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

[Helmut Schaa]

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.

Helmut