Subject: Re: [PATCH v7 01/33] net: add name_assign_type netdev attribute

From: Arend van Spriel <[email-masked]>
Date: Thu, 10 Jul 2014 21:58:46 +0200

On 10-07-14 10:17, Tom Gundersen wrote:
> Based on a patch by David Herrmann.
> 
> The name_assign_type attribute gives hints where the interface name of a
> given net-device comes from. These values are currently defined:
>   NET_NAME_ENUM:
>     The ifname is provided by the kernel with an enumerated
>     suffix, typically based on order of discovery. Names may
>     be reused and unpredictable.
>   NET_NAME_PREDICTABLE:
>     The ifname has been assigned by the kernel in a predictable way
>     that is guaranteed to avoid reuse and always be the same for a
>     given device. Examples include statically created devices like
>     the loopback device and names deduced from hardware properties
>     (including being given explicitly by the firmware). Names
>     depending on the order of discovery, or in any other way on the
>     existence of other devices, must not be marked as PREDICTABLE.
>   NET_NAME_USER:
>     The ifname was provided by user-space during net-device setup.
>   NET_NAME_RENAMED:
>     The net-device has been renamed from userspace. Once this type is set,
>     it cannot change again.
>   NET_NAME_UNKNOWN:
>     This is an internal placeholder to indicate that we yet haven't yet
>     categorized the name. It will not be exposed to userspace, rather
>     -EINVAL is returned.
> 
> The aim of these patches is to improve user-space renaming of interfaces. As
> a general rule, userspace must rename interfaces to guarantee that names stay
> the same every time a given piece of hardware appears (at boot, or when
> attaching it). However, there are several situations where userspace should
> not perform the renaming, and that depends on both the policy of the local
> admin, but crucially also on the nature of the current interface name.
> 
> If an interface was created in repsonse to a userspace request, and userspace
> already provided a name, we most probably want to leave that name alone. The
> main instance of this is wifi-P2P devices created over nl80211, which currently
> have a long-standing bug where they are getting renamed by udev. We label such
> names NET_NAME_USER.
> 
> If an interface, unbeknown to us, has already been renamed from userspace, we
> most probably want to leave also that alone. This will typically happen when
> third-party plugins (for instance to udev, but the interface is generic so could
> be from anywhere) renames the interface without informing udev about it. A
> typical situation is when you switch root from an installer or an initrd to the
> real system and the new instance of udev does not know what happened before
> the switch. These types of problems have caused repeated issues in the past. To
> solve this, once an interface has been renamed, its name is labelled
> NET_NAME_RENAMED.
> 
> In many cases, the kernel is actually able to name interfaces in such a
> way that there is no need for userspace to rename them. This is the case when
> the enumeration order of devices, or in fact any other (non-parent) device on
> the system, can not influence the name of the interface. Examples include
> statically created devices, or any naming schemes based on hardware properties
> of the interface. In this case the admin may prefer to use the kernel-provided
> names, and to make that possible we label such names NET_NAME_PREDICTABLE.
> We want the kernel to have tho possibilty of performing predictable interface
> naming itself (and exposing to userspace that it has), as the information
> necessary for a proper naming scheme for a certain class of devices may not
> be exposed to userspace.
> 
> The case where renaming is almost certainly desired, is when the kernel has
> given the interface a name using global device enumeration based on order of
> discovery (ethX, wlanY, etc). These naming schemes are labelled NET_NAME_ENUM.
> 
> Lastly, a fallback is left as NET_NAME_UNKNOWN, to indicate that a driver has
> not yet been ported. This is mostly useful as a transitionary measure, allowing
> us to label the various naming schemes bit by bit.
> 
> Signed-off-by: Tom Gundersen <[email-masked]>
> Reviewed-by: David Herrmann <[email-masked]>
> Reviewed-by: Kay Sievers <[email-masked]>
> ---
>  Documentation/ABI/testing/sysfs-class-net | 11 +++++++++++
>  include/linux/netdevice.h                 |  2 ++
>  include/uapi/linux/netdevice.h            |  6 ++++++
>  net/core/net-sysfs.c                      | 20 ++++++++++++++++++++
>  4 files changed, 39 insertions(+)
> 
> diff --git a/Documentation/ABI/testing/sysfs-class-net b/Documentation/ABI/testing/sysfs-class-net
> index 416c5d5..d34280a 100644
> --- a/Documentation/ABI/testing/sysfs-class-net
> +++ b/Documentation/ABI/testing/sysfs-class-net
> @@ -1,3 +1,14 @@
> +What:		/sys/class/net/<iface>/name_assign_type
> +Date:		July 2014
> +KernelVersion:	3.2

Is this a copy&paste error. I guess it will be 3.17+, right?

> +Contact:	[email-masked]
> +Description:
> +		Indicates the name assignment type. Possible values are:
> +		1: enumerated by the kernel, possibly in an unpredictable way
> +		2: predictably named by the kernel
> +		3: named by userspace
> +		4: renamed
> +
>  What:		/sys/class/net/<iface>/addr_assign_type
>  Date:		July 2010
>  KernelVersion:	3.2
> diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
> index 66f9a04..551e187 100644
> --- a/include/linux/netdevice.h
> +++ b/include/linux/netdevice.h
> @@ -1379,6 +1379,8 @@ struct net_device {
>  	struct kset		*queues_kset;
>  #endif
>  
> +	unsigned char		name_assign_type;
> +
>  	bool			uc_promisc;
>  	unsigned int		promiscuity;
>  	unsigned int		allmulti;
> diff --git a/include/uapi/linux/netdevice.h b/include/uapi/linux/netdevice.h
> index fdfbd1c..82e630a 100644
> --- a/include/uapi/linux/netdevice.h
> +++ b/include/uapi/linux/netdevice.h
> @@ -37,6 +37,12 @@
>  #define INIT_NETDEV_GROUP	0
>  
>  
> +/* interface name assignment types (sysfs name_assign_type attribute) */
> +#define NET_NAME_UNKNOWN	0	/* unknown origin (not exposed to userspace) */
> +#define NET_NAME_ENUM		1	/* enumerated by kernel */
> +#define NET_NAME_PREDICTABLE	2       /* predictably named by the kernel */
> +#define NET_NAME_USER		3	/* provided by user-space */
> +#define NET_NAME_RENAMED	4	/* renamed by user-space */
>  
>  /* Media selection options. */
>  enum {
> diff --git a/net/core/net-sysfs.c b/net/core/net-sysfs.c
> index 1cac29e..7752f2a 100644
> --- a/net/core/net-sysfs.c
> +++ b/net/core/net-sysfs.c
> @@ -112,6 +112,25 @@ NETDEVICE_SHOW_RO(ifindex, fmt_dec);
>  NETDEVICE_SHOW_RO(type, fmt_dec);
>  NETDEVICE_SHOW_RO(link_mode, fmt_dec);
>  
> +static ssize_t format_name_assign_type(const struct net_device *net, char *buf)
> +{
> +	return sprintf(buf, fmt_dec, net->name_assign_type);
> +}
> +
> +static ssize_t name_assign_type_show(struct device *dev,
> +				     struct device_attribute *attr,
> +				     char *buf)
> +{
> +	struct net_device *net = to_net_dev(dev);
> +	ssize_t ret = -EINVAL;
> +
> +	if (net->name_assign_type != NET_NAME_UNKNOWN)
> +		ret = netdev_show(dev, attr, buf, format_name_assign_type);
> +
> +	return ret;
> +}
> +static DEVICE_ATTR_RO(name_assign_type);
> +
>  /* use same locking rules as GIFHWADDR ioctl's */
>  static ssize_t address_show(struct device *dev, struct device_attribute *attr,
>  			    char *buf)
> @@ -387,6 +406,7 @@ static struct attribute *net_class_attrs[] = {
>  	&dev_attr_dev_port.attr,
>  	&dev_attr_iflink.attr,
>  	&dev_attr_ifindex.attr,
> +	&dev_attr_name_assign_type.attr,
>  	&dev_attr_addr_assign_type.attr,
>  	&dev_attr_addr_len.attr,
>  	&dev_attr_link_mode.attr,
>