[libvirt] [PATCH] qemu: hotplug: unify "not found" logs when detaching device

[Chen Hanxiao]

At 2017-12-18 21:57:11, "John Ferlan" <jferlan at redhat.com> wrote:
>
>
>On 12/15/2017 09:50 PM, Chen Hanxiao wrote:
>> 
>> 
>> At 2017-12-16 09:26:32, "John Ferlan" <jferlan at redhat.com> wrote:
>>>
>>>
>>> On 12/14/2017 06:16 AM, Chen Hanxiao wrote:
>>>> From: Chen Hanxiao <chenhanxiao at gmail.com>
>>>>
>>>> Some services, such as Nova, check whether device was not found
>>>> by errror messages "not found". [1]
>>>
>>> error
>>>
>>>>
>>>> This patch unify logs of qemuDomainDetachDeviceLive, which will be helpful.
>>>>
>>>> [1] https://github.com/openstack/nova/blob/master/nova/virt/libvirt/guest.py#L406
>>>>
>>>> Signed-off-by: Chen Hanxiao <chenhanxiao at gmail.com>
>>>> ---
>>>>  src/qemu/qemu_hotplug.c | 18 +++++++++++-------
>>>>  1 file changed, 11 insertions(+), 7 deletions(-)
>>>>
>>>
>>> Something about a tool that parses the error message(s) looking for a
>>> specific message string in English and needing to alter libvirt sources
>>> to match that tools' needs strikes me as incorrect and a "slippery
>>> slope" to follow.
>>>
>>> I'm not in favor of this because we'll be constantly chasing these types
>>> of bugs to match some other tools' (what I think is) incorrect means to
>>> handle errors.
>>>
>> 
>> Agree.
>> But we don't have enough error code to cover all of scenario.
>> 
>
>Then there'd be a "different" fix required - adding an error code...
>Perhaps VIR_ERR_NO_DEVICE which would have error text "device %s not found"?

Thanks for the review.
I'll post a patch to throw VIR_ERR_NO_DEVICE  for hot_plug cases.

>
>Of course that would require up the stack source code changes as well.
>Still better than scanning the error message which only works for a
>specific language set. IOW: how would this work for non "English" languages?
>
>> For qemuDomainDetachDeviceDiskLive, VIR_ERR_OPERATION_FAILED can be
>> "disk not found", also can be "cannot hot unplug multifunction PCI device"
>> in the following call of qemuDomainDetachVirtioDiskDevice.
>
>So it's "OK" to have a different operational failure? I assume that'll
>cause a failure elsewhere in the code. I didn't go digging on the source
>code - just a quick look at the _try_detach_device method from the above
>nova link.
>
>> 
>> So the tools powered by libvirt had to find a workaround by 
>> analyzing error messages...
>
>Again, wouldn't those tools be broken without the right language set
>being used?
>

Thanks for the detail clarification.
Checking words in error log is a bad way to catch errors and should be fixed.

Regards,
- Chen