A new OpenGL extension exposed by the Nouveau NVC0 Gallium3D driver is ARB_indirect_parameters support. In order to wire up this extension, he added the support to Mesa. ARB_indirect_parameters brings the concept of a parameter buffer to store parameters for certain drawing commands.
This extension is related to ARB_multi_draw_indirect, which Mirkin has been working to improve. So today thanks to other work he added the real ARB_multi_draw_indirect implementation to NVC0 and as part of that added a new Mesa indirect draw interface.
It will certainly be interesting to see how far the open-source developers are able to get this year on the OpenGL 4.x support for the prominent Linux graphics drivers.