slim: Unable to uncompress kernel

[sertys3]

Greetings,
i'm trying to build qcow2 images from the ubuntu-20.04-cloud-init image, but am running into an issue.

Uncompressing compressed kernel
events.js:291
throw er; // Unhandled 'error' event
^

Error: incorrect header check
at Zlib.zlibOnError [as onerror] (zlib.js:182:17)
Emitted 'error' event on Gunzip instance at:
at errorOrDestroy (internal/streams/destroy.js:108:12)
at Gunzip.onerror (_stream_readable.js:754:7)
at Gunzip.emit (events.js:314:20)
at Zlib.zlibOnError [as onerror] (zlib.js:185:8) {
errno: -3,
code: 'Z_DATA_ERROR'
}

From what i can see the vmlinuz file is not compressed and the library is raising an error.

Are we certain that the docker kernel is at all compressed?

Regards,
Daniel

[chrisparnin]

There have been quite a few big changes in the code base, so the qcow2 build pipeline might have been fully tested.

My guess for this issue: Differences in arm64/intel releases of the linux use different formats for the kernel.

• For, arm64, vmlinuz is gzipped, and the new MacOS hypervisor bootloader needs the kernel to be uncompressed.
• For, intel, vmlinuz a bzImage with containing a compressed kernel.

The quick work around is to use -f raw which would build a raw disk image, that can be manually converted to qcow2 using qemu-convert, etc.

const formatSteps = {
    'vhd': [dockerBuild, dockerExport, buildEfiImage, makeVhd],
    'raw': [dockerBuild, dockerExport, buildRootfsImage, cleanup],
    'initrd-m1': [dockerBuild, dockerExtract, uncompressKernel, cpioPack],
    'initrd': [dockerBuild, dockerExtract, cpioPack],
    'special': [dockerBuild, dockerExport, buildRootfsImage, dockerExtract, uncompressKernel, cpioPack],
    'iso': [dockerBuild, dockerExtract, uncompressKernel, rawExtract, buildRootfsImage, isoBuild, cleanup],
    'qcow2': [dockerBuild, dockerExtract, uncompressKernel, rawExtract, buildRootfsImage, isoBuild, qcowBuild, cleanup]
};

Simply removing the uncompressKernel step for qcow2 will probably work.

Longer term, I want to introduce the idea of pipelines to make it easier to pick what processing steps you want to do on images.