[Buildroot] [RFC 1/2] Makefile: add target-genimage

[Vivien Didelot]

genimage is a convenient host tool which eases the generation of images
and partition layout by providing simple configuration files.

This patch adds a new BR2_ROOTFS_GENIMAGE_CFG menuconfig entry, which is
a space-separated list of config files. Indeed, you may want to split
images in different files, or put them all together in the same file.

BR2_ROOTFS_GENIMAGE_HOST_DEPENDENCIES is meant to auto-select the
packages that genimage may use, such as mkdosfs or mcopy (which copies
files from/to unmounted vfat images).

The rational behind adding this to Buildroot is that genimage requires
an overhead configuration to use it, like temporary directories, host
dependencies, and images path, that Buildroot is all aware of. This
minimal addition is optional and allows the user not to write the same
post-image script to wrap the genimage call.

Finally, the new "target-genimage" make target is called before
target-post-image so that the post-image script can still clean
intermediate generated images and do whatever with the very final image.

Signed-off-by: Vivien Didelot <vivien.didelot at savoirfairelinux.com>
---
 Makefile         | 17 +++++++++++++++--
 system/Config.in | 22 ++++++++++++++++++++++
 2 files changed, 37 insertions(+), 2 deletions(-)

diff --git a/Makefile b/Makefile
index 338c992..1eb1619 100644
--- a/Makefile
+++ b/Makefile
@@ -434,7 +434,7 @@ world: target-post-image
 
 .PHONY: all world toolchain dirs clean distclean source outputmakefile \
 	legal-info legal-info-prepare legal-info-clean printvars \
-	target-finalize target-post-image \
+	target-finalize target-genimage target-post-image \
 	$(TARGETS) $(TARGETS_ROOTFS) \
 	$(TARGETS_DIRCLEAN) $(TARGETS_SOURCE) $(TARGETS_LEGAL_INFO) \
 	$(BUILD_DIR) $(STAGING_DIR) $(TARGET_DIR) \
@@ -621,7 +621,20 @@ endif
 		$(call MESSAGE,"Executing post-build script $(s)"); \
 		$(EXTRA_ENV) $(s) $(TARGET_DIR) $(call qstrip,$(BR2_ROOTFS_POST_SCRIPT_ARGS))$(sep))
 
-target-post-image: $(TARGETS_ROOTFS) target-finalize
+target-genimage: $(TARGETS_ROOTFS) target-finalize
+	@$(foreach cfg, $(call qstrip,$(BR2_ROOTFS_GENIMAGE_CFG)), \
+	$(call MESSAGE,"Executing genimage with config $(cfg)"); \
+	  T=$$(mktemp -d $(BUILD_DIR)/.genimage.XXXXXXXXXX); \
+	  mkdir -p $$T/{root,tmp}; \
+	  $(EXTRA_ENV) output/host/usr/bin/genimage \
+	  --rootpath $$T/root \
+	  --tmppath $$T/tmp \
+	  --inputpath output/images/ \
+	  --outputpath output/images/ \
+	  --config $(cfg); \
+	  rm -rf $$T$(sep))
+
+target-post-image: target-genimage
 	@$(foreach s, $(call qstrip,$(BR2_ROOTFS_POST_IMAGE_SCRIPT)), \
 		$(call MESSAGE,"Executing post-image script $(s)"); \
 		$(EXTRA_ENV) $(s) $(BINARIES_DIR) $(call qstrip,$(BR2_ROOTFS_POST_SCRIPT_ARGS))$(sep))
diff --git a/system/Config.in b/system/Config.in
index 95e10ab..2596da8 100644
--- a/system/Config.in
+++ b/system/Config.in
@@ -421,6 +421,28 @@ config BR2_ROOTFS_POST_BUILD_SCRIPT
 	  argument. Make sure the exit code of those scripts are 0, otherwise
 	  make will stop after calling them.
 
+config BR2_ROOTFS_GENIMAGE_CFG
+	string "genimage config files to prepare custom images"
+	default ""
+	help
+	  Specify a space-separated list of configuration files for genimage to be
+	  run after the build has finished and after Buildroot has packed the files
+	  into selected filesystem images.
+
+	  This can for example be used to generate a card image with an vfat
+	  partition containing some boot files, and an ext4 rootfs.
+
+	  genimage is executed from the main Buildroot source directory, with input
+	  and output paths configured to output/images.
+
+config BR2_ROOTFS_GENIMAGE_HOST_DEPENDENCIES
+	bool "genimage host dependencies"
+	default y
+	depends on BR2_ROOTFS_GENIMAGE_CFG != ""
+	select BR2_PACKAGE_HOST_GENIMAGE
+	select BR2_PACKAGE_HOST_DOSFSTOOLS
+	select BR2_PACKAGE_HOST_MTOOLS
+
 config BR2_ROOTFS_POST_IMAGE_SCRIPT
 	string "Custom scripts to run after creating filesystem images"
 	default ""
-- 
2.3.0