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Re: [libvirt] any better way to treat device-detach timeout ?



On Fri, Mar 11, 2016 at 07:40:54 +0000, Zhangbo (Oscar) wrote:
> Hi,all:
> 
>    I find that we remove devices only after DEVICE_DELETED event.(patch:3fbf78bd).
>    And it treats TIMEOUT as success. The detailed codes are shown as below:
>         rc = qemuDomainWaitForDeviceRemoval(vm);
>         if (rc == 0 || rc == 1)
>           ret = qemuDomainRemoveDiskDevice(driver, vm, detach);
>         else
>           ret = 0;
> 
> 
>    Here comes the problem:
>    If 
>    1. We pass flags=3(VIR_DOMAIN_AFFECT_LIVE|VIR_DOMAIN_AFFECT_CONFIG) to virDomainDetachDeviceFlags,  
>    2. It timed out to receive DEVICE_DELETED event, virDomainDetachDeviceFlags api will return 0(succeed).
>      Please be aware that:  vm->newdef(persistent) removes the device while vm->def(transient) keeps it untouched.
>    3. Then we try to attach the same device with flag 3, because it differs in newDef and def, the API virDomainDetachDeviceFlags() returns ERROR.
>      Consequent attach/detach jobs all fail after then.
> 
>    So, shall we make it return FAIL when it fails in qemuDomainWaitForDeviceRemoval()?

No.

> Or just remove the device in def after we get the DEVICE_DELETED event? 

Yes, and we already do that. The API is explicitly documented as a
request to detach a device. It returns 0 when this request was
successfully passed to the guest OS. Some devices (e.g., USB devices)
are detached immediately, but others may require guest cooperation and
may take long time to detach or the guest may even completely ignore the
request. Thus, once virDomainDetachDeviceFlags returns 0, you need to
either periodically check the active XML to see if the device was
removed or you can register a callback for
VIR_DOMAIN_EVENT_ID_DEVICE_REMOVED event which is emitted when libvirt
really removes the device from the domain (after getting DEVICE_DELETED
from QEMU).

Jirka


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