Hi, the bug can be reproduced like that:

> QEMU 5.1.50 monitor - type 'help' for more information
> (qemu) netdev_add
> type=tap,id=net0,script=/home/and/SRCS/qemu/ifup.sh,downscript=no
> (qemu) info network
> hub 0
>  \ hub0port1: __org.qemu.net1: index=0,type=user,net=10.0.2.0,restrict=off
>  \ hub0port0: e1000e.0:
> index=0,type=nic,model=e1000e,macaddr=52:54:00:12:34:56
> dnet0: index=0,type=nic,model=virtio-net-pci,macaddr=52:54:00:12:34:57
> net0:
> index=0,type=tap,ifname=tap0,script=/home/and/SRCS/qemu/ifup.sh,downscript=no
> (qemu) netdev_del net0
> (qemu) info network
> hub 0
>  \ hub0port1: __org.qemu.net1: index=0,type=user,net=10.0.2.0,restrict=off
>  \ hub0port0: e1000e.0:
> index=0,type=nic,model=e1000e,macaddr=52:54:00:12:34:56
> dnet0: index=0,type=nic,model=virtio-net-pci,macaddr=52:54:00:12:34:57
> (qemu) netdev_add
> type=tap,id=net0,script=/home/and/SRCS/qemu/ifup.sh,downscript=no
> Try "help netdev_add" for more information
> (qemu) info network
> hub 0
>  \ hub0port1: __org.qemu.net1: index=0,type=user,net=10.0.2.0,restrict=off
>  \ hub0port0: e1000e.0:
> index=0,type=nic,model=e1000e,macaddr=52:54:00:12:34:56
> dnet0: index=0,type=nic,model=virtio-net-pci,macaddr=52:54:00:12:34:57
> (qemu)
>
>
Its still actual bug - I've checked it with the
master(2c6605389c1f76973d92b69b85d40d94b8f1092c).

On Sat, Nov 21, 2020 at 5:31 PM Yuri Benditovich <
yuri.benditovich@daynix.com> wrote:

>
>
> On Sat, Nov 21, 2020 at 5:24 PM Yuri Benditovich <
> yuri.benditovich@daynix.com> wrote:
>
>>
>>
>> On Fri, Nov 20, 2020 at 2:58 PM Markus Armbruster <armbru@redhat.com>
>> wrote:
>>
>>> Andrew Melnichenko <andrew@daynix.com> writes:
>>>
>>> > Ping
>>> >
>>> > On Thu, Jul 16, 2020 at 6:26 AM <andrew@daynix.com> wrote:
>>> >
>>> >> From: Andrew Melnychenko <andrew@daynix.com>
>>> >>
>>> >> There is an issue, that netdev can't be removed if it was added using
>>> hmp.
>>> >> The bug appears after 08712fcb851034228b61f75bd922863a984a4f60 commit.
>>> >> It happens because of unclear QemuOpts that was created during
>>> >> hmp_netdev_add(), now it uses qmp analog function -
>>> >> qmp_marshal_netdev_add().
>>> >>
>>> >> Signed-off-by: Andrew Melnychenko <andrew@daynix.com>
>>> >> ---
>>> >>  monitor/hmp-cmds.c | 15 +++------------
>>> >>  1 file changed, 3 insertions(+), 12 deletions(-)
>>> >>
>>> >> diff --git a/monitor/hmp-cmds.c b/monitor/hmp-cmds.c
>>> >> index 2b0b58a336..b747935687 100644
>>> >> --- a/monitor/hmp-cmds.c
>>> >> +++ b/monitor/hmp-cmds.c
>>> >> @@ -1597,19 +1597,10 @@ void hmp_migrate(Monitor *mon, const QDict
>>> *qdict)
>>> >>  void hmp_netdev_add(Monitor *mon, const QDict *qdict)
>>> >>  {
>>> >>      Error *err = NULL;
>>> >> -    QemuOpts *opts;
>>> >> -
>>> >> -    opts = qemu_opts_from_qdict(qemu_find_opts("netdev"), qdict,
>>> &err);
>>> >> -    if (err) {
>>> >> -        goto out;
>>> >> -    }
>>> >> +    QDict *non_constant_dict = qdict_clone_shallow(qdict);
>>> >>
>>> >> -    netdev_add(opts, &err);
>>> >> -    if (err) {
>>> >> -        qemu_opts_del(opts);
>>> >> -    }
>>> >> -
>>> >> -out:
>>> >> +    qmp_marshal_netdev_add(non_constant_dict, NULL, &err);
>>> >> +    qobject_unref(non_constant_dict);
>>> >>      hmp_handle_error(mon, err);
>>> >>  }
>>>
>>> qmp_marshal_netdev_add() uses the QObject input visitor, which feels
>>> wrong for HMP input.
>>>
>>> What exactly is the problem you're trying to solve?  Can you show us a
>>> reproducer?
>>>
>>> The problem was found during work on hotplug/unplug problems with q35
>> run q35 VM with netdev and hotpluggable nic (virtio or e1000e)
>> unplug the nic (device_del)
>> delete the netdev ()
>> add netdev with the same id as before - fail (Duplicated ID)
>>
>> Q35 is not mandatory for reproduction, the same with '-machine pc'
>
>