Sprinkle some custom hooks in multiple key moments during build.

[rpardini]

These allow for more substantial changes to the build in a custom configuration (userpatches/config-xxx.conf), without having to change Armbian sources. Essentially it allows for more customization points (using functions). It should be safe, eg, every hook point tests for the existence of the hook function before calling it.
Having written those around 6 months ago and having done countless rebasing, I'm trying to offload them unto upstream.

Some possible uses:

• Override family-set values without changing family/include
• Replacing the onboarding process (eg, with cloud-init)
• Replacing NetworkManager with netplan
• Preconfiguring zram, zswap and some services
• Customizing the BSP package contents
• Dynamic calculation of image size
• Capturing the rootfs as an e2image dump for fast flashing
• Copy kernel-headers .deb to rootfs, but don't install it

Signed-off-by: Ricardo Pardini ricardo@pardini.net

Examples of usage

Mostly a mess, but some examples of usage can be seen on https://github.com/rpardini/armbian-build/tree/rpardini-stable/userpatches - for example:

• https://github.com/rpardini/armbian-build/blob/rpardini-stable/userpatches/config-rpardini-hc4.conf
  It uses a naive/hardcoded "fragment" composition using function calls, but this will soon be replaced by a module/fragment auto-aggregator (since bash lends itself so well to this kind of thing ;-) )
  This is most definitely not ready for merging yet -- probably not even for review.

Hope this is enough to warrant a merge, thanks

[lanefu]

@rpardini this is awesome...

Please confirm my understanding... The changes are all Conditionals checking for the existence of additional functions in a user patches file and not overriding/replacing existing functions correct?

Requested Changes:

If the functions the new code is checking for all reside in userpatches, can we prefix all the function names with user_config to make it more apparent these are optional overrides as was done [here]https://github.com/armbian/build/pull/2799/files#diff-e0cd262e64e226acc09b70a455b981c6e29544a4210f83e42e74796dfa9f9974R611l)

Could you modify example and create it as a template here, and assure all the possible functions are listed, and clearly documented above them?

Extra Credit:

Once merged, I'll do my best to update the documentation from your example, but if you'd like to add additional documentation here It would be greatly appreciated.

[rpardini]

@lanefu thanks for the review.
I just pushed another hook (pre initramfs), but that did not take your review into account.
There are a few changes that are not "only adds functions that are called if they exist" already in that I will try to review. I also need to be able to skip u-boot compilation and installation for some boards.
I have not paid attention to the naming of the funcions, some are user_config while others are config_ and others just a mess. I will try to review it all.
Thanks

[rpardini]

Closing this in favor of #2807 - a more complex implemention of this that should address most of the questions raised here.