[Buildroot] Adding post image hook

[Thomas Petazzoni <thomas.petazzoni@bootlin.com>]

Hello,

On Mon, 11 May 2020 16:35:10 +0200 (CEST)
lpdev at cordier.org wrote:

> I'm currently trying to improve my custom buildroot tree (that makes
> use of BR2_EXTERNAL), especially the final steps. For instance my
> external tree adds an extra steps through the
> BR2_ROOTFS_POST_IMAGE_SCRIPT to generate the firmware file. This step
> also retrieve the version of different softwares present in the final
> image.
> 
> However the post image script comes with a big limitation: we cannot
> take the advantage of reading variables defined in the Makefile.

You can actually do that, by running:

	make VARS=<some-variable-name> printvars

from your post-image script.

If what you need to retrieve is the version of the different packages,
you can also run:

	make show-info

from your post-image script, and parse the JSON output.

> # Export some useful variable that can be used in other scripts
> export BR2_CUSTOM_BOARDNAME := $(call qstrip,$(BR2_CUSTOM_BOARDNAME))
> export BR2_CUSTOM_BOARDVERSION := $(shell git -C $(BR2_EXTERNAL_CUSTOM_PATH) describe --tags --dirty=-dev)
> 
> # Make an Firmware Update package.
> ifeq ($(BR2_CUSTOM_GENERATE_FIRMWARE),y)
> genfirmware: target-post-image
> 	@$(call MESSAGE,"Compressing the filesystem...")
> 	pigz -9 -c -n $(BINARIES_DIR)/rootfs.ext4 > $(BINARIES_DIR)/rootfs.ext4.gz
> 
> 	@$(call MESSAGE,"Generating UEFI partition for the bootloader...")
> 	$(EXTRA_ENV) ./support/scripts/genimage.sh -c $(BR2_EXTERNAL_CUSTOM_PATH)/board/cstick/genimage_uefi.cfg
> 
> 	@$(call MESSAGE,"Generating firmware version $(BR2_CUSTOM_BOARDVERSION) for board $(BR2_CUSTOM_BOARDNAME) ")
> 	(We can use bash script here with any makefile variables defined at this point, such as BR2_OPENCV_VERSION for instance)
> 
> # Override the default world target.
> .PHONY: world
> world: genfirmware
> endif

Otherwise, what you did here looks OK to me. It is a hack of course,
but BR2_EXTERNAL is designed to allow hacks :-)

Thomas
-- 
Thomas Petazzoni, CTO, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com