[yocto] cannot build image using sstate

[Mircea Gliga]

Long story short: I have problems building an image, in a clean build 
directory, reusing the shared state cache and downloads from a previous 
build.
A file created in the do_deploy_append task is not created(restored) 
anymore when building using a previous sstate.

And now the long description:
In my custom layer, in a kernel recipe, linux-stable.bb, I have appended 
some operations to the `deploy` task, one of them is creating an U-Boot 
FIT image:

linux-stable.bb:
do_deploy_append() {
[...]
         #this line creates the image_signed.fit file
          mkimage  [...] image_signed.fit

[...]
}

Then in my image recipe, my-custom-image.bb, I'm creating an archive 
with some files, including the above created FIT image:

my-custom-image.bb:

LINUXIMAGE = "image_signed.fit"
do_makeArch() {
[...]
    tar --owner root --group root -C ${DEPLOY_DIR_IMAGE} -cvf 
${DEPLOY_DIR_IMAGE}/psf/${IMAGEFILE} -h ${LINUXIMAGE}
[...]
}

addtask do_makeArch after do_image_complete before do_build


Now, create a new build directory, set DL_DIR and SSTATE_DIR in local 
conf, start build:
# source oe-init-build-env build2
# bitbake my-custom-image
ERROR: my-custom-image-1.0-r0 do_makeArch: Function failed: do_makeArch
Log data follows:
| DEBUG: Executing shell function do_makeArch
| tar: image_signed.fit: Cannot stat: No such file or directory
| tar: Exiting with failure status due to previous errors

So the image build fails, because the image_signed.fit file is not present.
After some short time the build is started, in the deploy directory I 
see that the zimage is already there but the FIT image is missing ...

This is confirmed by the linux-stable.bb's logs: log.do_deploy_setscene. 
It lists all the files that are restored from the sstate cache, 
image_signed.fit
is not one of them:

DEBUG: Executing shell function sstate_unpack_package
deploy-linux-stable/
deploy-linux-stable/zImage-machine.bin
deploy-linux-stable/zImage--4.8.4+git0+a2b42342b2-r0.2-machine-20170308134915.bin
deploy-linux-stable/zImage-at91-machine.dtb
deploy-linux-stable/README_-_DO_NOT_DELETE_FILES_IN_THIS_DIRECTORY.txt
deploy-linux-stable/zImage--4.8.4+git0+a2b42342b2-r0.2-at91-machine-20170308134915.dtb
deploy-linux-stable/modules-machine.tgz
deploy-linux-stable/modules--4.8.4+git0+a2b42342b2-r0.2-machine-20170308134915.tgz
deploy-linux-stable/zImage
deploy-linux-stable/zImage-initramfs-4.8.4+gitAUTOINC+a2b42342b2-r0-machine-20170308134915.bin
deploy-linux-stable/zImage-initramfs-machine.bin
DEBUG: Shell function sstate_unpack_package finished


Any hints, on how to add my custom generated files to the sstate ? Or 
what am I doing wrong here ?
Thanks