[oe] Why PREFERRED_VERSION setting of <distro>.conf overrules local.conf setting ?

[Denys Dmytriyenko]

On Wed, Aug 11, 2010 at 12:13:08PM +0930, Graham Gower wrote:

> Ok, I'm not so passionate about this change... But I'd like to
> highlight why this is not particularly intuitive.
> My experience has been that only certain image targets will build
> without overrides in a local.conf.
> 
> But then i determined that udev 151 didn't like my old kernel, so I
> set  PREFERRED_VERSION_udev = "141". Only this doesn't work because
> the (angstrom) distro pins it and the 151 version is silently picked
> up. I now understand why, but I didn't at the time.

Yeah, udev > 141 doesn't like glibc < 2.9 either.

> So PREFERRED_VERSION_foo="123" might work, or it might not. And the
> same goes for PREFERRED_PROVIDER_foo, which is actually less
> consistent because some use a weak assignment in the conf files and
> others don't.
> 
> Oh, and where is the ?= operator documented? I would have expected to
> find it here: http://bitbake.berlios.de/manual/ch02.html

The only place I was able to find it explained is in OpenEmbedded manual under 
"Conditional assignment" of "Syntax of recipes" chapter:

http://docs.openembedded.org/usermanual/html/recipes_syntax.html

-- 
Denys