network driver info The HyperNews Linux KHG Discussion Pages network driver infoForum: Device DriversRe: Re: Network Device Drivers (Paul Gortmaker)Re: Re: Network Device Drivers (Neal Tucker)Keywords: network driver functionsDate: Sat, 15 Jun 1996 03:33:21 GMTFrom: Neal Tucker <[e-mail]>Earlier, I posted a pointer to a bit of info on network device drivers, and the site that the web page is on is going away, so I am including what was there here... How a Network Device Gets Added to the Kernel There is a global variable called dev_base which points to a linked list of "device" structures. Each record represents a network device, and contains a pointer to the device driver's initialization function. The initialization function is the first code from the driver to ever get executed, and is responsible for setting up the hooks to the other driver code.At boot time, the function device_setup (drivers/block/genhd.c) calls a function called net_dev_init (net/core/dev.c) which walks through the linked list pointed to by dev_base, calling each device's init function. If the init indicates failure (by returning a nonzero result), net_dev_init removes the device from the linked list and continues on.This brings up the question of how the devices get added to the linked list of devices before any of their code is executed. That is accomplished by a clever piece of C preprocessor work in drivers/net/Space.c. This file has the static declarations for each device's "device" struct, including the pointer to the next device in the list. How can we define these links statically without knowing which devices are going to be included? Here's how it's done (from drivers/net/Space.c): #define NEXT_DEV NULL #if defined(CONFIG_SLIP) static struct device slip_dev = { device name and some other info goes here ... NEXT_DEV, /* base_addr; if ((base_addr == 0xffe0) || (base_addr == 1)) return 1; if (1 /* note start of expression here */ #ifdef CONFIG_DGRS && dgrs_probe(dev) #endif #ifdef CONFIG_VORTEX && tc59x_probe(dev) #endif #ifdef CONFIG_NE2000 && ne_probe(dev) #endif && 1 ) { /* end of expression here */ return 1; } return 0; } The result is that the if statement bails out as false if any of the probe calls returns zero (success), and only one ethernet card is initialized and used, no matter how many drivers you have installed. For the drivers that aren't installed, the #ifdef removes the code completely, and the expression gets a bit smaller. The implications of this scheme are that supporting multiple ethernet cards is now a special case, and requires providing command line parameters to the kernel which cause ethif_probe to be executed multiple times. Messages Inline: Outline: 1. Network Driver Desprately Needed by Paul Atkinsonto: "network driver info"