[PATCH net v4] failover: allow name change on IFF_UP slave interfaces

[PATCH net v4] failover: allow name change on IFF_UP slave interfaces

[Si-Wei Liu]

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@oracle.com>
Reviewed-by: Liran Alon <liran.alon@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)
---
 net/core/dev.c | 24 +++++++++++++++++++++++-
 1 file changed, 23 insertions(+), 1 deletion(-)

diff --git a/net/core/dev.c b/net/core/dev.c
index 722d50d..6ae5874 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -1180,7 +1180,21 @@ 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);
@@ -1227,6 +1241,14 @@ 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;
+
+		change_info.flags_changed = 0;
+		call_netdevice_notifiers_info(NETDEV_CHANGE, dev,
+					      &change_info.info);
+	}
+
 	ret = call_netdevice_notifiers(NETDEV_CHANGENAME, dev);
 	ret = notifier_to_errno(ret);
 
-- 
1.8.3.1

Re: [PATCH net v4] failover: allow name change on IFF_UP slave interfaces

[Samudrala, Sridhar]

On 3/28/2019 4:47 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 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@oracle.com>
> Reviewed-by: Liran Alon <liran.alon@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)
> ---
>   net/core/dev.c | 24 +++++++++++++++++++++++-
>   1 file changed, 23 insertions(+), 1 deletion(-)
> 
> diff --git a/net/core/dev.c b/net/core/dev.c
> index 722d50d..6ae5874 100644
> --- a/net/core/dev.c
> +++ b/net/core/dev.c
> @@ -1180,7 +1180,21 @@ 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);
> @@ -1227,6 +1241,14 @@ 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;
> +
> +		change_info.flags_changed = 0;
> +		call_netdevice_notifiers_info(NETDEV_CHANGE, dev,
> +					      &change_info.info);

This function no longer takes the dev parameter in the net-next kernel.

Did you consider calling netdev_state_change() although it does send a 
RTM_NEWLINK message too. May be just fixing the notifier call should be 
fine.

> +	}
> +
>   	ret = call_netdevice_notifiers(NETDEV_CHANGENAME, dev);
>   	ret = notifier_to_errno(ret);
>   
> 

Re: [PATCH net v4] failover: allow name change on IFF_UP slave interfaces

[Samudrala, Sridhar]

On 3/28/2019 4:47 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 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@oracle.com>
> Reviewed-by: Liran Alon <liran.alon@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)
> ---
>   net/core/dev.c | 24 +++++++++++++++++++++++-
>   1 file changed, 23 insertions(+), 1 deletion(-)
> 
> diff --git a/net/core/dev.c b/net/core/dev.c
> index 722d50d..6ae5874 100644
> --- a/net/core/dev.c
> +++ b/net/core/dev.c
> @@ -1180,7 +1180,21 @@ 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);
> @@ -1227,6 +1241,14 @@ 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;
> +
> +		change_info.flags_changed = 0;
> +		call_netdevice_notifiers_info(NETDEV_CHANGE, dev,
> +					      &change_info.info);

This function no longer takes the dev parameter in the net-next kernel.

Did you consider calling netdev_state_change() although it does send a 
RTM_NEWLINK message too. May be just fixing the notifier call should be 
fine.

> +	}
> +
>   	ret = call_netdevice_notifiers(NETDEV_CHANGENAME, dev);
>   	ret = notifier_to_errno(ret);
>   
> 

Re: [PATCH net v4] failover: allow name change on IFF_UP slave interfaces

[kbuild test robot]

[-- Attachment #1: Type: text/plain, Size: 5112 bytes --]

Hi Si-Wei,

Thank you for the patch! Yet something to improve:

[auto build test ERROR on net/master]

url:    https://github.com/0day-ci/linux/commits/Si-Wei-Liu/failover-allow-name-change-on-IFF_UP-slave-interfaces/20190329-195445
config: x86_64-lkp (attached as .config)
compiler: gcc-7 (Debian 7.3.0-1) 7.3.0
reproduce:
        # save the attached .config to linux build tree
        make ARCH=x86_64 

All errors (new ones prefixed by >>):

   net/core/dev.c: In function 'dev_change_name':
>> net/core/dev.c:1252:48: error: passing argument 2 of 'call_netdevice_notifiers_info' from incompatible pointer type [-Werror=incompatible-pointer-types]
      call_netdevice_notifiers_info(NETDEV_CHANGE, dev,
                                                   ^~~
   net/core/dev.c:164:12: note: expected 'struct netdev_notifier_info *' but argument is of type 'struct net_device *'
    static int call_netdevice_notifiers_info(unsigned long val,
               ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>> net/core/dev.c:1252:3: error: too many arguments to function 'call_netdevice_notifiers_info'
      call_netdevice_notifiers_info(NETDEV_CHANGE, dev,
      ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~
   net/core/dev.c:164:12: note: declared here
    static int call_netdevice_notifiers_info(unsigned long val,
               ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~
   cc1: some warnings being treated as errors

vim +/call_netdevice_notifiers_info +1252 net/core/dev.c

  1166	
  1167	/**
  1168	 *	dev_change_name - change name of a device
  1169	 *	@dev: device
  1170	 *	@newname: name (or format string) must be at least IFNAMSIZ
  1171	 *
  1172	 *	Change name of a device, can pass format strings "eth%d".
  1173	 *	for wildcarding.
  1174	 */
  1175	int dev_change_name(struct net_device *dev, const char *newname)
  1176	{
  1177		unsigned char old_assign_type;
  1178		char oldname[IFNAMSIZ];
  1179		int err = 0;
  1180		int ret;
  1181		struct net *net;
  1182	
  1183		ASSERT_RTNL();
  1184		BUG_ON(!dev_net(dev));
  1185	
  1186		net = dev_net(dev);
  1187	
  1188		/* Allow failover slave to rename even when
  1189		 * it is up and running.
  1190		 *
  1191		 * Failover slaves are special, since userspace
  1192		 * might rename the slave after the interface
  1193		 * has been brought up and running due to
  1194		 * auto-enslavement.
  1195		 *
  1196		 * Failover users don't actually care about slave
  1197		 * name change, as they are only expected to operate
  1198		 * on master interface directly.
  1199		 */
  1200		if (dev->flags & IFF_UP &&
  1201		    likely(!(dev->priv_flags & IFF_FAILOVER_SLAVE)))
  1202			return -EBUSY;
  1203	
  1204		write_seqcount_begin(&devnet_rename_seq);
  1205	
  1206		if (strncmp(newname, dev->name, IFNAMSIZ) == 0) {
  1207			write_seqcount_end(&devnet_rename_seq);
  1208			return 0;
  1209		}
  1210	
  1211		memcpy(oldname, dev->name, IFNAMSIZ);
  1212	
  1213		err = dev_get_valid_name(net, dev, newname);
  1214		if (err < 0) {
  1215			write_seqcount_end(&devnet_rename_seq);
  1216			return err;
  1217		}
  1218	
  1219		if (oldname[0] && !strchr(oldname, '%'))
  1220			netdev_info(dev, "renamed from %s\n", oldname);
  1221	
  1222		old_assign_type = dev->name_assign_type;
  1223		dev->name_assign_type = NET_NAME_RENAMED;
  1224	
  1225	rollback:
  1226		ret = device_rename(&dev->dev, dev->name);
  1227		if (ret) {
  1228			memcpy(dev->name, oldname, IFNAMSIZ);
  1229			dev->name_assign_type = old_assign_type;
  1230			write_seqcount_end(&devnet_rename_seq);
  1231			return ret;
  1232		}
  1233	
  1234		write_seqcount_end(&devnet_rename_seq);
  1235	
  1236		netdev_adjacent_rename_links(dev, oldname);
  1237	
  1238		write_lock_bh(&dev_base_lock);
  1239		hlist_del_rcu(&dev->name_hlist);
  1240		write_unlock_bh(&dev_base_lock);
  1241	
  1242		synchronize_rcu();
  1243	
  1244		write_lock_bh(&dev_base_lock);
  1245		hlist_add_head_rcu(&dev->name_hlist, dev_name_hash(net, dev->name));
  1246		write_unlock_bh(&dev_base_lock);
  1247	
  1248		if (unlikely(dev->flags & IFF_UP)) {
  1249			struct netdev_notifier_change_info change_info;
  1250	
  1251			change_info.flags_changed = 0;
> 1252			call_netdevice_notifiers_info(NETDEV_CHANGE, dev,
  1253						      &change_info.info);
  1254		}
  1255	
  1256		ret = call_netdevice_notifiers(NETDEV_CHANGENAME, dev);
  1257		ret = notifier_to_errno(ret);
  1258	
  1259		if (ret) {
  1260			/* err >= 0 after dev_alloc_name() or stores the first errno */
  1261			if (err >= 0) {
  1262				err = ret;
  1263				write_seqcount_begin(&devnet_rename_seq);
  1264				memcpy(dev->name, oldname, IFNAMSIZ);
  1265				memcpy(oldname, newname, IFNAMSIZ);
  1266				dev->name_assign_type = old_assign_type;
  1267				old_assign_type = NET_NAME_RENAMED;
  1268				goto rollback;
  1269			} else {
  1270				pr_err("%s: name change rollback failed: %d\n",
  1271				       dev->name, ret);
  1272			}
  1273		}
  1274	
  1275		return err;
  1276	}
  1277	

---
0-DAY kernel test infrastructure                Open Source Technology Center
https://lists.01.org/pipermail/kbuild-all                   Intel Corporation

[-- Attachment #2: .config.gz --]
[-- Type: application/gzip, Size: 26574 bytes --]

Re: [PATCH net v4] failover: allow name change on IFF_UP slave interfaces

[kbuild test robot]

[-- Attachment #1: Type: text/plain, Size: 5112 bytes --]

Hi Si-Wei,

Thank you for the patch! Yet something to improve:

[auto build test ERROR on net/master]

url:    https://github.com/0day-ci/linux/commits/Si-Wei-Liu/failover-allow-name-change-on-IFF_UP-slave-interfaces/20190329-195445
config: x86_64-lkp (attached as .config)
compiler: gcc-7 (Debian 7.3.0-1) 7.3.0
reproduce:
        # save the attached .config to linux build tree
        make ARCH=x86_64 

All errors (new ones prefixed by >>):

   net/core/dev.c: In function 'dev_change_name':
>> net/core/dev.c:1252:48: error: passing argument 2 of 'call_netdevice_notifiers_info' from incompatible pointer type [-Werror=incompatible-pointer-types]
      call_netdevice_notifiers_info(NETDEV_CHANGE, dev,
                                                   ^~~
   net/core/dev.c:164:12: note: expected 'struct netdev_notifier_info *' but argument is of type 'struct net_device *'
    static int call_netdevice_notifiers_info(unsigned long val,
               ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>> net/core/dev.c:1252:3: error: too many arguments to function 'call_netdevice_notifiers_info'
      call_netdevice_notifiers_info(NETDEV_CHANGE, dev,
      ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~
   net/core/dev.c:164:12: note: declared here
    static int call_netdevice_notifiers_info(unsigned long val,
               ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~
   cc1: some warnings being treated as errors

vim +/call_netdevice_notifiers_info +1252 net/core/dev.c

  1166	
  1167	/**
  1168	 *	dev_change_name - change name of a device
  1169	 *	@dev: device
  1170	 *	@newname: name (or format string) must be at least IFNAMSIZ
  1171	 *
  1172	 *	Change name of a device, can pass format strings "eth%d".
  1173	 *	for wildcarding.
  1174	 */
  1175	int dev_change_name(struct net_device *dev, const char *newname)
  1176	{
  1177		unsigned char old_assign_type;
  1178		char oldname[IFNAMSIZ];
  1179		int err = 0;
  1180		int ret;
  1181		struct net *net;
  1182	
  1183		ASSERT_RTNL();
  1184		BUG_ON(!dev_net(dev));
  1185	
  1186		net = dev_net(dev);
  1187	
  1188		/* Allow failover slave to rename even when
  1189		 * it is up and running.
  1190		 *
  1191		 * Failover slaves are special, since userspace
  1192		 * might rename the slave after the interface
  1193		 * has been brought up and running due to
  1194		 * auto-enslavement.
  1195		 *
  1196		 * Failover users don't actually care about slave
  1197		 * name change, as they are only expected to operate
  1198		 * on master interface directly.
  1199		 */
  1200		if (dev->flags & IFF_UP &&
  1201		    likely(!(dev->priv_flags & IFF_FAILOVER_SLAVE)))
  1202			return -EBUSY;
  1203	
  1204		write_seqcount_begin(&devnet_rename_seq);
  1205	
  1206		if (strncmp(newname, dev->name, IFNAMSIZ) == 0) {
  1207			write_seqcount_end(&devnet_rename_seq);
  1208			return 0;
  1209		}
  1210	
  1211		memcpy(oldname, dev->name, IFNAMSIZ);
  1212	
  1213		err = dev_get_valid_name(net, dev, newname);
  1214		if (err < 0) {
  1215			write_seqcount_end(&devnet_rename_seq);
  1216			return err;
  1217		}
  1218	
  1219		if (oldname[0] && !strchr(oldname, '%'))
  1220			netdev_info(dev, "renamed from %s\n", oldname);
  1221	
  1222		old_assign_type = dev->name_assign_type;
  1223		dev->name_assign_type = NET_NAME_RENAMED;
  1224	
  1225	rollback:
  1226		ret = device_rename(&dev->dev, dev->name);
  1227		if (ret) {
  1228			memcpy(dev->name, oldname, IFNAMSIZ);
  1229			dev->name_assign_type = old_assign_type;
  1230			write_seqcount_end(&devnet_rename_seq);
  1231			return ret;
  1232		}
  1233	
  1234		write_seqcount_end(&devnet_rename_seq);
  1235	
  1236		netdev_adjacent_rename_links(dev, oldname);
  1237	
  1238		write_lock_bh(&dev_base_lock);
  1239		hlist_del_rcu(&dev->name_hlist);
  1240		write_unlock_bh(&dev_base_lock);
  1241	
  1242		synchronize_rcu();
  1243	
  1244		write_lock_bh(&dev_base_lock);
  1245		hlist_add_head_rcu(&dev->name_hlist, dev_name_hash(net, dev->name));
  1246		write_unlock_bh(&dev_base_lock);
  1247	
  1248		if (unlikely(dev->flags & IFF_UP)) {
  1249			struct netdev_notifier_change_info change_info;
  1250	
  1251			change_info.flags_changed = 0;
> 1252			call_netdevice_notifiers_info(NETDEV_CHANGE, dev,
  1253						      &change_info.info);
  1254		}
  1255	
  1256		ret = call_netdevice_notifiers(NETDEV_CHANGENAME, dev);
  1257		ret = notifier_to_errno(ret);
  1258	
  1259		if (ret) {
  1260			/* err >= 0 after dev_alloc_name() or stores the first errno */
  1261			if (err >= 0) {
  1262				err = ret;
  1263				write_seqcount_begin(&devnet_rename_seq);
  1264				memcpy(dev->name, oldname, IFNAMSIZ);
  1265				memcpy(oldname, newname, IFNAMSIZ);
  1266				dev->name_assign_type = old_assign_type;
  1267				old_assign_type = NET_NAME_RENAMED;
  1268				goto rollback;
  1269			} else {
  1270				pr_err("%s: name change rollback failed: %d\n",
  1271				       dev->name, ret);
  1272			}
  1273		}
  1274	
  1275		return err;
  1276	}
  1277	

---
0-DAY kernel test infrastructure                Open Source Technology Center
https://lists.01.org/pipermail/kbuild-all                   Intel Corporation

[-- Attachment #2: .config.gz --]
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[-- Attachment #3: Type: text/plain, Size: 183 bytes --]

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Re: [PATCH net v4] failover: allow name change on IFF_UP slave interfaces

[Stephen Hemminger]

On Thu, 28 Mar 2019 19:47:27 -0400
Si-Wei Liu <si-wei.liu@oracle.com> wrote:

> +	if (unlikely(dev->flags & IFF_UP)) {
> +		struct netdev_notifier_change_info change_info;
> +
> +		change_info.flags_changed = 0;

Simpler to use structure initialization, which also avoid any chance
of unititialized fields.

		struct netdev_notifier_change_info change_info
			= { .flags_changed =  0 };

Re: [PATCH net v4] failover: allow name change on IFF_UP slave interfaces

[Stephen Hemminger]

On Thu, 28 Mar 2019 19:47:27 -0400
Si-Wei Liu <si-wei.liu@oracle.com> wrote:

> +	if (unlikely(dev->flags & IFF_UP)) {
> +		struct netdev_notifier_change_info change_info;
> +
> +		change_info.flags_changed = 0;

Simpler to use structure initialization, which also avoid any chance
of unititialized fields.

		struct netdev_notifier_change_info change_info
			= { .flags_changed =  0 };

Re: [PATCH net v4] failover: allow name change on IFF_UP slave interfaces

[Jiri Pirko]

Fri, Mar 29, 2019 at 04:15:12PM CET, stephen@networkplumber.org wrote:
>On Thu, 28 Mar 2019 19:47:27 -0400
>Si-Wei Liu <si-wei.liu@oracle.com> wrote:
>
>> +	if (unlikely(dev->flags & IFF_UP)) {
>> +		struct netdev_notifier_change_info change_info;
>> +
>> +		change_info.flags_changed = 0;
>
>Simpler to use structure initialization, which also avoid any chance
>of unititialized fields.
>
>		struct netdev_notifier_change_info change_info
>			= { .flags_changed =  0 };
 
In fact, you can do just:
	struct netdev_notifier_change_info change_info = {};
to achieve the same.

Re: [PATCH net v4] failover: allow name change on IFF_UP slave interfaces

[Jiri Pirko]

Fri, Mar 29, 2019 at 04:15:12PM CET, stephen@networkplumber.org wrote:
>On Thu, 28 Mar 2019 19:47:27 -0400
>Si-Wei Liu <si-wei.liu@oracle.com> wrote:
>
>> +	if (unlikely(dev->flags & IFF_UP)) {
>> +		struct netdev_notifier_change_info change_info;
>> +
>> +		change_info.flags_changed = 0;
>
>Simpler to use structure initialization, which also avoid any chance
>of unititialized fields.
>
>		struct netdev_notifier_change_info change_info
>			= { .flags_changed =  0 };
 
In fact, you can do just:
	struct netdev_notifier_change_info change_info = {};
to achieve the same.

Re: [PATCH net v4] failover: allow name change on IFF_UP slave interfaces

[si-wei liu]

On 3/28/2019 10:55 PM, Samudrala, Sridhar wrote:
>
>
> On 3/28/2019 4:47 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 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@oracle.com>
>> Reviewed-by: Liran Alon <liran.alon@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)
>> ---
>>   net/core/dev.c | 24 +++++++++++++++++++++++-
>>   1 file changed, 23 insertions(+), 1 deletion(-)
>>
>> diff --git a/net/core/dev.c b/net/core/dev.c
>> index 722d50d..6ae5874 100644
>> --- a/net/core/dev.c
>> +++ b/net/core/dev.c
>> @@ -1180,7 +1180,21 @@ 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);
>> @@ -1227,6 +1241,14 @@ 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;
>> +
>> +        change_info.flags_changed = 0;
>> +        call_netdevice_notifiers_info(NETDEV_CHANGE, dev,
>> +                          &change_info.info);
>
> This function no longer takes the dev parameter in the net-next kernel.
OK. Will get my patch updated with the latest net-next tree.

>
> Did you consider calling netdev_state_change() although it does send a 
> RTM_NEWLINK message too. May be just fixing the notifier call should 
> be fine.
I did look at it and the extra RTM_NEWLINK message was indeed the reason 
I got it rewritten. You see, how the way of initialization is inherited.

Thanks,
-Siwei

>
>> +    }
>> +
>>       ret = call_netdevice_notifiers(NETDEV_CHANGENAME, dev);
>>       ret = notifier_to_errno(ret);
>>

Re: [PATCH net v4] failover: allow name change on IFF_UP slave interfaces

[si-wei liu]

On 3/29/2019 8:34 AM, Jiri Pirko wrote:
> Fri, Mar 29, 2019 at 04:15:12PM CET, stephen@networkplumber.org wrote:
>> On Thu, 28 Mar 2019 19:47:27 -0400
>> Si-Wei Liu <si-wei.liu@oracle.com> wrote:
>>
>>> +	if (unlikely(dev->flags & IFF_UP)) {
>>> +		struct netdev_notifier_change_info change_info;
>>> +
>>> +		change_info.flags_changed = 0;
>> Simpler to use structure initialization, which also avoid any chance
>> of unititialized fields.
>>
>> 		struct netdev_notifier_change_info change_info
>> 			= { .flags_changed =  0 };
>   
> In fact, you can do just:
> 	struct netdev_notifier_change_info change_info = {};
> to achieve the same.
Hmm, although it's same in effect, I'd opt for keeping explicit 
initialization around flags_changed, which has the benefit in terms of 
cscope/tags referencing. Just very minor point though.

Let me if you think it otherwise...

-Siwei

Re: [PATCH net v4] failover: allow name change on IFF_UP slave interfaces

[Michael S. Tsirkin]

On Fri, Mar 29, 2019 at 12:50:25PM -0700, si-wei liu wrote:
> 
> 
> On 3/28/2019 10:55 PM, Samudrala, Sridhar wrote:
> > 
> > 
> > On 3/28/2019 4:47 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 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@oracle.com>
> > > Reviewed-by: Liran Alon <liran.alon@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)
> > > ---
> > >   net/core/dev.c | 24 +++++++++++++++++++++++-
> > >   1 file changed, 23 insertions(+), 1 deletion(-)
> > > 
> > > diff --git a/net/core/dev.c b/net/core/dev.c
> > > index 722d50d..6ae5874 100644
> > > --- a/net/core/dev.c
> > > +++ b/net/core/dev.c
> > > @@ -1180,7 +1180,21 @@ 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);
> > > @@ -1227,6 +1241,14 @@ 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;
> > > +
> > > +        change_info.flags_changed = 0;
> > > +        call_netdevice_notifiers_info(NETDEV_CHANGE, dev,
> > > +                          &change_info.info);
> > 
> > This function no longer takes the dev parameter in the net-next kernel.
> OK. Will get my patch updated with the latest net-next tree.
> 
> > 
> > Did you consider calling netdev_state_change() although it does send a
> > RTM_NEWLINK message too. May be just fixing the notifier call should be
> > fine.
> I did look at it and the extra RTM_NEWLINK message was indeed the reason I
> got it rewritten. You see, how the way of initialization is inherited.
> 
> Thanks,
> -Siwei

More messages just increase the chance existing scripts will work.
Don't see what the harm is.

> > 
> > > +    }
> > > +
> > >       ret = call_netdevice_notifiers(NETDEV_CHANGENAME, dev);
> > >       ret = notifier_to_errno(ret);
> > > 

Re: [PATCH net v4] failover: allow name change on IFF_UP slave interfaces

[Michael S. Tsirkin]

On Fri, Mar 29, 2019 at 12:50:25PM -0700, si-wei liu wrote:
> 
> 
> On 3/28/2019 10:55 PM, Samudrala, Sridhar wrote:
> > 
> > 
> > On 3/28/2019 4:47 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 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@oracle.com>
> > > Reviewed-by: Liran Alon <liran.alon@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)
> > > ---
> > >   net/core/dev.c | 24 +++++++++++++++++++++++-
> > >   1 file changed, 23 insertions(+), 1 deletion(-)
> > > 
> > > diff --git a/net/core/dev.c b/net/core/dev.c
> > > index 722d50d..6ae5874 100644
> > > --- a/net/core/dev.c
> > > +++ b/net/core/dev.c
> > > @@ -1180,7 +1180,21 @@ 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);
> > > @@ -1227,6 +1241,14 @@ 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;
> > > +
> > > +        change_info.flags_changed = 0;
> > > +        call_netdevice_notifiers_info(NETDEV_CHANGE, dev,
> > > +                          &change_info.info);
> > 
> > This function no longer takes the dev parameter in the net-next kernel.
> OK. Will get my patch updated with the latest net-next tree.
> 
> > 
> > Did you consider calling netdev_state_change() although it does send a
> > RTM_NEWLINK message too. May be just fixing the notifier call should be
> > fine.
> I did look at it and the extra RTM_NEWLINK message was indeed the reason I
> got it rewritten. You see, how the way of initialization is inherited.
> 
> Thanks,
> -Siwei

More messages just increase the chance existing scripts will work.
Don't see what the harm is.

> > 
> > > +    }
> > > +
> > >       ret = call_netdevice_notifiers(NETDEV_CHANGENAME, dev);
> > >       ret = notifier_to_errno(ret);
> > > 

Re: [PATCH net v4] failover: allow name change on IFF_UP slave interfaces

[si-wei liu]

On 3/29/2019 3:31 PM, Michael S. Tsirkin wrote:
> On Fri, Mar 29, 2019 at 12:50:25PM -0700, si-wei liu wrote:
>>
>> On 3/28/2019 10:55 PM, Samudrala, Sridhar wrote:
>>>
>>> On 3/28/2019 4:47 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 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@oracle.com>
>>>> Reviewed-by: Liran Alon <liran.alon@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)
>>>> ---
>>>>    net/core/dev.c | 24 +++++++++++++++++++++++-
>>>>    1 file changed, 23 insertions(+), 1 deletion(-)
>>>>
>>>> diff --git a/net/core/dev.c b/net/core/dev.c
>>>> index 722d50d..6ae5874 100644
>>>> --- a/net/core/dev.c
>>>> +++ b/net/core/dev.c
>>>> @@ -1180,7 +1180,21 @@ 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);
>>>> @@ -1227,6 +1241,14 @@ 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;
>>>> +
>>>> +        change_info.flags_changed = 0;
>>>> +        call_netdevice_notifiers_info(NETDEV_CHANGE, dev,
>>>> +                          &change_info.info);
>>> This function no longer takes the dev parameter in the net-next kernel.
>> OK. Will get my patch updated with the latest net-next tree.
>>
>>> Did you consider calling netdev_state_change() although it does send a
>>> RTM_NEWLINK message too. May be just fixing the notifier call should be
>>> fine.
>> I did look at it and the extra RTM_NEWLINK message was indeed the reason I
>> got it rewritten. You see, how the way of initialization is inherited.
>>
>> Thanks,
>> -Siwei
> More messages just increase the chance existing scripts will work.
> Don't see what the harm is.
The NETDEV_CHANGENAME notifier right after could fail which would 
trigger the rollback to its original name. This may save an unnecessary 
(incorrect) message delivered to the userspace which could be confused 
by a name that doesn't exist.

I am not sure I understand why extra message is able to increase the 
chance script works. Once succeeds rtnetlink deliver the same message 
with exact same device state after getting notified by 
NETDEV_CHANGENAME. See rtnetlink_event().

-Siwei


>
>>>> +    }
>>>> +
>>>>        ret = call_netdevice_notifiers(NETDEV_CHANGENAME, dev);
>>>>        ret = notifier_to_errno(ret);
>>>>