[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 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.

Regards,
Jim