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init.c: only use KRUN_EXIT_CODE_IOCTL if root is really virtiofs #380

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Merged
merged 1 commit into from
Jul 31, 2025
Merged

init.c: only use KRUN_EXIT_CODE_IOCTL if root is really virtiofs #380

merged 1 commit into from
Jul 31, 2025

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@nohajc
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@nohajc nohajc commented Jul 25, 2025

I was playing with different VM configurations and was able to run a system from a raw disk image instead of virtiofs.
It basically works, I just need a custom cmdline and an actual copy of init.krun on the image filesystem.

The only issue is that init assumes root is always virtiofs and uses the KRUN_EXIT_CODE_IOCTL which will fail.
To avoid the error on conventional filesystems, we can first call statfs and check f_type.

@nohajc nohajc force-pushed the exit-code-ioctl-check branch 2 times, most recently from cd81951 to 7298634 Compare July 25, 2025 19:17
@nohajc nohajc marked this pull request as draft July 25, 2025 19:23
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ggoodman commented Jul 25, 2025

@nohajc not related to reviewing this PR, but if you have any examples of your setup to boot from an image it would be a valuable resource to share with the community 😄.

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nohajc commented Jul 25, 2025

@ggoodman Sure, my setup is very crude at this point. Just a couple of shell scripts to prepare the root filesystem and a lua script to interact with the C API. I also have a project built on top of libkrun but that's in Rust. Now I'm basically trying to make the microVMs scriptable but without using krunvm. I was definitely planning to share my results.

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init.c: only use KRUN_EXIT_CODE_IOCTL if root is really virtiofs
5f2e3cd 
Signed-off-by: Jan Noha <nohajc@gmail.com>
@nohajc nohajc force-pushed the exit-code-ioctl-check branch 2 times, most recently from 857f047 to 5f2e3cd Compare July 25, 2025 21:03
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nohajc commented Jul 25, 2025

@ggoodman I've seen your krun_set_rootfs_kernel_args pull request. The reason it works for me is that I already use a custom kernel image (krun_set_kernel) which lets me specify the entire kernel command line too.

Could be something like this

reboot=k panic=-1 panic_print=0 nomodule console=hvc0 root=/dev/vda rw quiet no-kvmapf init=/init.krun KRUN_INIT=/bin/bash KRUN_WORKDIR=/

@nohajc nohajc marked this pull request as ready for review July 25, 2025 21:09
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nohajc commented Jul 26, 2025

@ggoodman You can check out my setup here:
https://github.com/nohajc/anylinuxfs/tree/main/kernel-builder

slp
slp approved these changes Jul 31, 2025
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LGTM, thanks!

@slp slp merged commit 9b8e9eb into containers:main Jul 31, 2025
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