qcow2 disk option lazy_refcounts got disabled by cloud-hypervisor

[networkhermit]

Describe the bug

When using qcow2 disk with lazy refcounts: true, cloud-hypervisor would disable the lazy_refcounts option on startup, thus changing the image metadata.

To Reproduce

1. Check existing qcow2 disk uses lazy_refcounts:

❯ sudo qemu-img info fedora.qcow2 | grep 'lazy refcounts'
    lazy refcounts: true

2. Start the qcow2 disk using cloud-hypervisor

sudo cloud-hypervisor --cpus boot=4 --memory size=8G --kernel ./CLOUDHV.fd --console off --serial tty --net "tap=,mac=,ip=,mask=" --disk path=./fedora.qcow2

3. Check the qcow2 disk again, the lazy_refcounts now got disabled:

❯ sudo qemu-img info fedora.qcow2 | grep 'lazy refcounts'
    lazy refcounts: false

Version

cloud-hypervisor v38.0.0

VM configuration

What command line did you run (or JSON config data):

sudo cloud-hypervisor --cpus boot=4 --memory size=8G --kernel ./CLOUDHV.fd --console off --serial tty --net "tap=,mac=,ip=,mask=" --disk path=./fedora.qcow2

Guest OS version details: Fedora 39

Host OS version details: Arch Linux

Logs

Not relevant.

[rbradford]

Hi, @networkhermit thank you for opening an issue - the QCOW2 support is somewhat unmaintained as there is nobody on the project that has any particular expertise on it (most of it was just lifted from crosvm). I recommend using a raw file instead.

[networkhermit]

Hi, @networkhermit thank you for opening an issue - the QCOW2 support is somewhat unmaintained as there is nobody on the project that has any particular expertise on it (most of it was just lifted from crosvm). I recommend using a raw file instead.

Thanks for the clarification.

#6349 is also related with qcow2. I think it's better to warn users about qcow2 in the website/documents and perhaps also in cli.