iwconfig工具源码

Sane network interface management with Hotplug ---------------------------------------------- INTRODUCTION ------------ In the old days all wireless cards were managed by the excellent Pcmcia subsystem and its rich configuration scripts, and life was good. Then came the wireless PCI cards, then the wireless USB dongles. Some unification was needed, and rather than adapt the Pcmcia subsystem for PCI and USB, it was decided to create the much simpler Hotplug system. The USB subsystem already uses Hotplug. The Pcmcia subsystem is migrating to it : CardBus cards (32 bits) already use Hotplug, whereas Pcmcia cards (16 bits) still use the old Pcmcia scripts. The Hotplug system is still in its infancy, but already shows some good promise. Most users are disappointed at first by its apparent lack of features compared to the Pcmcia scripts. In this document, we will show how to fully exploit the Hotplug system and try to implement the equivalent of all the functionality of the Pcmcia scripts. ASSUMPTIONS ----------- The target audience of this document is mostly power users and distribution maintainers, but it should give enough clues to help newbies. You should have read and understood DISTRIBUTIONS.txt. The procedures described here are more advanced than the simple configuration described in DISTRIBUTIONS.txt. The main focus is of course on removable wireless interfaces, but we will to talk about network interface management in general, so this should apply also to built-in Ethernet cards. PROBLEM STATEMENT ----------------- Let's assume a Linux system and two or more network devices, Device A and Device B. Those devices may be built-in or removable, they may be present or absent from the system at any time, and they may activated in any particular order. The user wants to assign Configuration A to Device A and Configuration B to Device B, without the possibility that Device A gets assigned Configuration B. Different users may have different definitions of what is Device A. For some, it's a specific instance of a specific hardware, for others any hardware that meets some criteria (a wireless card, an Ethernet card). The user may also want to have multiple configurations for a given device such that the chosen configuration depends on various factors, just as with the old Pcmcia schemes. Device A may need Configuration A1 or Configuration A2 depending on those factors. By default, all network interfaces are created using default interface names (starting at "eth0" and going up). I call that the "all my cards are eth0" problem : im most distributions, "eth0" points to a single fixed configuration in the configuration database. Clearly, this won't satisfy our requirements. EXAMPLE SYSTEM -------------- The distribution I use is Debian 3.0, and some parts of what I say here will be specific to it. However, it should be easy to translate this material to other distributions and I welcome additions to this document. The example system is as follows : o Linux 2.6.X SMP kernel with hotplug support o Fully modular system (all network drivers as modules) o PCI Ethernet card : AMD PCnet LANCE (pcnet32 - eth4) o PCI Ethernet card : HP 100VG J2585B (hp100 - eth2) o ISA Wireless card : Old AT&T Wavelan (wavelan - eth3) o ISA-Pcmcia bridge : VADEM VG-469 (i82365 - slot 0) o PCI-CardBus bridge : Ricoh RL5c475 (yenta_socket - slot 2) o Pcmcia 802.11 card : Aironet 350 (airo_cs - eth0) o Pcmcia 802.11 card : Lucent Orinoco (orinoco_cs - eth0) o CardBus 802.11 card : SMC 2835W (prism54 - prism0) This system just happens to be my Linux development box. It has enough interfaces to make it interesting. All the examples I present in this document are extracted from this system. BASIC CONCEPTS -------------- Most of the concept and tricks presented here are not really new. The main contribution is to integrate them. 1) Removable network interfaces are managed by Hotplug (Pcmcia, CardBus, USB...). We can't assume that those interfaces are always present in this system and available at boot time (Pcmcia cards were not made to be soldered in the Pcmcia slot). Therefore Hotplug is the way to go. 2) Built-in PCI and ISA cards are managed by the init scripts, as they have always been. The ISA subsystem will never have Hotplug support, and hotplug is not necessary for PCI cards. 3) Built-in devices that are disable most of the time should be enabled manually by the user. Therefore both Hotplug and the init scripts should ignore those devices by default. 4) (1), (2) and (3) must be compatible on the same system and play nice with each other. 5) A well defined and consistent network interface name is assigned to each network hardware interface using 'ifrename'. Device A is always named 'ethA' (or whatever name you like such as 'mynetworkcard'). 6) No interface is called 'eth0' (or 'wlan0'). Any unknown device would be 'eth0', so known devices should be called something else. 7) Multiple configurations for a single interface (schemes) are managed by the ifup/ifdown subsystem. CONFIGURATION FROM INIT SCRIPTS ------------------------------- It may seem paradoxical, but before setting up Hotplug, we need to make sure that the initialisation of network cards via init scripts is done properly and doesn't get in the way of the Hotplug subsystem. The configuration of network cards via init scripts is the traditional way networking is initialised in Linux. The advantage of this method is that it's very well documented and understood, and has not changed much over the years. Unfortunately, it doesn't adequately support removable cards. The init scripts perform the following 3 functions in order : 1) Load necessary driver modules 2) Rename interface to name chosen by the user 3) Configure those network interfaces 1) Applicability ---------------- Configuration from init scripts is applicable to any built-in network interface (ISA, PCI...), i.e., interfaces available at boot time and that will never be removed from the system. The Hotplug subsystem also has the ability to configure some of the built-in network interfaces, such as PCI cards. However, there is a class of devices that will never have Hotplug support, such as ISA and EISA cards. 2) Loading driver modules (if/as needed) ---------------------------------------- Most distributions build the kernel drivers as modules. This modular setup allows to minimise the amount of memory used by the system and the flexible loading/unloading of drivers. You can also compile your kernel with static drivers (non-modular). In that case, the driver will always be available in the kernel, you don't need to configure the module subsystem, so you can skip directly to the next section. There are 3 alternatives to manage device drivers as modules. 1) Some distributions have an explicit list of modules that are loaded at boot time. If you want to use that feature you need to check the documentation of your distribution. 2) Some system, such as Hotplug, Discover or Kudzu, can scan the various buses of the PC and load the appropriate drivers. This is mostly configuration-free, but may not support all devices and may load unnecessary modules. 3) The module subsystem also allows to load modules 'on-demand'. When an application try to access or configure a network interface, the corresponding module is loaded. I personally prefer to use the 'on-demand' feature of the module subsystem, as this allow you to not have to specify a static list of modules that need to be loaded, and only modules really needed are loaded which saves kernel memory. You can also choose which module to load when there are multiple modules available that support your hardware (which happens quite often). With kernel 2.6.X the module subsystem is configured in the file /etc/modprobe.conf or files in the directory /etc/modprobe.d/. To configure 'on-demand' module loading, on my test system I need to add to the f