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

Marek Marczykowski-Górecki wrote: > On Thu, Feb 19, 2015 at 03:58:30PM -0700, Jim Fehlig wrote: > >> 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(a)invisiblethingslab.com&gt; >>>>>>>>>> --- >>>>>>>>>> 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. >> > > Is that true for libvirt generally (all drivers)? > > >> Back to virDomainHasNet? :-) Or checking for the >> duplicate directly in libxlDomainAttachNetDevice()? >> > > What do you mean by "directly"? This is exactly what my patch did (until > virDomainNetFindIdx stopped reporting duplicates). > I mean coding up the search for an existing mac directly in libxlDomainAttachNetDevice(). E.g.

static int libxlDomainAttachNetDevice(libxlDriverPrivatePtr driver, libxlDomainObjPrivatePtr priv, virDomainObjPtr vm, virDomainNetDefPtr net) { int actualType; libxl_device_nic nic; int ret = -1; size_t i; virDomainDefPtr def = vm->def; for (i = 0; i < def->nnets; i++) { if (virMacAddrCmp(&def->nets[i]->mac, &net->mac) == 0) error; } ... } Regards, Jim