[OE-core] Issues with PREFERRED_VERSION/PREFERRED_PROVIDER for the kernel

[Ulf Samuelsson]

1. If you define something in the <MACHINE>.conf and in <DISTRO>.conf
     then <DISTRO>.conf has higher priority.
     This is really non-intuitive.

2. If you define a PREFERRED_VERSION which does not have a corresponding 
".bb" file
     you do not get a warning, and the latest PREFERRED_PROVIDER is used.

3. If you define a PREFERRED_PROVIDER which does not have a 
corresponding ".bb" file
     you *do* get a warning, with a list of possible providers, and 
bitbake will bake the
     first in the list.
     It will also bake the *latest* version, even if that provider has a 
PREFERRED_VERSION.

4. If I define PREFERRED_PROVIDER_virtual/kernel = "linux-x"  in 
<machine>.conf,
     bitbake will bake "linux-x" using the latest version

5. If I define PREFERRED_VERSION_virtual/kernel = "3.7.0", this is ignored.

6. If I define PREFERRED_VERSION_linux-x = "3.7.0", this is accepted and 
linux-x_3.7.0.bb is used.

-------------------------------------------
Questions:
     You need to parse <machine>.conf before you parse the DISTRO since
     some things in the distro is machine dependent.

     I.E:  PREFERRED_VERSION_binutils_avr32 = "2.17"

(1) Would it be possible to reparse <machine>.conf
     after DISTRO has been parsed, resetting some stuff, overridden by 
the DISTRO?

(2)  Why no warning, if the PREFERRED_VERSION cannot be found.
     It would be good to have which versions are available.

     For the Beaglebone, you have a linux-mainline_3.7.bb, but if you set

     PREFERRED_VERSION_linux-mainline = "3.7"

     you still get "3.8.13" built, because "linux-mainline_3.7.bb" 
contains PV = "3.7.0"

     A warning would have been helpful!

(3) Why is PREFERRED_VERSION_virtual/kernel accepted without error 
message, but ignored?

(4) If bitbake cannot find a recommended PROVIDER, and selects something 
else,
      why not use the PREFERRED_VERSION if it exists?

BR
Ulf Samuelsson