Yocto SRCREV override

In our Yocto build, there are a few customized packages.  It is a pain to update SRCREV in multiple bb files individually.

It turns out, in either local.conf or any top level conf / bb files, people can specify

• SRCREV_default_pn-${recipe name} ?= "XXXX"

Then, in the corresponding recipe bb file, just change

• SRCREV = "XXXXX"

to

• SRCREV ?= "XXXXX"

This works for both applications and the Linux kernel / U-Boot.

file: /poky/bitbake/lib/bb/fetch2/__init__.py
https://stackoverflow.com/questions/42093482/how-to-conditionally-specify-a-variable-in-yocto-bb-recipe

In addition, it is also possible to create machine based SRCREV.