Allow GDALDriverManager::AutoLoadDrivers to be compiled out

[Kurt Schwehr]

Some environments may want to prevent compiling in the driver autoloading system for drivers to help with security.

Going to add ifdef wrappers around the relevant code.

#ifndef GDAL_NO_AUTOLOAD
    /* AutoLoadDrivers code. */
#endif

I am not planning to add a configure option in the near term unless people ask for it. People wanting this feature can use USER_DEFS or modify their GDALmake.opt for now.

[Kyle Shannon]

Isn't this the same as not calling GDALAllRegister() and registering drivers explicitly? It seems like it could cause issues if the GDAL_NO_AUTOLOAD is set and someone calls GDALAllRegister() and it's a no-op. Just curious on the use case I guess.

[Kurt Schwehr]

This will not change the normal compiled in driver behavior if you call GDALAllRegister. Only the stuff that would get loaded via GDAL_DRIVER_PATH or OGR_DRIVER_PATH. For most users, that would mean that compiling with GDAL_NO_AUTOLOAD would have no visible behavior changes. That define would block external plugins. That's why I think this removal should not be the default.

[Kyle Shannon]

That sounds perfectly reasonable to me, my mistake. Thanks for the explanation Kurt.

[Kurt Schwehr]

Kyle, Thanks for asking. My current proposed patch:

frmts/gdalallregister.cpp

@@ -62 +62 @@
 void CPL_STDCALL GDALAllRegister()
 
 {
+    // AutoLoadDrivers is a no-op if compiled with GDAL_NO_AUTOLOAD defined.
     GetGDALDriverManager()->AutoLoadDrivers();
 
 #ifdef FRMT_vrt

gcore/gdal_priv.h

@@ -1148 +1148 @@
     int         RegisterDriver( GDALDriver * );
     void        DeregisterDriver( GDALDriver * );
 
+    // AutoLoadDrivers is a no-op if compiled with GDAL_NO_AUTOLOAD defined.
     void        AutoLoadDrivers();
     void        AutoSkipDrivers();
 };

gcore/gdaldrivermanager.cpp

@@ -662 +662 @@
 void GDALDriverManager::AutoLoadDrivers()
 
 {
+#ifdef GDAL_NO_AUTOLOAD
+  CPLDebug( "GDAL", "GDALDriverManager::AutoLoadDrivers() not compiled in." );
+#else
     const char *pszGDAL_DRIVER_PATH = 
         CPLGetConfigOption( "GDAL_DRIVER_PATH", NULL );
     if( pszGDAL_DRIVER_PATH == NULL )
@@ -815 +818 @@
     }
 
     CSLDestroy( papszSearchPath );
+
+#endif  // GDAL_NO_AUTOLOAD
+
 }
 
 /************************************************************************/

[Kyle Shannon]

Sounds good to me. I didn't do a thorough review, but looks good.

[Kurt Schwehr]

r33546