274be6de55
This is a re-factor of element_dependencies to achieve two things -- centralising override policy and storing path names. Firstly we want to make the override policy for elements completely explicit. Currently, elements that wish to copy parts of other elements walk ELEMENTS_PATH themselves and look for elements in IMAGE_ELEMENT. How they handle duplicate elements can differ, leading to inconsistent behaviour. We introduce logic in element-info to find elements in each of the directories in ELEMENT_PATHS in *reverse* order -- that is to say, earlier entries in the paths will overwrite later ones. For example ELEMENT_PATHS=foo:bar:baz will mean that "foo/element" will override "baz/element", since "foo" is first. This should be sane to anyone familiar with $PATH. Documentation is clarified around this point and a test-case is added. The second thing is that we want to keep the complete path of the elements we have chosen. We want the aforementioned elements that walk the element list to use these canonical paths to pickup files; this way they don't need to make local decisions about element overrides, but can simply iterate a list and copy/merge files if they exist. A follow-on change (I7092e1845942f249175933d67ab121188f3511fd) will expose this data in a separate variable that can be parsed by elements (a further follow-on I0a64b45e9f2cfa28e84b2859d76b065a6c4590f0 modifies the elements to use this information). Thus this does not change the status-quo -- elements that are walking ELEMENTS_PATH themselves and can/will continue doing that. Change-Id: I2a29861c67de2d25c595cb35d850e92807d26ac6
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Invocation
The scripts can generally just be run. Options can be set on the command line or by exporting variables to override those present in lib/img-defaults. -h to get help.
The image building scripts expect to be able to invoke commands with sudo, so if you want them to run non-interactively, you should either run them as root, with sudo -E, or allow your build user to run any sudo command without password.
The variable ELEMENTS_PATH is a colon (:) separated path
list to search for elements. The included elements tree is
used when no path is supplied and is always added to the end of the path
if a path is supplied. Earlier elements will override later elements,
i.e. with ELEMENTS_PATH=foo:bar the element
my-element will be chosen from foo/my-element
over bar/my-element, or any in-built element of the same
name.
By default, the image building scripts will not overwrite existing
disk images, allowing you to compare the newly built image with the
existing one. To change that behaviour, set the variable
OVERWRITE_OLD_IMAGE to any value that isn't 0.
If this value is zero then any existing image will be moved before the
new image is written to the destination.
Setting the variable DIB_SHOW_IMAGE_USAGE will print out
a summarised disk-usage report for the final image of files and
directories over 10MiB in size. Setting
DIB_SHOW_IMAGE_USAGE_FULL will show all files and
directories. These settings can be useful additions to the logs in
automated build situations where debugging image-growth may be
important.