Message-ID: <d64368bc-8460-472b-de35-f48f38dd2ed8@oracle.com>
Date:   Tue, 9 Apr 2019 11:44:57 -0700
From:   si-wei liu <si-wei.liu@...cle.com>
To:     "Michael S. Tsirkin" <mst@...hat.com>
Cc:     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, liran.alon@...cle.com,
        boris.ostrovsky@...cle.com, vijay.balakrishna@...cle.com
Subject: Re: [PATCH net v8] failover: allow name change on IFF_UP slave
 interfaces



On 4/9/2019 9:13 AM, Michael S. Tsirkin wrote:
> On Mon, Apr 08, 2019 at 07:45:27PM -0400, 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
>> 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>
>
> OK let's start with that. We can always add more events.
Yep. Nothing is impossible but this is the least we should do. We can 
add more events based on *real use case*.


-Siwei
>
>> --
>> 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)
>>
>> v6 -> v7:
>> - Remove NETDEV_CHANGE notification that is deemed unnecessary
>>    (Stephen)
>>
>> v7 -> v8:
>> - Fix commit message that references link up/down events still
>>    (Michael)
>> ---
>>   include/linux/netdevice.h |  3 +++
>>   net/core/dev.c            | 16 +++++++++++++++-
>>   net/core/failover.c       |  6 +++---
>>   3 files changed, 21 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_RENAME_OK: rename is allowed while device is up and 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_RENAME_OK		= 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_RENAME_OK		IFF_LIVE_RENAME_OK
>>   
>>   /**
>>    *	struct net_device - The DEVICE structure.
>> diff --git a/net/core/dev.c b/net/core/dev.c
>> index 9823b77..1622d88 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_RENAME_OK)))
>>   		return -EBUSY;
>>   
>>   	write_seqcount_begin(&devnet_rename_seq);
>> 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_RENAME_OK);
>>   
>>   	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_RENAME_OK);
>>   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_RENAME_OK);
>>   
>>   	if (fops && fops->slave_unregister &&
>>   	    !fops->slave_unregister(slave_dev, failover_dev))
>> -- 
>> 1.8.3.1

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