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

[Jim Fehlig]

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.

Regards,
Jim