[yocto] The role of "distro" and "image"

[Chris Larson]

On Thu, Dec 15, 2011 at 10:29 AM, Koen Kooi <koen at beagleboard.org> wrote:
> Op 13 dec. 2011, om 22:45 heeft Chris Larson het volgende geschreven:
>
>> On Tue, Dec 13, 2011 at 2:36 PM, Richard Purdie
>> <richard.purdie at linuxfoundation.org> wrote:
>>> Not all images can be built with a given distro, our base config is
>>> rather ride ranging though for obvious reasons. You could "enforce" this
>>> by adding some anonymous python to the distro which does something like:
>>>
>>> if inherits("image") and PN != core-image-minimal:
>>>    raise SkipPackage("Image PN not compatible with DISTRO=XXX")
>>
>> This is a case where one is best 'controlling' this via policy, not
>> mechanism, in my opinion. This sort of arbitrary technical limitation
>> tends to be foolish and often bites someone somewhere down the line.
>> I'm sure you just wanted to note how it could be done, not recommend
>> that it should be done, but I thought it should be made clear. I
>> wouldn't recommend that anyone do this unless there is an extremely
>> good reason for it.
>
> We had a similar problem at work, people were sprinkling COMPATIBLE_MACHINE left and right just to mark "I tested recipe X on machine Y". You can guess what happened when new machines needed to get added.

Haha, ouch. It's also worth taking a moment to emphasize that the way
distro/machine/image is structured is by design, not accidental.
Having these pieces be orthogonal buys us a great deal of flexibility
and capability, which is why we did it this way. Now, whether a given
distro/machine/image combination is *useful* is a different question,
and one I think is best addressed via policy / documentation.
-- 
Christopher Larson