pkgCacheGenerator: Allow passing down an already created cache

If we already have opened a cache, there is no point in having
to open it again.

apt-pkg/cachefile.cc

@@ -96,7 +96,8 @@ bool pkgCacheFile::BuildCaches(OpProgress *Progress, bool WithLock)
    BuildSourceList(Progress);
 
    // Read the caches
-   bool Res = pkgCacheGenerator::MakeStatusCache(*SrcList,Progress,&Map, true);
+   Cache = nullptr;
+   bool Res = pkgCacheGenerator::MakeStatusCache(*SrcList,Progress,&Map, &Cache, true);
    if (Progress != NULL)
       Progress->Done();
    if (Res == false)
@@ -106,7 +107,8 @@ bool pkgCacheFile::BuildCaches(OpProgress *Progress, bool WithLock)
    if (_error->PendingError() == true)
       _error->Warning(_("You may want to run apt-get update to correct these problems"));
 
-   Cache = new pkgCache(Map);
+   if (Cache == nullptr)
+      Cache = new pkgCache(Map);
    if (_error->PendingError() == true)
       return false;
    return true;

apt-pkg/pkgcachegen.cc

@@ -1285,7 +1285,8 @@ static bool CheckValidity(const string &CacheFile,
                           pkgSourceList &List,
                           FileIterator const Start,
                           FileIterator const End,
-                          MMap **OutMap = 0)
+                          MMap **OutMap = 0,
+			  pkgCache **OutCache = 0)
 {
    ScopedErrorRevert ser;
    bool const Debug = _config->FindB("Debug::pkgCacheGen", false);
@@ -1309,7 +1310,8 @@ static bool CheckValidity(const string &CacheFile,
    std::unique_ptr<MMap> Map(new MMap(CacheF,0));
    if (unlikely(Map->validData()) == false)
       return false;
-   pkgCache Cache(Map.get());
+   std::unique_ptr<pkgCache> CacheP(new pkgCache(Map.get()));
+   pkgCache &Cache = *CacheP.get();
    if (_error->PendingError() || Map->Size() == 0)
    {
       if (Debug == true)
@@ -1399,6 +1401,8 @@ static bool CheckValidity(const string &CacheFile,
 
    if (OutMap != 0)
       *OutMap = Map.release();
+   if (OutCache != 0)
+      *OutCache = CacheP.release();
    return true;
 }
 									/*}}}*/
@@ -1562,6 +1566,11 @@ bool pkgMakeStatusCache(pkgSourceList &List,OpProgress &Progress,
    { return pkgCacheGenerator::MakeStatusCache(List, &Progress, OutMap, AllowMem); }
 bool pkgCacheGenerator::MakeStatusCache(pkgSourceList &List,OpProgress *Progress,
 			MMap **OutMap,bool)
+{
+   return pkgCacheGenerator::MakeStatusCache(List, Progress, OutMap, nullptr, true);
+}
+bool pkgCacheGenerator::MakeStatusCache(pkgSourceList &List,OpProgress *Progress,
+			MMap **OutMap,pkgCache **OutCache, bool)
 {
    // FIXME: deprecate the ignored AllowMem parameter
    bool const Debug = _config->FindB("Debug::pkgCacheGen", false);
@@ -1594,7 +1603,8 @@ bool pkgCacheGenerator::MakeStatusCache(pkgSourceList &List,OpProgress *Progress
    bool srcpkgcache_fine = false;
    bool volatile_fine = List.GetVolatileFiles().empty();
 
-   if (CheckValidity(CacheFile, List, Files.begin(), Files.end(), volatile_fine ? OutMap : NULL) == true)
+   if (CheckValidity(CacheFile, List, Files.begin(), Files.end(), volatile_fine ? OutMap : NULL,
+		     volatile_fine ? OutCache : NULL) == true)
    {
       if (Debug == true)
 	 std::clog << "pkgcache.bin is valid - no need to build any cache" << std::endl;

apt-pkg/pkgcachegen.h

@@ -113,6 +113,8 @@ class APT_HIDDEN pkgCacheGenerator					/*{{{*/
 
    APT_PUBLIC static bool MakeStatusCache(pkgSourceList &List,OpProgress *Progress,
 			MMap **OutMap = 0,bool AllowMem = false);
+   APT_HIDDEN static bool MakeStatusCache(pkgSourceList &List,OpProgress *Progress,
+			MMap **OutMap,pkgCache **OutCache, bool AllowMem = false);
    APT_PUBLIC static bool MakeOnlyStatusCache(OpProgress *Progress,DynamicMMap **OutMap);
 
    void ReMap(void const * const oldMap, void const * const newMap);