Re: Architecture of .wic approach; image of images

Maciej Pijanowski

On 28.11.2019 09:37, 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.
I think the rootfs is *always* assembled in the workdir (no matter which IMAGE_FSTYPES you choose.

The .wic image type however, builds an image from *images* rather than packages.
I'm not sure if this is correct. WIC is just one of the IMAGE_FSTYPES to choose from.
It does a little bit more then the tar.gz FSTYPE. The tar.gz just compresses the content
of rootfs. The WIC FSTYPE creates a disk image and installs the rootfs on a given
partition (depends on the WKS file chosen). The rootfs source is the same in
those both cases, no matter which FSTYPES you choose. It is made up of packages.

It therefore seems incorrect we can just add IMAGE_FSTYPES += "wic", because the corresponding .wks might depend on multiple other images than just ${PN}.

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)
I have not seen such case yet. IIUC, rootfs in the workdir is always populated when the image is built.



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Maciej Pijanowski
Embedded Systems Engineer | @3mdeb_com

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