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diff --git a/apt-pkg/pkgsystem.h b/apt-pkg/pkgsystem.h
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+// -*- mode: cpp; mode: fold -*-
+// Description								/*{{{*/
+/* ######################################################################
+
+   System - Abstraction for running on different systems.
+   
+   Instances of this class can be thought of as factories or meta-classes
+   for a variety of more specialized classes. Together this class and 
+   it's specialized offspring completely define the environment and how
+   to access resources for a specific system. There are several sub
+   areas that are all orthogonal - each system has a unique combination of
+   these sub areas:
+       - Versioning. Different systems have different ideas on versions.
+         Within a system all sub classes must follow the same versioning 
+         rules.
+       - Local tool locking to prevent multiple tools from accessing the
+         same database.
+       - Candidate Version selection policy - this is probably almost always
+         managed using a standard APT class
+       - Actual Package installation 
+         * Indication of what kind of binary formats are supported
+       - Selection of local 'status' indexes that make up the pkgCache.
+      
+   It is important to note that the handling of index files is not a 
+   function of the system. Index files are handled through a separate
+   abstraction - the only requirement is that the index files have the
+   same idea of versioning as the target system.
+   
+   Upon startup each supported system instantiates an instance of the
+   pkgSystem class (using a global constructor) which will make itself
+   available to the main APT init routine. That routine will select the
+   proper system and make it the global default.
+   
+   ##################################################################### */
+									/*}}}*/
+#ifndef PKGLIB_PKGSYSTEM_H
+#define PKGLIB_PKGSYSTEM_H
+
+#include <apt-pkg/pkgcache.h>
+
+#include <vector>
+
+
+class pkgDepCache;
+class pkgPackageManager;
+class pkgVersioningSystem;
+class Configuration;
+class pkgIndexFile;
+class OpProgress;
+
+class pkgSystemPrivate;
+class APT_PUBLIC pkgSystem
+{
+   public:
+
+   // Global list of supported systems
+   static pkgSystem **GlobalList;
+   static unsigned long GlobalListLen;
+   static pkgSystem *GetSystem(const char *Label);
+   
+   const char * const Label;
+   pkgVersioningSystem * const VS;
+   
+   /* Prevent other programs from touching shared data not covered by
+      other locks (cache or state locks) */
+   virtual bool Lock(OpProgress *const Progress = nullptr) = 0;
+   virtual bool UnLock(bool NoErrors = false) = 0;
+   
+   /* Various helper classes to interface with specific bits of this
+      environment */
+   virtual pkgPackageManager *CreatePM(pkgDepCache *Cache) const = 0;
+
+   /* Load environment specific configuration and perform any other setup
+      necessary */
+   virtual bool Initialize(Configuration &/*Cnf*/) {return true;};
+   
+   /* Type is some kind of Globally Unique way of differentiating
+      archive file types.. */
+   virtual bool ArchiveSupported(const char *Type) = 0;
+
+   // Return a list of system index files..
+   virtual bool AddStatusFiles(std::vector<pkgIndexFile *> &List) = 0;
+
+   virtual bool FindIndex(pkgCache::PkgFileIterator File,
+			  pkgIndexFile *&Found) const = 0;
+
+   /* Evaluate how 'right' we are for this system based on the filesystem
+      etc.. */
+   virtual signed Score(Configuration const &/*Cnf*/) {
+      return 0;
+   };
+
+   //FIXME: these methods should be virtual
+   /** does this system has support for MultiArch?
+    *
+    * Systems supporting only single arch (not systems which are single arch)
+    * are considered legacy systems and support for it will likely degrade over
+    * time.
+    *
+    * The default implementation returns always \b true.
+    *
+    * @return \b true if the system supports MultiArch, \b false if not.
+    */
+   virtual bool MultiArchSupported() const = 0;
+   /** architectures supported by this system
+    *
+    * A MultiArch capable system might be configured to use
+    * this capability.
+    *
+    * @return a list of all architectures (native + foreign) configured
+    * for on this system (aka: which can be installed without force)
+    */
+   virtual std::vector<std::string> ArchitecturesSupported() const  = 0;
+
+   APT_HIDDEN void SetVersionMapping(map_id_t const in, map_id_t const out);
+   APT_HIDDEN map_id_t GetVersionMapping(map_id_t const in) const;
+
+   pkgSystem(char const * const Label, pkgVersioningSystem * const VS);
+   virtual ~pkgSystem();
+
+
+   /* companions to Lock()/UnLock
+    *
+    * These functions can be called prior to calling dpkg to release an inner
+    * lock without releasing the overall outer lock, so that dpkg can run
+    * correctly but no other APT instance can acquire the system lock.
+    */
+   virtual bool LockInner(OpProgress *const Progress = 0, int timeOutSec = 0) = 0;
+   virtual bool UnLockInner(bool NoErrors = false)  = 0;
+   /// checks if the system is currently locked
+   virtual bool IsLocked() = 0;
+   private:
+   pkgSystemPrivate * const d;
+};
+
+// The environment we are operating in.
+APT_PUBLIC extern pkgSystem *_system;
+
+#endif