Re: [Qemu-devel] [RFC 0/4] Replace has_dynamic_sysbus with device type whitelist

[Juergen Gross]

On 23/03/17 22:28, Eduardo Habkost wrote:
> Summary
> -------
> 
> This series replaces the existing has_dynamic_sysbus flag (that
> makes the machine accept every single sysbus device type on the
> command-line) with a short whitelist.
> 
> This will be helpful when implementing the new query-device-slots
> command, because each machine type will include only the sysbus
> devices it really supports, instead of including a catch-all
> TYPE_SYS_BUS_DEVICE "slot".
> 
> Most of the machines already have an internal whitelist
> implemented using foreach_dynamic_sysbus_device(), so we just
> encode the existing behavior inside the new MachineClass field.
> 
> Caveat: q35
> -----------
> 
> The only problematic case is q35, that accepts all sysbus device
> types. In this case, instead of adding TYPE_SYS_BUS_DEVICE to the
> whitelist, I'm adding the existing list of existing sysbus device
> types to keep compatibility. After that, we can gradually and
> carefully remove unnecessary entries from the q35 whitelist.
> 
> Issue: xen_set_dynamic_sysbus() hack
> ------------------------------------
> 
> We still have an obstacle to get around: the callers of
> qdev_set_id() outside qdev_device_add() are breaking
> foreach_dynamic_sysbus_device(), and xen_set_dynamic_sysbus() is
> a workaround for that bug. We now need to fix that bug to be able
> to remove the xen_set_dynamic_sysbus() hack. This means the first
> patch of this series will probably break Xen, until we fix that
> bug.
> 
> Eduardo Habkost (4):
>   [UNTESTED] xen: Don't force has_dynamic_sysbus on machine class
>   machine: Replace has_dynamic_sysbus with a whitelist
>   q35: Remove ioapic devices from sysbus whitelist
>   q35: Remove fw_cfg* from sysbus whitelist
> 
>  include/hw/arm/sysbus-fdt.h |  7 +++++++
>  include/hw/boards.h         |  3 ++-
>  hw/arm/sysbus-fdt.c         | 10 ++++++++++
>  hw/arm/virt.c               |  4 +++-
>  hw/core/machine.c           | 43 +++++++++++++++++++++++++++++--------------
>  hw/i386/pc_q35.c            | 25 ++++++++++++++++++++++++-
>  hw/ppc/e500plat.c           |  4 +++-
>  hw/ppc/spapr.c              |  2 +-
>  hw/xen/xen_backend.c        | 11 -----------
>  9 files changed, 79 insertions(+), 30 deletions(-)
> 

This seems to break Xen. I got:

qemu-system-i386: Option '-device xen-backend' cannot be handled by this
machine

when using qemu as Xen backend driver.


Juergen