Date:   Fri, 5 Apr 2019 13:40:05 -0700
From:   si-wei liu <si-wei.liu@...cle.com>
To:     mst@...hat.com, sridhar.samudrala@...el.com,
        stephen@...workplumber.org, davem@...emloft.net, kubakici@...pl,
        alexander.duyck@...il.com, jiri@...nulli.us,
        netdev@...r.kernel.org, virtualization@...ts.linux-foundation.org
Cc:     liran.alon@...cle.com, boris.ostrovsky@...cle.com,
        vijay.balakrishna@...cle.com
Subject: Re: [PATCH net v6] failover: allow name change on IFF_UP slave
 interfaces

A gentle reminder. This patch still needs reviewer to acknowledge the 
change proposed.

-Siwei

On 4/2/2019 9:52 PM, Si-Wei Liu wrote:
> When a netdev appears through hot plug then gets enslaved by a failover
> master that is already up and running, the slave will be opened
> right away after getting enslaved. Today there's a race that userspace
> (udev) may fail to rename the slave if the kernel (net_failover)
> opens the slave earlier than when the userspace rename happens.
> Unlike bond or team, the primary slave of failover can't be renamed by
> userspace ahead of time, since the kernel initiated auto-enslavement is
> unable to, or rather, is never meant to be synchronized with the rename
> request from userspace.
>
> As the failover slave interfaces are not designed to be operated
> directly by userspace apps: IP configuration, filter rules with
> regard to network traffic passing and etc., should all be done on master
> interface. In general, userspace apps only care about the
> name of master interface, while slave names are less important as long
> as admin users can see reliable names that may carry
> other information describing the netdev. For e.g., they can infer that
> "ens3nsby" is a standby slave of "ens3", while for a
> name like "eth0" they can't tell which master it belongs to.
>
> Historically the name of IFF_UP interface can't be changed because
> there might be admin script or management software that is already
> relying on such behavior and assumes that the slave name can't be
> changed once UP. But failover is special: with the in-kernel
> auto-enslavement mechanism, the userspace expectation for device
> enumeration and bring-up order is already broken. Previously initramfs
> and various userspace config tools were modified to bypass failover
> slaves because of auto-enslavement and duplicate MAC address. Similarly,
> in case that users care about seeing reliable slave name, the new type
> of failover slaves needs to be taken care of specifically in userspace
> anyway.
>
> It's less risky to lift up the rename restriction on failover slave
> which is already UP. Although it's possible this change may potentially
> break userspace component (most likely configuration scripts or
> management software) that assumes slave name can't be changed while
> UP, it's relatively a limited and controllable set among all userspace
> components, which can be fixed specifically to listen for the rename
> and/or link down/up events on failover slaves. Userspace component
> interacting with slaves is expected to be changed to operate on failover
> master interface instead, as the failover slave is dynamic in nature
> which may come and go at any point.  The goal is to make the role of
> failover slaves less relevant, and userspace components should only
> deal with failover master in the long run.
>
> Fixes: 30c8bd5aa8b2 ("net: Introduce generic failover module")
> Signed-off-by: Si-Wei Liu <si-wei.liu@...cle.com>
> Reviewed-by: Liran Alon <liran.alon@...cle.com>
>
> --
> v1 -> v2:
> - Drop configurable module parameter (Sridhar)
>
> v2 -> v3:
> - Drop additional IFF_SLAVE_RENAME_OK flag (Sridhar)
> - Send down and up events around rename (Michael S. Tsirkin)
>
> v3 -> v4:
> - Simplify notification to be sent (Stephen Hemminger)
>
> v4 -> v5:
> - Sync up code with latest net-next (Sridhar)
> - Use proper structure initialization (Stephen, Jiri)
>
> v5 -> v6:
> - Make the property of live name change a generic flag (Stephen)
> ---
>   include/linux/netdevice.h |  3 +++
>   net/core/dev.c            | 25 ++++++++++++++++++++++++-
>   net/core/failover.c       |  6 +++---
>   3 files changed, 30 insertions(+), 4 deletions(-)
>
> diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
> index 78f5ec4e..ea9a63f 100644
> --- a/include/linux/netdevice.h
> +++ b/include/linux/netdevice.h
> @@ -1498,6 +1498,7 @@ 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_NAME_CHANGE: rename is allowed while device is running
>    */
>   enum netdev_priv_flags {
>   	IFF_802_1Q_VLAN			= 1<<0,
> @@ -1530,6 +1531,7 @@ enum netdev_priv_flags {
>   	IFF_FAILOVER			= 1<<27,
>   	IFF_FAILOVER_SLAVE		= 1<<28,
>   	IFF_L3MDEV_RX_HANDLER		= 1<<29,
> +	IFF_LIVE_NAME_CHANGE		= 1<<30,
>   };
>   
>   #define IFF_802_1Q_VLAN			IFF_802_1Q_VLAN
> @@ -1561,6 +1563,7 @@ 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_NAME_CHANGE		IFF_LIVE_NAME_CHANGE
>   
>   /**
>    *	struct net_device - The DEVICE structure.
> diff --git a/net/core/dev.c b/net/core/dev.c
> index 9823b77..48341d5 100644
> --- a/net/core/dev.c
> +++ b/net/core/dev.c
> @@ -1185,7 +1185,21 @@ int dev_change_name(struct net_device *dev, const char *newname)
>   	BUG_ON(!dev_net(dev));
>   
>   	net = dev_net(dev);
> -	if (dev->flags & IFF_UP)
> +
> +	/* 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_NAME_CHANGE)))
>   		return -EBUSY;
>   
>   	write_seqcount_begin(&devnet_rename_seq);
> @@ -1232,6 +1246,15 @@ int dev_change_name(struct net_device *dev, const char *newname)
>   	hlist_add_head_rcu(&dev->name_hlist, dev_name_hash(net, dev->name));
>   	write_unlock_bh(&dev_base_lock);
>   
> +	if (unlikely(dev->flags & IFF_UP)) {
> +		struct netdev_notifier_change_info change_info = {
> +			.info.dev = dev,
> +		};
> +
> +		call_netdevice_notifiers_info(NETDEV_CHANGE,
> +					      &change_info.info);
> +	}
> +
>   	ret = call_netdevice_notifiers(NETDEV_CHANGENAME, dev);
>   	ret = notifier_to_errno(ret);
>   
> diff --git a/net/core/failover.c b/net/core/failover.c
> index 4a92a98..b5cd3c7 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;
> +	slave_dev->priv_flags |= (IFF_FAILOVER_SLAVE | IFF_LIVE_NAME_CHANGE);
>   
>   	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;
> +	slave_dev->priv_flags &= ~(IFF_FAILOVER_SLAVE | IFF_LIVE_NAME_CHANGE);
>   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;
> +	slave_dev->priv_flags &= ~(IFF_FAILOVER_SLAVE | IFF_LIVE_NAME_CHANGE);
>   
>   	if (fops && fops->slave_unregister &&
>   	    !fops->slave_unregister(slave_dev, failover_dev))

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