Re: [PATCH v3,net-next] vlan: implement vlan id and protocol changes

[Ido Schimmel <idosch@idosch.org>]

On Tue, Jun 26, 2018 at 09:33:40AM -0400, Chas Williams wrote:
> On Tue, Jun 26, 2018 at 6:32 AM Ido Schimmel <idosch@idosch.org> wrote:
> 
> > On Mon, Jun 25, 2018 at 02:45:24PM -0600, David Ahern wrote:
> > > On 6/25/18 4:30 AM, Chas Williams wrote:
> > > > vlan_changelink silently ignores attempts to change the vlan id
> > > > or protocol id of an existing vlan interface.  Implement by adding
> > > > the new vlan id and protocol to the interface's vlan group and then
> > > > removing the old vlan id and protocol from the vlan group.
> > > >
> > > > Signed-off-by: Chas Williams <3chas3@gmail.com>
> > > > ---
> > > >  include/linux/netdevice.h |  1 +
> > > >  net/8021q/vlan.c          |  4 ++--
> > > >  net/8021q/vlan.h          |  2 ++
> > > >  net/8021q/vlan_netlink.c  | 38 ++++++++++++++++++++++++++++++++++++++
> > > >  net/core/dev.c            |  1 +
> > > >  5 files changed, 44 insertions(+), 2 deletions(-)
> > > >
> > > > diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
> > > > index 3ec9850c7936..a95ae238addf 100644
> > > > --- a/include/linux/netdevice.h
> > > > +++ b/include/linux/netdevice.h
> > > > @@ -2409,6 +2409,7 @@ enum netdev_cmd {
> > > >     NETDEV_CVLAN_FILTER_DROP_INFO,
> > > >     NETDEV_SVLAN_FILTER_PUSH_INFO,
> > > >     NETDEV_SVLAN_FILTER_DROP_INFO,
> > > > +   NETDEV_CHANGEVLAN,
> > > >  };
> > > >  const char *netdev_cmd_to_name(enum netdev_cmd cmd);
> > > >
> > >
> > > you add the new notifier, but do not add any hooks to catch and process
> > it.
> > >
> > > Personally, I think it is a bit sketchy to change the vlan id on an
> > > existing device and I suspect it will cause latent errors.
> >
> > +1
> >
> > >
> > > What's your use case for trying to implement the change versus causing
> > > it to generate an unsupported error?
> > >
> > > If this patch does get accepted, I believe the mlxsw switchdev driver
> > > will be impacted.
> >
> > Yes, at minimum we need to return an error for NETDEV_CHANGEVLAN, but
> > looking at the code it seems that there's no proper rollback.
> >
> 
> I would prefer not to bother with error handling on the notification.  If
> something misses the notification, something misses the notification.
> It happens.

The notification is used so that relevant users in the kernel can
potentially veto the operation and refuse it. See other notifications
such as NETDEV_PRECHANGEUPPER.

The driver David mentioned is one existing user that needs to refuse the
VLAN change as it can't support it.