网络设备之net_device结构与操作
net_device结构是二层中一个非常重要的结构，其结构中成员很多，包含了硬件信息，接口信息，其他辅助信息，以及设备操作函数等等；下面对其中重要的字段含义进行了标注，目前仍在阅读代码过程中，其中某些字段含义会在后面进行补充或者更新；
struct net_device {
/* 设备名称，如eth0 */
char name[IFNAMSIZ];
/* 名称hash */
struct hlist_node name_hlist;
char *ifalias;
/*
* I/O specific fields
* FIXME: Merge these and struct ifmap into one
*/
/*
描述设备所用的共享内存，用于设备与内核沟通
其初始化和访问只会在设备驱动程序内进行
*/
unsigned long mem_end;
unsigned long mem_start;
/* 设备自有内存映射到I/O内存的起始地址 */
unsigned long base_addr;
/*
设备与内核对话的中断编号，此值可由多个设备共享
驱动程序使用request_irq函数分配此变量，使用free_irq予以释放
*/
int irq;
/* 侦测网络状态的改变次数 */
atomic_t carrier_changes;
/*
* Some hardware also needs these fields (state,dev_list,
* napi_list,unreg_list,close_list) but they are not
* part of the usual set specified in Space.c.
*/
/*
网络队列子系统使用的一组标识
由__LINK_STATE_xxx标识
*/
unsigned long state;
struct list_head dev_list;
struct list_head napi_list;
struct list_head unreg_list;
struct list_head close_list;
/* 当前设备所有协议的链表 */
struct list_head ptype_all;
/* 当前设备特定协议的链表 */
struct list_head ptype_specific;
struct {
struct list_head upper;
struct list_head lower;
} adj_list;
/*
用于存在其他一些设备功能
可报告适配卡的功能，以便与CPU通信
使用NETIF_F_XXX标识功能特性
*/
netdev_features_t features;
netdev_features_t hw_features;
netdev_features_t wanted_features;
netdev_features_t vlan_features;
netdev_features_t hw_enc_features;
netdev_features_t mpls_features;
netdev_features_t gso_partial_features;
/* 网络设备索引号 */
int ifindex;
/* 设备组，默认都属于0组 */
int group;
struct net_device_stats stats;
atomic_long_t rx_dropped;
atomic_long_t tx_dropped;
atomic_long_t rx_nohandler;
#ifdef CONFIG_WIRELESS_EXT
const struct iw_handler_def *wireless_handlers;
struct iw_public_data *wireless_data;
#endif
/* 设备操作接口 */
const struct net_device_ops *netdev_ops;
/* ethtool操作接口 */
const struct ethtool_ops *ethtool_ops;
#ifdef CONFIG_NET_SWITCHDEV
const struct switchdev_ops *switchdev_ops;
#endif
#ifdef CONFIG_NET_L3_MASTER_DEV
const struct l3mdev_ops *l3mdev_ops;
#endif
#if IS_ENABLED(CONFIG_IPV6)
const struct ndisc_ops *ndisc_ops;
#endif
#ifdef CONFIG_XFRM
const struct xfrmdev_ops *xfrmdev_ops;
#endif
/* 头部一些操作，如链路层缓存，校验等 */
const struct header_ops *header_ops;
/* 标识接口特性，IFF_XXX，如IFF_UP */
unsigned int flags;
/*
用于存储用户空间不可见的标识
由VLAN和Bridge虚拟设备使用
*/
unsigned int priv_flags;
/* 几乎不使用，为了兼容保留 */
unsigned short gflags;
/* 结构对齐填充 */
unsigned short padded;
/* 与interface group mib中的IfOperStatus相关 */
unsigned char operstate;
unsigned char link_mode;
/*
接口使用的端口类型
*/
unsigned char if_port;
/*
设备使用的DMA通道
并非所有设备都可以用DMA，有些总线不支持DMA
*/
unsigned char dma;
/*
最大传输单元，标识设备能处理帧的最大尺寸
Ethernet-1500
*/
unsigned int mtu;
/* 最小mtu，Ethernet-68 */
unsigned int min_mtu;
/* 最大mut，Ethernet-65535 */
unsigned int max_mtu;
/* 设备所属类型
ARP模块中，用type判断接口的硬件地址类型
以太网接口为ARPHRD_ETHER
*/
unsigned short type;
/*
设备头部长度
Ethernet报头是ETH_HLEN=14字节
*/
unsigned short hard_header_len;
unsigned char min_header_len;
/* 必须的头部空间 */
unsigned short needed_headroom;
unsigned short needed_tailroom;
/* Interface address info. */
/* 硬件地址，通常在初始化过程中从硬件读取 */
unsigned char perm_addr[MAX_ADDR_LEN];
unsigned char addr_assign_type;
/* 硬件地址长度 */
unsigned char addr_len;
unsigned short neigh_priv_len;
unsigned short dev_id;
unsigned short dev_port;
spinlock_t addr_list_lock;
/* 设备名赋值类型，如NET_NAME_UNKNOWN */
unsigned char name_assign_type;
bool uc_promisc;
struct netdev_hw_addr_list uc;
struct netdev_hw_addr_list mc;
struct netdev_hw_addr_list dev_addrs;
#ifdef CONFIG_SYSFS
struct kset *queues_kset;
#endif
/* 混杂模式开启数量 */
unsigned int promiscuity;
/* 非零值时，设备监听所有多播地址 */
unsigned int allmulti;
/* Protocol-specific pointers */
/* 特定协议的指针 */
#if IS_ENABLED(CONFIG_VLAN_8021Q)
struct vlan_info __rcu *vlan_info;
#endif
#if IS_ENABLED(CONFIG_NET_DSA)
struct dsa_switch_tree *dsa_ptr;
#endif
#if IS_ENABLED(CONFIG_TIPC)
struct tipc_bearer __rcu *tipc_ptr;
#endif
void *atalk_ptr;
/* ip指向in_device结构 */
struct in_device __rcu *ip_ptr;
struct dn_dev __rcu *dn_ptr;
struct inet6_dev __rcu *ip6_ptr;
void *ax25_ptr;
struct wireless_dev *ieee80211_ptr;
struct wpan_dev *ieee802154_ptr;
#if IS_ENABLED(CONFIG_MPLS_ROUTING)
struct mpls_dev __rcu *mpls_ptr;
#endif
/*
* Cache lines mostly used on receive path (including eth_type_trans())
*/
/* Interface address info used in eth_type_trans() */
unsigned char *dev_addr;
#ifdef CONFIG_SYSFS
/* 接收队列 */
struct netdev_rx_queue *_rx;
/* 接收队列数 */
unsigned int num_rx_queues;
unsigned int real_num_rx_queues;
#endif
struct bpf_prog __rcu *xdp_prog;
unsigned long gro_flush_timeout;
/* 如网桥等的收包回调 */
rx_handler_func_t __rcu *rx_handler;
/* 回调参数 */
void __rcu *rx_handler_data;
#ifdef CONFIG_NET_CLS_ACT
struct tcf_proto __rcu *ingress_cl_list;
#endif
struct netdev_queue __rcu *ingress_queue;
#ifdef CONFIG_NETFILTER_INGRESS
/* netfilter入口 */
struct nf_hook_entry __rcu *nf_hooks_ingress;
#endif
/* 链路层广播地址 */
unsigned char broadcast[MAX_ADDR_LEN];
#ifdef CONFIG_RFS_ACCEL
struct cpu_rmap *rx_cpu_rmap;
#endif
/* 接口索引hash */
struct hlist_node index_hlist;
/*
* Cache lines mostly used on transmit path
*/
/* 发送队列 */
struct netdev_queue *_tx ____cacheline_aligned_in_smp;
/* 发送队列数 */
unsigned int num_tx_queues;
unsigned int real_num_tx_queues;
/* 排队规则 */
struct Qdisc *qdisc;
#ifdef CONFIG_NET_SCHED
DECLARE_HASHTABLE (qdisc_hash, );
#endif
/*
可在设备发送队列中排队的最大数据包数
*/
unsigned long tx_queue_len;
spinlock_t tx_global_lock;
/* 网络层确定传输超时，
调用驱动程序tx_timeout接口的最短时间
*/
int watchdog_timeo;
#ifdef CONFIG_XPS
struct xps_dev_maps __rcu *xps_maps;
#endif
#ifdef CONFIG_NET_CLS_ACT
struct tcf_proto __rcu *egress_cl_list;
#endif
/* These may be needed for future network-power-down code. */
/* watchdog定时器 */
struct timer_list watchdog_timer;
/* 引用计数 */
int __percpu *pcpu_refcnt;
/* 网络设备的注册和除名以两步进行，
该字段用于处理第二步
*/
struct list_head todo_list;
struct list_head link_watch_list;
/* 设备的注册状态 */
enum { NETREG_UNINITIALIZED=,
NETREG_REGISTERED, /* completed register_netdevice */
NETREG_UNREGISTERING, /* called unregister_netdevice */
NETREG_UNREGISTERED, /* completed unregister todo */
NETREG_RELEASED, /* called free_netdev */
NETREG_DUMMY, /* dummy device for NAPI poll */
} reg_state:;
/* 设备要被释放标记 */
bool dismantle;
enum {
RTNL_LINK_INITIALIZED,
RTNL_LINK_INITIALIZING,
} rtnl_link_state:;
bool needs_free_netdev;
void (*priv_destructor)(struct net_device *dev);
#ifdef CONFIG_NETPOLL
struct netpoll_info __rcu *npinfo;
#endif
possible_net_t nd_net;
/* mid-layer private */
union {
void *ml_priv;
struct pcpu_lstats __percpu *lstats;
struct pcpu_sw_netstats __percpu *tstats;
struct pcpu_dstats __percpu *dstats;
struct pcpu_vstats __percpu *vstats;
};
#if IS_ENABLED(CONFIG_GARP)
struct garp_port __rcu *garp_port;
#endif
#if IS_ENABLED(CONFIG_MRP)
struct mrp_port __rcu *mrp_port;
#endif
struct device dev;
const struct attribute_group *sysfs_groups[];
const struct attribute_group *sysfs_rx_queue_group;
const struct rtnl_link_ops *rtnl_link_ops;
/* for setting kernel sock attribute on TCP connection setup */
#define GSO_MAX_SIZE 65536
unsigned int gso_max_size;
#define GSO_MAX_SEGS 65535
u16 gso_max_segs;
#ifdef CONFIG_DCB
const struct dcbnl_rtnl_ops *dcbnl_ops;
#endif
u8 num_tc;
struct netdev_tc_txq tc_to_txq[TC_MAX_QUEUE];
u8 prio_tc_map[TC_BITMASK + ];
#if IS_ENABLED(CONFIG_FCOE)
unsigned int fcoe_ddp_xid;
#endif
#if IS_ENABLED(CONFIG_CGROUP_NET_PRIO)
struct netprio_map __rcu *priomap;
#endif
struct phy_device *phydev;
struct lock_class_key *qdisc_tx_busylock;
struct lock_class_key *qdisc_running_key;
bool proto_down;
};
上述net_device结构中的netdev_ops成员对应设备操作函数结构，用来初始化，销毁，开启，关闭，修改某些变量值等相关操作，结构如下，其中函数操作并未注释，在阅读代码的过程中，遇到具体实现具体分析；
struct net_device_ops {
int (*ndo_init)(struct net_device *dev);
void (*ndo_uninit)(struct net_device *dev);
int (*ndo_open)(struct net_device *dev);
int (*ndo_stop)(struct net_device *dev);
netdev_tx_t (*ndo_start_xmit)(struct sk_buff *skb,
struct net_device *dev);
netdev_features_t (*ndo_features_check)(struct sk_buff *skb,
struct net_device *dev,
netdev_features_t features);
u16 (*ndo_select_queue)(struct net_device *dev,
struct sk_buff *skb,
void *accel_priv,
select_queue_fallback_t fallback);
void (*ndo_change_rx_flags)(struct net_device *dev,
int flags);
void (*ndo_set_rx_mode)(struct net_device *dev);
int (*ndo_set_mac_address)(struct net_device *dev,
void *addr);
int (*ndo_validate_addr)(struct net_device *dev);
int (*ndo_do_ioctl)(struct net_device *dev,
struct ifreq *ifr, int cmd);
int (*ndo_set_config)(struct net_device *dev,
struct ifmap *map);
int (*ndo_change_mtu)(struct net_device *dev,
int new_mtu);
int (*ndo_neigh_setup)(struct net_device *dev,
struct neigh_parms *);
void (*ndo_tx_timeout) (struct net_device *dev);
void (*ndo_get_stats64)(struct net_device *dev,
struct rtnl_link_stats64 *storage);
bool (*ndo_has_offload_stats)(const struct net_device *dev, int attr_id);
int (*ndo_get_offload_stats)(int attr_id,
const struct net_device *dev,
void *attr_data);
struct net_device_stats* (*ndo_get_stats)(struct net_device *dev);
int (*ndo_vlan_rx_add_vid)(struct net_device *dev,
__be16 proto, u16 vid);
int (*ndo_vlan_rx_kill_vid)(struct net_device *dev,
__be16 proto, u16 vid);
#ifdef CONFIG_NET_POLL_CONTROLLER
void (*ndo_poll_controller)(struct net_device *dev);
int (*ndo_netpoll_setup)(struct net_device *dev,
struct netpoll_info *info);
void (*ndo_netpoll_cleanup)(struct net_device *dev);
#endif
int (*ndo_set_vf_mac)(struct net_device *dev,
int queue, u8 *mac);
int (*ndo_set_vf_vlan)(struct net_device *dev,
int queue, u16 vlan,
u8 qos, __be16 proto);
int (*ndo_set_vf_rate)(struct net_device *dev,
int vf, int min_tx_rate,
int max_tx_rate);
int (*ndo_set_vf_spoofchk)(struct net_device *dev,
int vf, bool setting);
int (*ndo_set_vf_trust)(struct net_device *dev,
int vf, bool setting);
int (*ndo_get_vf_config)(struct net_device *dev,
int vf,
struct ifla_vf_info *ivf);
int (*ndo_set_vf_link_state)(struct net_device *dev,
int vf, int link_state);
int (*ndo_get_vf_stats)(struct net_device *dev,
int vf,
struct ifla_vf_stats
*vf_stats);
int (*ndo_set_vf_port)(struct net_device *dev,
int vf,
struct nlattr *port[]);
int (*ndo_get_vf_port)(struct net_device *dev,
int vf, struct sk_buff *skb);
int (*ndo_set_vf_guid)(struct net_device *dev,
int vf, u64 guid,
int guid_type);
int (*ndo_set_vf_rss_query_en)(
struct net_device *dev,
int vf, bool setting);
int (*ndo_setup_tc)(struct net_device *dev,
u32 handle,
__be16 protocol,
struct tc_to_netdev *tc);
#if IS_ENABLED(CONFIG_FCOE)
int (*ndo_fcoe_enable)(struct net_device *dev);
int (*ndo_fcoe_disable)(struct net_device *dev);
int (*ndo_fcoe_ddp_setup)(struct net_device *dev,
u16 xid,
struct scatterlist *sgl,
unsigned int sgc);
int (*ndo_fcoe_ddp_done)(struct net_device *dev,
u16 xid);
int (*ndo_fcoe_ddp_target)(struct net_device *dev,
u16 xid,
struct scatterlist *sgl,
unsigned int sgc);
int (*ndo_fcoe_get_hbainfo)(struct net_device *dev,
struct netdev_fcoe_hbainfo *hbainfo);
#endif
#if IS_ENABLED(CONFIG_LIBFCOE)
#define NETDEV_FCOE_WWNN 0
#define NETDEV_FCOE_WWPN 1
int (*ndo_fcoe_get_wwn)(struct net_device *dev,
u64 *wwn, int type);
#endif
#ifdef CONFIG_RFS_ACCEL
int (*ndo_rx_flow_steer)(struct net_device *dev,
const struct sk_buff *skb,
u16 rxq_index,
u32 flow_id);
#endif
int (*ndo_add_slave)(struct net_device *dev,
struct net_device *slave_dev);
int (*ndo_del_slave)(struct net_device *dev,
struct net_device *slave_dev);
netdev_features_t (*ndo_fix_features)(struct net_device *dev,
netdev_features_t features);
int (*ndo_set_features)(struct net_device *dev,
netdev_features_t features);
int (*ndo_neigh_construct)(struct net_device *dev,
struct neighbour *n);
void (*ndo_neigh_destroy)(struct net_device *dev,
struct neighbour *n);
int (*ndo_fdb_add)(struct ndmsg *ndm,
struct nlattr *tb[],
struct net_device *dev,
const unsigned char *addr,
u16 vid,
u16 flags);
int (*ndo_fdb_del)(struct ndmsg *ndm,
struct nlattr *tb[],
struct net_device *dev,
const unsigned char *addr,
u16 vid);
int (*ndo_fdb_dump)(struct sk_buff *skb,
struct netlink_callback *cb,
struct net_device *dev,
struct net_device *filter_dev,
int *idx);
int (*ndo_bridge_setlink)(struct net_device *dev,
struct nlmsghdr *nlh,
u16 flags);
int (*ndo_bridge_getlink)(struct sk_buff *skb,
u32 pid, u32 seq,
struct net_device *dev,
u32 filter_mask,
int nlflags);
int (*ndo_bridge_dellink)(struct net_device *dev,
struct nlmsghdr *nlh,
u16 flags);
int (*ndo_change_carrier)(struct net_device *dev,
bool new_carrier);
int (*ndo_get_phys_port_id)(struct net_device *dev,
struct netdev_phys_item_id *ppid);
int (*ndo_get_phys_port_name)(struct net_device *dev,
char *name, size_t len);
void (*ndo_udp_tunnel_add)(struct net_device *dev,
struct udp_tunnel_info *ti);
void (*ndo_udp_tunnel_del)(struct net_device *dev,
struct udp_tunnel_info *ti);
void* (*ndo_dfwd_add_station)(struct net_device *pdev,
struct net_device *dev);
void (*ndo_dfwd_del_station)(struct net_device *pdev,
void *priv);
netdev_tx_t (*ndo_dfwd_start_xmit) (struct sk_buff *skb,
struct net_device *dev,
void *priv);
int (*ndo_get_lock_subclass)(struct net_device *dev);
int (*ndo_set_tx_maxrate)(struct net_device *dev,
int queue_index,
u32 maxrate);
int (*ndo_get_iflink)(const struct net_device *dev);
int (*ndo_change_proto_down)(struct net_device *dev,
bool proto_down);
int (*ndo_fill_metadata_dst)(struct net_device *dev,
struct sk_buff *skb);
void (*ndo_set_rx_headroom)(struct net_device *dev,
int needed_headroom);
int (*ndo_xdp)(struct net_device *dev,
struct netdev_xdp *xdp);
};
上述net_device结构中的header_ops成员用来进行链路头部操作，邻居子系统在发送数据包时会用到该结构的成员函数，比如以太网的实现，会通过cache函数将以太头缓存到邻居子系统的hh中，数据包发送前，直接拷贝缓存的以太头即可，无需重新组装；
struct header_ops {
int (*create) (struct sk_buff *skb, struct net_device *dev,
unsigned short type, const void *daddr,
const void *saddr, unsigned int len);
int (*parse)(const struct sk_buff *skb, unsigned char *haddr);
int (*cache)(const struct neighbour *neigh, struct hh_cache *hh, __be16 type);
void (*cache_update)(struct hh_cache *hh,
const struct net_device *dev,
const unsigned char *haddr);
bool (*validate)(const char *ll_header, unsigned int len);
};
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/************************************************************************* > File Name: L.cpp > ...
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