netdev - [PATCH net-next 1/1] veth: tweak creation of veth device

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Date:   Tue, 10 Oct 2017 16:08:44 -0400
From:   Roman Mashak <mrv@...atatu.com>
To:     davem@...emloft.net
Cc:     jhs@...atatu.com, netdev@...r.kernel.org,
        Roman Mashak <mrv@...atatu.com>
Subject: [PATCH net-next 1/1] veth: tweak creation of veth device

When creating veth pair, at first rtnl_new_link() creates veth_dev, i.e.
one end of the veth pipe, but not registers it; then veth_newlink() gets
invoked, where peer dev is created _and_ registered, followed by veth_dev
registration, which may fail if peer information, that is VETH_INFO_PEER
attribute, has not been provided and the kernel will allocate unique veth
name.

So, we should ask the kernel to allocate unique name for veth_dev only
when peer info is not available.

Example:

% ip link dev veth0 type veth
RTNETLINK answers: File exists

After fix:
% ip link dev veth0 type veth
% ip link show dev veth0
5: veth0@...h1: <BROADCAST,MULTICAST> mtu 1500 qdisc noop state DOWN mode DEFAULT group default qlen 1000
    link/ether f6:ef:8b:96:f4:ec brd ff:ff:ff:ff:ff:ff
%

Signed-off-by: Roman Mashak <mrv@...atatu.com>
---
 drivers/net/veth.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/net/veth.c b/drivers/net/veth.c
index f5438d0..00dce15 100644
--- a/drivers/net/veth.c
+++ b/drivers/net/veth.c
@@ -432,7 +432,7 @@ static int veth_newlink(struct net *src_net, struct net_device *dev,
 	if (tb[IFLA_ADDRESS] == NULL)
 		eth_hw_addr_random(dev);
 
-	if (tb[IFLA_IFNAME])
+	if (ifmp && tb[IFLA_IFNAME])
 		nla_strlcpy(dev->name, tb[IFLA_IFNAME], IFNAMSIZ);
 	else
 		snprintf(dev->name, IFNAMSIZ, DRV_NAME "%%d");
-- 
1.9.1