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Merge master.kernel.org:/pub/scm/linux/kernel/git/davem/net-2.6
* master.kernel.org:/pub/scm/linux/kernel/git/davem/net-2.6: [NET_SCHED]: HFSC: fix thinko in hfsc_adjust_levels() [IPV6]: skb leakage in inet6_csk_xmit [BRIDGE]: Do sysfs registration inside rtnl. [NET]: Do sysfs registration as part of register_netdevice. [TG3]: Fix possible NULL deref in tg3_run_loopback(). [NET] linkwatch: Handle jiffies wrap-around [IRDA]: Switching to a workqueue for the SIR work [IRDA]: smsc-ircc: Minimal hotplug support. [IRDA]: Removing unused EXPORT_SYMBOLs [IRDA]: New maintainer. [NET]: Make netdev_chain a raw notifier. [IPV4]: ip_options_fragment() has no effect on fragmentation [NET]: Add missing operstates documentation.
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1. Introduction | ||
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Linux distinguishes between administrative and operational state of an | ||
interface. Admininstrative state is the result of "ip link set dev | ||
<dev> up or down" and reflects whether the administrator wants to use | ||
the device for traffic. | ||
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However, an interface is not usable just because the admin enabled it | ||
- ethernet requires to be plugged into the switch and, depending on | ||
a site's networking policy and configuration, an 802.1X authentication | ||
to be performed before user data can be transferred. Operational state | ||
shows the ability of an interface to transmit this user data. | ||
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Thanks to 802.1X, userspace must be granted the possibility to | ||
influence operational state. To accommodate this, operational state is | ||
split into two parts: Two flags that can be set by the driver only, and | ||
a RFC2863 compatible state that is derived from these flags, a policy, | ||
and changeable from userspace under certain rules. | ||
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2. Querying from userspace | ||
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Both admin and operational state can be queried via the netlink | ||
operation RTM_GETLINK. It is also possible to subscribe to RTMGRP_LINK | ||
to be notified of updates. This is important for setting from userspace. | ||
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These values contain interface state: | ||
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ifinfomsg::if_flags & IFF_UP: | ||
Interface is admin up | ||
ifinfomsg::if_flags & IFF_RUNNING: | ||
Interface is in RFC2863 operational state UP or UNKNOWN. This is for | ||
backward compatibility, routing daemons, dhcp clients can use this | ||
flag to determine whether they should use the interface. | ||
ifinfomsg::if_flags & IFF_LOWER_UP: | ||
Driver has signaled netif_carrier_on() | ||
ifinfomsg::if_flags & IFF_DORMANT: | ||
Driver has signaled netif_dormant_on() | ||
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These interface flags can also be queried without netlink using the | ||
SIOCGIFFLAGS ioctl. | ||
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TLV IFLA_OPERSTATE | ||
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contains RFC2863 state of the interface in numeric representation: | ||
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IF_OPER_UNKNOWN (0): | ||
Interface is in unknown state, neither driver nor userspace has set | ||
operational state. Interface must be considered for user data as | ||
setting operational state has not been implemented in every driver. | ||
IF_OPER_NOTPRESENT (1): | ||
Unused in current kernel (notpresent interfaces normally disappear), | ||
just a numerical placeholder. | ||
IF_OPER_DOWN (2): | ||
Interface is unable to transfer data on L1, f.e. ethernet is not | ||
plugged or interface is ADMIN down. | ||
IF_OPER_LOWERLAYERDOWN (3): | ||
Interfaces stacked on an interface that is IF_OPER_DOWN show this | ||
state (f.e. VLAN). | ||
IF_OPER_TESTING (4): | ||
Unused in current kernel. | ||
IF_OPER_DORMANT (5): | ||
Interface is L1 up, but waiting for an external event, f.e. for a | ||
protocol to establish. (802.1X) | ||
IF_OPER_UP (6): | ||
Interface is operational up and can be used. | ||
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This TLV can also be queried via sysfs. | ||
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TLV IFLA_LINKMODE | ||
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contains link policy. This is needed for userspace interaction | ||
described below. | ||
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This TLV can also be queried via sysfs. | ||
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3. Kernel driver API | ||
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Kernel drivers have access to two flags that map to IFF_LOWER_UP and | ||
IFF_DORMANT. These flags can be set from everywhere, even from | ||
interrupts. It is guaranteed that only the driver has write access, | ||
however, if different layers of the driver manipulate the same flag, | ||
the driver has to provide the synchronisation needed. | ||
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__LINK_STATE_NOCARRIER, maps to !IFF_LOWER_UP: | ||
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The driver uses netif_carrier_on() to clear and netif_carrier_off() to | ||
set this flag. On netif_carrier_off(), the scheduler stops sending | ||
packets. The name 'carrier' and the inversion are historical, think of | ||
it as lower layer. | ||
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netif_carrier_ok() can be used to query that bit. | ||
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__LINK_STATE_DORMANT, maps to IFF_DORMANT: | ||
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Set by the driver to express that the device cannot yet be used | ||
because some driver controlled protocol establishment has to | ||
complete. Corresponding functions are netif_dormant_on() to set the | ||
flag, netif_dormant_off() to clear it and netif_dormant() to query. | ||
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On device allocation, networking core sets the flags equivalent to | ||
netif_carrier_ok() and !netif_dormant(). | ||
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Whenever the driver CHANGES one of these flags, a workqueue event is | ||
scheduled to translate the flag combination to IFLA_OPERSTATE as | ||
follows: | ||
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!netif_carrier_ok(): | ||
IF_OPER_LOWERLAYERDOWN if the interface is stacked, IF_OPER_DOWN | ||
otherwise. Kernel can recognise stacked interfaces because their | ||
ifindex != iflink. | ||
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netif_carrier_ok() && netif_dormant(): | ||
IF_OPER_DORMANT | ||
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netif_carrier_ok() && !netif_dormant(): | ||
IF_OPER_UP if userspace interaction is disabled. Otherwise | ||
IF_OPER_DORMANT with the possibility for userspace to initiate the | ||
IF_OPER_UP transition afterwards. | ||
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4. Setting from userspace | ||
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Applications have to use the netlink interface to influence the | ||
RFC2863 operational state of an interface. Setting IFLA_LINKMODE to 1 | ||
via RTM_SETLINK instructs the kernel that an interface should go to | ||
IF_OPER_DORMANT instead of IF_OPER_UP when the combination | ||
netif_carrier_ok() && !netif_dormant() is set by the | ||
driver. Afterwards, the userspace application can set IFLA_OPERSTATE | ||
to IF_OPER_DORMANT or IF_OPER_UP as long as the driver does not set | ||
netif_carrier_off() or netif_dormant_on(). Changes made by userspace | ||
are multicasted on the netlink group RTMGRP_LINK. | ||
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So basically a 802.1X supplicant interacts with the kernel like this: | ||
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-subscribe to RTMGRP_LINK | ||
-set IFLA_LINKMODE to 1 via RTM_SETLINK | ||
-query RTM_GETLINK once to get initial state | ||
-if initial flags are not (IFF_LOWER_UP && !IFF_DORMANT), wait until | ||
netlink multicast signals this state | ||
-do 802.1X, eventually abort if flags go down again | ||
-send RTM_SETLINK to set operstate to IF_OPER_UP if authentication | ||
succeeds, IF_OPER_DORMANT otherwise | ||
-see how operstate and IFF_RUNNING is echoed via netlink multicast | ||
-set interface back to IF_OPER_DORMANT if 802.1X reauthentication | ||
fails | ||
-restart if kernel changes IFF_LOWER_UP or IFF_DORMANT flag | ||
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if supplicant goes down, bring back IFLA_LINKMODE to 0 and | ||
IFLA_OPERSTATE to a sane value. | ||
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A routing daemon or dhcp client just needs to care for IFF_RUNNING or | ||
waiting for operstate to go IF_OPER_UP/IF_OPER_UNKNOWN before | ||
considering the interface / querying a DHCP address. | ||
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For technical questions and/or comments please e-mail to Stefan Rompf | ||
(stefan at loplof.de). |
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