snull.c

本源码是将述嵌入式LINUX驱动程序例程

/*
 * snull.c --  the Simple Network Utility
 *
 * Copyright (C) 2001 Alessandro Rubini and Jonathan Corbet
 * Copyright (C) 2001 O'Reilly & Associates
 *
 * The source code in this file can be freely used, adapted,
 * and redistributed in source or binary form, so long as an
 * acknowledgment appears in derived source files.  The citation
 * should list that the code comes from the book "Linux Device
 * Drivers" by Alessandro Rubini and Jonathan Corbet, published
 * by O'Reilly & Associates.   No warranty is attached;
 * we cannot take responsibility for errors or fitness for use.
 *
 * $Id: snull.c,v 1.17 2001/07/18 22:28:18 rubini Exp $
 */

#ifndef __KERNEL__
#  define __KERNEL__
#endif
#ifndef MODULE
#  define MODULE
#endif

#include <linux/config.h>
#include <linux/module.h>

#include <linux/sched.h>
#include <linux/kernel.h> /* printk() */
#include <linux/malloc.h> /* kmalloc() */
#include <linux/errno.h>  /* error codes */
#include <linux/types.h>  /* size_t */
#include <linux/interrupt.h> /* mark_bh */

#include <linux/in.h>
#include <linux/netdevice.h>   /* struct device, and other headers */
#include <linux/etherdevice.h> /* eth_type_trans */
#include <linux/ip.h>          /* struct iphdr */
#include <linux/tcp.h>         /* struct tcphdr */
#include <linux/skbuff.h>

#include "snull.h"

#ifdef LINUX_20
#  include <linux/if_ether.h>
#  define net_device_stats enet_statistics
#else
#  include <linux/in6.h>
#endif
#include <asm/checksum.h>

MODULE_AUTHOR("Alessandro Rubini");

/* This is a load-time options */
static int eth = 0; /* Call yourself "ethX". Default is "sn0"/"sn1" */
MODULE_PARM(eth, "i");

/*
 * Transmitter lockup simulation, normally disabled.
 */
static int lockup = 0;
MODULE_PARM(lockup, "i");

#ifdef HAVE_TX_TIMEOUT
static int timeout = SNULL_TIMEOUT;
MODULE_PARM(timeout, "i");
#endif

int snull_eth;


/*
 * This structure is private to each device. It is used to pass
 * packets in and out, so there is place for a packet
 */

struct snull_priv {
    struct net_device_stats stats;
    int status;
    int rx_packetlen;
    u8 *rx_packetdata;
    int tx_packetlen;
    u8 *tx_packetdata;
    struct sk_buff *skb;
    spinlock_t lock;
};

extern struct net_device snull_devs[];
void snull_tx_timeout (struct net_device *dev);
        

/*
 * Open and close
 */

int snull_open(struct net_device *dev)
{
    MOD_INC_USE_COUNT;
    
    /* request_region(), request_irq(), ....  (like fops->open) */
#if 0 && defined(LINUX_20)
    /*
     * We have no irq line, otherwise this assignment can be used to
     * grab a non-shared interrupt. To share interrupt lines use
     * the dev_id argument of request_irq. See snull_interrupt below.
     */
    irq2dev_map[dev->irq] = dev;
#endif

    /* 
     * Assign the hardware address of the board: use "\0SNULx", where
     * x is 0 or 1. The first byte is '\0' to avoid being a multicast
     * address (the first byte of multicast addrs is odd).
     */
    memcpy(dev->dev_addr, "\0SNUL0", ETH_ALEN);
    dev->dev_addr[ETH_ALEN-1] += (dev - snull_devs); /* the number */

#ifndef LINUX_24                
    dev->start = 1;             
#endif                          
    netif_start_queue(dev);
    return 0;
}

int snull_release(struct net_device *dev)
{
    /* release ports, irq and such -- like fops->close */

    netif_stop_queue(dev); /* can't transmit any more */
#ifndef LINUX_24                
    dev->start = 0;             
#endif                          
    MOD_DEC_USE_COUNT;
    /* if irq2dev_map was used (2.0 kernel), zero the entry here */
    return 0;
}

/*
 * Configuration changes (passed on by ifconfig)
 */
int snull_config(struct net_device *dev, struct ifmap *map)
{
    if (dev->flags & IFF_UP) /* can't act on a running interface */
        return -EBUSY;

    /* Don't allow changing the I/O address */
    if (map->base_addr != dev->base_addr) {
        printk(KERN_WARNING "snull: Can't change I/O address\n");
        return -EOPNOTSUPP;
    }

    /* Allow changing the IRQ */
    if (map->irq != dev->irq) {
        dev->irq = map->irq;
        /* request_irq() is delayed to open-time */
    }

    /* ignore other fields */
    return 0;
}

/*
 * Receive a packet: retrieve, encapsulate and pass over to upper levels
 */
void snull_rx(struct net_device *dev, int len, unsigned char *buf)
{
    struct sk_buff *skb;
    struct snull_priv *priv = (struct snull_priv *) dev->priv;

    /*
     * The packet has been retrieved from the transmission
     * medium. Build an skb around it, so upper layers can handle it
     */
    skb = dev_alloc_skb(len+2);
    if (!skb) {
        printk("snull rx: low on mem - packet dropped\n");
        priv->stats.rx_dropped++;
        return;
    }
    skb_reserve(skb, 2); /* align IP on 16B boundary */  
    memcpy(skb_put(skb, len), buf, len);

    /* Write metadata, and then pass to the receive level */
    skb->dev = dev;
    skb->protocol = eth_type_trans(skb, dev);
    skb->ip_summed = CHECKSUM_UNNECESSARY; /* don't check it */
    priv->stats.rx_packets++;
#ifndef LINUX_20                        
    priv->stats.rx_bytes += len;
#endif                                  
    netif_rx(skb);
    return;
}
    
        
/*
 * The typical interrupt entry point
 */
#ifdef LINUX_24
void snull_interrupt(int irq, void *dev_id, struct pt_regs *regs)
{
    int statusword;
    struct snull_priv *priv;
    /*
     * As usual, check the "device" pointer for shared handlers.
     * Then assign "struct device *dev"
     */
    struct net_device *dev = (struct net_device *)dev_id;
    /* ... and check with hw if it's really ours */

    if (!dev /*paranoid*/ ) return;

    /* Lock the device */
    priv = (struct snull_priv *) dev->priv;
    spin_lock(&priv->lock);

    /* retrieve statusword: real netdevices use I/O instructions */
    statusword = priv->status;
    if (statusword & SNULL_RX_INTR) {
        /* send it to snull_rx for handling */
        snull_rx(dev, priv->rx_packetlen, priv->rx_packetdata);
    }
    if (statusword & SNULL_TX_INTR) {
        /* a transmission is over: free the skb */
        priv->stats.tx_packets++;
        priv->stats.tx_bytes += priv->tx_packetlen;
        dev_kfree_skb(priv->skb);
    }

    /* Unlock the device and we are done */
    spin_unlock(&priv->lock);
    return;
}
#else /* LINUX_22 or earlier */

void snull_interrupt(int irq, void *dev_id, struct pt_regs *regs)
{
    int statusword;
    struct snull_priv *priv;
    /*
     * As usual, check the "device" pointer for shared handlers.
     * Then assign "struct device *dev"
     */
#if 0 && defined(LINUX_20)
    /* This is the way to do things for non-shared handlers */
    struct device *dev = (struct device *)(irq2dev_map[irq]);
#else
    /* Otherwise use this SA_SHIRQ-safe approach */
    struct net_device *dev = (struct net_device *)dev_id;
    /* ... and check with hw if it's really ours */
#endif

    if (!dev /*paranoid*/ ) return;

    /* Lock the device */
    priv = (struct snull_priv *) dev->priv;
    spin_lock(&priv->lock);
    dev->interrupt = 1;

    /* retrieve statusword: real netdevices use inb() or inw() */
    statusword = priv->status;
    if (statusword & SNULL_RX_INTR) {
        /* send it to snull_rx for handling */
        snull_rx(dev, priv->rx_packetlen, priv->rx_packetdata);
    }
    if (statusword & SNULL_TX_INTR) {
        /* a transmission is over: tell we are no more busy */
        priv->stats.tx_packets++;
#ifndef LINUX_20
        priv->stats.tx_bytes += priv->tx_packetlen;
#endif
        dev_kfree_skb(priv->skb);
    }
    spin_unlock(&priv->lock);
    dev->interrupt = 0;
    return;
}

#endif /* LINUX_22 or earlier */


/*
 * Transmit a packet (low level interface)
 */
void snull_hw_tx(char *buf, int len, struct net_device *dev)
{
    /*
     * This function deals with hw details. This interface loops
     * back the packet to the other snull interface (if any).
     * In other words, this function implements the snull behaviour,
     * while all other procedures are rather device-independent
     */
    struct iphdr *ih;
    struct net_device *dest;
    struct snull_priv *priv;
    u32 *saddr, *daddr;

    /* I am paranoid. Ain't I? */
    if (len < sizeof(struct ethhdr) + sizeof(struct iphdr)) {
        printk("snull: Hmm... packet too short (%i octets)\n",
               len);
        return;
    }

    if (0) { /* enable this conditional to look at the data */
        int i;
        PDEBUG("len is %i\n" KERN_DEBUG "data:",len);
        for (i=14 ; i<len; i++)
            printk(" %02x",buf[i]&0xff);
        printk("\n");
    }
    /*