Re: RFC - document network device carrier management
From: Ben Hutchings <hidden>
Date: 2012-08-20 21:34:28
On Wed, 2012-08-15 at 08:58 -0700, Stephen Hemminger wrote:
quoted hunk ↗ jump to hunk
Since carrier handling is often done incorrectly by new device drivers be explicit about carrier handling API. Signed-off-by: Stephen Hemminger <redacted> --- This is a meant as starting point for discussion, it's probably wrong as is. Since this isn't code, it could be applied for 3.6 and doesn't need for net-next.--- a/Documentation/networking/netdevices.txt 2012-06-22 08:27:46.729168196 -0700 +++ b/Documentation/networking/netdevices.txt 2012-08-15 08:56:31.120429994 -0700@@ -45,6 +45,36 @@ drop, truncate, or pass up oversize pack packets is preferred. +CARRIER +======= +Most network devices have an operational state that the device +monitors. The Linux kernel uses the name "carrier" for this flag which +is a historical reference to old modems. Carrier is reported to +userspace via the IFF_RUNNING flag from SIOCGIFFLAGS ioctl. +Carrier is controlled in the device driver +by the functions netif_carrier_on and netif_carrier_off. These +functions trigger the necessary netlink and userspace API changes; +device drivers must not change netdevice->flags directly. + +The carrier defaults to ON when the device is created and registered. +Simple devices (such as dummy) do not need to do anything. +Ethernet style devices should: + * alloc_etherdev in probe routine + * call netif_carrier_off + * register network device + * start auto negotiation with phy in open routine
Auto-negotiation is only one of several stages of link setup, and of course is not used in all Ethernet physical layers. I think the important point is that once the ndo_open method returns the hardware and driver should be ready to set up the link and report this state whenever a suitable partner is physically connected.
+ * call netif_carrier_on when link is up + +More complex RFC2863 style operational state is also possible +but not required (see operstates.txt).
Drivers are not allowed to set operstate directly.
+The monitoring of link state is the responsibility of the network +device driver. It can be done by polling, interrupt, or any other +mechanism. netif_carrier_on/netif_carrier_off are atomic and can +safely be called by an interrupt routine. Carrier events are +managed by the linkwatch work queue and limited to one per second +to avoid overwhelming management applications. + struct net_device synchronization rules ======================================= ndo_open:
-- Ben Hutchings, Staff Engineer, Solarflare Not speaking for my employer; that's the marketing department's job. They asked us to note that Solarflare product names are trademarked.