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-<!-- -*- mode: sgml; mode: fold -*- -->
-<!doctype debiandoc  PUBLIC  "-//DebianDoc//DTD DebianDoc//EN">
-<book>
-<title>APT Cache File Format</title>
-
-<author>Jason Gunthorpe <email>jgg@debian.org</email></author>
-<version>$Id: cache.sgml,v 1.11 2003/02/12 15:05:44 doogie Exp $</version>
-
-<abstract>
-This document describes the complete implementation and format of the APT
-Cache file. The APT Cache file is a way for APT to parse and store a 
-large number of package files for display in the UI. It's primary design 
-goal is to make display of a single package in the tree very fast by 
-pre-linking important things like dependencies and provides.
-
-The specification doubles as documentation for one of the in-memory 
-structures used by the package library and the APT GUI.
-
-</abstract>
-
-<copyright>
-Copyright &copy; Jason Gunthorpe, 1997-1998.
-<p>
-APT and this document are free software; you can redistribute them and/or
-modify them under the terms of the GNU General Public License as published
-by the Free Software Foundation; either version 2 of the License, or (at your
-option) any later version.
-
-<p>
-For more details, on Debian GNU/Linux systems, see the file
-/usr/share/common-licenses/GPL for the full license.
-</copyright>
-
-<toc sect>
-
-<chapt>Introduction
-<!-- Purpose		                                               {{{ -->
-<!-- ===================================================================== -->
-<sect>Purpose
-
-<p>
-This document describes the implementation of an architecture
-dependent binary cache file. The goal of this cache file is two fold, 
-firstly to speed loading and processing of the package file array and
-secondly to reduce memory consumption of the package file array.
-
-<p>
-The implementation is aimed at an environment with many primary package
-files, for instance someone that has a Package file for their CD-ROM, a
-Package file for the latest version of the distribution on the CD-ROM and a
-package file for the development version. Always present is the information
-contained in the status file which might be considered a separate package
-file.
-
-<p>
-Please understand, this is designed as a -CACHE FILE- it is not meant to be
-used on any system other than the one it was created for. It is not meant to
-be authoritative either, i.e. if a system crash or software failure occurs it
-must be perfectly acceptable for the cache file to be in an inconsistent
-state. Furthermore at any time the cache file may be erased without losing
-any information.
-
-<p>
-Also the structures and storage layout is optimized for use by the APT
-GUI and may not be suitable for all purposes. However it should be possible 
-to extend it with associate cache files that contain other information.
-
-<p>
-To keep memory use down the cache file only contains often used fields and
-fields that are inexpensive to store, the Package file has a full list of
-fields. Also the client may assume that all items are perfectly valid and
-need not perform checks against their correctness. Removal of information
-from the cache is possible, but blanks will be left in the file, and
-unused strings will also be present. The recommended implementation is to
-simply rebuild the cache each time any of the data files change. It is
-possible to add a new package file to the cache without any negative side
-effects.
-
-<sect1>Note on Pointer access
-<p>
-Every item in every structure is stored as the index to that structure.
-What this means is that once the files is mmaped every data access has to
-go through a fixup stage to get a real memory pointer. This is done
-by taking the index, multiplying it by the type size and then adding
-it to the start address of the memory block. This sounds complex, but
-in C it is a single array dereference. Because all items are aligned to 
-their size and indexes are stored as multiples of the size of the structure
-the format is immediately portable to all possible architectures - BUT the
-generated files are -NOT-.
-
-<p>
-This scheme allows code like this to be written:
-<example>
-  void *Map = mmap(...);
-  Package *PkgList = (Package *)Map;
-  Header *Head = (Header *)Map;
-  char *Strings = (char *)Map;
-  cout << (Strings + PkgList[Head->HashTable[0]]->Name) << endl;
-</example>
-<p>
-Notice the lack of casting or multiplication. The net result is to return
-the name of the first package in the first hash bucket, without error
-checks. 
-
-<p>
-The generator uses allocation pools to group similarly sized structures in
-large blocks to eliminate any alignment overhead. The generator also
-assures that no structures overlap and all indexes are unique. Although
-at first glance it may seem like there is the potential for two structures
-to exist at the same point the generator never allows this to happen.
-(See the discussion of free space pools)
-                                                                  <!-- }}} -->
-
-<chapt>Structures
-<!-- Header		                                               {{{ -->
-<!-- ===================================================================== -->
-<sect>Header
-<p>
-This is the first item in the file.
-<example>
-   struct Header
-   {
-      // Signature information
-      unsigned long Signature;
-      short MajorVersion;
-      short MinorVersion;
-      bool Dirty;
-       
-      // Size of structure values
-      unsigned short HeaderSz;
-      unsigned short PackageSz;
-      unsigned short PackageFileSz;
-      unsigned short VersionSz;
-      unsigned short DependencySz;
-      unsigned short ProvidesSz;
-      unsigned short VerFileSz;
-      
-      // Structure counts
-      unsigned long PackageCount;
-      unsigned long VersionCount;
-      unsigned long DependsCount;
-      unsigned long PackageFileCount;
-      
-      // Offsets
-      unsigned long FileList;              // PackageFile
-      unsigned long StringList;            // StringItem
-      unsigned long VerSysName;            // StringTable
-      unsigned long Architecture;          // StringTable
-      unsigned long MaxVerFileSize;
-      
-      // Allocation pools
-      struct
-      {
-         unsigned long ItemSize;
-	 unsigned long Start;
-	 unsigned long Count;
-      } Pools[7];
-
-      // Package name lookup
-      unsigned long HashTable[2*1024];        // Package
-   };
-</example>
-<taglist>
-<tag>Signature<item>
-This must contain the hex value 0x98FE76DC which is designed to verify
-that the system loading the image has the same byte order and byte size as
-the system saving the image
-
-<tag>MajorVersion
-<tag>MinorVersion<item>
-These contain the version of the cache file, currently 0.2.
-
-<tag>Dirty<item>
-Dirty is true if the cache file was opened for reading, the client expects
-to have written things to it and have not fully synced it. The file should
-be erased and rebuilt if it is true.
-
-<tag>HeaderSz
-<tag>PackageSz
-<tag>PackageFileSz
-<tag>VersionSz
-<tag>DependencySz
-<tag>VerFileSz
-<tag>ProvidesSz<item>
-*Sz contains the sizeof() that particular structure. It is used as an
-extra consistency check on the structure of the file.
-
-If any of the size values do not exactly match what the client expects then
-the client should refuse the load the file.
-
-<tag>PackageCount
-<tag>VersionCount
-<tag>DependsCount
-<tag>PackageFileCount<item>
-These indicate the number of each structure contained in the cache. 
-PackageCount is especially useful for generating user state structures. 
-See Package::Id for more info.
-
-<tag>VerSysName<item>
-String representing the version system used for this cache
-
-<tag>Architecture<item>
-Architecture the cache was built against.
-
-<tag>MaxVerFileSize<item>
-The maximum size of a raw entry from the original Package file 
-(i.e. VerFile::Size) is stored here.
-
-<tag>FileList<item>
-This contains the index of the first PackageFile structure. The PackageFile
-structures are singly linked lists that represent all package files that
-have been merged into the cache.
-
-<tag>StringList<item>
-This contains a list of all the unique strings (string item type strings) in 
-the cache. The parser reads this list into memory so it can match strings 
-against it.
-
-<tag>Pools<item>
-The Pool structures manage the allocation pools that the generator uses.
-Start indicates the first byte of the pool, Count is the number of objects
-remaining in the pool and ItemSize is the structure size (alignment factor)
-of the pool. An ItemSize of 0 indicates the pool is empty. There should be 
-the same number of pools as there are structure types. The generator 
-stores this information so future additions can make use of any unused pool 
-blocks.
-
-<tag>HashTable<item>
-HashTable is a hash table that provides indexing for all of the packages.
-Each package name is inserted into the hash table using the following has
-function:
-<example>
-   unsigned long Hash(string Str)
-   {
-      unsigned long Hash = 0;
-      for (const char *I = Str.begin(); I != Str.end(); I++)
-         Hash += *I * ((Str.end() - I + 1));
-      return Hash % _count(Head.HashTable);
-   }
-</example>
-<p>
-By iterating over each entry in the hash table it is possible to iterate over 
-the entire list of packages. Hash Collisions are handled with a singly linked
-list of packages based at the hash item. The linked list contains only 
-packages that match the hashing function.
-
-</taglist>
-                                                                  <!-- }}} -->
-<!-- Package		                                               {{{ -->
-<!-- ===================================================================== -->
-<sect>Package
-<p>
-This contains information for a single unique package. There can be any
-number of versions of a given package. Package exists in a singly
-linked list of package records starting at the hash index of the name in 
-the Header->HashTable.
-<example>
-   struct Pacakge
-   {
-      // Pointers
-      unsigned long Name;              // Stringtable
-      unsigned long VersionList;       // Version
-      unsigned long CurrentVer;        // Version
-      unsigned long Section;           // StringTable (StringItem)
-      
-      // Linked lists 
-      unsigned long NextPackage;       // Package
-      unsigned long RevDepends;        // Dependency
-      unsigned long ProvidesList;      // Provides
-       
-      // Install/Remove/Purge etc
-      unsigned char SelectedState;     // What
-      unsigned char InstState;         // Flags
-      unsigned char CurrentState;      // State
-
-      // Unique ID for this pkg
-      unsigned short ID;
-      unsigned long Flags;
-   };
-</example>   
-
-<taglist>
-<tag>Name<item>
-Name of the package.
-
-<tag>VersionList<item>
-Base of a singly linked list of version structures. Each structure 
-represents a unique version of the package. The version structures
-contain links into PackageFile and the original text file as well as
-detailed information about the size and dependencies of the specific
-package. In this way multiple versions of a package can be cleanly handled
-by the system. Furthermore, this linked list is guaranteed to be sorted
-from Highest version to lowest version with no duplicate entries.
-
-<tag>CurrentVer<item>
-CurrentVer is an index to the installed version, either can be
-0.
-
-<tag>Section<item>
-This indicates the deduced section. It should be "Unknown" or the section
-of the last parsed item.
-
-<tag>NextPackage<item>
-Next link in this hash item. This linked list is based at Header.HashTable
-and contains only packages with the same hash value.
-
-<tag>RevDepends<item>
-Reverse Depends is a linked list of all dependencies linked to this package.
-
-<tag>ProvidesList<item>
-This is a linked list of all provides for this package name.
-
-<tag>SelectedState
-<tag>InstState
-<tag>CurrentState<item>
-These correspond to the 3 items in the Status field found in the status
-file. See the section on defines for the possible values.
-<p>
-SelectedState is the state that the user wishes the package to be
-in.
-<p>
-InstState is the installation state of the package. This normally
-should be OK, but if the installation had an accident it may be otherwise.
-<p>
-CurrentState indicates if the package is installed, partially installed or
-not installed.
-
-<tag>ID<item>
-ID is a value from 0 to Header->PackageCount. It is a unique value assigned
-by the generator. This allows clients to create an array of size PackageCount
-and use it to store state information for the package map. For instance the
-status file emitter uses this to track which packages have been emitted 
-already.
-
-<tag>Flags<item>
-Flags are some useful indicators of the package's state. 
-
-</taglist>
-
-                                                                  <!-- }}} -->
-<!-- PackageFile	                                               {{{ -->
-<!-- ===================================================================== -->
-<sect>PackageFile
-<p>
-This contains information for a single package file. Package files are
-referenced by Version structures. This is a singly linked list based from
-Header.FileList
-<example>
-   struct PackageFile
-   {
-      // Names
-      unsigned long FileName;        // Stringtable
-      unsigned long Archive;         // Stringtable
-      unsigned long Component;       // Stringtable
-      unsigned long Version;         // Stringtable
-      unsigned long Origin;          // Stringtable
-      unsigned long Label;           // Stringtable
-      unsigned long Architecture;    // Stringtable
-      unsigned long Site;            // Stringtable
-      unsigned long IndexType;       // Stringtable
-      unsigned long Size;            
-
-      // Linked list
-      unsigned long NextFile;        // PackageFile
-      unsigned short ID;
-      unsigned long Flags;
-      time_t mtime;                  // Modification time
-   };
-</example>   
-<taglist>
-
-<tag>FileName<item>
-Refers the the physical disk file that this PacakgeFile represents.
-
-<tag>Archive
-<tag>Component
-<tag>Version
-<tag>Origin
-<tag>Label
-<tag>Architecture
-<tag>NotAutomatic<item>
-This is the release information. Please see the files document for a 
-description of what the release information means.
-
-<tag>Site<item>
-The site the index file was fetched from.
-
-<tag>IndexType<item>
-A string indicating what sort of index file this is.
-
-<tag>Size<item>
-Size is provided as a simple check to ensure that the package file has not
-been altered.
-
-<tag>ID<item>
-See Package::ID.
-
-<tag>Flags<item>
-Provides some flags for the PackageFile, see the section on defines.
-
-<tag>mtime<item>
-Modification time for the file at time of cache generation.
-
-</taglist>
-
-                                                                  <!-- }}} -->
-<!-- Version		                                               {{{ -->
-<!-- ===================================================================== -->
-<sect>Version
-<p>
-This contains the information for a single version of a package. This is a
-single linked list based from Package.Versionlist.
-
-<p>
-The version list is always sorted from highest version to lowest version by
-the generator. Also there may not be any duplicate entries in the list (same 
-VerStr).
-
-<example>
-   struct Version
-   {
-      unsigned long VerStr;            // Stringtable
-      unsigned long Section;           // StringTable (StringItem)
-      unsigned long Arch;              // StringTable
-      
-      // Lists
-      unsigned long FileList;          // VerFile
-      unsigned long NextVer;           // Version
-      unsigned long DependsList;       // Dependency
-      unsigned long ParentPkg;         // Package
-      unsigned long ProvidesList;      // Provides
-      
-      unsigned long Size;
-      unsigned long InstalledSize;
-      unsigned long Hash;
-      unsigned short ID;
-      unsigned char Priority;
-   };
-</example>
-<taglist>
-
-<tag>VerStr<item>
-This is the complete version string.
-
-<tag>FileList<item>
-References the all the PackageFile's that this version came out of. FileList 
-can be used to determine what distribution(s) the Version applies to. If 
-FileList is 0 then this is a blank version. The structure should also have 
-a 0 in all other fields excluding VerStr and Possibly NextVer.
-
-<tag>Section<item>
-This string indicates which section it is part of. The string should be
-contained in the StringItem list.
-
-<tag>Arch<item>
-Architecture the package was compiled for.
-
-<tag>NextVer<item>
-Next step in the linked list.
-
-<tag>DependsList<item>
-This is the base of the dependency list.
-
-<tag>ParentPkg<item>
-This links the version to the owning package, allowing reverse dependencies
-to determine the package.
-
-<tag>ProvidesList<item>
-Head of the linked list of Provides::NextPkgProv, forward provides.
-
-<tag>Size
-<tag>InstalledSize<item>
-The archive size for this version. For Debian this is the size of the .deb
-file. Installed size is the uncompressed size for this version
-
-<tag>Hash<item>
-This is a characteristic value representing this package. No two packages
-in existence should have the same VerStr and Hash with different contents.
-
-<tag>ID<item>
-See Package::ID.
-
-<tag>Priority<item>
-This is the parsed priority value of the package.
-</taglist>
-
-                                                                  <!-- }}} -->
-<!-- Dependency		                                               {{{ -->
-<!-- ===================================================================== -->
-<sect>Dependency
-<p>
-Dependency contains the information for a single dependency record. The records
-are split up like this to ease processing by the client. The base of list
-linked list is Version.DependsList. All forms of dependencies are recorded
-here including Conflicts, Breaks, Suggests and Recommends.
-
-<p>
-Multiple depends on the same package must be grouped together in 
-the Dependency lists. Clients should assume this is always true.
-
-<example>
-    struct Dependency
-    {
-       unsigned long Version;         // Stringtable
-       unsigned long Package;         // Package
-       unsigned long NextDepends;     // Dependency
-       unsigned long NextRevDepends;  // Reverse dependency linking
-       unsigned long ParentVer;       // Upwards parent version link
-       
-       // Specific types of depends
-       unsigned char Type;
-       unsigned char CompareOp;
-       unsigned short ID;
-    };
-</example>
-<taglist>
-<tag>Version<item>
-The string form of the version that the dependency is applied against.
-
-<tag>Package<item>
-The index of the package file this depends applies to. If the package file
-does not already exist when the dependency is inserted a blank one (no
-version records) should be created.
-
-<tag>NextDepends<item>
-Linked list based off a Version structure of all the dependencies in that
-version.
-
-<tag>NextRevDepends<item>
-Reverse dependency linking, based off a Package structure. This linked list
-is a list of all packages that have a depends line for a given package.
-
-<tag>ParentVer<item>
-Parent version linking, allows the reverse dependency list to link
-back to the version and package that the dependency are for.
-
-<tag>Type<item>
-Describes weather it is depends, predepends, recommends, suggests, etc.
-
-<tag>CompareOp<item>
-Describes the comparison operator specified on the depends line. If the high
-bit is set then it is a logical or with the previous record.
-
-<tag>ID<item>
-See Package::ID.
-
-</taglist>
-
-                                                                  <!-- }}} -->
-<!-- Provides		                                               {{{ -->
-<!-- ===================================================================== -->
-<sect>Provides
-<p>
-Provides handles virtual packages. When a Provides: line is encountered 
-a new provides record is added associating the package with a virtual 
-package name. The provides structures are linked off the package structures.
-This simplifies the analysis of dependencies and other aspects A provides 
-refers to a specific version of a specific package, not all versions need to 
-provide that provides.
-
-<p>
-There is a linked list of provided package names started from each 
-version that provides packages. This is the forwards provides mechanism.
-<example>
-    struct Provides
-    {
-       unsigned long ParentPkg;        // Package
-       unsigned long Version;          // Version
-       unsigned long ProvideVersion;   // Stringtable
-       unsigned long NextProvides;     // Provides
-       unsigned long NextPkgProv;      // Provides
-    };
-</example>
-<taglist>
-<tag>ParentPkg<item>
-The index of the package that head of this linked list is in. ParentPkg->Name
-is the name of the provides.
-
-<tag>Version<item>
-The index of the version this provide line applies to.
-
-<tag>ProvideVersion<item>
-Each provides can specify a version in the provides line. This version allows
-dependencies to depend on specific versions of a Provides, as well as allowing
-Provides to override existing packages. This is experimental.
-
-<tag>NextProvides<item>
-Next link in the singly linked list of provides (based off package)
-
-<tag>NextPkgProv<item>
-Next link in the singly linked list of provides for 'Version'.
-
-</taglist>
-
-                                                                  <!-- }}} -->
-<!-- VerFile		                                               {{{ -->
-<!-- ===================================================================== -->
-<sect>VerFile
-<p>
-VerFile associates a version with a PackageFile, this allows a full 
-description of all Versions in all files (and hence all sources) under
-consideration.
-
-<example>
-    struct pkgCache::VerFile
-    {
-       unsigned long File;           // PackageFile
-       unsigned long NextFile;       // PkgVerFile
-       unsigned long Offset;
-       unsigned short Size;
-    }
-</example>
-<taglist>
-<tag>File<item>
-The index of the package file that this version was found in.
-
-<tag>NextFile<item>
-The next step in the linked list.
-
-<tag>Offset
-<tag>Size<item>
-These describe the exact position in the package file for the section from 
-this version.
-</taglist>
-
-                                                                  <!-- }}} -->
-<!-- StringItem		                                               {{{ -->
-<!-- ===================================================================== -->
-<sect>StringItem
-<p>
-StringItem is used for generating single instances of strings. Some things
-like Section Name are are useful to have as unique tags. It is part of 
-a linked list based at Header::StringList.
-<example>
-   struct StringItem
-   {
-      unsigned long String;        // Stringtable
-      unsigned long NextItem;      // StringItem
-   };
-</example>
-<taglist>
-<tag>String<item>
-The string this refers to.
-
-<tag>NextItem<item>
-Next link in the chain.
-</taglist>
-                                                                  <!-- }}} -->
-<!-- StringTable	                                               {{{ -->
-<!-- ===================================================================== -->
-<sect>StringTable
-<p>
-All strings are simply inlined any place in the file that is natural for the
-writer. The client should make no assumptions about the positioning of
-strings. All stringtable values point to a byte offset from the start of the
-file that a null terminated string will begin.
-                                                                  <!-- }}} -->
-<!-- Defines		                                               {{{ -->
-<!-- ===================================================================== -->
-<sect>Defines
-<p>
-Several structures use variables to indicate things. Here is a list of all
-of them.
-
-<sect1>Definitions for Dependency::Type
-<p>
-<example>
-#define pkgDEP_Depends 1
-#define pkgDEP_PreDepends 2
-#define pkgDEP_Suggests 3
-#define pkgDEP_Recommends 4
-#define pkgDEP_Conflicts 5
-#define pkgDEP_Replaces 6
-#define pkgDEP_Breaks 8
-</example>
-</sect1>
-
-<sect1>Definitions for Dependency::CompareOp
-<p>
-<example>
-#define pkgOP_OR 0x10
-#define pkgOP_LESSEQ 0x1
-#define pkgOP_GREATEREQ 0x2
-#define pkgOP_LESS 0x3
-#define pkgOP_GREATER 0x4
-#define pkgOP_EQUALS 0x5
-</example>
-The lower 4 bits are used to indicate what operator is being specified and
-the upper 4 bits are flags. pkgOP_OR indicates that the next package is
-or'd with the current package.
-</sect1>
-
-<sect1>Definitions for Package::SelectedState
-<p>
-<example>
-#define pkgSTATE_Unkown 0
-#define pkgSTATE_Install 1
-#define pkgSTATE_Hold 2
-#define pkgSTATE_DeInstall 3
-#define pkgSTATE_Purge 4
-</example>
-</sect1>
-
-<sect1>Definitions for Package::InstState
-<p>
-<example>
-#define pkgSTATE_Ok 0
-#define pkgSTATE_ReInstReq 1
-#define pkgSTATE_Hold 2
-#define pkgSTATE_HoldReInstReq 3
-</example>
-</sect1>
-
-<sect1>Definitions for Package::CurrentState
-<p>
-<example>
-#define pkgSTATE_NotInstalled 0
-#define pkgSTATE_UnPacked 1
-#define pkgSTATE_HalfConfigured 2
-#define pkgSTATE_UnInstalled 3
-#define pkgSTATE_HalfInstalled 4
-#define pkgSTATE_ConfigFiles 5
-#define pkgSTATE_Installed 6
-#define pkgSTATE_TriggersAwaited 7
-#define pkgSTATE_TriggersPending 8
-</example>
-</sect1>
-
-<sect1>Definitions for Package::Flags
-<p>
-<example>
-#define pkgFLAG_Auto (1 << 0)
-#define pkgFLAG_New (1 << 1)
-#define pkgFLAG_Obsolete (1 << 2)
-#define pkgFLAG_Essential (1 << 3)
-#define pkgFLAG_ImmediateConf (1 << 4)
-</example>
-</sect1>
-
-<sect1>Definitions for Version::Priority
-<p>
-Zero is used for unparsable or absent Priority fields.
-<example>
-#define pkgPRIO_Important 1
-#define pkgPRIO_Required 2
-#define pkgPRIO_Standard 3
-#define pkgPRIO_Optional 4
-#define pkgPRIO_Extra 5
-</example>
-</sect1>
-
-<sect1>Definitions for PackageFile::Flags
-<p>
-<example>
-#define pkgFLAG_NotSource (1 << 0)
-#define pkgFLAG_NotAutomatic (1 << 1)
-</example>
-</sect1>
-
-                                                                  <!-- }}} -->
-
-<chapt>Notes on the Generator
-<!-- Notes on the Generator 	                                       {{{ -->
-<!-- ===================================================================== -->
-<p>
-The pkgCache::MergePackageFile function is currently the only generator of
-the cache file. It implements a conversion from the normal textual package
-file into the cache file.
-
-<p>
-The generator assumes any package declaration with a
-Status: line is a 'Status of the package' type of package declaration. 
-A Package with a Target-Version field should also really have a status field.
-The processing of a Target-Version field can create a place-holder Version
-structure that is empty to refer to the specified version (See Version
-for info on what a empty Version looks like). The Target-Version syntax
-allows the specification of a specific version and a target distribution. 
-
-<p>
-Different section names on different versions is supported, but I 
-do not expect to use it. To simplify the GUI it will merely use the section
-in the Package structure. This should be okay as I hope sections do not change
-much.
-
-<p>
-The generator goes through a number of post processing steps after producing
-a disk file. It sorts all of the version lists to be in descending order
-and then generates the reverse dependency lists for all of the packages.
-ID numbers and count values are also generated in the post processing step.
-
-<p>
-It is possible to extend many of the structures in the cache with extra data.
-This is done by using the ID member. ID will be a unique number from 0 to
-Header->??Count. For example
-<example>
-struct MyPkgData;
-MyPkgData *Data = new MyPkgData[Header->PackageCount];
-Data[Package->ID]->Item = 0;
-</example>
-This provides a one way reference between package structures and user data. To
-get a two way reference would require a member inside the MyPkgData structure.
-
-<p>
-The generators use of free space pools tend to make the package file quite
-large, and quite full of blank space. This could be fixed with sparse files.
-
-                                                                  <!-- }}} -->
-
-<chapt>Future Directions
-<!-- Future Directions		                                       {{{ -->
-<!-- ===================================================================== -->
-<p>
-Some good directions to take the cache file is into a cache directory that
-contains many associated caches that cache other important bits of
-information. (/var/cache/apt, FHS2) 
-
-<p>
-Caching of the info/*.list is an excellent place to start, by generating all
-the list files into a tree structure and reverse linking them to the package
-structures in the main cache file major speed gains in dpkg might be achieved.
-
-                                                                  <!-- }}} -->
-
-</book>