[yocto] Kernel change in YOCTO

[Zoran Stojsavljevic]

Hello,

I have a bit dummy question. I have older Pyro distro, compiled for
qemux86_64. It has there kernel 4.10.17, and there are two interesting
directories, where one can find definitions of the kernels:

[user at localhost poky]$ find . -name *.bbappend
...
./meta-yocto-bsp/recipes-kernel/linux/linux-yocto_4.1.bbappend
./meta-yocto-bsp/recipes-kernel/linux/linux-yocto_4.10.bbappend
./meta-yocto-bsp/recipes-kernel/linux/linux-yocto_4.12.bbappend <<===
Introduced later
./meta-yocto-bsp/recipes-kernel/linux/linux-yocto_4.4.bbappend
./meta-yocto-bsp/recipes-kernel/linux/linux-yocto_4.9.bbappend
...

And the .bb scripts are located in:
./meta/recipes-kernel/linux/linux-yocto-tiny_4.1.bb
./meta/recipes-kernel/linux/linux-dummy.bb
./meta/recipes-kernel/linux/linux-yocto_4.9.bb
./meta/recipes-kernel/linux/linux-yocto_4.1.bb
./meta/recipes-kernel/linux/linux-yocto-rt_4.1.bb
./meta/recipes-kernel/linux/linux-yocto-dev.bb
./meta/recipes-kernel/linux/linux-yocto-rt_4.12.bb
./meta/recipes-kernel/linux/linux-generic_4.13.3.bb <<=== Introduced later
(git HEAD checkout)
./meta/recipes-kernel/linux/linux-yocto-tiny_4.9.bb
./meta/recipes-kernel/linux/linux-yocto_4.10.bb
./meta/recipes-kernel/linux/linux-yocto-tiny_4.4.bb
./meta/recipes-kernel/linux/linux-yocto-rt_4.9.bb
./meta/recipes-kernel/linux/linux-yocto_4.4.bb
./meta/recipes-kernel/linux/linux-yocto_4.12.bb <<=== Introduced later
./meta/recipes-kernel/linux/linux-yocto-rt_4.4.bb
./meta/recipes-kernel/linux/kernel-devsrc.bb

Whatever I did (introduced kernel_4.12.12 with the same set of the scripts
from master - different git headers), I was not able to switch kernel while
building qemux86-64!?

Even at the end (in desperation to understand from where dependencies are
coming) I deleted .git in poky/, and deleted everything in build/, except
conf/bbappend.conf and conf/local.conf?!

But still, kernel 4.10.17 is always taken... No idea why?

user at localhost build]$ bitbake -c fetchall core-image-sato
WARNING: Host distribution "fedora-26" has not been validated with this
version of the build system; you may possibly experience unexpected
failures. It is recommended that you use a tested distribution.
Loading cache: 100%
|#################################################################################################################################################################|
Time: 0:00:01
Loaded 1300 entries from dependency cache.
NOTE: Resolving any missing task queue dependencies

Build Configuration:
BB_VERSION        = "1.34.0"
BUILD_SYS         = "x86_64-linux"
NATIVELSBSTRING   = "universal"
TARGET_SYS        = "x86_64-poky-linux"
MACHINE           = "qemux86-64"
DISTRO            = "poky"
DISTRO_VERSION    = "2.3.1"
TUNE_FEATURES     = "m64 core2"
TARGET_FPU        = ""
meta
meta-poky
*meta-yocto-bsp    = "<unknown>:<unknown>" <<=== .git deleted prior
fetching*

Initialising tasks: 100%
|############################################################################################################################################################|
Time: 0:00:18
NOTE: Executing RunQueue Tasks

Summary: There were 11 WARNING messages shown.
[user at localhost build]$
_______

Questions:
[1] Should I blindly follow:
http://www.yoctoproject.org/docs/2.3.2/kernel-dev/kernel-
dev.html#creating-and-preparing-a-layer
Where it is written that new layer must be introduced for the new kernel,
also (after layer and scripts creation) placed in
.../build/conf/bbappend.conf?

[2] If [1] is a must, where I can read about reasons why this requirement
exists?? Maybe BSP and kernel have some invisible dependencies??

[3] Where are these invisible kernel dependencies? So is there something
(?) kernel depends on, although I always believed that everything else is
dependent on kernel (kernel is HW dependend via device drivers), since
kernel lives on its own (except some BSP data - kernel command line passed
to it at the boot time, which should have no influence on dependency of any
kind between kernel boot-loader and kernel itself)?!

Thank you,
Zoran
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