[apt.git] / apt-pkg / algorithms.cc

// -*- mode: cpp; mode: fold -*-
// Description                                                          /*{{{*/
// $Id: algorithms.cc,v 1.44 2002/11/28 18:49:16 jgg Exp $
/* ######################################################################

   Algorithms - A set of misc algorithms

   The pkgProblemResolver class has become insanely complex and
   very sophisticated, it handles every test case I have thrown at it
   to my satisfaction. Understanding exactly why all the steps the class
   does are required is difficult and changing though not very risky
   may result in other cases not working.
   
   ##################################################################### */
                                                                        /*}}}*/
// Include Files                                                        /*{{{*/
#include <apt-pkg/algorithms.h>
#include <apt-pkg/error.h>
#include <apt-pkg/configuration.h>
#include <apt-pkg/version.h>
#include <apt-pkg/sptr.h>
#include <apt-pkg/acquire-item.h>
    
#include <apti18n.h>
#include <sys/types.h>
#include <cstdlib>
#include <algorithm>
#include <iostream>
                                                                        /*}}}*/
using namespace std;

pkgProblemResolver *pkgProblemResolver::This = 0;

// Simulate::Simulate - Constructor                                     /*{{{*/
// ---------------------------------------------------------------------
/* The legacy translations here of input Pkg iterators is obsolete, 
   this is not necessary since the pkgCaches are fully shared now. */
pkgSimulate::pkgSimulate(pkgDepCache *Cache) : pkgPackageManager(Cache),
                            iPolicy(Cache),
                            Sim(&Cache->GetCache(),&iPolicy),
                            group(Sim)
{
   Sim.Init(0);
   Flags = new unsigned char[Cache->Head().PackageCount];
   memset(Flags,0,sizeof(*Flags)*Cache->Head().PackageCount);

   // Fake a filename so as not to activate the media swapping
   string Jnk = "SIMULATE";
   for (unsigned int I = 0; I != Cache->Head().PackageCount; I++)
      FileNames[I] = Jnk;
}
                                                                        /*}}}*/
// Simulate::Describe - Describe a package                              /*{{{*/
// ---------------------------------------------------------------------
/* Parameter Current == true displays the current package version,
   Parameter Candidate == true displays the candidate package version */
void pkgSimulate::Describe(PkgIterator Pkg,ostream &out,bool Current,bool Candidate)
{
   VerIterator Ver(Sim);
 
   out << Pkg.FullName(true);

   if (Current == true)
   {
      Ver = Pkg.CurrentVer();
      if (Ver.end() == false)
         out << " [" << Ver.VerStr() << ']';
   }

   if (Candidate == true)
   {
      Ver = Sim[Pkg].CandidateVerIter(Sim);
      if (Ver.end() == true)
         return;
   
      out << " (" << Ver.VerStr() << ' ' << Ver.RelStr() << ')';
   }
}
                                                                        /*}}}*/
// Simulate::Install - Simulate unpacking of a package                  /*{{{*/
// ---------------------------------------------------------------------
/* */
bool pkgSimulate::Install(PkgIterator iPkg,string /*File*/)
{
   // Adapt the iterator
   PkgIterator Pkg = Sim.FindPkg(iPkg.Name(), iPkg.Arch());
   Flags[Pkg->ID] = 1;
   
   cout << "Inst ";
   Describe(Pkg,cout,true,true);
   Sim.MarkInstall(Pkg,false);

   if (strcmp(Pkg.Arch(),"all") == 0)
   {
      pkgCache::GrpIterator G = Pkg.Group();
      pkgCache::GrpIterator iG = iPkg.Group();
      for (pkgCache::PkgIterator P = G.FindPkg("any"); P.end() != true; P = G.NextPkg(P))
      {
         if (strcmp(P.Arch(), "all") == 0)
            continue;
         if (iG.FindPkg(P.Arch())->CurrentVer == 0)
            continue;
         Flags[P->ID] = 1;
         Sim.MarkInstall(P, false);
      }
   }

   // Look for broken conflicts+predepends.
   for (PkgIterator I = Sim.PkgBegin(); I.end() == false; I++)
   {
      if (Sim[I].InstallVer == 0)
         continue;
      
      for (DepIterator D = Sim[I].InstVerIter(Sim).DependsList(); D.end() == false;)
      {
         DepIterator Start;
         DepIterator End;
         D.GlobOr(Start,End);
         if (Start->Type == pkgCache::Dep::Conflicts ||
             Start->Type == pkgCache::Dep::DpkgBreaks ||
             Start->Type == pkgCache::Dep::Obsoletes ||
             End->Type == pkgCache::Dep::PreDepends)
         {
            if ((Sim[End] & pkgDepCache::DepGInstall) == 0)
            {
               cout << " [" << I.FullName(false) << " on " << Start.TargetPkg().FullName(false) << ']';
               if (Start->Type == pkgCache::Dep::Conflicts)
                  _error->Error("Fatal, conflicts violated %s",I.FullName(false).c_str());
            }       
         }
      }      
   }

   if (Sim.BrokenCount() != 0)
      ShortBreaks();
   else
      cout << endl;
   return true;
}
                                                                        /*}}}*/
// Simulate::Configure - Simulate configuration of a Package            /*{{{*/
// ---------------------------------------------------------------------
/* This is not an acurate simulation of relatity, we should really not
   install the package.. For some investigations it may be necessary 
   however. */
bool pkgSimulate::Configure(PkgIterator iPkg)
{
   // Adapt the iterator
   PkgIterator Pkg = Sim.FindPkg(iPkg.Name(), iPkg.Arch());
   
   Flags[Pkg->ID] = 2;

   if (strcmp(Pkg.Arch(),"all") == 0)
   {
      pkgCache::GrpIterator G = Pkg.Group();
      for (pkgCache::PkgIterator P = G.FindPkg("any"); P.end() != true; P = G.NextPkg(P))
      {
         if (strcmp(P.Arch(), "all") == 0)
            continue;
         if (Flags[P->ID] == 1)
            Flags[P->ID] = 2;
      }
   }

//   Sim.MarkInstall(Pkg,false);
   if (Sim[Pkg].InstBroken() == true)
   {
      cout << "Conf " << Pkg.FullName(false) << " broken" << endl;

      Sim.Update();
      
      // Print out each package and the failed dependencies
      for (pkgCache::DepIterator D = Sim[Pkg].InstVerIter(Sim).DependsList(); D.end() == false; D++)
      {
         if (Sim.IsImportantDep(D) == false || 
             (Sim[D] & pkgDepCache::DepInstall) != 0)
            continue;
         
         if (D->Type == pkgCache::Dep::Obsoletes)
            cout << " Obsoletes:" << D.TargetPkg().FullName(false);
         else if (D->Type == pkgCache::Dep::Conflicts)
            cout << " Conflicts:" << D.TargetPkg().FullName(false);
         else if (D->Type == pkgCache::Dep::DpkgBreaks)
            cout << " Breaks:" << D.TargetPkg().FullName(false);
         else
            cout << " Depends:" << D.TargetPkg().FullName(false);
      }     
      cout << endl;

      _error->Error("Conf Broken %s",Pkg.FullName(false).c_str());
   }   
   else
   {
      cout << "Conf "; 
      Describe(Pkg,cout,false,true);
   }

   if (Sim.BrokenCount() != 0)
      ShortBreaks();
   else
      cout << endl;
   
   return true;
}
                                                                        /*}}}*/
// Simulate::Remove - Simulate the removal of a package                 /*{{{*/
// ---------------------------------------------------------------------
/* */
bool pkgSimulate::Remove(PkgIterator iPkg,bool Purge)
{
   // Adapt the iterator
   PkgIterator Pkg = Sim.FindPkg(iPkg.Name(), iPkg.Arch());

   Flags[Pkg->ID] = 3;
   Sim.MarkDelete(Pkg);

   if (strcmp(Pkg.Arch(),"all") == 0)
   {
      pkgCache::GrpIterator G = Pkg.Group();
      pkgCache::GrpIterator iG = iPkg.Group();
      for (pkgCache::PkgIterator P = G.FindPkg("any"); P.end() != true; P = G.NextPkg(P))
      {
         if (strcmp(P.Arch(), "all") == 0)
            continue;
         if (iG.FindPkg(P.Arch())->CurrentVer == 0)
            continue;
         Flags[P->ID] = 3;
         Sim.MarkDelete(P);
      }
   }

   if (Purge == true)
      cout << "Purg ";
   else
      cout << "Remv ";
   Describe(Pkg,cout,true,false);

   if (Sim.BrokenCount() != 0)
      ShortBreaks();
   else
      cout << endl;

   return true;
}
                                                                        /*}}}*/
// Simulate::ShortBreaks - Print out a short line describing all breaks /*{{{*/
// ---------------------------------------------------------------------
/* */
void pkgSimulate::ShortBreaks()
{
   cout << " [";
   for (PkgIterator I = Sim.PkgBegin(); I.end() == false; I++)
   {
      if (Sim[I].InstBroken() == true)
      {
         if (Flags[I->ID] == 0)
            cout << I.FullName(false) << ' ';
/*       else
            cout << I.Name() << "! ";*/
      }      
   }
   cout << ']' << endl;
}
                                                                        /*}}}*/
// ApplyStatus - Adjust for non-ok packages                             /*{{{*/
// ---------------------------------------------------------------------
/* We attempt to change the state of the all packages that have failed
   installation toward their real state. The ordering code will perform 
   the necessary calculations to deal with the problems. */
bool pkgApplyStatus(pkgDepCache &Cache)
{
   pkgDepCache::ActionGroup group(Cache);

   for (pkgCache::PkgIterator I = Cache.PkgBegin(); I.end() == false; I++)
   {
      if (I->VersionList == 0)
         continue;
         
      // Only choice for a ReInstReq package is to reinstall
      if (I->InstState == pkgCache::State::ReInstReq ||
          I->InstState == pkgCache::State::HoldReInstReq)
      {
         if (I->CurrentVer != 0 && I.CurrentVer().Downloadable() == true)
            Cache.MarkKeep(I, false, false);
         else
         {
            // Is this right? Will dpkg choke on an upgrade?
            if (Cache[I].CandidateVer != 0 &&
                 Cache[I].CandidateVerIter(Cache).Downloadable() == true)
               Cache.MarkInstall(I, false, 0, false);
            else
               return _error->Error(_("The package %s needs to be reinstalled, "
                                    "but I can't find an archive for it."),I.FullName(true).c_str());
         }
         
         continue;
      }
      
      switch (I->CurrentState)
      {
         /* This means installation failed somehow - it does not need to be
            re-unpacked (probably) */
         case pkgCache::State::UnPacked:
         case pkgCache::State::HalfConfigured:
         case pkgCache::State::TriggersAwaited:
         case pkgCache::State::TriggersPending:
         if ((I->CurrentVer != 0 && I.CurrentVer().Downloadable() == true) ||
             I.State() != pkgCache::PkgIterator::NeedsUnpack)
            Cache.MarkKeep(I, false, false);
         else
         {
            if (Cache[I].CandidateVer != 0 &&
                 Cache[I].CandidateVerIter(Cache).Downloadable() == true)
               Cache.MarkInstall(I, true, 0, false);
            else
               Cache.MarkDelete(I);
         }
         break;

         // This means removal failed
         case pkgCache::State::HalfInstalled:
         Cache.MarkDelete(I);
         break;
         
         default:
         if (I->InstState != pkgCache::State::Ok)
            return _error->Error("The package %s is not ok and I "
                                 "don't know how to fix it!",I.FullName(false).c_str());
      }
   }
   return true;
}
                                                                        /*}}}*/
// FixBroken - Fix broken packages                                      /*{{{*/
// ---------------------------------------------------------------------
/* This autoinstalls every broken package and then runs the problem resolver
   on the result. */
bool pkgFixBroken(pkgDepCache &Cache)
{
   pkgDepCache::ActionGroup group(Cache);

   // Auto upgrade all broken packages
   for (pkgCache::PkgIterator I = Cache.PkgBegin(); I.end() == false; I++)
      if (Cache[I].NowBroken() == true)
         Cache.MarkInstall(I, true, 0, false);
   
   /* Fix packages that are in a NeedArchive state but don't have a
      downloadable install version */
   for (pkgCache::PkgIterator I = Cache.PkgBegin(); I.end() == false; I++)
   {
      if (I.State() != pkgCache::PkgIterator::NeedsUnpack ||
          Cache[I].Delete() == true)
         continue;
      
      if (Cache[I].InstVerIter(Cache).Downloadable() == false)
         continue;

      Cache.MarkInstall(I, true, 0, false);
   }
   
   pkgProblemResolver Fix(&Cache);
   return Fix.Resolve(true);
}
                                                                        /*}}}*/
// DistUpgrade - Distribution upgrade                                   /*{{{*/
// ---------------------------------------------------------------------
/* This autoinstalls every package and then force installs every 
   pre-existing package. This creates the initial set of conditions which 
   most likely contain problems because too many things were installed.
   
   The problem resolver is used to resolve the problems.
 */
bool pkgDistUpgrade(pkgDepCache &Cache)
{
   pkgDepCache::ActionGroup group(Cache);

   /* Auto upgrade all installed packages, this provides the basis 
      for the installation */
   for (pkgCache::PkgIterator I = Cache.PkgBegin(); I.end() == false; I++)
      if (I->CurrentVer != 0)
         Cache.MarkInstall(I, true, 0, false);

   /* Now, auto upgrade all essential packages - this ensures that
      the essential packages are present and working */
   for (pkgCache::PkgIterator I = Cache.PkgBegin(); I.end() == false; I++)
      if ((I->Flags & pkgCache::Flag::Essential) == pkgCache::Flag::Essential)
         Cache.MarkInstall(I, true, 0, false);
   
   /* We do it again over all previously installed packages to force 
      conflict resolution on them all. */
   for (pkgCache::PkgIterator I = Cache.PkgBegin(); I.end() == false; I++)
      if (I->CurrentVer != 0)
         Cache.MarkInstall(I, false, 0, false);

   pkgProblemResolver Fix(&Cache);

   // Hold back held packages.
   if (_config->FindB("APT::Ignore-Hold",false) == false)
   {
      for (pkgCache::PkgIterator I = Cache.PkgBegin(); I.end() == false; I++)
      {
         if (I->SelectedState == pkgCache::State::Hold)
         {
            Fix.Protect(I);
            Cache.MarkKeep(I, false, false);
         }
      }
   }
   
   return Fix.Resolve();
}
                                                                        /*}}}*/
// AllUpgrade - Upgrade as many packages as possible                    /*{{{*/
// ---------------------------------------------------------------------
/* Right now the system must be consistent before this can be called.
   It also will not change packages marked for install, it only tries
   to install packages not marked for install */
bool pkgAllUpgrade(pkgDepCache &Cache)
{
   pkgDepCache::ActionGroup group(Cache);

   pkgProblemResolver Fix(&Cache);

   if (Cache.BrokenCount() != 0)
      return false;
   
   // Upgrade all installed packages
   for (pkgCache::PkgIterator I = Cache.PkgBegin(); I.end() == false; I++)
   {
      if (Cache[I].Install() == true)
         Fix.Protect(I);
          
      if (_config->FindB("APT::Ignore-Hold",false) == false)
         if (I->SelectedState == pkgCache::State::Hold)
            continue;
      
      if (I->CurrentVer != 0 && Cache[I].InstallVer != 0)
         Cache.MarkInstall(I, false, 0, false);
   }
      
   return Fix.ResolveByKeep();
}
                                                                        /*}}}*/
// MinimizeUpgrade - Minimizes the set of packages to be upgraded       /*{{{*/
// ---------------------------------------------------------------------
/* This simply goes over the entire set of packages and tries to keep 
   each package marked for upgrade. If a conflict is generated then 
   the package is restored. */
bool pkgMinimizeUpgrade(pkgDepCache &Cache)
{   
   pkgDepCache::ActionGroup group(Cache);

   if (Cache.BrokenCount() != 0)
      return false;
   
   // We loop for 10 tries to get the minimal set size.
   bool Change = false;
   unsigned int Count = 0;
   do
   {
      Change = false;
      for (pkgCache::PkgIterator I = Cache.PkgBegin(); I.end() == false; I++)
      {
         // Not interesting
         if (Cache[I].Upgrade() == false || Cache[I].NewInstall() == true)
            continue;

         // Keep it and see if that is OK
         Cache.MarkKeep(I, false, false);
         if (Cache.BrokenCount() != 0)
            Cache.MarkInstall(I, false, 0, false);
         else
         {
            // If keep didnt actually do anything then there was no change..
            if (Cache[I].Upgrade() == false)
               Change = true;
         }       
      }      
      Count++;
   }
   while (Change == true && Count < 10);

   if (Cache.BrokenCount() != 0)
      return _error->Error("Internal Error in pkgMinimizeUpgrade");
   
   return true;
}
                                                                        /*}}}*/
// ProblemResolver::pkgProblemResolver - Constructor                    /*{{{*/
// ---------------------------------------------------------------------
/* */
pkgProblemResolver::pkgProblemResolver(pkgDepCache *pCache) : Cache(*pCache)
{
   // Allocate memory
   unsigned long Size = Cache.Head().PackageCount;
   Scores = new signed short[Size];
   Flags = new unsigned char[Size];
   memset(Flags,0,sizeof(*Flags)*Size);
   
   // Set debug to true to see its decision logic
   Debug = _config->FindB("Debug::pkgProblemResolver",false);
}
                                                                        /*}}}*/
// ProblemResolver::~pkgProblemResolver - Destructor                    /*{{{*/
// ---------------------------------------------------------------------
/* */
pkgProblemResolver::~pkgProblemResolver()
{
   delete [] Scores;
   delete [] Flags;
}
                                                                        /*}}}*/
// ProblemResolver::ScoreSort - Sort the list by score                  /*{{{*/
// ---------------------------------------------------------------------
/* */
int pkgProblemResolver::ScoreSort(const void *a,const void *b)
{
   Package const **A = (Package const **)a;
   Package const **B = (Package const **)b;
   if (This->Scores[(*A)->ID] > This->Scores[(*B)->ID])
      return -1;
   if (This->Scores[(*A)->ID] < This->Scores[(*B)->ID])
      return 1;
   return 0;
}
                                                                        /*}}}*/
// ProblemResolver::MakeScores - Make the score table                   /*{{{*/
// ---------------------------------------------------------------------
/* */
void pkgProblemResolver::MakeScores()
{
   unsigned long Size = Cache.Head().PackageCount;
   memset(Scores,0,sizeof(*Scores)*Size);

   // Important Required Standard Optional Extra
   signed short PrioMap[] = {
      0,
      (signed short) _config->FindI("pkgProblemResolver::Scores::Important",3),
      (signed short) _config->FindI("pkgProblemResolver::Scores::Required",2),
      (signed short) _config->FindI("pkgProblemResolver::Scores::Standard",1),
      (signed short) _config->FindI("pkgProblemResolver::Scores::Optional",-1),
      (signed short) _config->FindI("pkgProblemResolver::Scores::Extra",-2)
   };
   signed short PrioEssentials = _config->FindI("pkgProblemResolver::Scores::Essentials",100);
   signed short PrioInstalledAndNotObsolete = _config->FindI("pkgProblemResolver::Scores::NotObsolete",1);
   signed short PrioDepends = _config->FindI("pkgProblemResolver::Scores::Depends",1);
   signed short PrioRecommends = _config->FindI("pkgProblemResolver::Scores::Recommends",1);
   signed short AddProtected = _config->FindI("pkgProblemResolver::Scores::AddProtected",10000);
   signed short AddEssential = _config->FindI("pkgProblemResolver::Scores::AddEssential",5000);

   if (_config->FindB("Debug::pkgProblemResolver::ShowScores",false) == true)
      clog << "Settings used to calculate pkgProblemResolver::Scores::" << endl
         << "  Important => " << PrioMap[1] << endl
         << "  Required => " << PrioMap[2] << endl
         << "  Standard => " << PrioMap[3] << endl
         << "  Optional => " << PrioMap[4] << endl
         << "  Extra => " << PrioMap[5] << endl
         << "  Essentials => " << PrioEssentials << endl
         << "  InstalledAndNotObsolete => " << PrioInstalledAndNotObsolete << endl
         << "  Depends => " << PrioDepends << endl
         << "  Recommends => " << PrioRecommends << endl
         << "  AddProtected => " << AddProtected << endl
         << "  AddEssential => " << AddEssential << endl;

   // Generate the base scores for a package based on its properties
   for (pkgCache::PkgIterator I = Cache.PkgBegin(); I.end() == false; I++)
   {
      if (Cache[I].InstallVer == 0)
         continue;
      
      signed short &Score = Scores[I->ID];
      
      /* This is arbitrary, it should be high enough to elevate an
         essantial package above most other packages but low enough
         to allow an obsolete essential packages to be removed by
         a conflicts on a powerfull normal package (ie libc6) */
      if ((I->Flags & pkgCache::Flag::Essential) == pkgCache::Flag::Essential)
         Score += PrioEssentials;

      // We transform the priority
      if (Cache[I].InstVerIter(Cache)->Priority <= 5)
         Score += PrioMap[Cache[I].InstVerIter(Cache)->Priority];
      
      /* This helps to fix oddball problems with conflicting packages
         on the same level. We enhance the score of installed packages 
         if those are not obsolete
      */
      if (I->CurrentVer != 0 && Cache[I].CandidateVer != 0 && Cache[I].CandidateVerIter(Cache).Downloadable())
         Score += PrioInstalledAndNotObsolete;
   }

   // Now that we have the base scores we go and propogate dependencies
   for (pkgCache::PkgIterator I = Cache.PkgBegin(); I.end() == false; I++)
   {
      if (Cache[I].InstallVer == 0)
         continue;
      
      for (pkgCache::DepIterator D = Cache[I].InstVerIter(Cache).DependsList(); D.end() == false; D++)
      {
         if (D->Type == pkgCache::Dep::Depends || 
             D->Type == pkgCache::Dep::PreDepends)
            Scores[D.TargetPkg()->ID] += PrioDepends;
         else if (D->Type == pkgCache::Dep::Recommends)
            Scores[D.TargetPkg()->ID] += PrioRecommends;
      }
   }   
   
   // Copy the scores to advoid additive looping
   SPtrArray<signed short> OldScores = new signed short[Size];
   memcpy(OldScores,Scores,sizeof(*Scores)*Size);
      
   /* Now we cause 1 level of dependency inheritance, that is we add the 
      score of the packages that depend on the target Package. This 
      fortifies high scoring packages */
   for (pkgCache::PkgIterator I = Cache.PkgBegin(); I.end() == false; I++)
   {
      if (Cache[I].InstallVer == 0)
         continue;
      
      for (pkgCache::DepIterator D = I.RevDependsList(); D.end() == false; D++)
      {
         // Only do it for the install version
         if ((pkgCache::Version *)D.ParentVer() != Cache[D.ParentPkg()].InstallVer ||
             (D->Type != pkgCache::Dep::Depends && 
              D->Type != pkgCache::Dep::PreDepends &&
              D->Type != pkgCache::Dep::Recommends))
            continue;    
         
         Scores[I->ID] += abs(OldScores[D.ParentPkg()->ID]);
      }      
   }

   /* Now we propogate along provides. This makes the packages that 
      provide important packages extremely important */
   for (pkgCache::PkgIterator I = Cache.PkgBegin(); I.end() == false; I++)
   {
      for (pkgCache::PrvIterator P = I.ProvidesList(); P.end() == false; P++)
      {
         // Only do it once per package
         if ((pkgCache::Version *)P.OwnerVer() != Cache[P.OwnerPkg()].InstallVer)
            continue;
         Scores[P.OwnerPkg()->ID] += abs(Scores[I->ID] - OldScores[I->ID]);
      }
   }

   /* Protected things are pushed really high up. This number should put them
      ahead of everything */
   for (pkgCache::PkgIterator I = Cache.PkgBegin(); I.end() == false; I++)
   {
      if ((Flags[I->ID] & Protected) != 0)
         Scores[I->ID] += AddProtected;
      if ((I->Flags & pkgCache::Flag::Essential) == pkgCache::Flag::Essential)
         Scores[I->ID] += AddEssential;
   }
}
                                                                        /*}}}*/
// ProblemResolver::DoUpgrade - Attempt to upgrade this package         /*{{{*/
// ---------------------------------------------------------------------
/* This goes through and tries to reinstall packages to make this package
   installable */
bool pkgProblemResolver::DoUpgrade(pkgCache::PkgIterator Pkg)
{
   pkgDepCache::ActionGroup group(Cache);

   if ((Flags[Pkg->ID] & Upgradable) == 0 || Cache[Pkg].Upgradable() == false)
      return false;
   if ((Flags[Pkg->ID] & Protected) == Protected)
      return false;
   
   Flags[Pkg->ID] &= ~Upgradable;
   
   bool WasKept = Cache[Pkg].Keep();
   Cache.MarkInstall(Pkg, false, 0, false);

   // This must be a virtual package or something like that.
   if (Cache[Pkg].InstVerIter(Cache).end() == true)
      return false;
   
   // Isolate the problem dependency
   bool Fail = false;
   for (pkgCache::DepIterator D = Cache[Pkg].InstVerIter(Cache).DependsList(); D.end() == false;)
   {
      // Compute a single dependency element (glob or)
      pkgCache::DepIterator Start = D;
      pkgCache::DepIterator End = D;
      unsigned char State = 0;
      for (bool LastOR = true; D.end() == false && LastOR == true;)
      {
         State |= Cache[D];
         LastOR = (D->CompareOp & pkgCache::Dep::Or) == pkgCache::Dep::Or;
         D++;
         if (LastOR == true)
            End = D;
      }
      
      // We only worry about critical deps.
      if (End.IsCritical() != true)
         continue;
            
      // Iterate over all the members in the or group
      while (1)
      {
         // Dep is ok now
         if ((Cache[End] & pkgDepCache::DepGInstall) == pkgDepCache::DepGInstall)
            break;
         
         // Do not change protected packages
         PkgIterator P = Start.SmartTargetPkg();
         if ((Flags[P->ID] & Protected) == Protected)
         {
            if (Debug == true)
               clog << "    Reinst Failed because of protected " << P.FullName(false) << endl;
            Fail = true;
         }      
         else
         {
            // Upgrade the package if the candidate version will fix the problem.
            if ((Cache[Start] & pkgDepCache::DepCVer) == pkgDepCache::DepCVer)
            {
               if (DoUpgrade(P) == false)
               {
                  if (Debug == true)
                     clog << "    Reinst Failed because of " << P.FullName(false) << endl;
                  Fail = true;
               }
               else
               {
                  Fail = false;
                  break;
               }            
            }
            else
            {
               /* We let the algorithm deal with conflicts on its next iteration,
                it is much smarter than us */
               if (Start->Type == pkgCache::Dep::Conflicts || 
                   Start->Type == pkgCache::Dep::DpkgBreaks || 
                   Start->Type == pkgCache::Dep::Obsoletes)
                   break;
               
               if (Debug == true)
                  clog << "    Reinst Failed early because of " << Start.TargetPkg().FullName(false) << endl;
               Fail = true;
            }     
         }
         
         if (Start == End)
            break;
         Start++;
      }
      if (Fail == true)
         break;
   }
   
   // Undo our operations - it might be smart to undo everything this did..
   if (Fail == true)
   {
      if (WasKept == true)
         Cache.MarkKeep(Pkg, false, false);
      else
         Cache.MarkDelete(Pkg);
      return false;
   }     
   
   if (Debug == true)
      clog << "  Re-Instated " << Pkg.FullName(false) << endl;
   return true;
}
                                                                        /*}}}*/
// ProblemResolver::Resolve - Run the resolution pass                   /*{{{*/
// ---------------------------------------------------------------------
/* This routines works by calculating a score for each package. The score
   is derived by considering the package's priority and all reverse 
   dependents giving an integer that reflects the amount of breakage that
   adjusting the package will inflict. 
      
   It goes from highest score to lowest and corrects all of the breaks by 
   keeping or removing the dependant packages. If that fails then it removes
   the package itself and goes on. The routine should be able to intelligently
   go from any broken state to a fixed state. 
 
   The BrokenFix flag enables a mode where the algorithm tries to 
   upgrade packages to advoid problems. */
bool pkgProblemResolver::Resolve(bool BrokenFix)
{
   pkgDepCache::ActionGroup group(Cache);

   unsigned long Size = Cache.Head().PackageCount;

   // Record which packages are marked for install
   bool Again = false;
   do
   {
      Again = false;
      for (pkgCache::PkgIterator I = Cache.PkgBegin(); I.end() == false; I++)
      {
         if (Cache[I].Install() == true)
            Flags[I->ID] |= PreInstalled;
         else
         {
            if (Cache[I].InstBroken() == true && BrokenFix == true)
            {
               Cache.MarkInstall(I, false, 0, false);
               if (Cache[I].Install() == true)
                  Again = true;
            }
            
            Flags[I->ID] &= ~PreInstalled;
         }
         Flags[I->ID] |= Upgradable;
      }
   }
   while (Again == true);

   if (Debug == true)
      clog << "Starting" << endl;
   
   MakeScores();
   
   /* We have to order the packages so that the broken fixing pass 
      operates from highest score to lowest. This prevents problems when
      high score packages cause the removal of lower score packages that
      would cause the removal of even lower score packages. */
   SPtrArray<pkgCache::Package *> PList = new pkgCache::Package *[Size];
   pkgCache::Package **PEnd = PList;
   for (pkgCache::PkgIterator I = Cache.PkgBegin(); I.end() == false; I++)
      *PEnd++ = I;
   This = this;
   qsort(PList,PEnd - PList,sizeof(*PList),&ScoreSort);

   if (_config->FindB("Debug::pkgProblemResolver::ShowScores",false) == true)
   {
      clog << "Show Scores" << endl;
      for (pkgCache::Package **K = PList; K != PEnd; K++)
         if (Scores[(*K)->ID] != 0)
         {
           pkgCache::PkgIterator Pkg(Cache,*K);
           clog << Scores[(*K)->ID] << ' ' << Pkg << std::endl;
         }
   }

   if (Debug == true)
      clog << "Starting 2" << endl;

   /* Now consider all broken packages. For each broken package we either
      remove the package or fix it's problem. We do this once, it should
      not be possible for a loop to form (that is a < b < c and fixing b by
      changing a breaks c) */
   bool Change = true;
   bool const TryFixByInstall = _config->FindB("pkgProblemResolver::FixByInstall", true);
   for (int Counter = 0; Counter != 10 && Change == true; Counter++)
   {
      Change = false;
      for (pkgCache::Package **K = PList; K != PEnd; K++)
      {
         pkgCache::PkgIterator I(Cache,*K);

         /* We attempt to install this and see if any breaks result,
            this takes care of some strange cases */
         if (Cache[I].CandidateVer != Cache[I].InstallVer &&
             I->CurrentVer != 0 && Cache[I].InstallVer != 0 &&
             (Flags[I->ID] & PreInstalled) != 0 &&
             (Flags[I->ID] & Protected) == 0 &&
             (Flags[I->ID] & ReInstateTried) == 0)
         {
            if (Debug == true)
               clog << " Try to Re-Instate (" << Counter << ") " << I.FullName(false) << endl;
            unsigned long OldBreaks = Cache.BrokenCount();
            pkgCache::Version *OldVer = Cache[I].InstallVer;
            Flags[I->ID] &= ReInstateTried;
            
            Cache.MarkInstall(I, false, 0, false);
            if (Cache[I].InstBroken() == true || 
                OldBreaks < Cache.BrokenCount())
            {
               if (OldVer == 0)
                  Cache.MarkDelete(I);
               else
                  Cache.MarkKeep(I, false, false);
            }       
            else
               if (Debug == true)
                  clog << "Re-Instated " << I.FullName(false) << " (" << OldBreaks << " vs " << Cache.BrokenCount() << ')' << endl;
         }
            
         if (Cache[I].InstallVer == 0 || Cache[I].InstBroken() == false)
            continue;
         
         if (Debug == true)
            clog << "Investigating (" << Counter << ") " << I << endl;
         
         // Isolate the problem dependency
         PackageKill KillList[100];
         PackageKill *LEnd = KillList;
         bool InOr = false;
         pkgCache::DepIterator Start;
         pkgCache::DepIterator End;
         PackageKill *OldEnd = LEnd;
         
         enum {OrRemove,OrKeep} OrOp = OrRemove;
         for (pkgCache::DepIterator D = Cache[I].InstVerIter(Cache).DependsList();
              D.end() == false || InOr == true;)
         {
            // Compute a single dependency element (glob or)
            if (Start == End)
            {
               // Decide what to do
               if (InOr == true && OldEnd == LEnd)
               {
                  if (OrOp == OrRemove)
                  {
                     if ((Flags[I->ID] & Protected) != Protected)
                     {
                        if (Debug == true)
                           clog << "  Or group remove for " << I.FullName(false) << endl;
                        Cache.MarkDelete(I);
                        Change = true;
                     }
                  }
                  else if (OrOp == OrKeep)
                  {
                     if (Debug == true)
                        clog << "  Or group keep for " << I.FullName(false) << endl;
                     Cache.MarkKeep(I, false, false);
                     Change = true;
                  }
               }
               
               /* We do an extra loop (as above) to finalize the or group
                  processing */
               InOr = false;
               OrOp = OrRemove;
               D.GlobOr(Start,End);
               if (Start.end() == true)
                  break;

               // We only worry about critical deps.
               if (End.IsCritical() != true)
                  continue;

               InOr = Start != End;
               OldEnd = LEnd;
            }
            else
            {
               Start++;
               // We only worry about critical deps.
               if (Start.IsCritical() != true)
                  continue;
            }

            // Dep is ok
            if ((Cache[End] & pkgDepCache::DepGInstall) == pkgDepCache::DepGInstall)
            {
               InOr = false;
               continue;
            }
            
            if (Debug == true)
               clog << "Broken " << Start << endl;

            /* Look across the version list. If there are no possible
               targets then we keep the package and bail. This is necessary
               if a package has a dep on another package that cant be found */
            SPtrArray<pkgCache::Version *> VList = Start.AllTargets();
            if (*VList == 0 && (Flags[I->ID] & Protected) != Protected &&
                Start->Type != pkgCache::Dep::Conflicts &&
                Start->Type != pkgCache::Dep::DpkgBreaks &&
                Start->Type != pkgCache::Dep::Obsoletes &&
                Cache[I].NowBroken() == false)
            {          
               if (InOr == true)
               {
                  /* No keep choice because the keep being OK could be the
                     result of another element in the OR group! */
                  continue;
               }
               
               Change = true;
               Cache.MarkKeep(I, false, false);
               break;
            }
            
            bool Done = false;
            for (pkgCache::Version **V = VList; *V != 0; V++)
            {
               pkgCache::VerIterator Ver(Cache,*V);
               pkgCache::PkgIterator Pkg = Ver.ParentPkg();

               /* Ignore a target that is not a candidate
                  This can happen if:
                    installed package provides video-6
                    candidate provides video-8
                  now if a package Start breaks/conflicts video-6
                  Start.AllTargets() will return the now-installed
                  versions even though these are not candidates
                  we can ignore them
               */
               if (Cache[Pkg].CandidateVerIter(Cache) != Ver)
               {
                  if (Debug)
                     clog << "  Version " << Ver.VerStr() << " for "
                          << Pkg.Name() << " is not a candidate, ignoring"
                          << endl;
                 continue;
               }

               if (Debug == true)
                  clog << "  Considering " << Pkg.FullName(false) << ' ' << (int)Scores[Pkg->ID] <<
                  " as a solution to " << I.FullName(false) << ' ' << (int)Scores[I->ID] << endl;

               /* Try to fix the package under consideration rather than
                  fiddle with the VList package */
               if (Scores[I->ID] <= Scores[Pkg->ID] ||
                   ((Cache[Start] & pkgDepCache::DepNow) == 0 &&
                    End->Type != pkgCache::Dep::Conflicts &&
                    End->Type != pkgCache::Dep::DpkgBreaks &&
                    End->Type != pkgCache::Dep::Obsoletes))
               {
                  // Try a little harder to fix protected packages..
                  if ((Flags[I->ID] & Protected) == Protected)
                  {
                     if (DoUpgrade(Pkg) == true)
                     {
                        if (Scores[Pkg->ID] > Scores[I->ID])
                           Scores[Pkg->ID] = Scores[I->ID];
                        break;
                     }
                     
                     continue;
                  }
                  
                  /* See if a keep will do, unless the package is protected,
                     then installing it will be necessary */
                  bool Installed = Cache[I].Install();
                  Cache.MarkKeep(I, false, false);
                  if (Cache[I].InstBroken() == false)
                  {
                     // Unwind operation will be keep now
                     if (OrOp == OrRemove)
                        OrOp = OrKeep;
                     
                     // Restore
                     if (InOr == true && Installed == true)
                        Cache.MarkInstall(I, false, 0, false);
                     
                     if (Debug == true)
                        clog << "  Holding Back " << I.FullName(false) << " rather than change " << Start.TargetPkg().FullName(false) << endl;
                  }               
                  else
                  {                  
                     if (BrokenFix == false || DoUpgrade(I) == false)
                     {
                        // Consider other options
                        if (InOr == false)
                        {
                           if (Debug == true)
                              clog << "  Removing " << I.FullName(false) << " rather than change " << Start.TargetPkg().FullName(false) << endl;
                           Cache.MarkDelete(I);
                           if (Counter > 1 && Scores[Pkg->ID] > Scores[I->ID])
                              Scores[I->ID] = Scores[Pkg->ID];
                        }
                        else if (TryFixByInstall == true &&
                                 Start.TargetPkg()->CurrentVer == 0 &&
                                 Cache[Start.TargetPkg()].Delete() == false &&
                                 Cache.GetCandidateVer(Start.TargetPkg()).end() == false)
                        {
                           /* Before removing or keeping the package with the broken dependency
                              try instead to install the first not previously installed package
                              solving this dependency. This helps every time a previous solver
                              is removed by the resolver because of a conflict or alike but it is
                              dangerous as it could trigger new breaks/conflicts… */
                           if (Debug == true)
                              clog << "  Try Installing " << Start.TargetPkg() << " before changing " << I.FullName(false) << std::endl;
                           unsigned long const OldBroken = Cache.BrokenCount();
                           Cache.MarkInstall(Start.TargetPkg(), true, 1, false);
                           // FIXME: we should undo the complete MarkInstall process here
                           if (Cache[Start.TargetPkg()].InstBroken() == true || Cache.BrokenCount() > OldBroken)
                              Cache.MarkDelete(Start.TargetPkg(), false, 1, false);
                        }
                     }
                  }
                                  
                  Change = true;
                  Done = true;
                  break;
               }
               else
               {
                  /* This is a conflicts, and the version we are looking
                     at is not the currently selected version of the 
                     package, which means it is not necessary to 
                     remove/keep */
                  if (Cache[Pkg].InstallVer != Ver &&
                      (Start->Type == pkgCache::Dep::Conflicts ||
                       Start->Type == pkgCache::Dep::Obsoletes))
                     continue;

                  if (Start->Type == pkgCache::Dep::DpkgBreaks)
                  {
                     // first, try upgrading the package, if that
                     // does not help, the breaks goes onto the
                     // kill list
                     // FIXME: use DoUpgrade(Pkg) instead?
                     if (Cache[End] & pkgDepCache::DepGCVer) 
                     {
                        if (Debug)
                           clog << "  Upgrading " << Pkg.FullName(false) << " due to Breaks field in " << I.FullName(false) << endl;
                        Cache.MarkInstall(Pkg, false, 0, false);
                        continue;
                     }
                  }

                  // Skip adding to the kill list if it is protected
                  if ((Flags[Pkg->ID] & Protected) != 0)
                     continue;
                
                  if (Debug == true)
                     clog << "  Added " << Pkg.FullName(false) << " to the remove list" << endl;
                  
                  LEnd->Pkg = Pkg;
                  LEnd->Dep = End;
                  LEnd++;
                  
                  if (Start->Type != pkgCache::Dep::Conflicts &&
                      Start->Type != pkgCache::Dep::DpkgBreaks &&
                      Start->Type != pkgCache::Dep::Obsoletes)
                     break;
               }
            }

            // Hm, nothing can possibly satisify this dep. Nuke it.
            if (VList[0] == 0 && 
                Start->Type != pkgCache::Dep::Conflicts &&
                Start->Type != pkgCache::Dep::DpkgBreaks &&
                Start->Type != pkgCache::Dep::Obsoletes &&
                (Flags[I->ID] & Protected) != Protected)
            {
               bool Installed = Cache[I].Install();
               Cache.MarkKeep(I);
               if (Cache[I].InstBroken() == false)
               {
                  // Unwind operation will be keep now
                  if (OrOp == OrRemove)
                     OrOp = OrKeep;
                  
                  // Restore
                  if (InOr == true && Installed == true)
                     Cache.MarkInstall(I, false, 0, false);
                  
                  if (Debug == true)
                     clog << "  Holding Back " << I.FullName(false) << " because I can't find " << Start.TargetPkg().FullName(false) << endl;
               }               
               else
               {
                  if (Debug == true)
                     clog << "  Removing " << I.FullName(false) << " because I can't find " << Start.TargetPkg().FullName(false) << endl;
                  if (InOr == false)
                     Cache.MarkDelete(I);
               }

               Change = true;
               Done = true;
            }
            
            // Try some more
            if (InOr == true)
               continue;
            
            if (Done == true)
               break;
         }
         
         // Apply the kill list now
         if (Cache[I].InstallVer != 0)
         {
            for (PackageKill *J = KillList; J != LEnd; J++)
            {
               Change = true;
               if ((Cache[J->Dep] & pkgDepCache::DepGNow) == 0)
               {
                  if (J->Dep->Type == pkgCache::Dep::Conflicts || 
                      J->Dep->Type == pkgCache::Dep::DpkgBreaks ||
                      J->Dep->Type == pkgCache::Dep::Obsoletes)
                  {
                     if (Debug == true)
                        clog << "  Fixing " << I.FullName(false) << " via remove of " << J->Pkg.FullName(false) << endl;
                     Cache.MarkDelete(J->Pkg);
                  }
               }
               else
               {
                  if (Debug == true)
                     clog << "  Fixing " << I.FullName(false) << " via keep of " << J->Pkg.FullName(false) << endl;
                  Cache.MarkKeep(J->Pkg, false, false);
               }

               if (Counter > 1)
               {
                  if (Scores[I->ID] > Scores[J->Pkg->ID])                 
                     Scores[J->Pkg->ID] = Scores[I->ID];
               }               
            }      
         }
      }      
   }

   if (Debug == true)
      clog << "Done" << endl;
      
   if (Cache.BrokenCount() != 0)
   {
      // See if this is the result of a hold
      pkgCache::PkgIterator I = Cache.PkgBegin();
      for (;I.end() != true; I++)
      {
         if (Cache[I].InstBroken() == false)
            continue;
         if ((Flags[I->ID] & Protected) != Protected)
            return _error->Error(_("Error, pkgProblemResolver::Resolve generated breaks, this may be caused by held packages."));
      }
      return _error->Error(_("Unable to correct problems, you have held broken packages."));
   }
   
   // set the auto-flags (mvo: I'm not sure if we _really_ need this)
   pkgCache::PkgIterator I = Cache.PkgBegin();
   for (;I.end() != true; I++) {
      if (Cache[I].NewInstall() && !(Flags[I->ID] & PreInstalled)) {
         if(_config->FindI("Debug::pkgAutoRemove",false)) {
            std::clog << "Resolve installed new pkg: " << I.FullName(false) 
                      << " (now marking it as auto)" << std::endl;
         }
         Cache[I].Flags |= pkgCache::Flag::Auto;
      }
   }


   return true;
}
                                                                        /*}}}*/
// ProblemResolver::ResolveByKeep - Resolve problems using keep         /*{{{*/
// ---------------------------------------------------------------------
/* This is the work horse of the soft upgrade routine. It is very gental 
   in that it does not install or remove any packages. It is assumed that the
   system was non-broken previously. */
bool pkgProblemResolver::ResolveByKeep()
{
   pkgDepCache::ActionGroup group(Cache);

   unsigned long Size = Cache.Head().PackageCount;

   MakeScores();
   
   /* We have to order the packages so that the broken fixing pass 
      operates from highest score to lowest. This prevents problems when
      high score packages cause the removal of lower score packages that
      would cause the removal of even lower score packages. */
   pkgCache::Package **PList = new pkgCache::Package *[Size];
   pkgCache::Package **PEnd = PList;
   for (pkgCache::PkgIterator I = Cache.PkgBegin(); I.end() == false; I++)
      *PEnd++ = I;
   This = this;
   qsort(PList,PEnd - PList,sizeof(*PList),&ScoreSort);

   if (_config->FindB("Debug::pkgProblemResolver::ShowScores",false) == true)
   {
      clog << "Show Scores" << endl;
      for (pkgCache::Package **K = PList; K != PEnd; K++)
         if (Scores[(*K)->ID] != 0)
         {
           pkgCache::PkgIterator Pkg(Cache,*K);
           clog << Scores[(*K)->ID] << ' ' << Pkg << std::endl;
         }
   }

   if (Debug == true)
      clog << "Entering ResolveByKeep" << endl;

   // Consider each broken package 
   pkgCache::Package **LastStop = 0;
   for (pkgCache::Package **K = PList; K != PEnd; K++)
   {
      pkgCache::PkgIterator I(Cache,*K);

      if (Cache[I].InstallVer == 0 || Cache[I].InstBroken() == false)
         continue;

      /* Keep the package. If this works then great, otherwise we have
         to be significantly more agressive and manipulate its dependencies */
      if ((Flags[I->ID] & Protected) == 0)
      {
         if (Debug == true)
            clog << "Keeping package " << I.FullName(false) << endl;
         Cache.MarkKeep(I, false, false);
         if (Cache[I].InstBroken() == false)
         {
            K = PList - 1;
            continue;
         }
      }
      
      // Isolate the problem dependencies
      for (pkgCache::DepIterator D = Cache[I].InstVerIter(Cache).DependsList(); D.end() == false;)
      {
         DepIterator Start;
         DepIterator End;
         D.GlobOr(Start,End);

         // We only worry about critical deps.
         if (End.IsCritical() != true)
            continue;
         
         // Dep is ok
         if ((Cache[End] & pkgDepCache::DepGInstall) == pkgDepCache::DepGInstall)
            continue;

         /* Hm, the group is broken.. I suppose the best thing to do is to
            is to try every combination of keep/not-keep for the set, but thats
            slow, and this never happens, just be conservative and assume the
            list of ors is in preference and keep till it starts to work. */
         while (true)
         {
            if (Debug == true)
               clog << "Package " << I.FullName(false) << " " << Start << endl;

            // Look at all the possible provides on this package
            SPtrArray<pkgCache::Version *> VList = Start.AllTargets();
            for (pkgCache::Version **V = VList; *V != 0; V++)
            {
               pkgCache::VerIterator Ver(Cache,*V);
               pkgCache::PkgIterator Pkg = Ver.ParentPkg();
               
               // It is not keepable
               if (Cache[Pkg].InstallVer == 0 ||
                   Pkg->CurrentVer == 0)
                  continue;
               
               if ((Flags[I->ID] & Protected) == 0)
               {
                  if (Debug == true)
                     clog << "  Keeping Package " << Pkg.FullName(false) << " due to " << Start.DepType() << endl;
                  Cache.MarkKeep(Pkg, false, false);
               }
               
               if (Cache[I].InstBroken() == false)
                  break;
            }
            
            if (Cache[I].InstBroken() == false)
               break;

            if (Start == End)
               break;
            Start++;
         }
              
         if (Cache[I].InstBroken() == false)
            break;
      }

      if (Cache[I].InstBroken() == true)
         continue;
      
      // Restart again.
      if (K == LastStop)
         return _error->Error("Internal Error, pkgProblemResolver::ResolveByKeep is looping on package %s.",I.FullName(false).c_str());
      LastStop = K;
      K = PList - 1;
   }   

   return true;
}
                                                                        /*}}}*/
// ProblemResolver::InstallProtect - Install all protected packages     /*{{{*/
// ---------------------------------------------------------------------
/* This is used to make sure protected packages are installed */
void pkgProblemResolver::InstallProtect()
{
   pkgDepCache::ActionGroup group(Cache);

   for (pkgCache::PkgIterator I = Cache.PkgBegin(); I.end() == false; I++)
   {
      if ((Flags[I->ID] & Protected) == Protected)
      {
         if ((Flags[I->ID] & ToRemove) == ToRemove)
            Cache.MarkDelete(I);
         else 
         {
            // preserve the information whether the package was auto
            // or manually installed
            bool autoInst = (Cache[I].Flags & pkgCache::Flag::Auto);
            Cache.MarkInstall(I, false, 0, !autoInst);
         }
      }
   }   
}
                                                                        /*}}}*/
// PrioSortList - Sort a list of versions by priority                   /*{{{*/
// ---------------------------------------------------------------------
/* This is ment to be used in conjunction with AllTargets to get a list 
   of versions ordered by preference. */
static pkgCache *PrioCache;
static int PrioComp(const void *A,const void *B)
{
   pkgCache::VerIterator L(*PrioCache,*(pkgCache::Version **)A);
   pkgCache::VerIterator R(*PrioCache,*(pkgCache::Version **)B);
   
   if ((L.ParentPkg()->Flags & pkgCache::Flag::Essential) == pkgCache::Flag::Essential &&
       (R.ParentPkg()->Flags & pkgCache::Flag::Essential) != pkgCache::Flag::Essential)
     return 1;
   if ((L.ParentPkg()->Flags & pkgCache::Flag::Essential) != pkgCache::Flag::Essential &&
       (R.ParentPkg()->Flags & pkgCache::Flag::Essential) == pkgCache::Flag::Essential)
     return -1;
   
   if (L->Priority != R->Priority)
      return R->Priority - L->Priority;
   return strcmp(L.ParentPkg().Name(),R.ParentPkg().Name());
}
void pkgPrioSortList(pkgCache &Cache,pkgCache::Version **List)
{
   unsigned long Count = 0;
   PrioCache = &Cache;
   for (pkgCache::Version **I = List; *I != 0; I++)
      Count++;
   qsort(List,Count,sizeof(*List),PrioComp);
}
                                                                        /*}}}*/
// CacheFile::ListUpdate - update the cache files                       /*{{{*/
// ---------------------------------------------------------------------
/* This is a simple wrapper to update the cache. it will fetch stuff
 * from the network (or any other sources defined in sources.list)
 */
bool ListUpdate(pkgAcquireStatus &Stat, 
                pkgSourceList &List, 
                int PulseInterval)
{
   pkgAcquire::RunResult res;
   pkgAcquire Fetcher;
   if (Fetcher.Setup(&Stat, _config->FindDir("Dir::State::Lists")) == false)
      return false;

   // Populate it with the source selection
   if (List.GetIndexes(&Fetcher) == false)
         return false;

   // Run scripts
   RunScripts("APT::Update::Pre-Invoke");
   
   // check arguments
   if(PulseInterval>0)
      res = Fetcher.Run(PulseInterval);
   else
      res = Fetcher.Run();

   if (res == pkgAcquire::Failed)
      return false;

   bool Failed = false;
   bool TransientNetworkFailure = false;
   for (pkgAcquire::ItemIterator I = Fetcher.ItemsBegin(); 
        I != Fetcher.ItemsEnd(); I++)
   {
      if ((*I)->Status == pkgAcquire::Item::StatDone)
         continue;

      (*I)->Finished();

      ::URI uri((*I)->DescURI());
      uri.User.clear();
      uri.Password.clear();
      string descUri = string(uri);
      _error->Warning(_("Failed to fetch %s  %s\n"), descUri.c_str(),
              (*I)->ErrorText.c_str());

      if ((*I)->Status == pkgAcquire::Item::StatTransientNetworkError) 
      {
         TransientNetworkFailure = true;
         continue;
      }

      Failed = true;
   }
   
   // Clean out any old list files
   // Keep "APT::Get::List-Cleanup" name for compatibility, but
   // this is really a global option for the APT library now
   if (!TransientNetworkFailure && !Failed &&
       (_config->FindB("APT::Get::List-Cleanup",true) == true &&
        _config->FindB("APT::List-Cleanup",true) == true))
   {
      if (Fetcher.Clean(_config->FindDir("Dir::State::lists")) == false ||
          Fetcher.Clean(_config->FindDir("Dir::State::lists") + "partial/") == false)
         // something went wrong with the clean
         return false;
   }
   
   if (TransientNetworkFailure == true)
      _error->Warning(_("Some index files failed to download, they have been ignored, or old ones used instead."));
   else if (Failed == true)
      return _error->Error(_("Some index files failed to download, they have been ignored, or old ones used instead."));


   // Run the success scripts if all was fine
   if(!TransientNetworkFailure && !Failed)
      RunScripts("APT::Update::Post-Invoke-Success");

   // Run the other scripts
   RunScripts("APT::Update::Post-Invoke");
   return true;
}
                                                                        /*}}}*/