[RFC,net] failover: allow name change on IFF_UP slave interfaces

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.

For that to work, now introduce a module-level tunable,
"slave_rename_ok" that allows users to lift up the rename restriction on
failover slave which is already UP. Although it's possible this change
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 work with the new naming
behavior of the failover slave. Userspace component interacting with
slaves should be changed to operate on failover master 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
all userspace should only deal with master in the long run. The default
for the "slave_rename_ok" is set to true(1). If userspace doesn't have
the right support in place meanwhile users don't care about reliable
userspace naming, the value can be set to false(0).

Signed-off-by: Si-Wei.Liu@oracle.com
Reviewed-by: Liran Alon <liran.alon@oracle.com>
---
 include/linux/netdevice.h |  3 +++
 net/core/dev.c            |  3 ++-
 net/core/failover.c       | 11 +++++++++--
 3 files changed, 14 insertions(+), 3 deletions(-)

Please disregard patch emails previously sent with similar subject. The 
patch target is set to net rather than net-next. Any discussion or 
comment around this patch should go after this email.

-Siwei


On 3/4/2019 4:53 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.
>
> For that to work, now introduce a module-level tunable,
> "slave_rename_ok" that allows users to lift up the rename restriction on
> failover slave which is already UP. Although it's possible this change
> 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 work with the new naming
> behavior of the failover slave. Userspace component interacting with
> slaves should be changed to operate on failover master 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
> all userspace should only deal with master in the long run. The default
> for the "slave_rename_ok" is set to true(1). If userspace doesn't have
> the right support in place meanwhile users don't care about reliable
> userspace naming, the value can be set to false(0).
>
> Signed-off-by: Si-Wei.Liu@oracle.com
> Reviewed-by: Liran Alon <liran.alon@oracle.com>
> ---
>   include/linux/netdevice.h |  3 +++
>   net/core/dev.c            |  3 ++-
>   net/core/failover.c       | 11 +++++++++--
>   3 files changed, 14 insertions(+), 3 deletions(-)
>
> diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
> index 857f8ab..6d9e4e0 100644
> --- a/include/linux/netdevice.h
> +++ b/include/linux/netdevice.h
> @@ -1487,6 +1487,7 @@ struct net_device_ops {
>    * @IFF_NO_RX_HANDLER: device doesn't support the rx_handler hook
>    * @IFF_FAILOVER: device is a failover master device
>    * @IFF_FAILOVER_SLAVE: device is lower dev of a failover master device
> + * @IFF_SLAVE_RENAME_OK: rename is allowed while slave device is running
>    */
>   enum netdev_priv_flags {
>   	IFF_802_1Q_VLAN			= 1<<0,
> @@ -1518,6 +1519,7 @@ enum netdev_priv_flags {
>   	IFF_NO_RX_HANDLER		= 1<<26,
>   	IFF_FAILOVER			= 1<<27,
>   	IFF_FAILOVER_SLAVE		= 1<<28,
> +	IFF_SLAVE_RENAME_OK		= 1<<29,
>   };
>   
>   #define IFF_802_1Q_VLAN			IFF_802_1Q_VLAN
> @@ -1548,6 +1550,7 @@ enum netdev_priv_flags {
>   #define IFF_NO_RX_HANDLER		IFF_NO_RX_HANDLER
>   #define IFF_FAILOVER			IFF_FAILOVER
>   #define IFF_FAILOVER_SLAVE		IFF_FAILOVER_SLAVE
> +#define IFF_SLAVE_RENAME_OK		IFF_SLAVE_RENAME_OK
>   
>   /**
>    *	struct net_device - The DEVICE structure.
> diff --git a/net/core/dev.c b/net/core/dev.c
> index 722d50d..ae070de 100644
> --- a/net/core/dev.c
> +++ b/net/core/dev.c
> @@ -1180,7 +1180,8 @@ 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)
> +	if (dev->flags & IFF_UP &&
> +	    !(dev->priv_flags & IFF_SLAVE_RENAME_OK))
>   		return -EBUSY;
>   
>   	write_seqcount_begin(&devnet_rename_seq);
> diff --git a/net/core/failover.c b/net/core/failover.c
> index 4a92a98..1fd8bbb 100644
> --- a/net/core/failover.c
> +++ b/net/core/failover.c
> @@ -16,6 +16,11 @@
>   
>   static LIST_HEAD(failover_list);
>   static DEFINE_SPINLOCK(failover_lock);
> +static bool slave_rename_ok = true;
> +
> +module_param(slave_rename_ok, bool, (S_IRUGO | S_IWUSR));
> +MODULE_PARM_DESC(slave_rename_ok,
> +		 "If set allow renaming the slave when failover master is up");
>   
>   static struct net_device *failover_get_bymac(u8 *mac, struct failover_ops **ops)
>   {
> @@ -81,13 +86,15 @@ static int failover_slave_register(struct net_device *slave_dev)
>   	}
>   
>   	slave_dev->priv_flags |= IFF_FAILOVER_SLAVE;
> +	if (slave_rename_ok)
> +		slave_dev->priv_flags |= IFF_SLAVE_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_SLAVE_RENAME_OK);
>   err_upper_link:
>   	netdev_rx_handler_unregister(slave_dev);
>   done:
> @@ -121,7 +128,7 @@ 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_SLAVE_RENAME_OK);
>   
>   	if (fops && fops->slave_unregister &&
>   	    !fops->slave_unregister(slave_dev, failover_dev))

Why did you send this three times?

What's different in each of these copies?

Sorry for multiple sends. The patch is exactly same. I added a few 
people who were missing int the cc lines in the first attemt. And 
corrected the subject line in the second attempt.

-Siwei


On 3/4/2019 6:04 PM, David Miller wrote:
> Why did you send this three times?
>
> What's different in each of these copies?
>