Samudrala, Sridhar
2019-Mar-07 04:13 UTC
[PATCH net v2] failover: allow name change on IFF_UP slave interfaces
On 3/6/2019 7:08 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 work with the new naming > behavior of failover slaves. 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. > > 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> > Acked-by: Michael S. Tsirkin <mst at redhat.com> > > --- > v1 -> v2: > - Drop configurable module parameter (Sridhar) > > > include/linux/netdevice.h | 3 +++ > net/core/dev.c | 3 ++- > net/core/failover.c | 6 +++--- > 3 files changed, 8 insertions(+), 4 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;Without the configurable module parameter, i think we don't even need the new SLAVE_RENAME_OK private flag. Can't we simply check for IFF_FAILOVER_SLAVE ?> > write_seqcount_begin(&devnet_rename_seq); > diff --git a/net/core/failover.c b/net/core/failover.c > index 4a92a98..34c5c87 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_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 +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_SLAVE_RENAME_OK); > > if (fops && fops->slave_unregister && > !fops->slave_unregister(slave_dev, failover_dev)) >