netns: Coexist with the sysfs limitations

To make testing of the network namespace simpler allow
the network namespace code and the sysfs code to be
compiled and run at the same time.  To do this only
virtual devices are allowed in the additional network
namespaces and those virtual devices are not placed
in the kobject tree.

Since virtual devices don't actually do anything interesting
hardware wise that needs device management there should
be no loss in keeping them out of the kobject tree and
by implication sysfs.  The gain in ease of testing
and code coverage should be significant.

I.e. people running distributions that make it next to
impossible to boot without sysfs should at be able to
boot a test kernel now.

Plus no ABIs are harmed with this patch.

Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
---
 net/Kconfig          |    2 +-
 net/core/dev.c       |   12 +++++++++++-
 net/core/net-sysfs.c |    7 +++++++
 3 files changed, 19 insertions(+), 2 deletions(-)

Eric W. Biederman wrote:
> To make testing of the network namespace simpler allow
> the network namespace code and the sysfs code to be
> compiled and run at the same time.  To do this only
> virtual devices are allowed in the additional network
> namespaces and those virtual devices are not placed
> in the kobject tree.
> 
> Since virtual devices don't actually do anything interesting
> hardware wise that needs device management there should
> be no loss in keeping them out of the kobject tree and
> by implication sysfs.  The gain in ease of testing
> and code coverage should be significant.
> 
> I.e. people running distributions that make it next to
> impossible to boot without sysfs should at be able to
> boot a test kernel now.
> 
> Plus no ABIs are harmed with this patch.
> 
> Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>

Acked-by: Daniel Lezcano <dlezcano@fr.ibm.com>

> ---
>  net/Kconfig          |    2 +-
>  net/core/dev.c       |   12 +++++++++++-
>  net/core/net-sysfs.c |    7 +++++++
>  3 files changed, 19 insertions(+), 2 deletions(-)
> 
> diff --git a/net/Kconfig b/net/Kconfig
> index d789d79..8c3d97c 100644
> --- a/net/Kconfig
> +++ b/net/Kconfig
> @@ -27,7 +27,7 @@ menu "Networking options"
>  config NET_NS
>  	bool "Network namespace support"
>  	default n
> -	depends on EXPERIMENTAL && !SYSFS && NAMESPACES
> +	depends on EXPERIMENTAL && NAMESPACES
>  	help
>  	  Allow user space to create what appear to be multiple instances
>  	  of the network stack.
> diff --git a/net/core/dev.c b/net/core/dev.c
> index b8a4fd0..a7f0461 100644
> --- a/net/core/dev.c
> +++ b/net/core/dev.c
> @@ -4449,6 +4449,15 @@ int dev_change_net_namespace(struct net_device *dev, struct net *net, const char
>  	if (dev->features & NETIF_F_NETNS_LOCAL)
>  		goto out;
> 
> +#ifdef CONFIG_SYSFS
> +	/* Don't allow real devices to be moved when sysfs
> +	 * is enabled.
> +	 */
> +	err = -EINVAL;
> +	if (dev->dev.parent)
> +		goto out;
> +#endif
> +
>  	/* Ensure the device has been registrered */
>  	err = -EINVAL;
>  	if (dev->reg_state != NETREG_REGISTERED)
> @@ -4506,6 +4515,8 @@ int dev_change_net_namespace(struct net_device *dev, struct net *net, const char
>  	 */
>  	dev_addr_discard(dev);
> 
> +	netdev_unregister_kobject(dev);
> +
>  	/* Actually switch the network namespace */
>  	dev_net_set(dev, net);
> 
> @@ -4522,7 +4533,6 @@ int dev_change_net_namespace(struct net_device *dev, struct net *net, const char
>  	}
> 
>  	/* Fixup kobjects */
> -	netdev_unregister_kobject(dev);
>  	err = netdev_register_kobject(dev);
>  	WARN_ON(err);
> 
> diff --git a/net/core/net-sysfs.c b/net/core/net-sysfs.c
> index 92d6b94..85cb8bd 100644
> --- a/net/core/net-sysfs.c
> +++ b/net/core/net-sysfs.c
> @@ -476,6 +476,10 @@ void netdev_unregister_kobject(struct net_device * net)
>  	struct device *dev = &(net->dev);
> 
>  	kobject_get(&dev->kobj);
> +
> +	if (dev_net(net) != &init_net)
> +		return;
> +
>  	device_del(dev);
>  }
> 
> @@ -501,6 +505,9 @@ int netdev_register_kobject(struct net_device *net)
>  #endif
>  #endif /* CONFIG_SYSFS */
> 
> +	if (dev_net(net) != &init_net)
> +		return 0;
> +
>  	return device_add(dev);
>  }
>

Quoting Eric W. Biederman (ebiederm@xmission.com):
> 
> To make testing of the network namespace simpler allow
> the network namespace code and the sysfs code to be
> compiled and run at the same time.  To do this only
> virtual devices are allowed in the additional network
> namespaces and those virtual devices are not placed
> in the kobject tree.
> 
> Since virtual devices don't actually do anything interesting
> hardware wise that needs device management there should
> be no loss in keeping them out of the kobject tree and
> by implication sysfs.  The gain in ease of testing
> and code coverage should be significant.
> 
> I.e. people running distributions that make it next to
> impossible to boot without sysfs should at be able to
> boot a test kernel now.
> 
> Plus no ABIs are harmed with this patch.
> 
> Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>

Duh.

Tested-by: Serge Hallyn <serue@us.ibm.com>
Acked-by: Serge Hallyn <serue@us.ibm.com>

Thanks, Eric!  Thanks, Benjamin!

-serge
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Serge E. Hallyn wrote:
> Quoting Eric W. Biederman (ebiederm@xmission.com):
>> To make testing of the network namespace simpler allow
>> the network namespace code and the sysfs code to be
>> compiled and run at the same time.  To do this only
>> virtual devices are allowed in the additional network
>> namespaces and those virtual devices are not placed
>> in the kobject tree.
>>
>> Since virtual devices don't actually do anything interesting
>> hardware wise that needs device management there should
>> be no loss in keeping them out of the kobject tree and
>> by implication sysfs.  The gain in ease of testing
>> and code coverage should be significant.
>>
>> I.e. people running distributions that make it next to
>> impossible to boot without sysfs should at be able to
>> boot a test kernel now.
>>
>> Plus no ABIs are harmed with this patch.

>> Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
> 
> Duh.
> 
> Tested-by: Serge Hallyn <serue@us.ibm.com>
> Acked-by: Serge Hallyn <serue@us.ibm.com>

Oh, this patch is short, clean, and the limitation introduced isn't too
annoying for testing netns right now.

At least, my proposal provoked some reactions :)

BTW, there's a second limitation with your patch:
we can't rename the net devices in the additional network namespaces.

In net/core/dev.c, dev_change_name() fails: call to device_rename() 
return an (expected) -EINVAL error.
Maybe we should add a test on the net to only call it in init_net?

  rollback:
-       err = device_rename(&dev->dev, dev->name);
-       if (err) {
-               memcpy(dev->name, oldname, IFNAMSIZ);
-               return err;
+       if (net == &init_net) {
+               err = device_rename(&dev->dev, dev->name);
+               if (err) {
+                       memcpy(dev->name, oldname, IFNAMSIZ);
+                       return err;
+               }
         }

Otherwise,

Acked-by: Benjamin Thery <benjamin.thery@bull.net>

Thanks,
Benjamin

> 
> Thanks, Eric!  Thanks, Benjamin!
> 
> -serge
> 
>

Benjamin Thery <benjamin.thery@bull.net> writes:

> Serge E. Hallyn wrote:
>> Quoting Eric W. Biederman (ebiederm@xmission.com):
>>> To make testing of the network namespace simpler allow
>>> the network namespace code and the sysfs code to be
>>> compiled and run at the same time.  To do this only
>>> virtual devices are allowed in the additional network
>>> namespaces and those virtual devices are not placed
>>> in the kobject tree.
>>>
>>> Since virtual devices don't actually do anything interesting
>>> hardware wise that needs device management there should
>>> be no loss in keeping them out of the kobject tree and
>>> by implication sysfs.  The gain in ease of testing
>>> and code coverage should be significant.
>>>
>>> I.e. people running distributions that make it next to
>>> impossible to boot without sysfs should at be able to
>>> boot a test kernel now.
>>>
>>> Plus no ABIs are harmed with this patch.
>
>>> Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
>>
>> Duh.
>>
>> Tested-by: Serge Hallyn <serue@us.ibm.com>
>> Acked-by: Serge Hallyn <serue@us.ibm.com>
>
> Oh, this patch is short, clean, and the limitation introduced isn't too
> annoying for testing netns right now.
>
> At least, my proposal provoked some reactions :)

Yes.

> BTW, there's a second limitation with your patch:
> we can't rename the net devices in the additional network namespaces.
>
> In net/core/dev.c, dev_change_name() fails: call to device_rename() return an
> (expected) -EINVAL error.
> Maybe we should add a test on the net to only call it in init_net?

Yes.  Good catch.

Eric
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