netdev - Re: [PATCH] ipvlan: fix ipvlan MTU limits

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Date:   Wed, 10 Jan 2018 03:12:37 +0000
From:   liuqifa <liuqifa@...wei.com>
To:     Mahesh Bandewar (महेश बंडेवार) <maheshb@...gle.com>
CC:     David Miller <davem@...emloft.net>,
        "dsahern@...il.com" <dsahern@...il.com>,
        "mschiffer@...verse-factory.net" <mschiffer@...verse-factory.net>,
        "idosch@...lanox.com" <idosch@...lanox.com>,
        "fw@...len.de" <fw@...len.de>,
        "kjlx@...pleofstupid.com" <kjlx@...pleofstupid.com>,
        "girish.moodalbail@...cle.com" <girish.moodalbail@...cle.com>,
        "sainath.grandhi@...el.com" <sainath.grandhi@...el.com>,
        linux-netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH] ipvlan: fix ipvlan MTU limits


> On Mon, Jan 8, 2018 at 10:48 PM,  <liuqifa@...wei.com> wrote:
> > From: Keefe Liu <liuqifa@...wei.com>
> >
> > The MTU of ipvlan interface should not bigger than the phy device,
> > When we run following scripts, we will find there are some problems.
> > Step1:
> >         ip link add link eth0 name ipv1 type ipvlan mode l2
> >         ip netns add net1
> >         ip link set dev ipv1 netns net1
> > Step2:
> >         ip netns exec net1 ip link set dev ipv1 mtu 1501
> >         RTNETLINK answers: Invalid argument
> >         dmesg info: "ipv1: Invalid MTU 1501 requested, hw max 1500"
> > Step3:
> >         ip link set dev eth0 mtu 1600
> >         ip netns exec net1 ip link set dev ipv1 mtu 1501
> >         RTNETLINK answers: Invalid argument
> >         dmesg info: "ipv1: Invalid MTU 1501 requested, hw max 1500"
> > Step4:
> >         ip link set dev eth0 mtu 1400
> >         ip netns exec net1 ip link set dev ipv1 mtu 1500 The result of
> > Step2 is we expected, but the result of Step3 and Step4 are not.
> >
> > This patch set ipvlan's maximum MTU to ETH_MAX_MTU, and when we
> change
> > the ipvlan device's MTU, ipvlan_change_mtu() will make sure the new
> > MTU no larger than the phy device's MTU.
> >
> > Signed-off-by: Keefe Liu <liuqifa@...wei.com>
> > ---
> >  drivers/net/ipvlan/ipvlan_main.c | 14 ++++++++++++++
> >  1 file changed, 14 insertions(+)
> >
> > diff --git a/drivers/net/ipvlan/ipvlan_main.c
> > b/drivers/net/ipvlan/ipvlan_main.c
> > index 30cb803..84c007d 100644
> > --- a/drivers/net/ipvlan/ipvlan_main.c
> > +++ b/drivers/net/ipvlan/ipvlan_main.c
> > @@ -380,12 +380,24 @@ static int ipvlan_get_iflink(const struct net_device
> *dev)
> >         return ipvlan->phy_dev->ifindex;  }
> >
> > +static int ipvlan_change_mtu(struct net_device *dev, int new_mtu) {
> > +       struct ipvl_dev *ipvlan = netdev_priv(dev);
> > +
> > +       if (ipvlan->phy_dev->mtu < new_mtu)
> > +               return -EINVAL;
> > +
> > +       dev->mtu = new_mtu;
> > +       return 0;
> > +}
> > +
> >  static const struct net_device_ops ipvlan_netdev_ops = {
> >         .ndo_init               = ipvlan_init,
> >         .ndo_uninit             = ipvlan_uninit,
> >         .ndo_open               = ipvlan_open,
> >         .ndo_stop               = ipvlan_stop,
> >         .ndo_start_xmit         = ipvlan_start_xmit,
> > +       .ndo_change_mtu         = ipvlan_change_mtu,
> >         .ndo_fix_features       = ipvlan_fix_features,
> >         .ndo_change_rx_flags    = ipvlan_change_rx_flags,
> >         .ndo_set_rx_mode        = ipvlan_set_multicast_mac_filter,
> > @@ -680,6 +692,8 @@ void ipvlan_link_setup(struct net_device *dev)  {
> >         ether_setup(dev);
> >
> > +       dev->min_mtu = 0;
> should be ETH_MIN_MTU since we expect the underlying device to be
> ETH_ARPHDR and IPvlan deals with IPv4/IPv6.
> 
[liuqifa] Yes, I agree with you. But I have another question, I found in commit 9157208,  macvlan's min_mtu has been changed from ETH_MIN_MTU to 0, I'd like to know what's the difference between macvlan and ipvlan.
> > +       dev->max_mtu = ETH_MAX_MTU;
> >         dev->priv_flags &= ~(IFF_XMIT_DST_RELEASE | IFF_TX_SKB_SHARING);
> >         dev->priv_flags |= IFF_UNICAST_FLT | IFF_NO_QUEUE;
> >         dev->netdev_ops = &ipvlan_netdev_ops;
> > --
> > 1.8.3.1
> >
> >
> These changes are not sufficient if you want to have different per-slave mtu
> settings. One can always change the MTU of the master device and all  per-
> slave settings will get wiped. I don't think that's a desired outcome.
[liuqifa] I agree with you, I will reprogram the code to realize this goal.