[yocto] How to maintain a global DL_DIR?

[Patrick Doyle]

Oh this is ugly...
I tried setting BB_ENV_EXTRAWHITE to DL_DIR in my .bashrc, but found
that BB_ENV_EXTRAWHITE gets overwritten by oe-buildenv-internal as I
mentioned previously.

I tried setting BB_ENV_WHITELIST to DL_DIR in my .bashrc and found
that bitbake just stopped working.

After rereading the manual
(https://www.yoctoproject.org/docs/1.6/bitbake-user-manual/bitbake-user-manual.html#var-BB_ENV_WHITELIST)
I tried setting BB_ENV_WHITELIST to "BBPATH BB_RESERVE_ENV
BB_ENV_WHITELIST BB_ENV_EXTRAWHITE DL_DIR", and bitbake still didn't
work.

So I looked in poky/bitbake/lib/bb/utils.py and found the following:

def preserved_envvars_exported():
    """Variables which are taken from the environment and placed in and exported
    from the metadata"""
    return [
        'BB_TASKHASH',
        'HOME',
        'LOGNAME',
        'PATH',
        'PWD',
        'SHELL',
        'TERM',
        'USER',
    ]

def preserved_envvars():
    """Variables which are taken from the environment and placed in
the metadata"""
    v = [
        'BBPATH',
        'BB_PRESERVE_ENV',
        'BB_ENV_WHITELIST',
        'BB_ENV_EXTRAWHITE',
    ]
    return v + preserved_envvars_exported()

...
    if 'BB_ENV_WHITELIST' in os.environ:
        approved = os.environ['BB_ENV_WHITELIST'].split()
        approved.extend(['BB_ENV_WHITELIST'])
    else:
        approved = preserved_envvars()

This looks like, if BB_ENV_WHITELIST is defined in the environment,
bitbake will use it (arbitrarily appending BB_ENV_WHITELIST to the end
of whatever was defined in the environment variable).  If it is not
defined, then BB_ENV_WHITELIST is initialized to be:

['BBPATH', 'BB_PRESERVE_ENV', 'BB_ENV_WHITELIST', 'BB_ENV_EXTRAWHITE',
'BB_TASKHASH', 'HOME', ...]

So I finally tried setting BB_ENV_WHITELIST in .bashrc to be "BBPATH
BB_PRESERVE_ENV BB_ENV_EXTRAWHITE BB_TASKHASH HOME LOGNAME PATH PWD
SHELL TERM USER DL_DIR"

But it is very sadly ugly... not terribly maintainable... and makes me
think I'm missing something important.

Please tell me I'm missing something important.

--wpd