[ovs-dev] [PATCH] datapath: RHEL 7.5 ndo_change_mtu backward compatibility

Daniel Alvarez Sanchez dalvarez at redhat.com
Thu May 17 13:12:15 UTC 2018


Thanks Lucas, this makes sense. There is something that this patch is
fixing and I'm not sure why.
Maybe someone can shed some light:

Using datapath from OVS master, and a setup where we have a physical
interface connected to
an OVS bridge (br-ex) connected to another OVS bridge (br-int) through a
patch port, there's a lot
of retransmissions of TCP packets when connecting from the host to a VM
connected to br-int.
The retransmissions seem to be due to a wrong checksum from the VM to the
host and only after
a few attempts, the checksum is correct and the host sends the ACK back.
The packets I am
sending using netcat are very small so there shouldn't be a problem with
the MTU. However, could
it be a side effect of this patch that the checksum gets now correctly
received at the host?

As a side not: if instead from connecting to the VM from the host I do it
from a namespace where
I have an OVS internal port connected to br-ex, then I don't see the
checksum problems.

Acked-by: Daniel Alvarez <dalvarez at redhat.com>
Tested-by: Daniel Alvarez <dalvarez at redhat.com>

On Thu, May 17, 2018 at 1:27 PM, <lucasagomes at gmail.com> wrote:

> From: Lucas Alvares Gomes <lucasagomes at gmail.com>
>
> The commit [0] partially fixed the problem but in RHEL 7.5 neither
> .{min, max}_mtu or 'ndo_change_mtu' were being set/implemented for
> vport-internal_dev.c.
>
> As pointed out by commit [0], the ndo_change_mtu function pointer has been
> moved from 'struct net_device_ops' to 'struct net_device_ops_extended'
> on RHEL 7.5.
>
> So this patch fixes the backport issue by setting the
> .extended.ndo_change_mtu when necessary.
>
> [0] 39ca338374abe367e28a2247bac9159695f19710
> ---
>  datapath/vport-internal_dev.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/datapath/vport-internal_dev.c b/datapath/vport-internal_dev.c
> index 3cb8d06b2..16f4aaeee 100644
> --- a/datapath/vport-internal_dev.c
> +++ b/datapath/vport-internal_dev.c
> @@ -88,7 +88,7 @@ static const struct ethtool_ops internal_dev_ethtool_ops
> = {
>         .get_link       = ethtool_op_get_link,
>  };
>
> -#if    !defined(HAVE_NET_DEVICE_WITH_MAX_MTU) &&
> !defined(HAVE_RHEL7_MAX_MTU)
> +#ifndef HAVE_NET_DEVICE_WITH_MAX_MTU
>  static int internal_dev_change_mtu(struct net_device *dev, int new_mtu)
>  {
>         if (new_mtu < ETH_MIN_MTU) {
> @@ -155,6 +155,8 @@ static const struct net_device_ops
> internal_dev_netdev_ops = {
>         .ndo_set_mac_address = eth_mac_addr,
>  #if    !defined(HAVE_NET_DEVICE_WITH_MAX_MTU) &&
> !defined(HAVE_RHEL7_MAX_MTU)
>         .ndo_change_mtu = internal_dev_change_mtu,
> +#elif  !defined(HAVE_NET_DEVICE_WITH_MAX_MTU) &&
> defined(HAVE_RHEL7_MAX_MTU)
> +       .extended.ndo_change_mtu = internal_dev_change_mtu,
>  #endif
>         .ndo_get_stats64 = (void *)internal_get_stats,
>  };
> --
> 2.17.0
>
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