[libvirt] [PATCH 07/10] libxl: prevent attaching multiple netdevs with the same MAC

[Jim Fehlig]

Marek Marczykowski-Górecki wrote:
> On Thu, Feb 19, 2015 at 03:10:13PM -0700, Jim Fehlig wrote:
>   
>> Jim Fehlig wrote:
>>     
>>> Marek Marczykowski-Górecki wrote:
>>>   
>>>       
>>>> On Thu, Feb 19, 2015 at 01:58:02PM -0700, Jim Fehlig wrote:
>>>>   
>>>>     
>>>>         
>>>>> Marek Marczykowski-Górecki wrote:
>>>>>     
>>>>>       
>>>>>           
>>>>>> On Thu, Feb 19, 2015 at 11:43:15AM -0700, Jim Fehlig wrote:
>>>>>>   
>>>>>>       
>>>>>>         
>>>>>>             
>>>>>>> Marek Marczykowski-Górecki wrote:
>>>>>>>     
>>>>>>>         
>>>>>>>           
>>>>>>>               
>>>>>>>> It will not be possible to detach such device later. Also improve
>>>>>>>> logging in such cases.
>>>>>>>>
>>>>>>>> Signed-off-by: Marek Marczykowski-Górecki <marmarek at invisiblethingslab.com>
>>>>>>>> ---
>>>>>>>>  src/libxl/libxl_driver.c | 41 +++++++++++++++++++++++++++++++++++++++--
>>>>>>>>  1 file changed, 39 insertions(+), 2 deletions(-)
>>>>>>>>
>>>>>>>> diff --git a/src/libxl/libxl_driver.c b/src/libxl/libxl_driver.c
>>>>>>>> index ce3a99b..005cc96 100644
>>>>>>>> --- a/src/libxl/libxl_driver.c
>>>>>>>> +++ b/src/libxl/libxl_driver.c
>>>>>>>> @@ -2787,6 +2787,7 @@ libxlDomainAttachNetDevice(libxlDriverPrivatePtr driver,
>>>>>>>>      int actualType;
>>>>>>>>      libxl_device_nic nic;
>>>>>>>>      int ret = -1;
>>>>>>>> +    char mac[VIR_MAC_STRING_BUFLEN];
>>>>>>>>  
>>>>>>>>      /* preallocate new slot for device */
>>>>>>>>      if (VIR_REALLOC_N(vm->def->nets, vm->def->nnets + 1) < 0)
>>>>>>>> @@ -2801,6 +2802,14 @@ libxlDomainAttachNetDevice(libxlDriverPrivatePtr driver,
>>>>>>>>  
>>>>>>>>      actualType = virDomainNetGetActualType(net);
>>>>>>>>  
>>>>>>>> +    /* -2 means "multiple matches" so then fail also */
>>>>>>>>   
>>>>>>>>       
>>>>>>>>           
>>>>>>>>             
>>>>>>>>                 
>>>>>>> No longer true after commit 2fbae1b2.  I think you just want to check if
>>>>>>> virDomainNetFindIdx() >= 0, meaning the def already contains a net
>>>>>>> device with the same mac address.
>>>>>>>     
>>>>>>>         
>>>>>>>           
>>>>>>>               
>>>>>> But here the error is when the device *is* found, so the opposite case
>>>>>> than already reported as an error by virDomainNetFindIdx.
>>>>>>       
>>>>>>         
>>>>>>             
>>>>> If you find an idx >= 0, then the domain def already contains a net
>>>>> device with the same mac address, right?  In that case, you report an
>>>>> error and return failure from libxlDomainAttachNetDevice().
>>>>>     
>>>>>       
>>>>>           
>>>> Right, but if I do not find one (idx == -1), I will proceed with
>>>> (possibly successful) adding the device, while the error was already
>>>> reported by virDomainNetFindIdx.
>>>>   
>>>>     
>>>>         
>>> Ah, right :-/.
>>>
>>> Another option: introduce virDomainHasNet() to detect if the domain def
>>> already contains the net device.
>>>   
>>>       
>> A better option would be to fix this in libxl, for the benefit of other
>> libxl apps.
>>     
>
> Actually libxl has no problem with duplicated mac addresses, its libvirt
> that makes problem.

Yeah, it appears duplicate mac addresses are only valid if on different
PCI devices.  Back to virDomainHasNet? :-)  Or checking for the
duplicate directly in libxlDomainAttachNetDevice()?

Regards,
Jim