Format=uki not consuming specified Initrds=

[hsitter]

mkosi commit the issue has been seen with

main

Used host distribution

KDE Linux

Used target distribution

custom

Linux kernel version used

No response

CPU architectures issue was seen on

None

Unexpected behaviour you saw

The defined initrd is not used, instead the uki build generates a new initrd (which is also dumber about what to include 😢)

Example tree at https://invent.kde.org/sitter/mkosi-uki-bug

Basically demonstrating that Initrds=default correctly generates a tiny initrd but then during assembling of the uki it generates a new initrd with extra data that were not in the initrd's tree, blowing up the size. Note build.sh.

Used mkosi config

[Distribution]
Distribution=custom

[Output]
ImageId=mkosi
Format=uki
OutputDirectory=mkosi.output

[Content]
BaseTrees=base
Initrds=default

mkosi output

+ rm -rf mkosi.output
+ dd bs=100M count=1 iflag=fullblock if=/dev/urandom of=base/usr/lib/modules/7.0.11/foo.ko
1+0 records in
1+0 records out
104857600 bytes (105 MB, 100 MiB) copied, 0.350596 s, 299 MB/s
+ mkosi
‣ Distribution of your host can't be detected or isn't a supported target. Defaulting to Distribution=custom.
‣ Validating certificates and keys
‣ Syncing package manager metadata: no incremental images, no caches to preserve
‣ Syncing package manager metadata
‣ Building default-initrd image
‣ [default-initrd]  Copying in base trees…
‣ [default-initrd]  Installing extra packages for Custom
‣ [default-initrd]  Generating hardware database
No hwdb files found, skipping.
‣ [default-initrd]  Copying in extra file trees…
‣ [default-initrd]  Generating system users
‣ [default-initrd]  Generating volatile files
‣ [default-initrd]  Applying presets…
‣ [default-initrd]  Applying first boot settings
/buildroot: /etc/locale.conf written.
‣ [default-initrd]  Removing files…
‣ [default-initrd]  Creating cpio archive /home/me/.cache/mkosi/mkosi-workspace-0dceoa4s/staging/initrd.cpio…
‣ [default-initrd]  Compressing /home/me/.cache/mkosi/mkosi-workspace-0dceoa4s/staging/initrd.cpio with zstd
‣ [default-initrd] Could not rename /home/me/.cache/mkosi/mkosi-workspace-0dceoa4s/staging/initrd.cpio.zst to /home/me/src/mkosi-uki/mkosi.output/initrd.cpio.zst as they are located on different devices, falling back to copying
‣ [default-initrd]  /home/me/src/mkosi-uki/mkosi.output/initrd.cpio.zst size is 1.2K, consumes 4.0K.
‣ [default-initrd] Building main image
‣ [main]  Copying in base trees…
‣ [main]  Running depmod for 7.0.11
‣ [main]  Generating hardware database
No hwdb files found, skipping.
‣ [main]  Generating system users
‣ [main]  Generating volatile files
‣ [main]  Applying presets…
‣ [main]  Running depmod for 7.0.11
‣ [main]  Building microcode initrd
‣ [main] /usr/lib/firmware/{amd-ucode,intel-ucode} not found, not adding microcode
‣ [main]  Building kernel modules initrd
‣ [main]   Applying firmware include/exclude configuration
‣ [main]   Creating cpio archive /home/me/.cache/mkosi/mkosi-workspace-t0terg9z/kernel-modules-7.0.11.initrd…
‣ [main]  Creating cpio archive /home/me/.cache/mkosi/mkosi-workspace-t0terg9z/initrd…
‣ [main]  Compressing /home/me/.cache/mkosi/mkosi-workspace-t0terg9z/initrd with zstd
‣ [main]  Generating unified kernel image for kernel version 7.0.11
Wrote unsigned /work/home/me/.cache/mkosi/mkosi-workspace-t0terg9z/staging/mkosi.efi
‣ [main] Could not rename /home/me/.cache/mkosi/mkosi-workspace-t0terg9z/staging/mkosi.vmlinuz to /home/me/src/mkosi-uki/mkosi.output/mkosi.vmlinuz as they are located on different devices, falling back to copying
‣ [main] Could not rename /home/me/.cache/mkosi/mkosi-workspace-t0terg9z/staging/mkosi.initrd to /home/me/src/mkosi-uki/mkosi.output/mkosi.initrd as they are located on different devices, falling back to copying
‣ [main] Could not rename /home/me/.cache/mkosi/mkosi-workspace-t0terg9z/staging/mkosi.efi to /home/me/src/mkosi-uki/mkosi.output/mkosi.efi as they are located on different devices, falling back to copying
‣ [main]  /home/me/src/mkosi-uki/mkosi.output/mkosi.efi size is 138.6M, consumes 138.6M.

[behrmann]

Thanks for the report.

Before I look into this, just to be clear: Your goal is that mkosi generates a default initrd but uses the supplied base tree, is that correct?

Seeing that you use a custom distribution and this being KDE I assume this is for some KDE equivalent of GnomeOS, i.e. an image-based KDE-centric distribution? What does the build system look like? Is it something like buildstream?

[hsitter]

Correct on all points :)

Essentially I am trying to move us to have mkosi generate the entire initrd+uki instead of relying on dracut or whatever to supply an initrd. That's when I found the bug.

I'll explain my prototype below, but it's a lot of text so the tl;dr is: AFAIU UKI images do not use kmod.py tech. This leads to them being huge. Initrds=default would generate a version that runs through kmod.py. Initrds=default doesn't prevent UKI images from generating their oversized initrds. Thus a UKI build always has an oversized initrd even when it would have a better default-initrd.

---

Here's how my prototype works.

The full build system is a bit convoluted but as far as initrd is concerned things look like this:

• we have a buildstream element that composes the base of the initrd
• the entire tree then gets checked out into a dir
• we invoke mkosi with a baseline conf for the rootfs, an initrd.conf for the mkosi generated initrd, and UKI subimages

There are actually three subimages:

• uki: defines the main uki; depends on initrd-build subimage
• uki.live: defines the live iso uki; depends on initrd-build subimage; essentially just a version of the uki with extra cmdline args
• initrd-build: defines the initrd and only the initrd. the ukis then consume that prepared initrd rather than the initrd tree from buildstream. I'll explain why in a minute.

The basetrees thus are:

• mkosi.conf: checkout of the rootfs
• initrd.conf: checkout of the maximum contents of the initrd
• initrd-build: has no actual base, it only generates the initrd from initrd.conf
• uki: the initrd created by initrd-build
• uki.live: same as uki

So far so complicated.

The point of the initrd-build is twofold. For one we only build the initrd once but consume it twice; not super important. But it also means we hit up different initrd generation code paths inside mkosi. When generating a default-initrd (for a non-uki images) the code eventually seems to run through kmod.py to drop firmwares and unneeded modules. The initrd generation, as part of a uki build, simply cpios whatever base tree you give it. Essentially the default-initrd will be some hundred megabytes, while the uki initrd of the same base tree will be a gigabyte because it includes all files.

That's when I noticed the bug. Right now I can't have the uki subimages declare Initrds=default to generate a "smart" initrd. It will always generate a "dumb" initrd because it is a UKI.

The workaround for the bug at hand is to have this initrd-build assistive image. It produces a directory of the "smart" initrd and then I use that as a base tree for the ukis, forcing them to also be smart 😅

[okias]

it seems you're not alone, BengalOS fights with this issue too