* doc/cache.sgml:

  - drop the file in favor of inplace documentation with doxygen

1 files changed, 385 insertions, 84 deletions

diff --git a/apt-pkg/pkgcache.h b/apt-pkg/pkgcache.h
index 577eebad9..a2e63ff03 100644
--- a/apt-pkg/pkgcache.h
+++ b/apt-pkg/pkgcache.h
@@ -1,20 +1,75 @@
 // -*- mode: cpp; mode: fold -*-
 // Description								/*{{{*/
-// $Id: pkgcache.h,v 1.25 2001/07/01 22:28:24 jgg Exp $
-/* ######################################################################
-   
-   Cache - Structure definitions for the cache file
-   
-   Please see doc/apt-pkg/cache.sgml for a more detailed description of 
-   this format. Also be sure to keep that file up-to-date!!
-   
+/**\file pkgcache.h
+   \brief pkgCache - Structure definitions for the cache file
+
+   The goal of the 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.
+
+   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.
+
+   Please understand, this is designed as a <b>Cache file</b> 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.
+
+   Also the structures and storage layout is optimized for use by the APT
+   and may not be suitable for all purposes. However it should be possible
+   to extend it with associate cache files that contain other information.
+
+   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.
+
+   <b>Note on Pointer access</b>
    Clients should always use the CacheIterators classes for access to the
-   cache. They provide a simple STL-like method for traversing the links
-   of the datastructure.
-   
-   See pkgcachegen.h for information about generating cache structures.
-   
-   ##################################################################### */
+   cache and the data in it. They also provide a simple STL-like method for
+   traversing the links of the datastructure.
+
+   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 fix up 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-.
+
+   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>
+   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.
+
+   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)
+
+   See \ref pkgcachegen.h for more information about generating cache structures. */
 									/*}}}*/
 #ifndef PKGLIB_PKGCACHE_H
 #define PKGLIB_PKGCACHE_H
@@ -66,12 +121,20 @@ class pkgCache								/*{{{*/
    {
       enum DepType {Depends=1,PreDepends=2,Suggests=3,Recommends=4,
 	 Conflicts=5,Replaces=6,Obsoletes=7,DpkgBreaks=8,Enhances=9};
+      /** \brief available compare operators
+
+          The lower 4 bits are used to indicate what operator is being specified and
+          the upper 4 bits are flags. OR indicates that the next package is
+          or'd with the current package. */
       enum DepCompareOp {Or=0x10,NoOp=0,LessEq=0x1,GreaterEq=0x2,Less=0x3,
 	 Greater=0x4,Equals=0x5,NotEquals=0x6};
    };
    
    struct State
    {
+      /** \brief priority of a package version
+
+          Zero is used for unparsable or absent Priority fields. */
       enum VerPriority {Important=1,Required=2,Standard=3,Optional=4,Extra=5};
       enum PkgSelectedState {Unknown=0,Install=1,Hold=2,DeInstall=3,Purge=4};
       enum PkgInstState {Ok=0,ReInstReq=1,HoldInst=2,HoldReInstReq=3};
@@ -120,7 +183,7 @@ class pkgCache								/*{{{*/
    inline unsigned long Hash(const string &S) const {return sHash(S);};
    inline unsigned long Hash(const char *S) const {return sHash(S);};
 
-   // Usefull transformation things
+   // Useful transformation things
    const char *Priority(unsigned char Priority);
    
    // Accessors
@@ -157,13 +220,29 @@ private:
 // Header structure							/*{{{*/
 struct pkgCache::Header
 {
-   // Signature information
+   /** \brief Signature information
+
+       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 */
    unsigned long Signature;
+   /** These contain the version of the cache file */
    short MajorVersion;
    short MinorVersion;
+   /** \brief indicates if the cache should be erased
+
+       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. */
    bool Dirty;
-   
-   // Size of structure values
+
+   /** \brief Size of structure values
+
+       All *Sz variables 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. */
    unsigned short HeaderSz;
    unsigned short PackageSz;
    unsigned short PackageFileSz;
@@ -173,8 +252,12 @@ struct pkgCache::Header
    unsigned short ProvidesSz;
    unsigned short VerFileSz;
    unsigned short DescFileSz;
-   
-   // Structure counts
+
+   /** \brief Structure counts
+
+       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. */
    unsigned long GroupCount;
    unsigned long PackageCount;
    unsigned long VersionCount;
@@ -184,22 +267,48 @@ struct pkgCache::Header
    unsigned long VerFileCount;
    unsigned long DescFileCount;
    unsigned long ProvidesCount;
-   
-   // Offsets
-   map_ptrloc FileList;              // struct PackageFile
-   map_ptrloc StringList;            // struct StringItem
-   map_ptrloc VerSysName;            // StringTable
-   map_ptrloc Architecture;          // StringTable
+
+   /** \brief 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. */
+   map_ptrloc FileList;
+   /** \brief index of the first StringItem structure
+
+       The cache contains a list of all the unique strings (StringItems).
+       The parser reads this list into memory so it can match strings
+       against it.*/
+   map_ptrloc StringList;
+   /** \brief String representing the version system used */
+   map_ptrloc VerSysName;
+   /** \brief Architecture(s) the cache was built against */
+   map_ptrloc Architecture;
+   /** \brief The maximum size of a raw entry from the original Package file */
    unsigned long MaxVerFileSize;
+   /** \brief The maximum size of a raw entry from the original Translation file */
    unsigned long MaxDescFileSize;
 
-   /* Allocation pools, there should be one of these for each structure
-      excluding the header */
+   /** \brief 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. */
    DynamicMMap::Pool Pools[9];
    
-   // Rapid package and group name lookup
-   // Notice: Increase only both table sizes as the
-   // hashmethod assume the size of the Pkg one
+   /** \brief hash tables providing rapid group/package name lookup
+
+       Each group/package name is inserted into the hash table using pkgCache::Hash(const &string)
+       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.
+       In the PkgHashTable is it possible that multiple packages have the same name -
+       these packages are stored as a sequence in the list.
+
+       Beware: The Hashmethod assumes that the hash table sizes are equal */
    map_ptrloc PkgHashTable[2*1048];
    map_ptrloc GrpHashTable[2*1048];
 
@@ -207,140 +316,332 @@ struct pkgCache::Header
    Header();
 };
 									/*}}}*/
-struct pkgCache::Group {						/*{{{*/
-	map_ptrloc Name;	// Stringtable
+// Group structure							/*{{{*/
+/** \brief groups architecture depending packages together
 
-	// Linked List
-	map_ptrloc FirstPackage;// Package
-	map_ptrloc LastPackage;	// Package
-	map_ptrloc Next;	// Group
+    On or more packages with the same name form a group, so we have
+    a simple way to access a package built for different architectures
+    Group exists in a singly linked list of group records starting at
+    the hash index of the name in the pkgCache::Header::GrpHashTable */
+struct pkgCache::Group
+{
+   /** \brief Name of the group */
+   map_ptrloc Name;		// StringItem
+
+   // Linked List
+   /** Link to the first package which belongs to the group */
+   map_ptrloc FirstPackage;	// Package
+   /** Link to the last package which belongs to the group */
+   map_ptrloc LastPackage;	// Package
+   /** Link to the next Group */
+   map_ptrloc Next;		// Group
 };
 									/*}}}*/
-struct pkgCache::Package						/*{{{*/
+// Package structure							/*{{{*/
+/** \brief 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 pkgCache::Header::PkgHashTable
+
+    A package can be created for every architecture so package names are
+    not unique, but it is garanteed that packages with the same name
+    are sequencel ordered in the list. Packages with the same name can be
+    accessed with the Group.
+*/
+struct pkgCache::Package
 {
-   // Pointers
-   map_ptrloc Name;              // Stringtable
-   map_ptrloc Arch;              // StringTable (StringItem)
+   /** \brief Name of the package */
+   map_ptrloc Name;              // StringItem
+   /** \brief Architecture of the package */
+   map_ptrloc Arch;              // StringItem
+   /** \brief Base of a singly linked list of versions
+
+       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. */
    map_ptrloc VersionList;       // Version
+   /** \brief index to the installed version */
    map_ptrloc CurrentVer;        // Version
-   map_ptrloc Section;           // StringTable (StringItem)
+   /** \brief indicates the deduced section
+
+       Should be the index to the string "Unknown" or to the section
+       of the last parsed item. */
+   map_ptrloc Section;           // StringItem
+   /** \brief index of the group this package belongs to */
    map_ptrloc Group;             // Group the Package belongs to
-      
-   // Linked list 
+
+   // Linked list
+   /** \brief Link to the next package in the same bucket */
    map_ptrloc NextPackage;       // Package
+   /** \brief List of all dependencies on this package */
    map_ptrloc RevDepends;        // Dependency
+   /** \brief List of all "packages" this package provide */
    map_ptrloc ProvidesList;      // Provides
 
    // Install/Remove/Purge etc
+   /** \brief state that the user wishes the package to be in */
    unsigned char SelectedState;     // What
+   /** \brief installation state of the package
+
+       This should be "ok" but in case the installation failed
+       it will be different.
+   */
    unsigned char InstState;         // Flags
+   /** \brief indicates if the package is installed */
    unsigned char CurrentState;      // State
-   
+
+   /** \brief unique sequel ID
+
+       ID is a unique value from 0 to Header->PackageCount 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. */
    unsigned int ID;
+   /** \brief some useful indicators of the package's state */
    unsigned long Flags;
 };
 									/*}}}*/
-struct pkgCache::PackageFile						/*{{{*/
+// Package File structure						/*{{{*/
+/** \brief stores information about the files used to generate the cache
+
+    Package files are referenced by Version structures to be able to know
+    after the generation still from which Packages file includes this Version
+    as we need this information later on e.g. for pinning. */
+struct pkgCache::PackageFile
 {
-   // Names
-   map_ptrloc FileName;        // Stringtable
-   map_ptrloc Archive;         // Stringtable
-   map_ptrloc Codename;        // Stringtable
-   map_ptrloc Component;       // Stringtable
-   map_ptrloc Version;         // Stringtable
-   map_ptrloc Origin;          // Stringtable
-   map_ptrloc Label;           // Stringtable
-   map_ptrloc Architecture;    // Stringtable
-   map_ptrloc Site;            // Stringtable
-   map_ptrloc IndexType;       // Stringtable
-   unsigned long Size;            
+   /** \brief physical disk file that this PackageFile represents */
+   map_ptrloc FileName;        // StringItem
+   /** \brief the release information
+
+       Please see the files document for a description of what the
+       release information means. */
+   map_ptrloc Archive;         // StringItem
+   map_ptrloc Codename;        // StringItem
+   map_ptrloc Component;       // StringItem
+   map_ptrloc Version;         // StringItem
+   map_ptrloc Origin;          // StringItem
+   map_ptrloc Label;           // StringItem
+   map_ptrloc Architecture;    // StringItem
+   /** \brief The site the index file was fetched from */
+   map_ptrloc Site;            // StringItem
+   /** \brief indicates what sort of index file this is
+
+       @TODO enumerate at least the possible indexes */
+   map_ptrloc IndexType;       // StringItem
+   /** \brief Size of the file
+
+       Used together with the modification time as a
+       simple check to ensure that the Packages
+       file has not been altered since Cache generation. */
+   unsigned long Size;
+   /** \brief Modification time for the file */
+   time_t mtime;
+
+   /* @TODO document PackageFile::Flags */
    unsigned long Flags;
-   
+
    // Linked list
+   /** \brief Link to the next PackageFile in the Cache */
    map_ptrloc NextFile;        // PackageFile
+   /** \brief unique sequel ID */
    unsigned int ID;
-   time_t mtime;                  // Modification time for the file
 };
 									/*}}}*/
-struct pkgCache::VerFile						/*{{{*/
+// VerFile structure							/*{{{*/
+/** \brief associates a version with a PackageFile
+
+    This allows a full description of all Versions in all files
+    (and hence all sources) under consideration. */
+struct pkgCache::VerFile
 {
+   /** \brief index of the package file that this version was found in */
    map_ptrloc File;           // PackageFile
+   /** \brief next step in the linked list */
    map_ptrloc NextFile;       // PkgVerFile
+   /** \brief position in the package file */
    map_ptrloc Offset;         // File offset
+   /* @TODO document pkgCache::VerFile::Size */
    unsigned long Size;
 };
 									/*}}}*/
-struct pkgCache::DescFile						/*{{{*/
+// DescFile structure							/*{{{*/
+/** \brief associates a description with a Translation file */
+struct pkgCache::DescFile
 {
+   /** \brief index of the file that this description was found in */
    map_ptrloc File;           // PackageFile
+   /** \brief next step in the linked list */
    map_ptrloc NextFile;       // PkgVerFile
+   /** \brief position in the file */
    map_ptrloc Offset;         // File offset
+   /* @TODO document pkgCache::DescFile::Size */
    unsigned long Size;
 };
 									/*}}}*/
-struct pkgCache::Version						/*{{{*/
+// Version structure							/*{{{*/
+/** \brief information for a single version of a package
+
+    The version list is always sorted from highest version to lowest
+    version by the generator. Equal version numbers are either merged
+    or handled as separate versions based on the Hash value. */
+struct pkgCache::Version
 {
-   map_ptrloc VerStr;            // Stringtable
-   map_ptrloc Section;           // StringTable (StringItem)
+   /** \brief complete version string */
+   map_ptrloc VerStr;            // StringItem
+   /** \brief section this version is filled in */
+   map_ptrloc Section;           // StringItem
+   /** \brief stores the MultiArch capabilities of this version
+
+       None is the default and doesn't trigger special behaviour,
+       Foreign means that this version can fulfill dependencies even
+       if it is built for another architecture as the requester.
+       Same indicates that builds for different architectures can
+       be co-installed on the system and All is the marker for a
+       version with the Architecture: all. */
    enum {None, All, Foreign, Same, Allowed} MultiArch;
 
-   // Lists
+   /** \brief references all the PackageFile's that this version came from
+
+       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
+       pkgCache::Version::VerStr and Possibly pkgCache::Version::NextVer. */
    map_ptrloc FileList;          // VerFile
+   /** \brief next (lower or equal) version in the linked list */
    map_ptrloc NextVer;           // Version
+   /** \brief next description in the linked list */
    map_ptrloc DescriptionList;   // Description
+   /** \brief base of the dependency list */
    map_ptrloc DependsList;       // Dependency
+   /** \brief links to the owning package
+
+       This allows reverse dependencies to determine the package */
    map_ptrloc ParentPkg;         // Package
+   /** \brief list of pkgCache::Provides */
    map_ptrloc ProvidesList;      // Provides
-   
+
+   /** \brief archive size for this version
+
+       For Debian this is the size of the .deb file. */
    map_ptrloc Size;              // These are the .deb size
+   /** \brief uncompressed size for this version */
    map_ptrloc InstalledSize;
+   /** \brief characteristic value representing this version
+
+       No two packages in existence should have the same VerStr
+       and Hash with different contents. */
    unsigned short Hash;
+   /** \brief unique sequel ID */
    unsigned int ID;
+   /** \brief parsed priority value */
    unsigned char Priority;
 };
 									/*}}}*/
-struct pkgCache::Description						/*{{{*/
+// Description structure						/*{{{*/
+/** \brief datamember of a linked list of available description for a version */
+struct pkgCache::Description
 {
-   // Language Code store the description translation language code. If
-   // the value has a 0 lenght then this is readed using the Package
-   // file else the Translation-CODE are used.
-   map_ptrloc language_code;     // StringTable
-   map_ptrloc md5sum;            // StringTable
+   /** \brief Language code of this description (translation)
+
+       If the value has a 0 length then this is read using the Package
+       file else the Translation-CODE file is used. */
+   map_ptrloc language_code;     // StringItem
+   /** \brief MD5sum of the original description
+
+       Used to map Translations of a description to a version
+       and to check that the Translation is up-to-date. */
+   map_ptrloc md5sum;            // StringItem
 
-   // Linked list 
+   /* @TODO document pkgCache::Description::FileList */
    map_ptrloc FileList;          // DescFile
+   /** \brief next translation for this description */
    map_ptrloc NextDesc;          // Description
+   /** \brief the text is a description of this package */
    map_ptrloc ParentPkg;         // Package
 
+   /** \brief unique sequel ID */
    unsigned int ID;
 };
 									/*}}}*/
-struct pkgCache::Dependency						/*{{{*/
+// Dependency structure							/*{{{*/
+/** \brief information for a single dependency record
+
+    The records are split up like this to ease processing by the client.
+    The base of the linked list is pkgCache::Version::DependsList.
+    All forms of dependencies are recorded here including Depends,
+    Recommends, Suggests, Enhances, Conflicts, Replaces and Breaks. */
+struct pkgCache::Dependency
 {
-   map_ptrloc Version;         // Stringtable
+   /** \brief string of the version the dependency is applied against */
+   map_ptrloc Version;         // StringItem
+   /** \brief index of the package this depends applies to
+
+       The generator will - if the package does not already exist -
+       create a blank (no version records) package. */
    map_ptrloc Package;         // Package
+   /** \brief next dependency of this version */
    map_ptrloc NextDepends;     // Dependency
+   /** \brief next reverse dependency of this package */
    map_ptrloc NextRevDepends;  // Dependency
+   /** \brief version of the package which has the reverse depends */
    map_ptrloc ParentVer;       // Version
-   
-   // Specific types of depends
-   map_ptrloc ID;   
+
+   /** \brief unique sequel ID */
+   map_ptrloc ID;
+   /** \brief Dependency type - Depends, Recommends, Conflicts, etc */
    unsigned char Type;
+   /** \brief comparison operator specified on the depends line
+
+       If the high bit is set then it is a logical OR with the previous record. */
    unsigned char CompareOp;
 };
 									/*}}}*/
-struct pkgCache::Provides						/*{{{*/
+// Provides structure							/*{{{*/
+/** \brief 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.*/
+struct pkgCache::Provides
 {
-   map_ptrloc ParentPkg;        // Pacakge
+   /** \brief index of the package providing this */
+   map_ptrloc ParentPkg;        // Package
+   /** \brief index of the version this provide line applies to */
    map_ptrloc Version;          // Version
-   map_ptrloc ProvideVersion;   // Stringtable
+   /** \brief version in the provides line (if any)
+
+       This version allows dependencies to depend on specific versions of a
+       Provides, as well as allowing Provides to override existing packages.
+       This is experimental. Note that Debian doesn't allow versioned provides */
+   map_ptrloc ProvideVersion;   // StringItem
+   /** \brief next provides (based of package) */
    map_ptrloc NextProvides;     // Provides
+   /** \brief next provides (based of version) */
    map_ptrloc NextPkgProv;      // Provides
 };
 									/*}}}*/
-struct pkgCache::StringItem						/*{{{*/
+// StringItem structure							/*{{{*/
+/** \brief 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 pkgCache::Header::StringList
+
+    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 StringItems should be null-terminated. */
+struct pkgCache::StringItem
 {
-   map_ptrloc String;        // Stringtable
+   /** \brief string this refers to */
+   map_ptrloc String;        // StringItem
+   /** \brief Next link in the chain */
    map_ptrloc NextItem;      // StringItem
 };
 									/*}}}*/