Kernel replacement

[JosSamLoh]

Why?

As I was attempting to get a currently unsupported game running on Fedora, I remembered about gpu passthrough. And while I was able to get everything set-up and working via layering virt-manager, and looking-glass-client from a copr repo, I was still experiencing one single issue: buggy usb passthrough. The remedy was to replace the kernel with one that included the acs patch, or to build and patch the kernel myself, to pass through my usb controller as a pci device with no issues.

How?

So far I have been able to create a script script that replaces the installed kernel packages with the sentry/kernel-fsync kernel packages.

You can also use this script while on a stock Silverblue install, as long as you comment out the rpm-ostree cliwrap install-to-root / && \ line. I have only tested this script on stock Silverblue and uBlue Silverblue.

Problems

Unfortunately the script only works on stock Silverblue images because of dependency issues with the added kernel packages, and more, in uBlue images.

[KE0VVT]

Thank you for figuring out how to do this. I tried adapting your script to my own kernel RPMs, but it gave me an error.

[JosSamLoh]

Looking at the url you're trying to grab from, it only contains 2 RPM packages, where my script intends to replace all already installed kernel package with their counterparts from a specified repo.

Most of what I've done so far is to automate the process as much as possible with the current scripts, so I can drag and drop when I fork main and nvidia, I also have an "easy" replacement script for when you only want to replace with a specific kernel for a single image build, I should have that on the repo soon, it's already on the discord as of writing.

[KE0VVT]

What would I need to do, to get my kernel to install? Normally, I can just rpm-ostree replace the RPM on Silverblue, and it installs, but putting the command in pre/ or post/ did not succeed.

[JosSamLoh]

The errors are coming from the the fact that the rpm-ostree override replace command is looking to replace every file matching the names of already existing kernel packages, and they don't exist in the repo you're downloading from, so it fails. So far this script has been specific for the sentry/kernel-fsync repo as when I attempt rpm-ostree override replace https://download.copr.fedorainfracloud.org/results/sentry/kernel-fsync/fedora-38-x86_64/05937107-kernel/kernel-6.3.3-201.fsync.fc38.x86_64.rpm it fails with:

error: Could not depsolve transaction; 1 problem detected:
 Problem: conflicting requests
  - nothing provides kernel-core-uname-r = 6.3.3-201.fsync.fc38.x86_64 needed by kernel-6.3.3-201.fsync.fc38.x86_64 from @commandline
  - nothing provides kernel-modules-core-uname-r = 6.3.3-201.fsync.fc38.x86_64 needed by kernel-6.3.3-201.fsync.fc38.x86_64 from @commandline
  - nothing provides kernel-modules-uname-r = 6.3.3-201.fsync.fc38.x86_64 needed by kernel-6.3.3-201.fsync.fc38.x86_64 from @commandline

Thus that script downloads all files from the directory locally and THEN replaces the required ones.

I have found success in a vm for your case by simply enabling the required repo, which can be easily put in the recipe, then running rpm-ostree override replace https://linux-libre.fsfla.org/pub/linux-libre/rpmfreedom/latest/RPMS/x86_64/kernel-6.3.5_gnu-1.x86_64.rpm. This, however, only replaces only the kernel package. If this is what you want then that's all you should need to do, but not much else can be done afaik unless the other kernel package rpms are built or are packaged in that repo. You may also need to put rpm-ostree cliwrap install-to-root / && \ before the replace command.

[JosSamLoh]

I have updated the repo with another, easier, kernel replacement script, with stock silverblue replaced with xanmod kernel as another example. Previous script has also been updated and improved.

[KE0VVT]

I added your easy script but I get an error. Is this because my replacement package is also called kernel?

[wyndon]

Worth nothing that if you want to use a custom kernel with nvidia drivers, then you're pretty much out of luck and would need to do that manually by layering the packages.

In my experience, installing a custom kernel and the nvidia drivers in a Containerfile leads to the custom kernel being uninstalled and replaced by the default kernel, aside from some things like headers.

You also can't really use ublue images as a base because they contain packages that conflicts with the replacement of the kernel, as stated by OP.

[plata]

Can we include this in https://github.com/ublue-os/startingpoint?

I'm trying to use the linux-surface kernel in plata/ublue-surface#3 but when building I get

dracut: Executing: /usr/libexec/rpm-ostree/wrapped/dracut --no-hostonly --kver 6.4.7-1.surface.fc38.x86_64 --reproducible -v --add ostree -f /tmp/.tmpJfJd11/initramfs.img
dracut: dracut module 'busybox' will not be installed, because command 'busybox' could not be found!
dracut: dracut module 'rngd' will not be installed, because command 'rngd' could not be found!
dracut: dracut module 'multipath' will not be installed, because command 'multipath' could not be found!
dracut: dracut module 'biosdevname' will not be installed, because command 'biosdevname' could not be found!
dracut-install: ERROR: installing '/root'
dracut: FAILED: /usr/lib/dracut/dracut-install -D /var/tmp/dracut.xqOSve/initramfs /root

Any ideas?