Build system

This page explains internals of the Gluon build system. It is currently very incomplete; please contribute if you can!

Feed management

Rather that relying on the feed.conf mechanism of OpenWrt directly, Gluon manages its feeds (“modules”) using a collection of scripts. This solution was selected for multiple reasons:

  • Feeds lists from Gluon base and the site repository are combined
  • Patchsets are applied to downloaded feed repositories automatically

The following variables specifically affect the feed management:

List of base feeds; defined in file modules in Gluon base
List of site feeds; defined in file modules in site config
Git repository URL, branch and commit ID of the feeds to use. The branch name may be omitted; the default branch will be used in this case.
Additional feed definitions to be added to feeds.conf verbatim. By default, this contains a reference to the Gluon base packages; when using the Gluon build system to build a non-Gluon system, the variable can be set to the empty string.

Helper scripts

Several tasks of the build process have been separated from the Makefile into external scripts, which are stored in the scripts directory. This was done to ease maintenance of these scripts and the Makefile, by avoiding a lot of escaping. These scripts are either bash or Lua scripts that run on the build system.
Defines the constant DEFAULT_FEEDS with the names of all feeds listed in openwrt/feeds.conf.default. This script is only used as an include by other scripts.
Creates the openwrt/feeds.conf file from FEEDS and DEFAULT_FEEDS. The feeds from FEEDS are linked to the matching subfolder of packages/ and not explicitly defined feeds of DEFAULT_FEEDS are setup as dummy (src-dummy). This openwrt/feeds.conf is used to reinstall all packages of all feeds with the openwrt/scripts/feeds tool.

Defines the constants GLUON_MODULES and FEEDS by reading the modules files of the Gluon repository root and the site configuration. The returned variables look like:

  • FEEDS: “feedA feedB …
  • GLUON_MODULES: “openwrt packages/feedA packages/feedB …

This script is only used as an include by other scripts.

(Re-)applies the patches from the patches directory to all GLUON_MODULES and checks out the files to the filesystem. This is done for each repo by:

  • creating a temporary clone of the repo to patch - only branch base is used
  • applying all patches via git am on top of this temporary base branch - this branch is named patched
  • copying the temporary clone to the openwrt (for OpenWrt Base) or packages (for feeds) folder - git fetch is used with the temporary clone as source - git checkout is called to update the filesystem
  • updating all git submodules

This solution with a temporary clone ensures that the timestamps of checked out files are not changed by any intermediate patch steps, but only when updating the checkout with the final result. This avoids triggering unnecessary rebuilds.
Sets up a working clone of the GLUON_MODULES (external repos) from the external source and installs it into packages/ directory. It simply tries to set the base branch of the cloned repo to the correct commit. If this fails it fetches the upstream branch and tries again to set the local base branch.

Used to determine the version numbers of the repositories of Gluon and the site configuraiton, to be included in the built firmware images as /lib/gluon/gluon-version and /lib/gluon/site-version.

By default, this uses git describe to generate a version number based on the last git tag. This can be overridden by putting a file called .scmversion into the root of the respective repositories.

A command like rm -f .scmversion; echo "$(./scripts/ .)" > .scmversion can be used before applying local patches to ensure that the reported version numbers refer to an upstream commit ID rather than an arbitrary local one after git am.