Date:   Tue, 26 Mar 2019 19:13:42 -0700
From:   Stephen Hemminger <stephen@...workplumber.org>
To:     Si-Wei Liu <si-wei.liu@...cle.com>
Cc:     mst@...hat.com, sridhar.samudrala@...el.com, 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 v3] failover: allow name change on IFF_UP slave
 interfaces

On Tue, 26 Mar 2019 19:48:13 -0400
Si-Wei Liu <si-wei.liu@...cle.com> 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>


Why do you need to do dev_close/dev_open which will bounce
the link?

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