net_device結構體，定義在include/linux/netdevice.h中，這是一個很複雜的結構體，先把代碼清單列出來，再用到的過程中，逐步分析，最後來這裏做個總結。
下面的代碼是linux-2.6.38中的。
1 /*
2 * The DEVICE structure.
3 * Actually, this whole structure is a big mistake. It mixes I/O
4 * data with strictly "high-level" data, and it has to know about
5 * almost every data structure used in the INET module.
6 *
7 * FIXME: cleanup struct net_device such that network protocol info
8 * moves out.
9 */
10
11 struct net_device {
12
13 /*
14 * This is the first field of the "visible" part of this structure
15 * (i.e. as seen by users in the "Space.c" file). It is the name
16 * of the interface.
17 */
18 char name[IFNAMSIZ];
19
20 struct pm_qos_request_list pm_qos_req;
21
22 /* device name hash chain */
23 struct hlist_node name_hlist;
24 /* snmp alias */
25 char *ifalias;
26
27 /*
28 * I/O specific fields
29 * FIXME: Merge these and struct ifmap into one
30 */
31 unsigned long mem_end; /* shared mem end */
32 unsigned long mem_start; /* shared mem start */
33 unsigned long base_addr; /* device I/O address */
34 unsigned int irq; /* device IRQ number */
35
36 /*
37 * Some hardware also needs these fields, but they are not
38 * part of the usual set specified in Space.c.
39 */
40
41 unsigned char if_port; /* Selectable AUI, TP,..*/
42 unsigned char dma; /* DMA channel */
43
44 unsigned long state;
45
46 struct list_head dev_list;
47 struct list_head napi_list;
48 struct list_head unreg_list;
49
50 /* Net device features */
51 unsigned long features;
52 #define NETIF_F_SG 1 /* Scatter/gather IO. */
53 #define NETIF_F_IP_CSUM 2 /* Can checksum TCP/UDP over IPv4. */
54 #define NETIF_F_NO_CSUM 4 /* Does not require checksum. F.e. loopack. */
55 #define NETIF_F_HW_CSUM 8 /* Can checksum all the packets. */
56 #define NETIF_F_IPV6_CSUM 16 /* Can checksum TCP/UDP over IPV6 */
57 #define NETIF_F_HIGHDMA 32 /* Can DMA to high memory. */
58 #define NETIF_F_FRAGLIST 64 /* Scatter/gather IO. */
59 #define NETIF_F_HW_VLAN_TX 128 /* Transmit VLAN hw acceleration */
60 #define NETIF_F_HW_VLAN_RX 256 /* Receive VLAN hw acceleration */
61 #define NETIF_F_HW_VLAN_FILTER 512 /* Receive filtering on VLAN */
62 #define NETIF_F_VLAN_CHALLENGED 1024 /* Device cannot handle VLAN packets */
63 #define NETIF_F_GSO 2048 /* Enable software GSO. */
64 #define NETIF_F_LLTX 4096 /* LockLess TX - deprecated. Please */
65 /* do not use LLTX in new drivers */
66 #define NETIF_F_NETNS_LOCAL 8192 /* Does not change network namespaces */
67 #define NETIF_F_GRO 16384 /* Generic receive offload */
68 #define NETIF_F_LRO 32768 /* large receive offload */
69
70 /* the GSO_MASK reserves bits 16 through 23 */
71 #define NETIF_F_FCOE_CRC (1 << 24) /* FCoE CRC32 */
72 #define NETIF_F_SCTP_CSUM (1 << 25) /* SCTP checksum offload */
73 #define NETIF_F_FCOE_MTU (1 << 26) /* Supports max FCoE MTU, 2158 bytes*/
74 #define NETIF_F_NTUPLE (1 << 27) /* N-tuple filters supported */
75 #define NETIF_F_RXHASH (1 << 28) /* Receive hashing offload */
76
77 /* Segmentation offload features */
78 #define NETIF_F_GSO_SHIFT 16
79 #define NETIF_F_GSO_MASK 0x00ff0000
80 #define NETIF_F_TSO (SKB_GSO_TCPV4 << NETIF_F_GSO_SHIFT)
81 #define NETIF_F_UFO (SKB_GSO_UDP << NETIF_F_GSO_SHIFT)
82 #define NETIF_F_GSO_ROBUST (SKB_GSO_DODGY << NETIF_F_GSO_SHIFT)
83 #define NETIF_F_TSO_ECN (SKB_GSO_TCP_ECN << NETIF_F_GSO_SHIFT)
84 #define NETIF_F_TSO6 (SKB_GSO_TCPV6 << NETIF_F_GSO_SHIFT)
85 #define NETIF_F_FSO (SKB_GSO_FCOE << NETIF_F_GSO_SHIFT)
86
87 /* List of features with software fallbacks. */
88 #define NETIF_F_GSO_SOFTWARE (NETIF_F_TSO | NETIF_F_TSO_ECN | \
89 NETIF_F_TSO6 | NETIF_F_UFO)
90
91
92 #define NETIF_F_GEN_CSUM (NETIF_F_NO_CSUM | NETIF_F_HW_CSUM)
93 #define NETIF_F_V4_CSUM (NETIF_F_GEN_CSUM | NETIF_F_IP_CSUM)
94 #define NETIF_F_V6_CSUM (NETIF_F_GEN_CSUM | NETIF_F_IPV6_CSUM)
95 #define NETIF_F_ALL_CSUM (NETIF_F_V4_CSUM | NETIF_F_V6_CSUM)
96
97 /*
98 * If one device supports one of these features, then enable them
99 * for all in netdev_increment_features.
100 */
101 #define NETIF_F_ONE_FOR_ALL (NETIF_F_GSO_SOFTWARE | NETIF_F_GSO_ROBUST | \
102 NETIF_F_SG | NETIF_F_HIGHDMA | \
103 NETIF_F_FRAGLIST)
104
105 /* Interface index. Unique device identifier */
106 int ifindex;
107 int iflink;
108
109 struct net_device_stats stats;
110 atomic_long_t rx_dropped; /* dropped packets by core network
111 * Do not use this in drivers.
112 */
113
114 #ifdef CONFIG_WIRELESS_EXT
115 /* List of functions to handle Wireless Extensions (instead of ioctl).
116 * See <net/iw_handler.h> for details. Jean II */
117 const struct iw_handler_def * wireless_handlers;
118 /* Instance data managed by the core of Wireless Extensions. */
119 struct iw_public_data * wireless_data;
120 #endif
121 /* Management operations */
122 const struct net_device_ops *netdev_ops;
123 const struct ethtool_ops *ethtool_ops;
124
125 /* Hardware header description */
126 const struct header_ops *header_ops;
127
128 unsigned int flags; /* interface flags (a la BSD) */
129 unsigned short gflags;
130 unsigned int priv_flags; /* Like 'flags' but invisible to userspace. */
131 unsigned short padded; /* How much padding added by alloc_netdev() */
132
133 unsigned char operstate; /* RFC2863 operstate */
134 unsigned char link_mode; /* mapping policy to operstate */
135
136 unsigned int mtu; /* interface MTU value */
137 unsigned short type; /* interface hardware type */
138 unsigned short hard_header_len; /* hardware hdr length */
139
140 /* extra head- and tailroom the hardware may need, but not in all cases
141 * can this be guaranteed, especially tailroom. Some cases also use
142 * LL_MAX_HEADER instead to allocate the skb.
143 */
144 unsigned short needed_headroom;
145 unsigned short needed_tailroom;
146
147 /* Interface address info. */
148 unsigned char perm_addr[MAX_ADDR_LEN]; /* permanent hw address */
149 unsigned char addr_assign_type; /* hw address assignment type */
150 unsigned char addr_len; /* hardware address length */
151 unsigned short dev_id; /* for shared network cards */
152
153 spinlock_t addr_list_lock;
154 struct netdev_hw_addr_list uc; /* Unicast mac addresses */
155 struct netdev_hw_addr_list mc; /* Multicast mac addresses */
156 int uc_promisc;
157 unsigned int promiscuity;
158 unsigned int allmulti;
159
160
161 /* Protocol specific pointers */
162
163 #if defined(CONFIG_VLAN_8021Q) || defined(CONFIG_VLAN_8021Q_MODULE)
164 struct vlan_group __rcu *vlgrp; /* VLAN group */
165 #endif
166 #ifdef CONFIG_NET_DSA
167 void *dsa_ptr; /* dsa specific data */
168 #endif
169 void *atalk_ptr; /* AppleTalk link */
170 struct in_device __rcu *ip_ptr; /* IPv4 specific data */
171 struct dn_dev __rcu *dn_ptr; /* DECnet specific data */
172 struct inet6_dev __rcu *ip6_ptr; /* IPv6 specific data */
173 void *ec_ptr; /* Econet specific data */
174 void *ax25_ptr; /* AX.25 specific data */
175 struct wireless_dev *ieee80211_ptr; /* IEEE 802.11 specific data,
176 assign before registering */
177
178 /*
179 * Cache lines mostly used on receive path (including eth_type_trans())
180 */
181 unsigned long last_rx; /* Time of last Rx
182 * This should not be set in
183 * drivers, unless really needed,
184 * because network stack (bonding)
185 * use it if/when necessary, to
186 * avoid dirtying this cache line.
187 */
188
189 struct net_device *master; /* Pointer to master device of a group,
190 * which this device is member of.
191 */
192
193 /* Interface address info used in eth_type_trans() */
194 unsigned char *dev_addr; /* hw address, (before bcast
195 because most packets are
196 unicast) */
197
198 struct netdev_hw_addr_list dev_addrs; /* list of device
199 hw addresses */
200
201 unsigned char broadcast[MAX_ADDR_LEN]; /* hw bcast add */
202
203 #ifdef CONFIG_RPS
204 struct kset *queues_kset;
205
206 struct netdev_rx_queue *_rx;
207
208 /* Number of RX queues allocated at register_netdev() time */
209 unsigned int num_rx_queues;
210
211 /* Number of RX queues currently active in device */
212 unsigned int real_num_rx_queues;
213 #endif
214
215 rx_handler_func_t __rcu *rx_handler;
216 void __rcu *rx_handler_data;
217
218 struct netdev_queue __rcu *ingress_queue;
219
220 /*
221 * Cache lines mostly used on transmit path
222 */
223 struct netdev_queue *_tx ____cacheline_aligned_in_smp;
224
225 /* Number of TX queues allocated at alloc_netdev_mq() time */
226 unsigned int num_tx_queues;
227
228 /* Number of TX queues currently active in device */
229 unsigned int real_num_tx_queues;
230
231 /* root qdisc from userspace point of view */
232 struct Qdisc *qdisc;
233
234 unsigned long tx_queue_len; /* Max frames per queue allowed */
235 spinlock_t tx_global_lock;
236
237 #ifdef CONFIG_XPS
238 struct xps_dev_maps __rcu *xps_maps;
239 #endif
240
241 /* These may be needed for future network-power-down code. */
242
243 /*
244 * trans_start here is expensive for high speed devices on SMP,
245 * please use netdev_queue->trans_start instead.
246 */
247 unsigned long trans_start; /* Time (in jiffies) of last Tx */
248
249 int watchdog_timeo; /* used by dev_watchdog() */
250 struct timer_list watchdog_timer;
251
252 /* Number of references to this device */
253 int __percpu *pcpu_refcnt;
254
255 /* delayed register/unregister */
256 struct list_head todo_list;
257 /* device index hash chain */
258 struct hlist_node index_hlist;
259
260 struct list_head link_watch_list;
261
262 /* register/unregister state machine */
263 enum { NETREG_UNINITIALIZED=0,
264 NETREG_REGISTERED, /* completed register_netdevice */
265 NETREG_UNREGISTERING, /* called unregister_netdevice */
266 NETREG_UNREGISTERED, /* completed unregister todo */
267 NETREG_RELEASED, /* called free_netdev */
268 NETREG_DUMMY, /* dummy device for NAPI poll */
269 } reg_state:16;
270
271 enum {
272 RTNL_LINK_INITIALIZED,
273 RTNL_LINK_INITIALIZING,
274 } rtnl_link_state:16;
275
276 /* Called from unregister, can be used to call free_netdev */
277 void (*destructor)(struct net_device *dev);
278
279 #ifdef CONFIG_NETPOLL
280 struct netpoll_info *npinfo;
281 #endif
282
283 #ifdef CONFIG_NET_NS
284 /* Network namespace this network device is inside */
285 struct net *nd_net;
286 #endif
287
288 /* mid-layer private */
289 union {
290 void *ml_priv;
291 struct pcpu_lstats __percpu *lstats; /* loopback stats */
292 struct pcpu_tstats __percpu *tstats; /* tunnel stats */
293 struct pcpu_dstats __percpu *dstats; /* dummy stats */
294 };
295 /* GARP */
296 struct garp_port __rcu *garp_port;
297
298 /* class/net/name entry */
299 struct device dev;
300 /* space for optional device, statistics, and wireless sysfs groups */
301 const struct attribute_group *sysfs_groups[4];
302
303 /* rtnetlink link ops */
304 const struct rtnl_link_ops *rtnl_link_ops;
305
306 /* VLAN feature mask */
307 unsigned long vlan_features;
308
309 /* for setting kernel sock attribute on TCP connection setup */
310 #define GSO_MAX_SIZE 65536
311 unsigned int gso_max_size;
312
313 #ifdef CONFIG_DCB
314 /* Data Center Bridging netlink ops */
315 const struct dcbnl_rtnl_ops *dcbnl_ops;
316 #endif
317
318 #if defined(CONFIG_FCOE) || defined(CONFIG_FCOE_MODULE)
319 /* max exchange id for FCoE LRO by ddp */
320 unsigned int fcoe_ddp_xid;
321 #endif
322 /* n-tuple filter list attached to this device */
323 struct ethtool_rx_ntuple_list ethtool_ntuple_list;
324
325 /* phy device may attach itself for hardware timestamping */
326 struct phy_device *phydev;
327 };