[Buildroot] [RFC] BR2_DEFCONFIG not saved in defconfig, why? (or: can we change that?)

Thomas De Schampheleire patrickdepinguin+buildroot at gmail.com
Thu Jul 18 09:46:23 UTC 2013


Following commit:

added a configurable option to select the destination file of 'make
The default is 'defconfig'. However, this new option BR2_DEFCONFIG is
not saved in the defconfig itself. This is intentional, says the
commit message:

"The BR2_DEFCONFIG value itself is not saved into the generated
defconfig, since Kconfig considers it at its default. This is
intentional, to avoid hard-coding an absolute path in the defconfig.
It will anyway be set again when the defconfig is used with the 'make
BR2_DEFCONFIG=... defconfig' command."

Due to this, I fail to see how I can benefit from BR2_DEFCONFIG.
My use case (before using BR2_DEFCONFIG) is as follows: I have
defconfigs for various projects stored inside the configs/
subdirectory. To build a given project, I run:
make <name_of_defconfig>
If I make changes to the configuration (through 'make menuconfig' or
manual changes in .config), I update the stored configuration as
make savedefconfig
mv defconfig configs/<name_of_defconfig>

I wanted to use BR2_DEFCONFIG to make these last steps simple. I had
expected to set BR2_DEFCONFIG in the configuration to
'configs/<name_of_defconfig>' or maybe
'$(CONFIG_DIR)/configs/<name_of_defconfig>' or
$(TOPDIR)/configs/name_of_defconfig), and then be able to run
make <name_of_defconfig>
to set a configuration, and
make savedefconfig
to store one.

However, in my current understanding of the feature, I am forced to use
make defconfig BR2_DEFCONFIG=configs/<name_of_defconfig>
to set a configuration, and then
make savedefconfig to store one.

To me, the command to set a configuration is overcomplicated.
Originally it was as simple as passing the name of the config file,
now you not only have to pass its actual path (configs/), but also you
have to give it in a variable BR2_DEFCONFIG, *and* use the defconfig
rule. So, I feel better off with the original behavior.

My question is: is it really needed that the value of BR2_DEFCONFIG is
kept out of the defconfig itself? It is perfectly possible to set a
relative path in it, or one based on a variable like TOPDIR or
CONFIG_DIR, like so many other options already do. If someone does
store an absolute path in it, I'd say this is the fault of the

What do you think?


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