Jiri Pirko
2019-Mar-27 11:11 UTC
[PATCH net v3] failover: allow name change on IFF_UP slave interfaces
Wed, Mar 27, 2019 at 12:48:13AM CET, si-wei.liu at oracle.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 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) >--- > net/core/dev.c | 37 ++++++++++++++++++++++++++++++++++--- > 1 file changed, 34 insertions(+), 3 deletions(-) > >diff --git a/net/core/dev.c b/net/core/dev.c >index 722d50d..3e0cd80 100644 >--- a/net/core/dev.c >+++ b/net/core/dev.c >@@ -1171,6 +1171,7 @@ int dev_get_valid_name(struct net *net, struct net_device *dev, > int dev_change_name(struct net_device *dev, const char *newname) > { > unsigned char old_assign_type; >+ bool reopen_needed = false; > char oldname[IFNAMSIZ]; > int err = 0; > int ret; >@@ -1180,8 +1181,24 @@ 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) >- return -EBUSY; >+ >+ /* 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) { >+ if (likely(!(dev->priv_flags & IFF_FAILOVER_SLAVE))) >+ return -EBUSY; >+ reopen_needed = true; >+ } > > write_seqcount_begin(&devnet_rename_seq); > >@@ -1198,6 +1215,9 @@ int dev_change_name(struct net_device *dev, const char *newname) > return err; > } > >+ if (reopen_needed) >+ dev_close(dev);Ugh. Don't dev_close/dev_open on name change.>+ > if (oldname[0] && !strchr(oldname, '%')) > netdev_info(dev, "renamed from %s\n", oldname); > >@@ -1210,7 +1230,9 @@ int dev_change_name(struct net_device *dev, const char *newname) > memcpy(dev->name, oldname, IFNAMSIZ); > dev->name_assign_type = old_assign_type; > write_seqcount_end(&devnet_rename_seq); >- return ret; >+ if (err >= 0) >+ err = ret; >+ goto reopen; > } > > write_seqcount_end(&devnet_rename_seq); >@@ -1246,6 +1268,15 @@ int dev_change_name(struct net_device *dev, const char *newname) > } > } > >+reopen: >+ if (reopen_needed) { >+ ret = dev_open(dev); >+ if (ret) { >+ pr_err("%s: reopen device failed: %d\n", >+ dev->name, ret); >+ } >+ } >+ > return err; > } > >-- >1.8.3.1 >