Re: Fwd: Adding devices via QMP's device_add don't have their bootindex setting respected

[Paolo Bonzini <pbonzini@redhat.com>]

On 18/05/21 14:22, Thomas Parrott wrote:
> Due to QEMU moving towards a QMP configuration mechanism and away from 
> config file support, the LXD team are currently in the process of 
> migrating to using QMP to add devices to VMs (so that we can support the 
> use of QEMU 6.0).

If the only issue you have is with -spice, that's just a bug that we 
need to fix.  -readconfig is still supposed to work, even though 
-writeconfig is deprecated and I'd like to remove it as soon as 6.1.

In particular, the issue you reported below is not a bug.  Devices that 
are added after startup are considered hotplugged, and the boot index 
list is frozen until the next reset.  QMP-based configuration of 
coldplugged devices is in the works, but unfortunately it is not yet ready.

Paolo

> Currently we are using the `-S` flag to freeze CPU at startup, then 
> using QMP to add NIC devices via the `device_add` command, and then 
> using the `cont` command to start the VM guest.
> 
> This is working mostly fine, but there is one issue; the provided 
> "bootindex" property is not respected.
> 
> E.g.
> 
> device_add 
> {"addr":"00.0","bootindex":"0","bus":"qemu_pcie4","driver":"virtio-net-pci","id":"dev-lxd_eth0","mac":"00:16:3e:0c:69:e7","mq":"on","multifunction":"off","netdev":"lxd_eth0","vectors":"6"}
> 
> The device is seen within the VM guest and the VM BIOS, but its boot 
> order is last rather than first.
> 
> We've also tried using a non-zero bootindex of 1 and that has the same 
> effect.
> 
> After discussions on #qemu IRC channel, we found that running 
> `system_reset` after adding the devices allowed the `bootindex` property 
> to be respected.
> 
> So this looks like bug. Perhaps we can discuss it in one of the 
> forthcoming community calls?
> 
> Thanks
> Tom Parrott