[ovs-dev] [PATCH 2/2] netdev-linux: Let interface flags survive port setup

[Helmut Schaa]

On Thu, Jan 9, 2014 at 5:48 PM, Ben Pfaff <blp at nicira.com> wrote:
> On Thu, Jan 09, 2014 at 08:51:00AM +0100, Helmut Schaa wrote:
>> On Thu, Jan 9, 2014 at 1:59 AM, Ben Pfaff <blp at nicira.com> wrote:
>> > On Wed, Jan 08, 2014 at 04:43:47PM +0100, Helmut Schaa wrote:
>> >> Due to a race condition when bringing up an internal port on Linux
>> >> some interface flags (e.g. IFF_MULTICAST) are falsely reset. This
>> >> happens because netlink events may be processed after the according
>> >> netdev has been brought up (which sets interface flags).
>> >>
>> >> Fix this by reading the interface flags just before updating them
>> >> if they have not been updated by from the kernel yet.
>> >>
>> >> Signed-off-by: Helmut Schaa <helmut.schaa at googlemail.com>
>> >
>> > Hmm.  I see the problem.  Thanks for finding and reporting it, and for
>> > the patch.
>> >
>> > I have two ideas here:
>> >
>> >         1. Add (back) VALID_FLAGS and check for it here.  (It will
>> >            generally be valid, except in the case of initial
>> >            construction of internal devices.)  I think that this would
>> >            probably be better than abusing VALID_DRVINFO.
>>
>> Agreed, that makes sense ...
>>
>> >         2. Instead of using an ioctl and ifreq to set interface flags,
>> >            use rtnetlink with RTM_SETLINK, with ifi_flags and
>> >            ifi_change.  In Linux 2.6.22 and later, this allows one to
>> >            set a subset of flags, rather than all flags overall, and
>> >            that generally reflects OVS userspace intent, which never
>> >            tries to change more than one flag at a time.  I think that
>> >            we could even look at ifi_change in the Netlink response to
>> >            see whether the change actually made a difference and (in
>> >            pre-2.6.22) spot whether it had some unintended effect so
>> >            that we could reverse it.
>> >
>> > Ideally, we'd do both.
>> >
>> > What do you think?
>>
>> Hmm, good point. Let me look into this.
>
> Thank you!

I haven't found time to respin this yet. Maybe I'll go with just adding
the VALID_FLAGS back to get this fixed within a reasonable time frame.
Helmut