netdev - [PATCH net] vrf: fix maximum MTU

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Message-Id: <20210608145951.24985-1-nicolas.dichtel@6wind.com>
Date:   Tue,  8 Jun 2021 16:59:51 +0200
From:   Nicolas Dichtel <nicolas.dichtel@...nd.com>
To:     davem@...emloft.net, kuba@...nel.org
Cc:     netdev@...r.kernel.org, dsahern@...il.com,
        Nicolas Dichtel <nicolas.dichtel@...nd.com>,
        Miaohe Lin <linmiaohe@...wei.com>
Subject: [PATCH net] vrf: fix maximum MTU

My initial goal was to fix the default MTU, which is set to 65536, ie above
the maximum defined in the driver: 65535 (ETH_MAX_MTU).

In fact, it's seems more consistent, wrt min_mtu, to set the max_mtu to
IP6_MAX_MTU (65535 + sizeof(struct ipv6hdr)) and use it by default.

Let's also, for consistency, set the mtu in vrf_setup(). This function
calls ether_setup(), which set the mtu to 1500. Thus, the whole mtu config
is done in the same function.

Before the patch:
$ ip link add blue type vrf table 1234
$ ip link list blue
9: blue: <NOARP,MASTER> mtu 65536 qdisc noop state DOWN mode DEFAULT group default qlen 1000
    link/ether fa:f5:27:70:24:2a brd ff:ff:ff:ff:ff:ff
$ ip link set dev blue mtu 65535
$ ip link set dev blue mtu 65536
Error: mtu greater than device maximum.

Fixes: 5055376a3b44 ("net: vrf: Fix ping failed when vrf mtu is set to 0")
CC: Miaohe Lin <linmiaohe@...wei.com>
Signed-off-by: Nicolas Dichtel <nicolas.dichtel@...nd.com>
---
 drivers/net/vrf.c | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/drivers/net/vrf.c b/drivers/net/vrf.c
index 503e2fd7ce51..28a6c4cfe9b8 100644
--- a/drivers/net/vrf.c
+++ b/drivers/net/vrf.c
@@ -1183,9 +1183,6 @@ static int vrf_dev_init(struct net_device *dev)
 
 	dev->flags = IFF_MASTER | IFF_NOARP;
 
-	/* MTU is irrelevant for VRF device; set to 64k similar to lo */
-	dev->mtu = 64 * 1024;
-
 	/* similarly, oper state is irrelevant; set to up to avoid confusion */
 	dev->operstate = IF_OPER_UP;
 	netdev_lockdep_set_classes(dev);
@@ -1685,7 +1682,8 @@ static void vrf_setup(struct net_device *dev)
 	 * which breaks networking.
 	 */
 	dev->min_mtu = IPV6_MIN_MTU;
-	dev->max_mtu = ETH_MAX_MTU;
+	dev->max_mtu = IP6_MAX_MTU;
+	dev->mtu = dev->max_mtu;
 }
 
 static int vrf_validate(struct nlattr *tb[], struct nlattr *data[],
-- 
2.30.0