Why does the yocto bblayers.conf file use absolute paths?

Question

The yocto project allows the use of relative path in most of its configuration files but not within the ./build/conf/bblayers.conf file. What is the reason for blocking the use of anything but absolute paths for the BBLAYERS and BBLAYERS_NON_REMOVABLE variables?

I have looked at the BitBake user manual for yocto version 2.0 (current release) but that does not explain the reasoning. I also checked some of the older manual versions but they do not seem to mention the reasoning when talking of the bblayers.conf file or the BBLAYERS variable. The same file also contains BBPATH = "${TOPDIR}" which is at least dynamically assigned and not that far away from the root yotco directory.

My best guess is that the bblayers.conf file is specific to the system it is being run on. That would make it unsuitable for sharing between developers via source control and the absolute paths would force people to edit the file whenever they received a copy. That did not seem like a very good reason though, hence the question.

Answer 1

I found a way to use relative paths.

You can use inline python to traverse the file system. The following script uses the provided TOPDIR variable and then navigates to its parent via python's os.path api.

# LAYER_CONF_VERSION is increased each time build/conf/bblayers.conf
# changes incompatibly
LCONF_VERSION = "6"

BBPATH = "${TOPDIR}"
BBFILES ?= ""

YOCTOROOT = "${@os.path.abspath(os.path.join("${TOPDIR}", os.pardir))}"

BBLAYERS ?= " \
  ${YOCTOROOT}/poky/meta \
  ${YOCTOROOT}/poky/meta-yocto \
  ${YOCTOROOT}/poky/meta-yocto-bsp \
"

BBLAYERS_NON_REMOVABLE ?= " \
  ${YOCTOROOT}/poky/meta \
  ${YOCTOROOT}/poky/meta-yocto \
"

References

• OpenEmbedded's bitbake.conf
• Advanced functionality with python
• How do I get the parent directory in Python?