[PATCH v3 net-next] net: vxlan: use custom ndo_change_mtu handler

[PATCH v3 net-next] net: vxlan: use custom ndo_change_mtu handler

[Daniel Borkmann]

When adding a new vxlan device to an "underlying carrier" (here:
dst->remote_ifindex), the MTU size assigned to the vxlan device
is the MTU at setup time of the carrier - needed headroom, when
adding a vxlan device w/o explicit carrier, then it defaults
to 1500.

In case of an explicit carrier that supports jumbo frames, we
currently cannot change vxlan MTU via ip(8) to > 1500 in
post-setup time, as vxlan driver uses eth_change_mtu() as default
method for manually setting MTU.

Hence, use a custom implementation that only falls back to
eth_change_mtu() in case we didn't use a dev parameter on device
setup time, and otherwise allow a max MTU setting of the carrier
incl. adjustment for headroom.

Reported-by: Shahed Shaikh <shahed.shaikh@qlogic.com>
Signed-off-by: Daniel Borkmann <dborkman@redhat.com>
---
 v1->v2:
  - applied Stephen's feedback
 v2->v3:
  - use dst directly in __dev_get_by_index()

 drivers/net/vxlan.c | 25 ++++++++++++++++++++++++-
 1 file changed, 24 insertions(+), 1 deletion(-)

diff --git a/drivers/net/vxlan.c b/drivers/net/vxlan.c
index 58f6a0c..c379c24 100644
--- a/drivers/net/vxlan.c
+++ b/drivers/net/vxlan.c
@@ -2014,6 +2014,29 @@ static void vxlan_set_multicast_list(struct net_device *dev)
 {
 }
 
+static int vxlan_change_mtu(struct net_device *dev, int new_mtu)
+{
+	struct vxlan_dev *vxlan = netdev_priv(dev);
+	struct vxlan_rdst *dst = &vxlan->default_dst;
+	struct net_device *lowerdev;
+	int max_mtu;
+
+	lowerdev = __dev_get_by_index(dev_net(dev), dst->remote_ifindex);
+	if (lowerdev == NULL)
+		return eth_change_mtu(dev, new_mtu);
+
+	if (dst->remote_ip.sa.sa_family == AF_INET6)
+		max_mtu = lowerdev->mtu - VXLAN6_HEADROOM;
+	else
+		max_mtu = lowerdev->mtu - VXLAN_HEADROOM;
+
+	if (new_mtu < 68 || new_mtu > max_mtu)
+		return -EINVAL;
+
+	dev->mtu = new_mtu;
+	return 0;
+}
+
 static const struct net_device_ops vxlan_netdev_ops = {
 	.ndo_init		= vxlan_init,
 	.ndo_uninit		= vxlan_uninit,
@@ -2022,7 +2045,7 @@ static const struct net_device_ops vxlan_netdev_ops = {
 	.ndo_start_xmit		= vxlan_xmit,
 	.ndo_get_stats64	= ip_tunnel_get_stats64,
 	.ndo_set_rx_mode	= vxlan_set_multicast_list,
-	.ndo_change_mtu		= eth_change_mtu,
+	.ndo_change_mtu		= vxlan_change_mtu,
 	.ndo_validate_addr	= eth_validate_addr,
 	.ndo_set_mac_address	= eth_mac_addr,
 	.ndo_fdb_add		= vxlan_fdb_add,
-- 
1.8.3.1

Re: [PATCH v3 net-next] net: vxlan: use custom ndo_change_mtu handler

[Stephen Hemminger]

On Wed, 18 Dec 2013 00:21:08 +0100
Daniel Borkmann <dborkman@redhat.com> wrote:

> When adding a new vxlan device to an "underlying carrier" (here:
> dst->remote_ifindex), the MTU size assigned to the vxlan device
> is the MTU at setup time of the carrier - needed headroom, when
> adding a vxlan device w/o explicit carrier, then it defaults
> to 1500.
> 
> In case of an explicit carrier that supports jumbo frames, we
> currently cannot change vxlan MTU via ip(8) to > 1500 in
> post-setup time, as vxlan driver uses eth_change_mtu() as default
> method for manually setting MTU.
> 
> Hence, use a custom implementation that only falls back to
> eth_change_mtu() in case we didn't use a dev parameter on device
> setup time, and otherwise allow a max MTU setting of the carrier
> incl. adjustment for headroom.
> 
> Reported-by: Shahed Shaikh <shahed.shaikh@qlogic.com>
> Signed-off-by: Daniel Borkmann <dborkman@redhat.com>

This code is good thanks.

Acked-by: Stephen Hemminger <stephen@networkplumber.org>

P.s: I wonder if notifier handler would be good to handle changes
to underlying device MTU on the fly.

Re: [PATCH v3 net-next] net: vxlan: use custom ndo_change_mtu handler

[David Miller]

From: Daniel Borkmann <dborkman@redhat.com>
Date: Wed, 18 Dec 2013 00:21:08 +0100

> When adding a new vxlan device to an "underlying carrier" (here:
> dst->remote_ifindex), the MTU size assigned to the vxlan device
> is the MTU at setup time of the carrier - needed headroom, when
> adding a vxlan device w/o explicit carrier, then it defaults
> to 1500.
> 
> In case of an explicit carrier that supports jumbo frames, we
> currently cannot change vxlan MTU via ip(8) to > 1500 in
> post-setup time, as vxlan driver uses eth_change_mtu() as default
> method for manually setting MTU.
> 
> Hence, use a custom implementation that only falls back to
> eth_change_mtu() in case we didn't use a dev parameter on device
> setup time, and otherwise allow a max MTU setting of the carrier
> incl. adjustment for headroom.
> 
> Reported-by: Shahed Shaikh <shahed.shaikh@qlogic.com>
> Signed-off-by: Daniel Borkmann <dborkman@redhat.com>

Applied, thanks Daniel.

Re: [PATCH v3 net-next] net: vxlan: use custom ndo_change_mtu handler

[David Miller]

From: Stephen Hemminger <stephen@networkplumber.org>
Date: Tue, 17 Dec 2013 15:40:52 -0800

> P.s: I wonder if notifier handler would be good to handle changes
> to underlying device MTU on the fly.

I think it would be a good idea.