Re: [PATCH] hw/block/block: add 'throttle-group' property

[Kevin Wolf <kwolf@redhat.com>]

Am 16.01.2026 um 15:39 hat Fiona Ebner geschrieben:
> With '-drive', it is possible to specify the throttle configuration
> directly on the commandline. Add the possibility to do the same when
> using the modern way with '-blockdev' and a front-end device. Using a
> throttle filter block node is not always an option: in particular, the
> mirror block job operates on a root block node and it might be desired
> to throttle only the guest IO, but not to the block job.

Hm, is there still a reason why we require a root node for the source?

> There already is a 'block_set_io_throttle' QMP command, but it's nicer
> to be able to do it via the commandline too.
> 
> Signed-off-by: Fiona Ebner <f.ebner@proxmox.com>
> ---
> 
> Hope I didn't miss a way to do this already.
> 
> Should changing via qom-set be supported? Currently, an attempt fails:
> > Error: Attempt to set property 'throttle-group' on device 'scsi0'
> > (type 'scsi-hd') after it was realized
> but there already is the 'block_set_io_throttle' QMP command.

It would be nice, but I don't think runtime writable properties are used
much in devices because I believe this would have to be done with plain
QOM properties, i.e. outside of qdev.

Though if it's actually easy, we could consider implementing it.

>  hw/block/block.c           | 15 +++++++++++++++
>  include/hw/block/block.h   |  4 +++-
>  tests/qemu-iotests/172.out | 38 ++++++++++++++++++++++++++++++++++++++
>  3 files changed, 56 insertions(+), 1 deletion(-)

Looks good to me, though maybe we could also use a qemu-iotests case
that actually tries to set the property instead of only updating the
output everywhere for having no throttle group.

Kevin