apt-pkg/pkgsystem.h

   1 // -*- mode: cpp; mode: fold -*-
   2 // Description                                                          /*{{{*/
   3 // $Id: pkgsystem.h,v 1.3 2001/03/11 07:35:49 jgg Exp $
   4 /* ######################################################################
   5
   6    System - Abstraction for running on different systems.
   7
   8    Instances of this class can be thought of as factories or meta-classes
   9    for a variety of more specialized classes. Together this class and
  10    it's speciallized offspring completely define the environment and how
  11    to access resources for a specific system. There are several sub
  12    areas that are all orthogonal - each system has a unique combination of
  13    these sub areas:
  14        - Versioning. Different systems have different ideas on versions.
  15          Within a system all sub classes must follow the same versioning
  16          rules.
  17        - Local tool locking to prevent multiple tools from accessing the
  18          same database.
  19        - Candidate Version selection policy - this is probably almost always
  20          managed using a standard APT class
  21        - Actual Package installation
  22          * Indication of what kind of binary formats are supported
  23        - Selection of local 'status' indexes that make up the pkgCache.
  24
  25    It is important to note that the handling of index files is not a
  26    function of the system. Index files are handled through a seperate
  27    abstraction - the only requirement is that the index files have the
  28    same idea of versioning as the target system.
  29
  30    Upon startup each supported system instantiates an instance of the
  31    pkgSystem class (using a global constructor) which will make itself
  32    available to the main APT init routine. That routine will select the
  33    proper system and make it the global default.
  34
  35    ##################################################################### */
  36                                                                         /*}}}*/
  37 #ifndef PKGLIB_PKGSYSTEM_H
  38 #define PKGLIB_PKGSYSTEM_H
  39
  40 #ifdef __GNUG__
  41 #pragma interface "apt-pkg/pkgsystem.h"
  42 #endif
  43
  44 #include <apt-pkg/depcache.h>
  45 #include <vector.h>
  46
  47 class pkgPackageManager;
  48 class pkgVersioningSystem;
  49 class Configuration;
  50 class pkgIndexFile;
  51
  52 class pkgSystem
  53 {
  54    public:
  55
  56    // Global list of supported systems
  57    static pkgSystem **GlobalList;
  58    static unsigned long GlobalListLen;
  59    static pkgSystem *GetSystem(const char *Label);
  60
  61    const char *Label;
  62    pkgVersioningSystem *VS;
  63
  64    /* Prevent other programs from touching shared data not covered by
  65       other locks (cache or state locks) */
  66    virtual bool Lock() = 0;
  67    virtual bool UnLock(bool NoErrors = false) = 0;
  68
  69    /* Various helper classes to interface with specific bits of this
  70       environment */
  71    virtual pkgPackageManager *CreatePM(pkgDepCache *Cache) const = 0;
  72
  73    /* Load environment specific configuration and perform any other setup
  74       necessary */
  75    virtual bool Initialize(Configuration &/*Cnf*/) {return true;};
  76
  77    /* Type is some kind of Globally Unique way of differentiating
  78       archive file types.. */
  79    virtual bool ArchiveSupported(const char *Type) = 0;
  80
  81    // Return a list of system index files..
  82    virtual bool AddStatusFiles(vector<pkgIndexFile *> &List) = 0;
  83
  84    /* Evauluate how 'right' we are for this system based on the filesystem
  85       etc.. */
  86    virtual signed Score(Configuration const &/*Cnf*/) {return 0;};
  87
  88    pkgSystem();
  89    virtual ~pkgSystem() {};
  90 };
  91
  92 // The environment we are operating in.
  93 extern pkgSystem *_system;
  94
  95 #endif