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[173.76.246.42]) by smtp.gmail.com with ESMTPSA id x191sm16949365qka.78.2019.04.08.14.00.50 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Mon, 08 Apr 2019 14:00:51 -0700 (PDT) Date: Mon, 8 Apr 2019 17:00:49 -0400 From: "Michael S. Tsirkin" To: Si-Wei Liu Cc: sridhar.samudrala@intel.com, stephen@networkplumber.org, davem@davemloft.net, kubakici@wp.pl, alexander.duyck@gmail.com, jiri@resnulli.us, netdev@vger.kernel.org, virtualization@lists.linux-foundation.org, liran.alon@oracle.com, boris.ostrovsky@oracle.com, vijay.balakrishna@oracle.com Subject: Re: [PATCH net v7] failover: allow name change on IFF_UP slave interfaces Message-ID: <20190408165058-mutt-send-email-mst@kernel.org> References: <1554755085-29098-1-git-send-email-si-wei.liu@oracle.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1554755085-29098-1-git-send-email-si-wei.liu@oracle.com> Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On Mon, Apr 08, 2019 at 04:24:45PM -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. This was correct with v6. With v7 link down/up events are no longer emitted. > 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 > Reviewed-by: Liran Alon > > -- > 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) > --- I preferred v6 better. If we emit NETDEV_CHANGE then userspace that expects that name never changes for up interfaces will work since it will think state changed. > 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