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Date:	Thu, 10 Jul 2014 22:01:01 +0200
From:	Tom Gundersen <teg@...m.no>
To:	Arend van Spriel <arend@...adcom.com>
Cc:	netdev <netdev@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	David Miller <davem@...emloft.net>,
	David Herrmann <dh.herrmann@...il.com>,
	Kay Sievers <kay@...y.org>
Subject: Re: [PATCH v7 01/33] net: add name_assign_type netdev attribute

On Thu, Jul 10, 2014 at 9:58 PM, Arend van Spriel <arend@...adcom.com> wrote:
> 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 <teg@...m.no>
>> Reviewed-by: David Herrmann <dh.herrmann@...il.com>
>> Reviewed-by: Kay Sievers <kay@...y.org>
>> ---
>>  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?

Yeah. Fixed that one too.

Thanks.

Tom

>> +Contact:     netdev@...r.kernel.org
>> +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,
>>
>
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