685343fc3b
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.
v8: minor documentation fixes
v9: move comment to the right commit
Signed-off-by: Tom Gundersen <teg@jklm.no>
Reviewed-by: David Herrmann <dh.herrmann@gmail.com>
Reviewed-by: Kay Sievers <kay@vrfy.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
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README
This directory attempts to document the ABI between the Linux kernel and userspace, and the relative stability of these interfaces. Due to the everchanging nature of Linux, and the differing maturity levels, these interfaces should be used by userspace programs in different ways. We have four different levels of ABI stability, as shown by the four different subdirectories in this location. Interfaces may change levels of stability according to the rules described below. The different levels of stability are: stable/ This directory documents the interfaces that the developer has defined to be stable. Userspace programs are free to use these interfaces with no restrictions, and backward compatibility for them will be guaranteed for at least 2 years. Most interfaces (like syscalls) are expected to never change and always be available. testing/ This directory documents interfaces that are felt to be stable, as the main development of this interface has been completed. The interface can be changed to add new features, but the current interface will not break by doing this, unless grave errors or security problems are found in them. Userspace programs can start to rely on these interfaces, but they must be aware of changes that can occur before these interfaces move to be marked stable. Programs that use these interfaces are strongly encouraged to add their name to the description of these interfaces, so that the kernel developers can easily notify them if any changes occur (see the description of the layout of the files below for details on how to do this.) obsolete/ This directory documents interfaces that are still remaining in the kernel, but are marked to be removed at some later point in time. The description of the interface will document the reason why it is obsolete and when it can be expected to be removed. removed/ This directory contains a list of the old interfaces that have been removed from the kernel. Every file in these directories will contain the following information: What: Short description of the interface Date: Date created KernelVersion: Kernel version this feature first showed up in. Contact: Primary contact for this interface (may be a mailing list) Description: Long description of the interface and how to use it. Users: All users of this interface who wish to be notified when it changes. This is very important for interfaces in the "testing" stage, so that kernel developers can work with userspace developers to ensure that things do not break in ways that are unacceptable. It is also important to get feedback for these interfaces to make sure they are working in a proper way and do not need to be changed further. How things move between levels: Interfaces in stable may move to obsolete, as long as the proper notification is given. Interfaces may be removed from obsolete and the kernel as long as the documented amount of time has gone by. Interfaces in the testing state can move to the stable state when the developers feel they are finished. They cannot be removed from the kernel tree without going through the obsolete state first. It's up to the developer to place their interfaces in the category they wish for it to start out in. Notable bits of non-ABI, which should not under any circumstances be considered stable: - Kconfig. Userspace should not rely on the presence or absence of any particular Kconfig symbol, in /proc/config.gz, in the copy of .config commonly installed to /boot, or in any invocation of the kernel build process. - Kernel-internal symbols. Do not rely on the presence, absence, location, or type of any kernel symbol, either in System.map files or the kernel binary itself. See Documentation/stable_api_nonsense.txt.