You create this file in your custom layer.
You also name it accordingly based on the linux-yocto recipe
you are using.
For example, if you are modifying the
meta/recipes-kernel/linux/linux-yocto_3.4.bb
recipe, the append file will typical be located as follows
within your custom layer:
<your-layer>/recipes-kernel/linux/linux-yocto_3.4.bbappend
The append file should initially contain the following text:
FILESEXTRAPATHS := "${THISDIR}/${PN}"
The path ${THISDIR}/${
PN
}
expands
to "linux-yocto" in the current directory for this example.
If you add any new files that modify the kernel recipe,
you need to place them in your layer in the following area:
<your-layer>/recipes-kernel/linux/linux-yocto/