allow overriding qemu binary ($QEMU_SYSTEM_X86_64, $QEMU_SYSTEM_AARCH64)

[AkihiroSuda]

Passing args is also possible (only for debugging purpose), e.g., "QEMU_SYSTEM_X86_64=/opt/qemu/bin/qemu-system-x86_64 -snapshot" .

Fix #27
Fix #14

[jandubois]

I think it would be good if qemu.CmdLine would check for certain options if they are already provided by the override, and then don't add the built-in values for them (e.g. for -cpu, -machine, -smp, -boot, -display from a cursory scan). Since you are prefixing with the environment variable, there is no way to overwrite the builtin settings otherwise.

Maybe write a custom appendIfMissing(args, "-option", ...) that only appends the additional arguments when args doesn't yet have an entry equal to "-option"?

[jandubois]

BTW, providing options to qemu for debugging without recompiling lima is the main point of this change for me.

For providing the location of an alternate qemu binary $PATH works just as well as $QEMU_SYSTEM_X86_64.

[AkihiroSuda]

e.g. for -cpu, -machine, -smp, -boot, -display from a cursory scan

I'm not sure we want to support overriding these flags, as most of them are configurable via the YAML, though I guess it wouldn't hurt to support overriding -cpu and -machine.

A workaround is to specify a custom script like this via the env.

#!/bin/sh
set -eu
exec qemu-system-x86_64 (echo $@ | sed -e 's/-cpu [^ ]* /-cpu SOMETHING /')

[AkihiroSuda]

added commit qemu: allow overriding -cpu, -machine, .. as $QEMU_SYSTEM_X86_64

[jandubois]

LGTM

Also tested with QEMU_SYSTEM_X86_64="qemu-system-x86_64 -display cocoa" limactl start --tty=false and worked as expected.