[PATCH net-next v2] net/core: Allow live renaming when an interface is up

[Andy Ren <andy.ren@getcruise.com>]

We should allow a network interface to be renamed when the interface
is up.

Live renaming was added as a failover in the past, and there has been no
arising issues of the user space breaking. Furthermore, it seems that this
flag was added because in the past, IOCTL was used for renaming, which
would not notify the user space. Nowadays, it appears that the user
space receives notifications regardless of the state of the network
device (e.g. rtnetlink_event()). The listeners for NETDEV_CHANGENAME
also do not strictly ensure that the netdev is up or not.

Hence, we should remove the live renaming flag and checks due
to the aforementioned reasons.

The changes are as the following:
- Remove IFF_LIVE_RENAME_OK flag declarations
- Remove check in dev_change_name that checks whether device is up and
if IFF_LIVE_RENAME_OK is set by the network device's priv_flags
- Remove references of IFF_LIVE_RENAME_OK in the failover module

Changes from v1->v2
- Added placeholder comment in place of removed IFF_LIVE_RENAME_OK flag
- Added extra logging hints to indicate whether a network interface was
renamed while UP

Signed-off-by: Andy Ren <andy.ren@getcruise.com>
---
 include/linux/netdevice.h |  4 +---
 net/core/dev.c            | 19 ++-----------------
 net/core/failover.c       |  6 +++---
 3 files changed, 6 insertions(+), 23 deletions(-)

diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index d45713a06568..4be87b89e481 100644
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -1650,7 +1650,6 @@ struct net_device_ops {
  * @IFF_FAILOVER: device is a failover master device
  * @IFF_FAILOVER_SLAVE: device is lower dev of a failover master device
  * @IFF_L3MDEV_RX_HANDLER: only invoke the rx handler of L3 master device
- * @IFF_LIVE_RENAME_OK: rename is allowed while device is up and running
  * @IFF_TX_SKB_NO_LINEAR: device/driver is capable of xmitting frames with
  *	skb_headlen(skb) == 0 (data starts from frag0)
  * @IFF_CHANGE_PROTO_DOWN: device supports setting carrier via IFLA_PROTO_DOWN
@@ -1686,7 +1685,7 @@ enum netdev_priv_flags {
 	IFF_FAILOVER			= 1<<27,
 	IFF_FAILOVER_SLAVE		= 1<<28,
 	IFF_L3MDEV_RX_HANDLER		= 1<<29,
-	IFF_LIVE_RENAME_OK		= 1<<30,
+	/* was IFF_LIVE_RENAME_OK */
 	IFF_TX_SKB_NO_LINEAR		= BIT_ULL(31),
 	IFF_CHANGE_PROTO_DOWN		= BIT_ULL(32),
 };
@@ -1721,7 +1720,6 @@ enum netdev_priv_flags {
 #define IFF_FAILOVER			IFF_FAILOVER
 #define IFF_FAILOVER_SLAVE		IFF_FAILOVER_SLAVE
 #define IFF_L3MDEV_RX_HANDLER		IFF_L3MDEV_RX_HANDLER
-#define IFF_LIVE_RENAME_OK		IFF_LIVE_RENAME_OK
 #define IFF_TX_SKB_NO_LINEAR		IFF_TX_SKB_NO_LINEAR
 
 /* Specifies the type of the struct net_device::ml_priv pointer */
diff --git a/net/core/dev.c b/net/core/dev.c
index 3bacee3bee78..707de6b841d0 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -1163,22 +1163,6 @@ int dev_change_name(struct net_device *dev, const char *newname)
 
 	net = dev_net(dev);
 
-	/* Some auto-enslaved devices e.g. failover slaves are
-	 * special, as userspace might rename the device after
-	 * the interface had been brought up and running since
-	 * the point kernel initiated auto-enslavement. Allow
-	 * live name change even when these slave devices are
-	 * up and running.
-	 *
-	 * Typically, users of these auto-enslaving devices
-	 * don't actually care about slave name change, as
-	 * they are supposed to operate on master interface
-	 * directly.
-	 */
-	if (dev->flags & IFF_UP &&
-	    likely(!(dev->priv_flags & IFF_LIVE_RENAME_OK)))
-		return -EBUSY;
-
 	down_write(&devnet_rename_sem);
 
 	if (strncmp(newname, dev->name, IFNAMSIZ) == 0) {
@@ -1195,7 +1179,8 @@ int dev_change_name(struct net_device *dev, const char *newname)
 	}
 
 	if (oldname[0] && !strchr(oldname, '%'))
-		netdev_info(dev, "renamed from %s\n", oldname);
+		netdev_info(dev, "renamed from %s%s\n", oldname,
+			    dev->flags & IFF_UP ? " (while UP)" : "");
 
 	old_assign_type = dev->name_assign_type;
 	dev->name_assign_type = NET_NAME_RENAMED;
diff --git a/net/core/failover.c b/net/core/failover.c
index 864d2d83eff4..655411c4ca51 100644
--- a/net/core/failover.c
+++ b/net/core/failover.c
@@ -80,14 +80,14 @@ static int failover_slave_register(struct net_device *slave_dev)
 		goto err_upper_link;
 	}
 
-	slave_dev->priv_flags |= (IFF_FAILOVER_SLAVE | IFF_LIVE_RENAME_OK);
+	slave_dev->priv_flags |= IFF_FAILOVER_SLAVE;
 
 	if (fops && fops->slave_register &&
 	    !fops->slave_register(slave_dev, failover_dev))
 		return NOTIFY_OK;
 
 	netdev_upper_dev_unlink(slave_dev, failover_dev);
-	slave_dev->priv_flags &= ~(IFF_FAILOVER_SLAVE | IFF_LIVE_RENAME_OK);
+	slave_dev->priv_flags &= ~IFF_FAILOVER_SLAVE;
 err_upper_link:
 	netdev_rx_handler_unregister(slave_dev);
 done:
@@ -121,7 +121,7 @@ int failover_slave_unregister(struct net_device *slave_dev)
 
 	netdev_rx_handler_unregister(slave_dev);
 	netdev_upper_dev_unlink(slave_dev, failover_dev);
-	slave_dev->priv_flags &= ~(IFF_FAILOVER_SLAVE | IFF_LIVE_RENAME_OK);
+	slave_dev->priv_flags &= ~IFF_FAILOVER_SLAVE;
 
 	if (fops && fops->slave_unregister &&
 	    !fops->slave_unregister(slave_dev, failover_dev))
-- 
2.38.1