Sync

Author: jgg
Date: 1998-07-07 04:17:00 GMT
Sync

1 files changed, 829 insertions, 0 deletions

diff --git a/apt-pkg/orderlist.cc b/apt-pkg/orderlist.cc
new file mode 100644
index 000000000..f79a063bd
--- /dev/null
+++ b/apt-pkg/orderlist.cc
@@ -0,0 +1,829 @@
+// -*- mode: cpp; mode: fold -*-
+// Description								/*{{{*/
+// $Id: orderlist.cc,v 1.1 1998/07/07 04:17:01 jgg Exp $
+/* ######################################################################
+
+   Order List - Represents and Manipulates an ordered list of packages.
+   
+   A list of packages can be ordered by a number of conflicting criteria
+   each given a specific priority. Each package also has a set of flags
+   indicating some usefull things about it that are derived in the 
+   course of sorting. The pkgPackageManager class uses this class for
+   all of it's installation ordering needs.
+
+   This is a modified version of Manoj's Routine B. It consists of four
+   independent ordering algorithms that can be applied at for different
+   points in the ordering. By appling progressivly fewer ordering
+   operations it is possible to give each consideration it's own
+   priority and create an order that satisfies the lowest applicable
+   consideration.
+   
+   The rules for unpacking ordering are:
+    1) Unpacking ignores Depends: on all packages
+    2) Unpacking requires Conflicts: on -ALL- packages to be satisfied
+    3) Unpacking requires PreDepends: on this package only to be satisfied
+    4) Removing requires that no packages depend on the package to be
+       removed.
+   
+   And the rule for configuration ordering is:
+    1) Configuring requires that the Depends: of the package be satisfied
+       Conflicts+PreDepends are ignored because unpacking says they are 
+       already correct [exageration, it does check but we need not be 
+       concerned]
+
+   And some features that are valuable for unpacking ordering.
+     f1) Unpacking a new package should advoid breaking dependencies of
+         configured packages
+     f2) Removal should not require a force, corrolory of f1
+     f3) Unpacking should order by depends rather than fall back to random
+         ordering.  
+   
+   Each of the features can be enabled in the sorting routine at an 
+   arbitary priority to give quite abit of control over the final unpacking
+   order.
+
+   The rules listed above my never be violated and are called Critical.
+   When a critical rule is violated then a loop condition is recorded
+   and will have to be delt with in the caller.
+   
+   ##################################################################### */
+									/*}}}*/
+// Include Files							/*{{{*/
+#ifdef __GNUG__
+#pragma implementation "pkglib/orderlist.h"
+#endif 
+#include <pkglib/orderlist.h>
+#include <pkglib/depcache.h>
+#include <pkglib/error.h>
+#include <pkglib/version.h>
+									/*}}}*/
+
+pkgOrderList *pkgOrderList::Me = 0;
+
+// OrderList::pkgOrderList - Constructor				/*{{{*/
+// ---------------------------------------------------------------------
+/* */
+pkgOrderList::pkgOrderList(pkgDepCache &Cache) : Cache(Cache)
+{
+   Primary = 0;
+   Secondary = 0;
+   RevDepends = 0;
+   Remove = 0;
+   LoopCount = -1;
+
+   /* Construct the arrays, egcs 1.0.1 bug requires the package count
+      hack */
+   unsigned long Size = Cache.HeaderP->PackageCount;
+   Flags = new unsigned char[Size];
+   End = List = new Package *[Size];
+   memset(Flags,0,sizeof(*Flags)*Size);
+}
+									/*}}}*/
+// OrderList::~pkgOrderList - Destructor				/*{{{*/
+// ---------------------------------------------------------------------
+/* */
+pkgOrderList::~pkgOrderList()
+{
+   delete [] List;
+   delete [] Flags;
+}
+									/*}}}*/
+
+// OrderList::DoRun - Does an order run					/*{{{*/
+// ---------------------------------------------------------------------
+/* The caller is expeted to have setup the desired probe state */
+bool pkgOrderList::DoRun()
+{
+   // Temp list
+   unsigned long Size = Cache.HeaderP->PackageCount;
+   Package **NList = new Package *[Size];
+
+   Depth = 0;
+   WipeFlags(Added | AddPending | Loop | InList);
+
+   for (iterator I = List; I != End; I++)
+      Flag(*I,InList);
+   
+   // Rebuild the main list into the temp list.
+   iterator OldEnd = End;
+   End = NList;
+   for (iterator I = List; I != OldEnd; I++)
+      if (VisitNode(PkgIterator(Cache,*I)) == false)
+      {
+	 End = OldEnd;
+	 delete [] NList;
+	 return false;
+      }
+   
+   // Swap the main list to the new list
+   delete [] List;
+   List = NList;
+   return true;
+}
+									/*}}}*/
+// OrderList::OrderCritical - Perform critical unpacking ordering	/*{{{*/
+// ---------------------------------------------------------------------
+/* This performs predepends and immediate configuration ordering only. 
+   This is termed critical unpacking ordering. Any loops that form are
+   fatal and indicate that the packages cannot be installed. */
+bool pkgOrderList::OrderCritical()
+{
+   Primary = &DepUnPackPre;
+   Secondary = 0;
+   RevDepends = 0;
+   Remove = 0;
+   LoopCount = 0;
+   
+   // Sort
+   Me = this;
+   qsort(List,End - List,sizeof(*List),&OrderCompareB);   
+   
+   if (DoRun() == false)
+      return false;
+   
+   if (LoopCount != 0)
+      return _error->Error("Fatal, predepends looping detected");
+   return true;
+}
+									/*}}}*/
+// OrderList::OrderUnpack - Perform complete unpacking ordering		/*{{{*/
+// ---------------------------------------------------------------------
+/* This performs complete unpacking ordering and creates an order that is
+   suitable for unpacking */
+bool pkgOrderList::OrderUnpack()
+{
+   Primary = &DepUnPackCrit;
+   Secondary = &DepConfigure;
+   RevDepends = &DepUnPackDep;
+   Remove = &DepRemove;
+   LoopCount = -1;
+
+   // Sort
+   Me = this;
+   qsort(List,End - List,sizeof(*List),&OrderCompareA);
+   
+   if (DoRun() == false)
+      return false;
+   
+   Secondary = 0;
+   if (DoRun() == false)
+      return false;
+
+   LoopCount = 0;
+   RevDepends = 0;
+   Remove = 0;             // Otherwise the libreadline remove problem occures
+   if (DoRun() == false)
+      return false;
+
+   LoopCount = 0;
+   Primary = &DepUnPackPre;
+   if (DoRun() == false)
+      return false;
+
+/*   cout << "----------END" << endl;
+
+   for (iterator I = List; I != End; I++)
+   {
+      PkgIterator P(Cache,*I);
+      cout << P.Name() << endl;
+   }*/
+
+   return true;
+}
+									/*}}}*/
+// OrderList::OrderConfigure - Perform configuration ordering		/*{{{*/
+// ---------------------------------------------------------------------
+/* This orders by depends only and produces an order which is suitable
+   for configuration */
+bool pkgOrderList::OrderConfigure()
+{
+   Primary = &DepConfigure;
+   Secondary = 0;
+   RevDepends = 0;
+   Remove = 0;
+   LoopCount = -1;
+   return DoRun();
+}
+									/*}}}*/
+
+// OrderList::Score - Score the package for sorting			/*{{{*/
+// ---------------------------------------------------------------------
+/* Higher scores order earlier */
+int pkgOrderList::Score(PkgIterator Pkg)
+{
+   // Removal is always done first
+   if (Cache[Pkg].Delete() == true)
+      return 200;
+
+   int Score = 0;
+   if ((Pkg->Flags & pkgCache::Flag::Essential) == pkgCache::Flag::Essential)
+      Score += 100;
+
+   for (DepIterator D = Cache[Pkg].InstVerIter(Cache).DependsList(); 
+	D.end() == false; D++)
+      if (D->Type == pkgCache::Dep::PreDepends)
+      {
+	 Score += 50;
+	 break;
+      }
+      
+   // Important Required Standard Optional Extra
+   signed short PrioMap[] = {0,5,4,3,1,0};
+   if (Cache[Pkg].InstVerIter(Cache)->Priority <= 5)
+      Score += PrioMap[Cache[Pkg].InstVerIter(Cache)->Priority];
+   return Score;
+}
+									/*}}}*/
+// OrderList::FileCmp - Compare by package file				/*{{{*/
+// ---------------------------------------------------------------------
+/* This compares by the package file that the install version is in. */
+int pkgOrderList::FileCmp(PkgIterator A,PkgIterator B)
+{
+   if (Cache[A].Delete() == true && Cache[B].Delete() == true)
+      return 0;
+   if (Cache[A].Delete() == true)
+      return -1;
+   if (Cache[B].Delete() == true)
+      return 1;
+   
+   if (Cache[A].InstVerIter(Cache).FileList().end() == true)
+      return -1;
+   if (Cache[A].InstVerIter(Cache).FileList().end() == true)
+      return 1;
+   
+   pkgCache::PackageFile *FA = Cache[A].InstVerIter(Cache).FileList().File();
+   pkgCache::PackageFile *FB = Cache[B].InstVerIter(Cache).FileList().File();
+   if (FA < FB)
+      return -1;
+   if (FA > FB)
+      return 1;
+   return 0;
+}
+									/*}}}*/
+// OrderList::OrderCompareA - Order the installation by op		/*{{{*/
+// ---------------------------------------------------------------------
+/* This provides a first-pass sort of the list and gives a decent starting
+    point for further complete ordering. It is used by OrderUnpack only */
+int pkgOrderList::OrderCompareA(const void *a, const void *b)
+{
+   PkgIterator A(Me->Cache,*(Package **)a);
+   PkgIterator B(Me->Cache,*(Package **)b);
+
+   if (A.State() != pkgCache::PkgIterator::NeedsNothing && 
+       B.State() == pkgCache::PkgIterator::NeedsNothing)
+      return -1;
+
+   if (A.State() == pkgCache::PkgIterator::NeedsNothing && 
+       B.State() != pkgCache::PkgIterator::NeedsNothing)
+      return 1;
+   
+   int ScoreA = Me->Score(A);
+   int ScoreB = Me->Score(B);
+   if (ScoreA > ScoreB)
+      return -1;
+   
+   if (ScoreA < ScoreB)
+      return 1;
+
+   return strcmp(A.Name(),B.Name());
+}
+									/*}}}*/
+// OrderList::OrderCompareB - Order the installation by source		/*{{{*/
+// ---------------------------------------------------------------------
+/* This orders by installation source. This is usefull to handle
+   inter-source breaks */
+int pkgOrderList::OrderCompareB(const void *a, const void *b)
+{
+   PkgIterator A(Me->Cache,*(Package **)a);
+   PkgIterator B(Me->Cache,*(Package **)b);
+
+   if (A.State() != pkgCache::PkgIterator::NeedsNothing && 
+       B.State() == pkgCache::PkgIterator::NeedsNothing)
+      return -1;
+
+   if (A.State() == pkgCache::PkgIterator::NeedsNothing && 
+       B.State() != pkgCache::PkgIterator::NeedsNothing)
+      return 1;
+   
+   int F = Me->FileCmp(A,B);
+   if (F != 0)
+   {
+      if (F > 0)
+	 return -1;
+      return 1;
+   }
+   
+   int ScoreA = Me->Score(A);
+   int ScoreB = Me->Score(B);
+   if (ScoreA > ScoreB)
+      return -1;
+   
+   if (ScoreA < ScoreB)
+      return 1;
+
+   return strcmp(A.Name(),B.Name());
+}
+									/*}}}*/
+
+// OrderList::VisitDeps - Visit forward install dependencies		/*{{{*/
+// ---------------------------------------------------------------------
+/* This calls the dependency function for the normal forwards dependencies
+   of the package */
+bool pkgOrderList::VisitDeps(DepFunc F,PkgIterator Pkg)
+{
+   if (F == 0 || Pkg.end() == true || Cache[Pkg].InstallVer == 0)
+      return true;
+   
+   return (this->*F)(Cache[Pkg].InstVerIter(Cache).DependsList());
+}
+									/*}}}*/
+// OrderList::VisitRDeps - Visit reverse dependencies			/*{{{*/
+// ---------------------------------------------------------------------
+/* This calls the dependency function for all of the normal reverse depends
+   of the package */
+bool pkgOrderList::VisitRDeps(DepFunc F,PkgIterator Pkg)
+{
+   if (F == 0 || Pkg.end() == true)
+      return true;
+   
+   return (this->*F)(Pkg.RevDependsList());
+}
+									/*}}}*/
+// OrderList::VisitRProvides - Visit provides reverse dependencies	/*{{{*/
+// ---------------------------------------------------------------------
+/* This calls the dependency function for all reverse dependencies
+   generated by the provides line on the package. */
+bool pkgOrderList::VisitRProvides(DepFunc F,VerIterator Ver)
+{
+   if (F == 0 || Ver.end() == true)
+      return true;
+   
+   bool Res = true;
+   for (PrvIterator P = Ver.ProvidesList(); P.end() == false; P++)
+      Res &= (this->*F)(P.ParentPkg().RevDependsList());
+   return true;
+}
+									/*}}}*/
+// OrderList::VisitProvides - Visit all of the providing packages	/*{{{*/
+// ---------------------------------------------------------------------
+/* This routine calls visit on all providing packages. */
+bool pkgOrderList::VisitProvides(DepIterator D)
+{
+   Version **List = D.AllTargets();
+   for (Version **I = List; *I != 0; I++)
+   {
+      VerIterator Ver(Cache,*I);
+      PkgIterator Pkg = Ver.ParentPkg();
+      
+      if (Cache[Pkg].Keep() == true)
+	 continue;
+      
+      if (D->Type != pkgCache::Dep::Conflicts && Cache[Pkg].InstallVer != *I)
+	 continue;
+      
+      if (D->Type == pkgCache::Dep::Conflicts && (Version *)Pkg.CurrentVer() != *I)
+	 continue;
+      
+      if (VisitNode(Pkg) == false)
+      {
+	 delete [] List;
+	 return false;
+      }
+   }
+   delete [] List;
+   return true;
+}
+									/*}}}*/
+// OrderList::VisitNode - Recursive ordering director			/*{{{*/
+// ---------------------------------------------------------------------
+/* This is the core ordering routine. It calls the set dependency
+   consideration functions which then potentialy call this again. Finite
+   depth is achived through the colouring mechinism. */
+bool pkgOrderList::VisitNode(PkgIterator Pkg)
+{
+   // Looping or irrelevent.
+   if (Pkg.end() == true || IsFlag(Pkg,Added) == true || 
+       IsFlag(Pkg,AddPending) == true || IsFlag(Pkg,InList) == false)
+      return true;
+
+/* for (int j = 0; j != Depth; j++) cout << ' ';
+ cout << "Visit " << Pkg.Name() << endl;*/
+   Depth++;
+   
+   // Color grey
+   Flag(Pkg,AddPending);
+
+   DepFunc Old = Primary;
+   
+   // Perform immedate configuration of the package if so flagged.
+   if (IsFlag(Pkg,Immediate) == true && Primary != &DepUnPackPre)
+      Primary = &DepUnPackPreD;
+      
+   bool Res = true;
+   if (Cache[Pkg].Delete() == false)
+   {
+      // Primary
+      Res &= Res && VisitDeps(Primary,Pkg);
+      Res &= Res && VisitRDeps(Primary,Pkg);
+      Res &= Res && VisitRProvides(Primary,Pkg.CurrentVer());
+      Res &= Res && VisitRProvides(Primary,Cache[Pkg].InstVerIter(Cache));
+      
+      // RevDep
+      Res &= Res && VisitRDeps(RevDepends,Pkg);
+      Res &= Res && VisitRProvides(RevDepends,Pkg.CurrentVer());
+      Res &= Res && VisitRProvides(RevDepends,Cache[Pkg].InstVerIter(Cache));
+	
+      // Secondary
+      Res &= Res && VisitDeps(Secondary,Pkg);
+      Res &= Res && VisitRDeps(Secondary,Pkg);
+      Res &= Res && VisitRProvides(Secondary,Pkg.CurrentVer());
+      Res &= Res && VisitRProvides(Secondary,Cache[Pkg].InstVerIter(Cache));
+   }
+   else
+   { 
+      // RevDep
+      Res &= Res && VisitRDeps(Remove,Pkg);
+      Res &= Res && VisitRProvides(Remove,Pkg.CurrentVer());
+   }
+
+   if (IsFlag(Pkg,Added) == false)
+   {
+      Flag(Pkg,Added,Added | AddPending);
+      *End = Pkg;
+      End++;
+   }
+   
+   Primary = Old;
+   Depth--;
+   
+/* for (int j = 0; j != Depth; j++) cout << ' ';
+   cout << "Leave " << Pkg.Name() << ' ' << IsFlag(Pkg,Added) << ',' << IsFlag(Pkg,AddPending) << endl;*/
+
+   return true;
+}
+									/*}}}*/
+
+// OrderList::DepUnPackCrit - Critical UnPacking ordering		/*{{{*/
+// ---------------------------------------------------------------------
+/* Critical unpacking ordering strives to satisfy Conflicts: and 
+   PreDepends: only. When a prdepends is encountered the Primary 
+   DepFunc is changed to be DepUnPackPreD. 
+
+   Loops are preprocessed and logged. */
+bool pkgOrderList::DepUnPackCrit(DepIterator D)
+{
+   for (; D.end() == false; D++)
+   {
+      if (D.Reverse() == true)
+      {
+	 /* Reverse depenanices are only interested in conflicts,
+	    predepend breakage is ignored here */
+	 if (D->Type != pkgCache::Dep::Conflicts)
+	    continue;
+
+	 // Duplication elimination, consider only the current version
+	 if (D.ParentPkg().CurrentVer() != D.ParentVer())
+	    continue;
+	 
+	 /* For reverse dependencies we wish to check if the
+	    dependency is satisifed in the install state. The
+	    target package (caller) is going to be in the installed
+	    state. */
+	 if (CheckDep(D) == true)
+	    continue;
+
+	 if (VisitNode(D.ParentPkg()) == false)
+	    return false;
+      }
+      else
+      {
+	 /* Forward critical dependencies MUST be correct before the 
+	    package can be unpacked. */
+	 if (D->Type != pkgCache::Dep::Conflicts && D->Type != pkgCache::Dep::PreDepends)
+	    continue;
+	 	 	 	 
+	 /* We wish to check if the dep is okay in the now state of the
+	    target package against the install state of this package. */
+	 if (CheckDep(D) == true)
+	 {
+	    /* We want to catch predepends loops with the code below.
+	       Conflicts loops that are Dep OK are ignored */
+	    if (IsFlag(D.TargetPkg(),AddPending) == false ||
+		D->Type != pkgCache::Dep::PreDepends)
+	       continue;
+	 }
+
+	 // This is the loop detection
+	 if (IsFlag(D.TargetPkg(),Added) == true || 
+	     IsFlag(D.TargetPkg(),AddPending) == true)
+	 {
+	    if (IsFlag(D.TargetPkg(),AddPending) == true)
+	       AddLoop(D);
+	    continue;
+	 }
+
+	 /* Predepends require a special ordering stage, they must have
+	    all dependents installed as well */
+	 DepFunc Old = Primary;
+	 bool Res = false;
+	 if (D->Type == pkgCache::Dep::PreDepends)
+	    Primary = &DepUnPackPreD;
+	 Res = VisitProvides(D);
+	 Primary = Old;
+	 if (Res == false)
+	    return false;
+      }	 
+   }   
+   return true;
+}
+									/*}}}*/
+// OrderList::DepUnPackPreD - Critical UnPacking ordering with depends	/*{{{*/
+// ---------------------------------------------------------------------
+/* Critical PreDepends (also configure immediate and essential) strives to
+   ensure not only that all conflicts+predepends are met but that this
+   package will be immediately configurable when it is unpacked. 
+
+   Loops are preprocessed and logged. */
+bool pkgOrderList::DepUnPackPreD(DepIterator D)
+{
+   if (D.Reverse() == true)
+      return DepUnPackCrit(D);
+   
+   for (; D.end() == false; D++)
+   {
+      if (D.IsCritical() == false)
+	 continue;
+
+      /* We wish to check if the dep is okay in the now state of the
+         target package against the install state of this package. */
+      if (CheckDep(D) == true)
+      {
+	 /* We want to catch predepends loops with the code below.
+	    Conflicts loops that are Dep OK are ignored */
+	 if (IsFlag(D.TargetPkg(),AddPending) == false ||
+	     D->Type != pkgCache::Dep::PreDepends)
+	    continue;
+      }
+      
+      // This is the loop detection
+      if (IsFlag(D.TargetPkg(),Added) == true || 
+	  IsFlag(D.TargetPkg(),AddPending) == true)
+      {
+	 if (IsFlag(D.TargetPkg(),AddPending) == true)
+	    AddLoop(D);
+	 continue;
+      }
+      
+      if (VisitProvides(D) == false)
+	 return false;
+   }   
+   return true;
+}
+									/*}}}*/
+// OrderList::DepUnPackPre - Critical Predepends ordering		/*{{{*/
+// ---------------------------------------------------------------------
+/* Critical PreDepends (also configure immediate and essential) strives to
+   ensure not only that all conflicts+predepends are met but that this
+   package will be immediately configurable when it is unpacked. 
+
+   Loops are preprocessed and logged. All loops will be fatal. */
+bool pkgOrderList::DepUnPackPre(DepIterator D)
+{
+   if (D.Reverse() == true)
+      return true;
+   
+   for (; D.end() == false; D++)
+   {
+      /* Only consider the PreDepends or Depends. Depends are only
+       	 considered at the lowest depth or in the case of immediate
+       	 configure */
+      if (D->Type != pkgCache::Dep::PreDepends)
+      {
+	 if (D->Type == pkgCache::Dep::Depends)
+	 {
+	    if (Depth == 1 && IsFlag(D.ParentPkg(),Immediate) == false)
+	       continue;
+	 }
+	 else
+	    continue;
+      }
+
+      /* We wish to check if the dep is okay in the now state of the
+         target package against the install state of this package. */
+      if (CheckDep(D) == true)
+      {
+	 /* We want to catch predepends loops with the code below.
+	    Conflicts loops that are Dep OK are ignored */
+	 if (IsFlag(D.TargetPkg(),AddPending) == false)
+	    continue;
+      }
+      
+      // This is the loop detection
+      if (IsFlag(D.TargetPkg(),Added) == true || 
+	  IsFlag(D.TargetPkg(),AddPending) == true)
+      {
+	 if (IsFlag(D.TargetPkg(),AddPending) == true)
+	    AddLoop(D);
+	 continue;
+      }
+      
+      if (VisitProvides(D) == false)
+	 return false;
+   }   
+   return true;
+}
+									/*}}}*/
+// OrderList::DepUnPackDep - Reverse dependency considerations		/*{{{*/
+// ---------------------------------------------------------------------
+/* Reverse dependencies are considered to determine if unpacking this
+   package will break any existing dependencies. If so then those
+   packages are ordered before this one so that they are in the
+   UnPacked state. 
+ 
+   The forwards depends loop is designed to bring the packages dependents
+   close to the package. This helps reduce deconfigure time. 
+   
+   Loops are irrelevent to this. */
+bool pkgOrderList::DepUnPackDep(DepIterator D)
+{
+   
+   for (; D.end() == false; D++)
+      if (D.IsCritical() == true)
+      {
+	 if (D.Reverse() == true)
+	 {
+	    /* Duplication prevention. We consider rev deps only on
+	       the current version, a not installed package
+	       cannot break */
+	    if (D.ParentPkg()->CurrentVer == 0 ||
+		D.ParentPkg().CurrentVer() != D.ParentVer())
+	       continue;
+
+	    // The dep will not break so it is irrelevent.
+	    if (CheckDep(D) == true)
+	       continue;
+	    
+	    if (VisitNode(D.ParentPkg()) == false)
+	       return false;
+	 }
+	 else
+	    if (D->Type == pkgCache::Dep::Depends)
+	       if (VisitProvides(D) == false)
+		  return false;
+      }
+   return true;
+}
+									/*}}}*/
+// OrderList::DepConfigure - Configuration ordering			/*{{{*/
+// ---------------------------------------------------------------------
+/* Configuration only ordering orders by the Depends: line only. It
+   orders configuration so that when a package comes to be configured it's
+   dependents are configured. 
+ 
+   Loops are ingored. Depends loop entry points are chaotic. */
+bool pkgOrderList::DepConfigure(DepIterator D)
+{
+   // Never consider reverse configuration dependencies.
+   if (D.Reverse() == true)
+      return true;
+   
+   for (; D.end() == false; D++)
+      if (D->Type == pkgCache::Dep::Depends)
+	 if (VisitProvides(D) == false)
+	    return false;
+   return true;
+}
+									/*}}}*/
+// OrderList::DepRemove - Removal ordering				/*{{{*/
+// ---------------------------------------------------------------------
+/* Removal visits all reverse depends. It considers if the dependency
+   of the Now state version to see if it is okay with removing this
+   package. This check should always fail, but is provided for symetery
+   with the other critical handlers.
+ 
+   Loops are preprocessed and logged. Removal loops can also be
+   detected in the critical handler. They are characterized by an
+   old version of A depending on B but the new version of A conflicting
+   with B, thus either A or B must break to install. */
+bool pkgOrderList::DepRemove(DepIterator D)
+{
+   if (D.Reverse() == false)
+      return true;
+   for (; D.end() == false; D++)
+      if (D->Type == pkgCache::Dep::Depends || D->Type == pkgCache::Dep::PreDepends)
+      {
+	 // Duplication elimination, consider the current version only
+	 if (D.ParentPkg().CurrentVer() != D.ParentVer())
+	    continue;
+
+	 /* We wish to see if the dep on the parent package is okay
+	    in the removed (install) state of the target pkg. */	 
+	 if (CheckDep(D) == true)
+	 {
+	    // We want to catch loops with the code below.
+	    if (IsFlag(D.ParentPkg(),AddPending) == false)
+	       continue;
+	 }
+
+	 // This is the loop detection
+	 if (IsFlag(D.ParentPkg(),Added) == true || 
+	     IsFlag(D.ParentPkg(),AddPending) == true)
+	 {
+	    if (IsFlag(D.ParentPkg(),AddPending) == true)
+	       AddLoop(D);
+	    continue;
+	 }
+
+	 if (VisitNode(D.ParentPkg()) == false)
+	    return false;
+      }
+   
+   return true;
+}
+									/*}}}*/
+
+// OrderList::AddLoop - Add a loop to the loop list			/*{{{*/
+// ---------------------------------------------------------------------
+/* We record the loops. This is a relic since loop breaking is done 
+   genericaly as part of the safety routines. */
+bool pkgOrderList::AddLoop(DepIterator D)
+{
+   if (LoopCount < 0 || LoopCount >= 20)
+      return false;  
+   
+   // Skip dups
+   if (LoopCount != 0)
+   {
+      if (Loops[LoopCount - 1].ParentPkg() == D.ParentPkg() ||
+	  Loops[LoopCount - 1].TargetPkg() == D.ParentPkg())
+	 return true;
+   }
+   
+   Loops[LoopCount++] = D;
+   
+   // Mark the packages as being part of a loop.
+   Flag(D.TargetPkg(),Loop);
+   Flag(D.ParentPkg(),Loop);
+   return true;
+}
+									/*}}}*/
+// OrderList::WipeFlags - Unset the given flags from all packages	/*{{{*/
+// ---------------------------------------------------------------------
+/* */
+void pkgOrderList::WipeFlags(unsigned long F)
+{
+   unsigned long Size = Cache.HeaderP->PackageCount;
+   for (unsigned long I = 0; I != Size; I++)
+      Flags[I] &= ~F;
+}
+									/*}}}*/
+// OrderList::CheckDep - Check a dependency for truth			/*{{{*/
+// ---------------------------------------------------------------------
+/* This performs a complete analysis of the dependency wrt to the
+   current add list. It returns true if after all events are
+   performed it is still true. This sort of routine can be approximated
+   by examining the DepCache, however in convoluted cases of provides
+   this fails to produce a suitable result. */
+bool pkgOrderList::CheckDep(DepIterator D)
+{
+   Version **List = D.AllTargets();
+   for (Version **I = List; *I != 0; I++)
+   {
+      VerIterator Ver(Cache,*I);
+      PkgIterator Pkg = Ver.ParentPkg();
+      
+      /* The meaning of Added and AddPending is subtle. AddPending is
+       	 an indication that the package is looping. Because of the
+       	 way ordering works Added means the package will be unpacked
+       	 before this one and AddPending means after. It is therefore
+       	 correct to ignore AddPending in all cases, but that exposes
+       	 reverse-ordering loops which should be ignore. */
+      if (IsFlag(Pkg,Added) == true || 
+	  (IsFlag(Pkg,AddPending) == true && D.Reverse() == true))
+      {
+	 if (Cache[Pkg].InstallVer != *I)
+	    continue;
+      }
+      else
+	 if ((Version *)Pkg.CurrentVer() != *I || 
+	     Pkg.State() != PkgIterator::NeedsNothing)
+	    continue;
+      
+      delete [] List;
+      
+      /* Conflicts requires that all versions are not present, depends
+         just needs one */
+      if (D->Type != pkgCache::Dep::Conflicts)
+	 return true;
+      else
+	 return false;
+   }
+   delete [] List;
+ 
+   /* Conflicts requires that all versions are not present, depends
+      just needs one */
+   if (D->Type == pkgCache::Dep::Conflicts)
+      return true;
+   return false;
+}
+									/*}}}*/