Michael S. Tsirkin
2019-Apr-02 21:50 UTC
[PATCH net v5] failover: allow name change on IFF_UP slave interfaces
On Mon, Apr 01, 2019 at 07:04:53PM -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 > 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 at oracle.com> > Reviewed-by: Liran Alon <liran.alon at oracle.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) > ---Acked-by: Michael S. Tsirkin <mst at redhat.com>> net/core/dev.c | 25 ++++++++++++++++++++++++- > 1 file changed, 24 insertions(+), 1 deletion(-) > > diff --git a/net/core/dev.c b/net/core/dev.c > index 9823b77..b694184 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) > + > + /* Allow failover slave to rename even when > + * it is up and running. > + * > + * Failover slaves are special, since userspace > + * might rename the slave after the interface > + * has been brought up and running due to > + * auto-enslavement. > + * > + * Failover users don't actually care about slave > + * name change, as they are only expected to operate > + * on master interface directly. > + */ > + if (dev->flags & IFF_UP && > + likely(!(dev->priv_flags & IFF_FAILOVER_SLAVE))) > 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); > > -- > 1.8.3.1
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- [PATCH net v4] failover: allow name change on IFF_UP slave interfaces
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