[Buildroot] Split per-package dirs for dependencies and installation
thomas.petazzoni at bootlin.com
Fri Feb 28 13:33:48 UTC 2020
During the Buildroot Developers Meeting, we discussed the progress of
the top-level parallel build support, and identified two issues:
(1) The per-package host and target directories are read/write, and
due to the fact that we use hardlinks, if a package has the bad
idea of modifying/overwriting a file that was installed by
another package, this change is visible in all other per-package
host/target directories, which violates the isolation between the
build of the different packages.
(2) The per-package logic breaks the <pkg>-reconfigure, <pkg>-rebuild
and <pkg>-reinstall targets, as I explained in a previous e-mail
As part of the Buildroot Developers Meeting, we thought of the
- The host/target directories of package A dependencies are collected
in $(PER_PACKAGE_DIR)/A/host-deps and
- These folders are made read-only once the dependencies have been
rsynced into them. This prevents incorrect modifications of files
in these folders.
- During the configure/build steps, HOST_DIR points to
$(PER_PACKAGE_DIR)/A/host-deps and TARGET_DIR points to
$(PER_PACKAGE_DIR)/A/target-deps. However, at installation time,
HOST_DIR and TARGET_DIR points to other, empty directories, which
are writable. The aim here was to also solve the issue of the
So, I took a stab at implementing this, and well, it's not that easy:
- As expected, some packages do more than installing stuff in their
install step. As a trivial example, for some funky reason, even a
"simple" package like Busybox calls ARCH-gcc during its install
step. Except that during the install step, HOST_DIR is empty, and
certainly does not contain any cross-compiler. The build fails.
- Worse is the case of host packages. We configure them with
--prefix=$(HOST_DIR)/usr, which points to
$(PER_PACKAGE_DIR)/A/host-deps. So when we run "make install", they
want to install in $(PER_PACKAGE_DIR)/A/host-deps, not in
$(PER_PACKAGE_DIR)/A/host, which is the read/write empty directory we
want packages to install into. I don't see any good way to fix that.
Overall, I am wondering if we couldn't instead keep a single
HOST_DIR/TARGET_DIR, but make only the *files* read-only. Having the
files read-only would prevent modifications of existing files, but
since the directories are read/write, additional files can be added by
the new package. This would solve issue (1) above.
It would however not solve issue (2). As outlined in my December
e-mail, another possible direction to solve issue (2) is to rely on
the package file list, but it's a bit annoying to rely on this as part
of the build process, as we so far do not rely on that.
Do you have some ideas or feedback ?
Thanks a lot,
Thomas Petazzoni, CTO, Bootlin
Embedded Linux and Kernel engineering
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