'file' driver requires '/dev/sdx' to be a regular file

Software environment

• Operating system: Arch Linux
• Architecture: x86_64
• kernel version: 5.13.13.arch1-1
• libvirt version: 7.7.0
• Hypervisor and version: QEMU 6.1.0

Description of problem

When trying to launch a domain which has a block device being passed as follows:

<disk type='block' device='disk'>
 <driver name='qemu' type='raw'/>
 <source dev='/dev/sdx'/>
</disk>

it fails with following error: internal error: process exited while connecting to monitor: 2021-09-04T09:03:30.420933Z qemu-system-x86_64: -blockdev {"driver":"file","filename":"/dev/sdx","aio":"native","node-name":"libvirt-2-storage","cache":{"direct":true,"no-flush":false},"auto-read-only":true}: 'file' driver requires '/dev/sdx' to be a regular file.

Steps to reproduce

1. Create a QEMU/KVM domain
2. Add a disk to it which points to the block device at host
3. Try to launch the domain

Additional information

This seems to be a breaking change introduced in QEMU 6.0, as changelog says the following: The file block driver no longer permits use with block devices. Downgrading to QEMU 5.2 allows for domain to successfully boot up.

Judging from current documentation, in order to pass a block device, you have to use raw block driver instead.