Re: [Xen-devel] [PATCH v2] libxl_qmp: wait for completion of device removal

[Chao Gao <chao.gao@xxxxxxxxx>]

On Wed, Jul 03, 2019 at 05:03:17PM +0100, Anthony PERARD wrote:
>On Wed, Jul 03, 2019 at 01:56:13PM +0800, Chao Gao wrote:
>> To remove a device from a domain, a qmp command is sent to qemu. But it is
>> handled by qemu asychronously. Even the qmp command is claimed to be done,
>> the actual handling in qemu side may happen later.
>> This behavior brings two questions:
>> 1. Attaching a device back to a domain right after detaching the device from
>> that domain would fail with error:
>> 
>> libxl: error: libxl_qmp.c:341:qmp_handle_error_response: Domain 1:received an
>> error message from QMP server: Duplicate ID 'pci-pt-60_00.0' for device
>> 
>> 2. Accesses to PCI configuration space in Qemu may overlap with later device
>> reset issued by 'xl' or by pciback.
>> 
>> In order to avoid mentioned questions, wait for the completion of device
>> removal by querying all pci devices using qmp command and ensuring the target
>> device isn't listed. Only retry 5 times to avoid 'xl' potentially being 
>> blocked
>> by qemu.
>> 
>> Signed-off-by: Chao Gao <chao.gao@xxxxxxxxx>
>> ---
>> Changes in v2:
>>  - Break out early if we found an error during querying pci devices.
>>  - Print a message to warn admin that device removal may not be done
>>    in device model's side.
>
>Reviewed-by: Anthony PERARD <anthony.perard@xxxxxxxxxx>
>

Could we merge this patch? or need comments from someone else?

Thanks
Chao

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