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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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