generators.size();
 249   if (!tranformation_descriptions->WriteSizeVarint32(number_of_transformations))
 250     return C_STREAM_ERROR;
 251
 252   for (size_t i = 0;  i < number_of_transformations;  ++i) {
 253     ExecutableType kind = generators[i]->Kind();
 254     if (!tranformation_descriptions->WriteVarint32(kind))
 255       return C_STREAM_ERROR;
 256   }
 257
 258   for (size_t i = 0;  i < number_of_transformations;  ++i) {
 259     Status status =
 260         generators[i]->WriteInitialParameters(tranformation_descriptions);
 261     if (status != C_OK)
 262       return status;
 263   }
 264
 265   //
 266   // Generate sub-patch for parameters.
 267   //
 268   SinkStreamSet predicted_parameters_sink;
 269   SinkStreamSet corrected_parameters_sink;
 270
 271   for (size_t i = 0;  i < number_of_transformations;  ++i) {
 272     SinkStreamSet single_predicted_parameters;
 273     Status status;
 274     status = generators[i]->PredictTransformParameters(
 275         &single_predicted_parameters);
 276     if (status != C_OK)
 277       return status;
 278     if (!predicted_parameters_sink.WriteSet(&single_predicted_parameters))
 279       return C_STREAM_ERROR;
 280
 281     SinkStreamSet single_corrected_parameters;
 282     status = generators[i]->CorrectedTransformParameters(
 283         &single_corrected_parameters);
 284     if (status != C_OK)
 285       return status;
 286     if (!corrected_parameters_sink.WriteSet(&single_corrected_parameters))
 287       return C_STREAM_ERROR;
 288   }
 289
 290   SinkStream linearized_predicted_parameters;
 291   SinkStream linearized_corrected_parameters;
 292
 293   if (!predicted_parameters_sink.CopyTo(&linearized_predicted_parameters))
 294     return C_STREAM_ERROR;
 295   if (!corrected_parameters_sink.CopyTo(&linearized_corrected_parameters))
 296     return C_STREAM_ERROR;
 297
 298   SourceStream predicted_parameters_source;
 299   SourceStream corrected_parameters_source;
 300   predicted_parameters_source.Init(linearized_predicted_parameters);
 301   corrected_parameters_source.Init(linearized_corrected_parameters);
 302
 303   Status delta1_status = GenerateSimpleDelta(&predicted_parameters_source,
 304                                              &corrected_parameters_source,
 305                                              parameter_correction);
 306   if (delta1_status != C_OK)
 307     return delta1_status;
 308
 309   //
 310   // Generate sub-patch for elements.
 311   //
 312   corrected_parameters_source.Init(linearized_corrected_parameters);
 313   SourceStreamSet corrected_parameters_source_set;
 314   if (!corrected_parameters_source_set.Init(&corrected_parameters_source))
 315     return C_STREAM_ERROR;
 316
 317   SinkStreamSet predicted_transformed_elements;
 318   SinkStreamSet corrected_transformed_elements;
 319
 320   for (size_t i = 0;  i < number_of_transformations;  ++i) {
 321     SourceStreamSet single_parameters;
 322     if (!corrected_parameters_source_set.ReadSet(&single_parameters))
 323       return C_STREAM_ERROR;
 324     SinkStreamSet single_predicted_transformed_element;
 325     SinkStreamSet single_corrected_transformed_element;
 326     Status status = generators[i]->Transform(
 327         &single_parameters,
 328         &single_predicted_transformed_element,
 329         &single_corrected_transformed_element);
 330     if (status != C_OK)
 331       return status;
 332     if (!single_parameters.Empty())
 333       return C_STREAM_NOT_CONSUMED;
 334     if (!predicted_transformed_elements.WriteSet(
 335             &single_predicted_transformed_element))
 336       return C_STREAM_ERROR;
 337     if (!corrected_transformed_elements.WriteSet(
 338             &single_corrected_transformed_element))
 339       return C_STREAM_ERROR;
 340   }
 341
 342   if (!corrected_parameters_source_set.Empty())
 343     return C_STREAM_NOT_CONSUMED;
 344
 345   SinkStream linearized_predicted_transformed_elements;
 346   SinkStream linearized_corrected_transformed_elements;
 347
 348   if (!predicted_transformed_elements.CopyTo(
 349           &linearized_predicted_transformed_elements))
 350     return C_STREAM_ERROR;
 351   if (!corrected_transformed_elements.CopyTo(
 352           &linearized_corrected_transformed_elements))
 353     return C_STREAM_ERROR;
 354
 355   SourceStream predicted_transformed_elements_source;
 356   SourceStream corrected_transformed_elements_source;
 357   predicted_transformed_elements_source
 358       .Init(linearized_predicted_transformed_elements);
 359   corrected_transformed_elements_source
 360       .Init(linearized_corrected_transformed_elements);
 361
 362   Status delta2_status =
 363       GenerateSimpleDelta(&predicted_transformed_elements_source,
 364                           &corrected_transformed_elements_source,
 365                           transformed_elements_correction);
 366   if (delta2_status != C_OK)
 367     return delta2_status;
 368
 369   // Last use, free storage.
 370   linearized_predicted_transformed_elements.Retire();
 371
 372   //
 373   // Generate sub-patch for whole enchilada.
 374   //
 375   SinkStream predicted_ensemble;
 376
 377   if (!predicted_ensemble.Write(base->Buffer(), base->Remaining()))
 378     return C_STREAM_ERROR;
 379
 380   SourceStreamSet corrected_transformed_elements_source_set;
 381   corrected_transformed_elements_source
 382       .Init(linearized_corrected_transformed_elements);
 383   if (!corrected_transformed_elements_source_set
 384       .Init(&corrected_transformed_elements_source))
 385     return C_STREAM_ERROR;
 386
 387   for (size_t i = 0;  i < number_of_transformations;  ++i) {
 388     SourceStreamSet single_corrected_transformed_element;
 389     if (!corrected_transformed_elements_source_set.ReadSet(
 390             &single_corrected_transformed_element))
 391       return C_STREAM_ERROR;
 392     Status status = generators[i]->Reform(&single_corrected_transformed_element,
 393                                           &predicted_ensemble);
 394     if (status != C_OK)
 395       return status;
 396     if (!single_corrected_transformed_element.Empty())
 397       return C_STREAM_NOT_CONSUMED;
 398   }
 399
 400   if (!corrected_transformed_elements_source_set.Empty())
 401     return C_STREAM_NOT_CONSUMED;
 402
 403   // No more references to this stream's buffer.
 404   linearized_corrected_transformed_elements.Retire();
 405
 406   FreeGenerators(&generators);
 407
 408   size_t final_patch_input_size = predicted_ensemble.Length();
 409   SourceStream predicted_ensemble_source;
 410   predicted_ensemble_source.Init(predicted_ensemble);
 411   Status delta3_status = GenerateSimpleDelta(&predicted_ensemble_source,
 412                                              update,
 413                                              ensemble_correction);
 414   if (delta3_status != C_OK)
 415     return delta3_status;
 416
 417   //
 418   // Final output stream has a header followed by a StreamSet.
 419   //
 420   if (!final_patch->WriteVarint32(CourgettePatchFile::kMagic) ||
 421       !final_patch->WriteVarint32(CourgettePatchFile::kVersion) ||
 422       !final_patch->WriteVarint32(CalculateCrc(old_region.start(),
 423                                                old_region.length())) ||
 424       !final_patch->WriteVarint32(CalculateCrc(new_region.start(),
 425                                                new_region.length())) ||
 426       !final_patch->WriteSizeVarint32(final_patch_input_size) ||
 427       !patch_streams.CopyTo(final_patch)) {
 428     return C_STREAM_ERROR;
 429   }
 430
 431   VLOG(1) << "done GenerateEnsemblePatch "
 432           << (base::Time::Now() - start_time).InSecondsF() << "s";
 433
 434   return C_OK;
 435 }
 436
 437 }  // namespace