Re: Architecture of .wic approach; image of images

Josef Holzmayr <holzmayr@...>

On Thu, Nov 28, 2019 at 09:37:12AM +0100, Leon Woestenberg wrote:
Hello all,

What is the intended approach of building images using WIC?

Most image types (except .wic) build a (root or initial ram) filesystem
from *packages*, then create the respective archive or filesystem from it.

The .wic image type however, builds an image from *images* rather than
Thats *almost* correct. It builds an image from a *artifacts*.

It therefore seems incorrect we can just add IMAGE_FSTYPES += "wic",
because the corresponding .wks might depend on multiple other images than
just ${PN}.
If it does, then your dependency architecture is probably broken. You
have to understand that building an image might produce artifacts that
are not actually included in the rootfs: many systems expect the kernel
to be external to it, and even most do so for u-boot. Hence, the mindset
is as follows: the image recipe biulds everything that you need. It does
not care about the actual for those things shall be poured into.

Should we, or do we have a recipe example that builds only a .wic image,
based on one or more other existing images? (and thus not populate a
filesystem itself)
See above. The image recipe produces all the needed artififacts, that a
*seomthing* later in the pipeline needs. This *something* then takes
those artifacts and pours them into a binary form you can use. Its maybe
bad naming that the configuration of that binary output form is
IMAGE_FSTYPE, which suggests a relation to the image. But de factor,
mentally replace IMAGE_FSTYPE with BINARY_RESULT_FORMAT, and then it
should become clear that this is actually two seperate stages of the
build pipeline.



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Josef Holzmayr
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