Use both the -drive and -device options to set rootfs image

[ikitayama]

In an upcoming CXL related changes to the aarch64 target QEMU, the legacy -drive
option only does not work to set rootfs image; see below Jonathan's suggestions:

This is a challenge to fix at qemu side because it is relying on a bunch of old behavior.  For a while now legacy -drive parameters have been split into parts that go in -drive and a separate -device entry that covers the hardware - even with that though we'd need to specify a bus as on arm64 the default for -drive is virtio-blk which ends up I connected on the pcie bus.

Note this is just as broken if you use any pxb-pcie instances as those have similar fixed assumption that you can only hang root ports off them.

I think best solution is probably to stop use the old style

-drive file=root.img,format=raw,media=disk

and switch to fully expanded virtio solution along the lines of

-drive if=none,file=root.img,format=raw,media=disk,id=hd \ -device virtio-blk,bus=pcie.0,drive=hd

which should be fine on x86 and arm64 + any other architectures we support in the future and will always bring the disk up as an RCiEP on the main pcie root complex.

Jonathan

[marc-hb]

I'm guessing this is superseding this older PR?

• #201

Please always share a link to context (when there is context) in the discussion.

 
Code change looks good to me and it seems to be compatible even with the old QEMU 6.2.0 found on the old Ubuntu 22.04, Yay! So, no compatibility concern.

However:

• please provide a properly formatted commit message. It's OK to quote John at the end (even better: with an URL?) but the quote should not be the entire commit message.

• I would like some Intel QEMU expert to review this too. @stellarhopper anyone? You?