Detect and prevent multiple providers (branch yem/fix-virt-pkg)

index 6eca6d4..4e84e9a 100644
@@ -241,6 +241,25 @@ $(BUILD_DIR)/%/.stamp_dircleaned:
 	rm -Rf $(@D)
 
 ################################################################################
+# virt-provides-single -- check that provider-pkg is the declared provider for
+# the virtual package virt-pkg
+#
+# argument 1 is the lower-case name of the virtual package
+# argument 2 is the upper-case name of the virtual package
+# argument 3 is the lower-case name of the provider
+#
+# example:
+#   $(call virt-provides-single,libegl,LIBEGL,rpi-userland)
+################################################################################
+define virt-provides-single
+ifneq ($$(call qstrip,$$(BR2_PACKAGE_PROVIDES_$(2))),$(3))
+$$(error Configuration error: both "$(3)" and $$(BR2_PACKAGE_PROVIDES_$(2))\
+are selected as providers for virtual package "$(1)". Only one provider can\
+be selected at a time. Please fix your configuration)
+endif
+endef
+
+################################################################################
 # inner-generic-package -- generates the make targets needed to build a
 # generic package
 #

@@ -626,6 +645,13 @@ endif # ifneq ($(call qstrip,$$($(2)_SOURCE)),)
 # configuration
 ifeq ($$($$($(2)_KCONFIG_VAR)),y)
 
+# Ensure the calling package is the declared provider for all the virtual
+# packages it claims to be an implementation of.
+ifneq ($$($(2)_PROVIDES),)
+$$(foreach pkg,$$($(2)_PROVIDES),\
+	$$(eval $$(call virt-provides-single,$$(pkg),$$(call UPPERCASE,$$(pkg)),$(1))$$(sep)))
+endif
+
 TARGETS += $(1)
 PACKAGES_PERMISSIONS_TABLE += $$($(2)_PERMISSIONS)$$(sep)
 PACKAGES_DEVICES_TABLE += $$($(2)_DEVICES)$$(sep)

index f421651..d3fa45b 100644
@@ -304,6 +304,9 @@ information is (assuming the package name is +libfoo+) :
   a similar way, +HOST_LIBFOO_DEPENDENCIES+ lists the dependencies for
   the current host package.
 
+* +LIBFOO_PROVIDES+ lists all the virtual packages +libfoo+ is an
+  implementation of. See xref:virtual-package-tutorial[].
+
 * +LIBFOO_INSTALL_STAGING+ can be set to +YES+ or +NO+ (default). If
   set to +YES+, then the commands in the +LIBFOO_INSTALL_STAGING_CMDS+
   variables are executed to install the package into the staging

index 1c1116f..0cbe753 100644
@@ -39,7 +39,7 @@ In this file, we declare two options, +BR2_PACKAGE_HAS_SOMETHING_VIRTUAL+ and
 +BR2_PACKAGE_PROVIDES_SOMETHING_VIRTUAL+, whose values will be used by the
 providers.
 
-==== Virtual package's +*.mk+ file
+==== Virtual package's +.mk+ file
 
 The +.mk+ for the virtual package should just evaluate the +virtual-package+ macro:
 

@@ -59,8 +59,7 @@ The ability to have target and host packages is also available, with the
 ==== Provider's +Config.in+ file
 
 When adding a package as a provider, only the +Config.in+ file requires some
-modifications. The +*.mk+ file should follow the Buildroot infrastructure with
-no change at all.
+modifications.
 
 The +Config.in+ file of the package 'some-provider', which provides the
 functionalities of 'something-virtual', should contain:

@@ -84,6 +83,16 @@ On line 3, we select +BR2_PACKAGE_HAS_SOMETHING_VIRTUAL+, and on line 11, we
 set the value of +BR2_PACKAGE_PROVIDES_SOMETHING_VIRTUAL+ to the name of the
 provider, but only if it is selected.
 
+==== Provider's +.mk+ file
+
+The +.mk+ file should also declare an additional variable
++SOME_PROVIDER_PROVIDES+ to contain the names of all the virtual
+packages it is an implementation of:
+
+---------------------------
+01: SOME_PROVIDER_PROVIDES = something-virtual
+---------------------------
+
 Of course, do not forget to add the proper build and runtime dependencies for
 this package!
 

index 993015c..6db753d 100644
@@ -11,5 +11,6 @@ BELLAGIO_AUTORECONF = YES
 BELLAGIO_INSTALL_STAGING = YES
 BELLAGIO_LICENSE = LGPLv2.1+
 BELLAGIO_LICENSE_FILES = COPYING
+BELLAGIO_PROVIDES = libopenmax
 
 $(eval $(autotools-package))

index 8e5e83d..720c2e9 100644
@@ -25,6 +25,7 @@ EUDEV_CONF_OPT =		\
 	--enable-libkmod
 
 EUDEV_DEPENDENCIES = host-gperf host-pkgconf util-linux kmod
+EUDEV_PROVIDES = udev
 
 ifeq ($(BR2_PACKAGE_EUDEV_RULES_GEN),y)
 EUDEV_CONF_OPT += --enable-rule_generator

index e799fd2..49a8287 100644
@@ -23,6 +23,8 @@ GPU_VIV_BIN_MX6Q_LICENSE = Freescale Semiconductor Software License Agreement
 # for which a separate license is needed...
 GPU_VIV_BIN_MX6Q_REDISTRIBUTE = NO
 
+GPU_VIV_BIN_MX6Q_PROVIDES = libegl libgles
+
 # DirectFB is not supported (wrong version)
 ifeq ($(BR2_PACKAGE_XORG7),y)
 GPU_VIV_BIN_MX6Q_DEPENDENCIES = xlib_libXdamage xlib_libXext

index bc8799a..4f940ab 100644
@@ -14,6 +14,8 @@ LUA_INSTALL_STAGING = YES
 LUA_LICENSE = MIT
 LUA_LICENSE_FILES = COPYRIGHT
 
+LUA_PROVIDES = lua
+
 LUA_CFLAGS = -Wall -fPIC -DLUA_USE_POSIX
 
 ifeq ($(BR2_PACKAGE_LUA_5_2),y)

index c4b065d..61ea33b 100644
@@ -12,6 +12,8 @@ LUAJIT_LICENSE_FILES = COPYRIGHT
 
 LUAJIT_INSTALL_STAGING = YES
 
+LUAJIT_PROVIDES = lua
+
 ifneq ($(BR2_LARGEFILE),y)
 LUAJIT_NO_LARGEFILE = TARGET_LFSFLAGS=
 endif

index 63ba574..fa17177 100644
@@ -13,6 +13,8 @@ MESA3D_AUTORECONF = YES
 
 MESA3D_INSTALL_STAGING = YES
 
+MESA3D_PROVIDES =
+
 MESA3D_DEPENDENCIES = \
 	expat \
 	host-bison \

@@ -71,6 +73,7 @@ ifeq ($(MESA3D_DRI_DRIVERS-y),)
 MESA3D_CONF_OPT += \
 	--without-dri-drivers
 else
+MESA3D_PROVIDES += libgl
 MESA3D_CONF_OPT += \
 	--enable-dri \
 	--enable-shared-glapi \

@@ -85,6 +88,7 @@ endif
 MESA3D_CONF_OPT += --enable-opengl
 
 ifeq ($(BR2_PACKAGE_MESA3D_OPENGL_EGL),y)
+MESA3D_PROVIDES += libegl
 # egl depends on gbm, gbm depends on udev
 MESA3D_DEPENDENCIES += udev
 MESA3D_EGL_PLATFORMS = drm

@@ -105,6 +109,7 @@ MESA3D_CONF_OPT += \
 endif
 
 ifeq ($(BR2_PACKAGE_MESA3D_OPENGL_ES),y)
+MESA3D_PROVIDES += libgles
 MESA3D_CONF_OPT += --enable-gles1 --enable-gles2
 else
 MESA3D_CONF_OPT += --disable-gles1 --disable-gles2

index f6e4443..690fd1e 100644
@@ -11,6 +11,8 @@ RPI_USERLAND_LICENSE_FILES = LICENCE
 RPI_USERLAND_INSTALL_STAGING = YES
 RPI_USERLAND_CONF_OPT = -DVMCS_INSTALL_PREFIX=/usr -DBUILD_SHARED_LIBS=OFF
 
+RPI_USERLAND_PROVIDES = libegl libgles libopenmax libopenvg
+
 define RPI_USERLAND_POST_TARGET_CLEANUP
     rm -Rf $(TARGET_DIR)/usr/src
 endef

index c625c6e..c6900c8 100644
@@ -9,6 +9,7 @@ SUNXI_MALI_SITE = $(call github,linux-sunxi,sunxi-mali,$(SUNXI_MALI_VERSION))
 
 SUNXI_MALI_INSTALL_STAGING = YES
 SUNXI_MALI_DEPENDENCIES = sunxi-mali-prop
+SUNXI_MALI_PROVIDES = libegl libgles
 
 # The options below must be provided in the environment.  Providing these
 # through options overrides the value and prevents the makefiles from

index f7661ab..e1c984f 100644
@@ -17,6 +17,8 @@ SYSTEMD_DEPENDENCIES = \
 	kmod \
 	host-gperf
 
+SYSTEMD_PROVIDES = udev
+
 # Make sure that systemd will always be built after busybox so that we have
 # a consistent init setup between two builds
 ifeq ($(BR2_PACKAGE_BUSYBOX),y)

index e48715d..324e19c 100644
@@ -19,6 +19,7 @@ TI_GFX_LICENSE_FILES = TSPA.txt
 TI_GFX_INSTALL_STAGING = YES
 
 TI_GFX_DEPENDENCIES = linux
+TI_GFX_PROVIDES = libegl libgles powervr
 
 ifeq ($(BR2_PACKAGE_TI_GFX_ES3),y)
 TI_GFX_OMAPES = 3.x