manual: update the virtual package section with the new infrastructure

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Cc: Eric Le Bihan <eric.le.bihan.dev@free.fr>
Cc: Samuel Martin <s.martin49@gmail.com>
Reviewed-by: Samuel Martin <s.martin49@gmail.com>
Acked-by: Eric Le Bihan <eric.le.bihan.dev@free.fr>
Acked-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

docs/manual/adding-packages-virtual.txt

@@ -1,10 +1,10 @@
 // -*- mode:doc; -*-
 // vim: set syntax=asciidoc:
 
-[[virtual-package-tutorial]]
+Infrastructure for virtual packages
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
-Virtual package tutorial
-~~~~~~~~~~~~~~~~~~~~~~~~
+[[virtual-package-tutorial]]
 
 In Buildroot, a virtual package is a package whose functionalities are
 provided by one or more packages, referred to as 'providers'. The virtual
@@ -16,6 +16,9 @@ The implementation of this API is different for the 'Allwinner Tech Sunxi' and
 the 'Texas Instruments OMAP35xx' plaftorms. So +libgles+ will be a virtual
 package and +sunxi-mali+ and +ti-gfx+ will be the providers.
 
++virtual-package+ tutorial
+^^^^^^^^^^^^^^^^^^^^^^^^^^
+
 In the following example, we will explain how to add a new virtual package
 ('something-virtual') and a provider for it ('some-provider').
 
@@ -42,7 +45,7 @@ providers.
 Virtual package's +*.mk+ file
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
-The Makefile +package/something-virtual/something-virtual.mk+ should contain:
+The +.mk+ for the virtual package should just evaluate the +virtual-package+ macro:
 
 ---------------------------
 01: ################################################################################
@@ -51,20 +54,11 @@ The Makefile +package/something-virtual/something-virtual.mk+ should contain:
 04: #
 05: ################################################################################
 06:
-07: SOMETHING_VIRTUAL_SOURCE =
-08: SOMETHING_VIRTUAL_DEPENDENCIES = $(call qstrip,$(BR2_PACKAGE_PROVIDES_SOMETHING_VIRTUAL))
-09:
-10: ifeq ($(BR2_PACKAGE_HAS_SOMETHING_VIRTUAL),y)
-11: ifeq ($(SOMETHING_VIRTUAL_DEPENDENCIES),)
-12: $(error No something-virtual implementation selected. Configuration error.)
-13: endif
-14: endif
-15:
-16: $(eval $(generic-package))
+07: $(eval $(virtual-package))
 ---------------------------
 
-The Makefile is quite small as it will only check if a provider for the
-virtual package has been selected.
+The ability to have target and host packages is also available, with the
++host-virtual-package+ macro.
 
 Provider's +Config.in+ file
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^