Tales from the Kernel Parameter Side

Re:Tales from the Kernel Parameter Side by anderspitman on Saturday November 05, 2022 @04:10PM (#33485141)

I've been playing with QEMU a lot lately. Early on I encountered a fairly fundamental problem: how do you pass arbitrary data to a booting Linux system? I ended up discovering fw_cfg[0], but it feels pretty janky for this purpose and didn't seem to work for larger files like executables. Anyone aware of a better way?

[0]: https://www.kernel.org/doc/Documentation/ABI/testing/sysfs-f...

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Re:Tales from the Kernel Parameter Side by nrclark on Saturday November 05, 2022 @05:28PM (#33486014)

This isn't a perfect approach, but I've had pretty decent results with QEMU's virtfs for passing data into a QEMU VM (assuming your guest kernel is compiled with support for it).

QEMU's -virtfs option maps a folder on your host to a virtual filesystem. Inside your guest, you can mount the filesystem (assuming your kernel has CONFIG_NET_9P and CONFIG_NET_9P_VIRTIO enabled) and use it however you want.

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Re:Tales from the Kernel Parameter Side by anderspitman on Saturday November 05, 2022 @05:49PM (#33486218)

Unfortunately I need to support Windows hosts. I believe there's a patch in the works to add support, but it hasn't landed yet.

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Re:Tales from the Kernel Parameter Side by bombela on Saturday November 05, 2022 @05:53PM (#33486259)

Update the grub config directly. You can probably mount /boot from the outside?

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Re:Tales from the Kernel Parameter Side by 10000truths on Sunday November 06, 2022 @01:18AM (#33489727)

You can hook up the virtual serial port to stdin/stdout of the host by passing `-serial stdio` or `-nographic` in the QEMU args. You can then read from/write to the serial port in the VM.

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