网络设备的IP地址结构
====================

(1) 在TCPIP协议环境下,
网络设备结构(net_device)具有一个ip_ptr指针指向IP协议的设备参数块(in_device),
它包含设备IP地址结构(in_ifaddr)的链表指针(ifa_list).
IP地址结构链可以为一个网络设备配置多个IP地址,
使得局域网中的单台主机能模拟多台主机的作用. 

(2) 设备IP地址的配置由应用程序通过ioctl()系统调用使用ifreq参数结构来完成.
同一设备的不同IP地址用不同的设备别名来标识,
例如"eth0:1"和"eth0:2"分别代表设备eht0的两个地址. 当增加一个别名设备时,
如果它的地址与已有地址属于同一子网, 则它的地址被标记为"从属"(IFA_F_SECONDARY).
当设备{zh1}一个别名被删除时, 设备的IP参数块将被释放.设备地址参数发生改变时,
将通过地址消息链(inetaddr_chain)向有关子系统发送通知消息,
例如路由子系统用来刷新转发表和路由缓冲表.

struct net_device
{
 ...
 void   *ip_ptr; /* IPv4 specific data */  
 ...
}
struct in_device
{
 struct net_device  *dev;
 atomic_t  refcnt;
 rwlock_t  lock;
 int   dead;
 struct in_ifaddr *ifa_list; /* IP ifaddr chain  */
 struct ip_mc_list *mc_list; /* IP multicast filter chain    */
 unsigned long  mr_v1_seen;
 struct neigh_parms *arp_parms;
 struct ipv4_devconf cnf;
};
struct in_ifaddr
{
 struct in_ifaddr *ifa_next;
 struct in_device *ifa_dev;
 u32   ifa_local; 设备地址
 u32   ifa_address; 点对点设备的对端地址
 u32   ifa_mask; 网络地址掩码
 u32   ifa_broadcast; 设备的广播地址
 u32   ifa_anycast; 
 unsigned char  ifa_scope; 设备地址的寻址范围
 unsigned char  ifa_flags; 地址标志
 unsigned char  ifa_prefixlen; 设备网络地址长度
 char   ifa_label[IFNAMSIZ]; 设备IP地址标签
};

/*
 * Interface request structure used for socket
 * ioctl's.  All interface ioctl's must have parameter
 * definitions which begin with ifr_name.  The
 * remainder may be interface specific.
 */

struct ifreq 
{
#define IFHWADDRLEN 6
#define IFNAMSIZ 16
 union
 {
  char ifrn_name[IFNAMSIZ];  /* if name, e.g. "en0" */
 } ifr_ifrn;
 
 union {
  struct sockaddr ifru_addr;
  struct sockaddr ifru_dstaddr;
  struct sockaddr ifru_broadaddr;
  struct sockaddr ifru_netmask;
  struct  sockaddr ifru_hwaddr;
  short ifru_flags;
  int ifru_ivalue;
  int ifru_mtu;
  struct  ifmap ifru_map;
  char ifru_slave[IFNAMSIZ]; /* Just fits the size */
  char ifru_newname[IFNAMSIZ];
  char * ifru_data;
 } ifr_ifru;
};

; net/ipv4/devinet.c:

int devinet_ioctl(unsigned int cmd, void *arg)
{
 struct ifreq ifr; 
 struct sockaddr_in *sin = (struct sockaddr_in *)&ifr.ifr_addr;
 struct in_device *in_dev; 
 struct in_ifaddr **ifap = NULL;
 struct in_ifaddr *ifa = NULL;
 struct net_device *dev;
 char *colon;
 int ret = 0;

 /*
  * Fetch the caller's info block into kernel space
  */

 if (copy_from_user(&ifr, arg, sizeof(struct ifreq)))
  return -EFAULT;
 ifr.ifr_name[IFNAMSIZ-1] = 0;

 colon = strchr(ifr.ifr_name, ':'); 从设备地址标签中取设备名称
 if (colon)
  *colon = 0;

#ifdef CONFIG_KMOD
 dev_load(ifr.ifr_name); 加载相应名称的设备驱动模块
#endif

 switch(cmd) {
 case SIOCGIFADDR: /* Get interface address */
 case SIOCGIFBRDADDR: /* Get the broadcast address */
 case SIOCGIFDSTADDR: /* Get the destination address */
 case SIOCGIFNETMASK: /* Get the netmask for the interface */
  /* Note that this ioctls will not sleep,
     so that we do not impose a lock.
     One day we will be forced to put shlock here (I mean SMP)
   */
  memset(sin, 0, sizeof(*sin));
  sin->sin_family = AF_INET;
  break;

 case SIOCSIFFLAGS:
  if (!capable(CAP_NET_ADMIN))
   return -EACCES;
  break;
 case SIOCSIFADDR: /* Set interface address (and family) */
 case SIOCSIFBRDADDR: /* Set the broadcast address */
 case SIOCSIFDSTADDR: /* Set the destination address */
 case SIOCSIFNETMASK:  /* Set the netmask for the interface */
  if (!capable(CAP_NET_ADMIN)) 
   return -EACCES;
  if (sin->sin_family != AF_INET)
   return -EINVAL;
  break;
 default:
  return -EINVAL;
 }

 dev_probe_lock();
 rtnl_lock();

 if ((dev = __dev_get_by_name(ifr.ifr_name)) == NULL) { 取设备结构
  ret = -ENODEV;
  goto done;
 }

 if (colon)
  *colon = ':'; 恢复用户地址标签

 if ((in_dev=__in_dev_get(dev)) != NULL) { 取IP设备块
  for (ifap=&in_dev->ifa_list; (ifa=*ifap) != NULL; ifap=&ifa->ifa_next)
   if (strcmp(ifr.ifr_name, ifa->ifa_label) == 0)
    break; 取用户地址标签对应的设备地址结构
 }

 if (ifa == NULL && cmd != SIOCSIFADDR && cmd != SIOCSIFFLAGS) {
除了设置地址和设置标志
  ret = -EADDRNOTAVAIL; 
  goto done;
 }

 switch(cmd) {
  case SIOCGIFADDR: /* Get interface address */
   sin->sin_addr.s_addr = ifa->ifa_local; 取设备IP地址
   goto rarok;

  case SIOCGIFBRDADDR: /* Get the broadcast address */
   sin->sin_addr.s_addr = ifa->ifa_broadcast; 取设备IP广播地址
   goto rarok;

  case SIOCGIFDSTADDR: /* Get the destination address */
   sin->sin_addr.s_addr = ifa->ifa_address; 取点对点设备的对端IP地址
   goto rarok;

  case SIOCGIFNETMASK: /* Get the netmask for the interface */
   sin->sin_addr.s_addr = ifa->ifa_mask; 取设备的IP地址掩码
   goto rarok;

  case SIOCSIFFLAGS: 设置设备标志
   if (colon) {
    if (ifa == NULL) {
     ret = -EADDRNOTAVAIL;
     break;
    }
    if (!(ifr.ifr_flags&IFF_UP)) 如果标志为关闭设备
     inet_del_ifa(in_dev, ifap, 1); 破环性删除该地址结构
    break;
   }
   ret = dev_change_flags(dev, ifr.ifr_flags); 
   break;
 
  case SIOCSIFADDR: /* Set interface address (and family) */
   if (inet_abc_len(sin->sin_addr.s_addr) < 0) { 取网络地址位长
    ret = -EINVAL;
    break;
   }

   if (!ifa) { 如果设备尚无地址结构
    if ((ifa = inet_alloc_ifa()) == NULL) { 分配地址结构
     ret = -ENOBUFS;
     break;
    }
    if (colon) 如果地址标签为设备别名标签
     memcpy(ifa->ifa_label, ifr.ifr_name, IFNAMSIZ);
    else
     memcpy(ifa->ifa_label, dev->name, IFNAMSIZ);
   } else {  如果修改设备地址
    ret = 0;
    if (ifa->ifa_local == sin->sin_addr.s_addr)
     break; 
    inet_del_ifa(in_dev, ifap, 0); 从链接中删除该地址结构
    ifa->ifa_broadcast = 0;
    ifa->ifa_anycast = 0;
   }

   ifa->ifa_address =
   ifa->ifa_local = sin->sin_addr.s_addr; 将设备地址和对端地址设置为新地址

   if (!(dev->flags&IFF_POINTOPOINT)) { 如果非点对点设备
    ifa->ifa_prefixlen = inet_abc_len(ifa->ifa_address); 取地址的网络地址长度
    ifa->ifa_mask = inet_make_mask(ifa->ifa_prefixlen); 求网络掩码
    if ((dev->flags&IFF_BROADCAST) && ifa->ifa_prefixlen < 31) 
     ifa->ifa_broadcast = ifa->ifa_address|~ifa->ifa_mask; 设置标准广播地址
   } else {  如果是点对点设备
    ifa->ifa_prefixlen = 32; 网络地址长度为32
    ifa->ifa_mask = inet_make_mask(32);
   }
   ret = inet_set_ifa(dev, ifa); 添加设备地址
   break;

  case SIOCSIFBRDADDR: /* Set the broadcast address */
   if (ifa->ifa_broadcast != sin->sin_addr.s_addr) {
    inet_del_ifa(in_dev, ifap, 0);
    ifa->ifa_broadcast = sin->sin_addr.s_addr;
    inet_insert_ifa(ifa);
   }
   break;
 
  case SIOCSIFDSTADDR: /* Set the destination address */
   if (ifa->ifa_address != sin->sin_addr.s_addr) {
    if (inet_abc_len(sin->sin_addr.s_addr) < 0) {
     ret = -EINVAL;
     break;
    }
    inet_del_ifa(in_dev, ifap, 0);
    ifa->ifa_address = sin->sin_addr.s_addr;
    inet_insert_ifa(ifa);
   }
   break;

  case SIOCSIFNETMASK:  /* Set the netmask for the interface */

   /*
    * The mask we set must be legal.
    */
   if (bad_mask(sin->sin_addr.s_addr, 0)) {
    ret = -EINVAL;
    break;
   }

   if (ifa->ifa_mask != sin->sin_addr.s_addr) {
    inet_del_ifa(in_dev, ifap, 0);
    ifa->ifa_mask = sin->sin_addr.s_addr;
    ifa->ifa_prefixlen = inet_mask_len(ifa->ifa_mask);
    inet_insert_ifa(ifa);
   }
   break;
 }
done:
 rtnl_unlock();
 dev_probe_unlock();
 return ret;

rarok:
 rtnl_unlock();
 dev_probe_unlock();
 if (copy_to_user(arg, &ifr, sizeof(struct ifreq)))
  return -EFAULT;
 return 0;
}
static int
inet_set_ifa(struct net_device *dev, struct in_ifaddr *ifa)
{
 struct in_device *in_dev = __in_dev_get(dev); 

 ASSERT_RTNL();

 if (in_dev == NULL) { 如果IP设备块不存在
  in_dev = inetdev_init(dev); 分配IP设备块
  if (in_dev == NULL) {
   inet_free_ifa(ifa);
   return -ENOBUFS;
  }
 }
 if (ifa->ifa_dev != in_dev) { 
  BUG_TRAP(ifa->ifa_dev==NULL);
  in_dev_hold(in_dev);
  ifa->ifa_dev=in_dev; 将地址结构绑定到IP设备块上
 }
 if (LOOPBACK(ifa->ifa_local)) 如果设备地址是回送地址
  ifa->ifa_scope = RT_SCOPE_HOST; 地址的寻址范围为主机内部
 return inet_insert_ifa(ifa); 
}
static int
inet_insert_ifa(struct in_ifaddr *ifa)
{
 struct in_device *in_dev = ifa->ifa_dev;
 struct in_ifaddr *ifa1, **ifap, **last_primary;

 ASSERT_RTNL();

 if (ifa->ifa_local == 0) {
  inet_free_ifa(ifa);
  return 0;
 }

 ifa->ifa_flags &= ~IFA_F_SECONDARY; xx地址结构的从属标志
 last_primary = &in_dev->ifa_list; 取IP设备块地址链表指针地址

 for (ifap=&in_dev->ifa_list; (ifa1=*ifap)!=NULL; ifap=&ifa1->ifa_next) {
扫描IP设备块上的地址链
  if (!(ifa1->ifa_flags&IFA_F_SECONDARY) && ifa->ifa_scope <= ifa1->ifa_scope)
   last_primary = &ifa1->ifa_next; 
  if (ifa1->ifa_mask == ifa->ifa_mask && inet_ifa_match(ifa1->ifa_address, ifa)) {
   ; 如果与链中某个地址具有相同的网络地址
   if (ifa1->ifa_local == ifa->ifa_local) { 如果两者地址相同
    inet_free_ifa(ifa);
    return -EEXIST;
   }
   if (ifa1->ifa_scope != ifa->ifa_scope) { 如果两者寻址范围不同
    inet_free_ifa(ifa);
    return -EINVAL;
   } 
   ifa->ifa_flags |= IFA_F_SECONDARY; 标记为从属地址
  }
 }

 if (!(ifa->ifa_flags&IFA_F_SECONDARY)) {
  net_srandom(ifa->ifa_local); 
  ifap = last_primary;
 }

 ifa->ifa_next = *ifap; 
 write_lock_bh(&in_dev->lock);
 *ifap = ifa; 
 write_unlock_bh(&in_dev->lock);

 /* Send message first, then call notifier.
    Notifier will trigger FIB update, so that
    listeners of netlink will know about new ifaddr */
 rtmsg_ifa(RTM_NEWADDR, ifa);
 notifier_call_chain(&inetaddr_chain, NETDEV_UP, ifa); 发布设备启动消息

 return 0;
}
static void
inet_del_ifa(struct in_device *in_dev, struct in_ifaddr **ifap, int destroy)
{
 struct in_ifaddr *ifa1 = *ifap; 取要删除地址结构的地址

 ASSERT_RTNL();

 /* 1. Deleting primary ifaddr forces deletion all secondaries */

 if (!(ifa1->ifa_flags&IFA_F_SECONDARY)) { 如果删除的是设备主地址结构
  struct in_ifaddr *ifa;
  struct in_ifaddr **ifap1 = &ifa1->ifa_next; 取下一地址指针的地址

  while ((ifa=*ifap1) != NULL) {
   if (!(ifa->ifa_flags&IFA_F_SECONDARY) || 如果为主地址
       ifa1->ifa_mask != ifa->ifa_mask ||
       !inet_ifa_match(ifa1->ifa_address, ifa)) {
    ifap1 = &ifa->ifa_next;
    continue;
   }
   write_lock_bh(&in_dev->lock);
   *ifap1 = ifa->ifa_next;
   write_unlock_bh(&in_dev->lock);

   rtmsg_ifa(RTM_DELADDR, ifa);
   notifier_call_chain(&inetaddr_chain, NETDEV_DOWN, ifa); 发布设备停机消息
   inet_free_ifa(ifa);
  }
 }

 /* 2. Unlink it */

 write_lock_bh(&in_dev->lock);
 *ifap = ifa1->ifa_next; 从设备地址链中删除该地址标签
 write_unlock_bh(&in_dev->lock);

 /* 3. Announce address deletion */

 /* Send message first, then call notifier.
    At first sight, FIB update triggered by notifier
    will refer to already deleted ifaddr, that could confuse
    netlink listeners. It is not true: look, gated sees
    that route deleted and if it still thinks that ifaddr
    is valid, it will try to restore deleted routes... Grr.
    So that, this order is correct.
  */
 rtmsg_ifa(RTM_DELADDR, ifa1);
 notifier_call_chain(&inetaddr_chain, NETDEV_DOWN, ifa1);
 if (destroy) {
  inet_free_ifa(ifa1);

  if (in_dev->ifa_list == NULL)
   inetdev_destroy(in_dev);
 }
}
static void inetdev_destroy(struct in_device *in_dev)
{
 struct in_ifaddr *ifa;

 ASSERT_RTNL();

 in_dev->dead = 1;

 ip_mc_destroy_dev(in_dev);

 while ((ifa = in_dev->ifa_list) != NULL) {
  inet_del_ifa(in_dev, &in_dev->ifa_list, 0);
  inet_free_ifa(ifa);
 }

#ifdef CONFIG_SYSCTL
 devinet_sysctl_unregister(&in_dev->cnf);
#endif
 write_lock_bh(&inetdev_lock);
 in_dev->dev->ip_ptr = NULL;
 /* in_dev_put following below will kill the in_device */
 write_unlock_bh(&inetdev_lock);


 neigh_parms_release(&arp_tbl, in_dev->arp_parms);
 in_dev_put(in_dev);
}
struct in_device *inetdev_init(struct net_device *dev)
{
 struct in_device *in_dev;

 ASSERT_RTNL();

 in_dev = kmalloc(sizeof(*in_dev), GFP_KERNEL);
 if (!in_dev)
  return NULL;
 memset(in_dev, 0, sizeof(*in_dev));
 in_dev->lock = RW_LOCK_UNLOCKED;
 memcpy(&in_dev->cnf, &ipv4_devconf_dflt, sizeof(in_dev->cnf));
 in_dev->cnf.sysctl = NULL;
 in_dev->dev = dev;
 if ((in_dev->arp_parms = neigh_parms_alloc(dev, &arp_tbl)) == NULL) { 
  kfree(in_dev);
  return NULL;
 }
 inet_dev_count++;
 /* Reference in_dev->dev */
 dev_hold(dev);
#ifdef CONFIG_SYSCTL
 neigh_sysctl_register(dev, in_dev->arp_parms, NET_IPV4, NET_IPV4_NEIGH, "ipv4");
#endif
 write_lock_bh(&inetdev_lock);
 dev->ip_ptr = in_dev;
 /* Account for reference dev->ip_ptr */
 in_dev_hold(in_dev);
 write_unlock_bh(&inetdev_lock);
#ifdef CONFIG_SYSCTL
 devinet_sysctl_register(in_dev, &in_dev->cnf);
#endif
 if (dev->flags&IFF_UP)
  ip_mc_up(in_dev); 
 return in_dev;
}
static __inline__ void inet_free_ifa(struct in_ifaddr *ifa)
{
 if (ifa->ifa_dev)
  __in_dev_put(ifa->ifa_dev);
 kfree(ifa);
 inet_ifa_count--;
}
static struct in_ifaddr * inet_alloc_ifa(void)
{
 struct in_ifaddr *ifa;

 ifa = kmalloc(sizeof(*ifa), GFP_KERNEL);
 if (ifa) {
  memset(ifa, 0, sizeof(*ifa));
  inet_ifa_count++;
 }

 return ifa;
}
extern __inline__ struct in_device *
in_dev_get(const struct net_device *dev)
{
 struct in_device *in_dev;

 read_lock(&inetdev_lock);
 in_dev = dev->ip_ptr;
 if (in_dev)
  atomic_inc(&in_dev->refcnt);
 read_unlock(&inetdev_lock);
 return in_dev;
}

extern __inline__ struct in_device *
__in_dev_get(const struct net_device *dev)
{
 return (struct in_device*)dev->ip_ptr;
}

extern __inline__ void
in_dev_put(struct in_device *idev)
{
 if (atomic_dec_and_test(&idev->refcnt))
  in_dev_finish_destroy(idev);
}
void in_dev_finish_destroy(struct in_device *idev)
{
 struct net_device *dev = idev->dev;

 BUG_TRAP(idev->ifa_list==NULL);
 BUG_TRAP(idev->mc_list==NULL);
#ifdef NET_REFCNT_DEBUG
 printk(KERN_DEBUG "in_dev_finish_destroy: %p=%s\n", idev, dev ? dev->name : "NIL");
#endif
 dev_put(dev);
 if (!idev->dead) {
  printk("Freeing alive in_device %p\n", idev);
  return;
 }
 inet_dev_count--;
 kfree(idev);
}