struct Net_device network equipment structure body detailed

Transferred from: http://blog.csdn.net/viewsky11/article/details/53046787

A struct Net_device structure is used in Linux to describe each network device. At the same time, the struct net_device structure used to characterize the network device contains so many fields that the kernel developers feel that the struct net_device is a big mistake in the current Linux kernel.
In this article, only some of the fields in struct Net_device are introduced, and the other fields are used later.

#define IFNAMSIZ 32struct Net_device {The name of the device used to store the network device;Char Name[ifnamsiz];The alias of the network device;Char *ifalias;Network Device interface index value, unique network device identifier;int ifindex;This field is used to construct a hash list of network device names, while theThe name_hlist points to each hash list's linked list header;struct Hlist_node name_hlist;The hash list of interface index values used to build the network device, in struct netIndex_hlist the list header used to refer to the hash table of interface index values;struct Hlist_node index_hlist;For adding each network device to a network device in a network namespace double-linked liststruct List_head dev_list;The identifier of the network device interface, whose state type is defined in <linux/if.h>;Unsignedint flags;Identifier of the network device interface, but not visible to user space;UnsignedShort priv_flags;Interface hardware type, which defines each interface hardware type in <if_arp.h>;UnsignedShort type;The maximum transmission unit of the network device interface;Unsigned MTU;hardware connection oral length;UnsignedShort Hard_header_len;The MAC address of the network device interface;UnsignedChar *dev_addr;Unicast mode for network device interfacesint Uc_promisc;Promiscuous mode of network device interface;Unsignedint promiscuity;Full multicast mode for network device interface; unsigendint allmulti;Secondary unicast MAC Addressstruct Netdev_hw_addr_list UC;List of device HW address;struct Netdev_hw_addr_list Dev_addrs;HW broadcast address;UnsignedChar Broadcast[max_addr_len];multicast MAC address;struct Dev_addr_list *mac_list;Packet receiving queue for network device interface;struct Netdev_queue rx_queue;Packet sending queue for network device interface;struct Netdev_queue *tx; //number of TX queues allocated at ALLOC_NETDEV_MQ () time unsigned int num_tx_queues; //number of TX queues currently active in device; unsigned int real_num_tx_queues; //max frame per queue allowned; unsigned long tx_queue_len; //The status of the network device interface; unsigned long state; //Network Device interface statistical situation; struct net_device_state states; //Used to execute the namespace where the network device resides; struct net *nd_net;}            

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The following diagram shows how the Linux kernel uses struct net and struct net_device to form a network namespace:

1. Assign a network device function, that is, assign a struct net_device struct:alloc_netdev(sizeof_priv, name, setup); 

This alloc_netdev () function is essentially a macro definition:

    #define alloc_netdev(sizeof_priv, name, setup)  alloc_netdev_mq(sizeof_priv, name, setup, 1)struct net_device *alloc_netdev_mq(int sizeof_priv,    const char *name, void(*setup)(struct net_device*),    unsigned int queue_count) EXPORT_SYMBOL(alloc_netdev_mq)  

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Parameter description:
-Sizeof_priv: The size of the private space allocated to the network device;
-Name: Names of network devices;
-Setup: A callback function that initializes the assigned network device;
-Queue_count: Number of sub-queues allocated to network devices;

struct Net_device *alloc_netdev_mq (int Sizeof_priv,ConstChar *name,void (*setup) (struct Net_device *),Unsignedint Queue_count) {struct Net_device *dev;struct Netdev_queue *tx;int alloc_size; Alloc_size =sizeofstruct net_device); dev = Kzalloc (alloc_size, Gfp_kernel); tx = Kcalloc (Queue_count, sizeof (struct netdev_queue), GFP_ KERNEL); Dev_addr_init (Dev); //the Net_device member in the struct Dev_addrs; Dev_unicast_init (Dev); //initializes the UC members in the struct net_device; Dev_net_set (Dev, &init_net); //the namespace of the network device is initialized, the default is init_net; dev->_tx = TX; //set the send queue of the network device; dev->num_tx_queues = queue_count; dev->real_num_tx_queues = Queue_ Count; Netdev_init_queues (Dev); //initializes the Net_device members in the struct rx_queue; setup (dev); //the struct net_device structure to initialize; strcpy (dev->name, name); Span class= "Hljs-comment" >//set the device name of the network device;}export_symbol (ALLOC_NETDEV_MQ);       

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2. Release a network device:

void free_netdev(struct net_device *dev);EXPORT_SYMBOL(free_netdev);

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3. Register a network device, only after registering a network device, this network device will function in the kernel:

 int register_netdev(struct net_device *dev)EXPORT_SYMBOL(register_netdev);   

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return value:
-0: Registration is successful;
-A negative errno code: Indicates that the registration failed;

int Register_netdev (struct net_device*dev) {struct hlist_head*head; struct Hlist_node*p;    int ret; struct NET*net= Dev_net (dev);Gets the namespace in which the network device resides; Rtnl_lock ();Obtain the RTNL signal volume;If!dev_valid_name (Dev->name))Determine if the device name of the network device is valid; {} dev->ifindex= Dev_new_index (NET);Find a globally unique network from the namespace in which the network device residesinterface index value; dev->iflink = dev->ifindex; //is used to determine whether there is a network device with the same name in the network namespace; head = dev_name_hash (NET, Dev->name); Hlist_for_each (p,head) {struct net_device *d = hlist_entry (P, struct Net_device, name_hlist); if (! STRNCMP (D->name, Dev->name, 32 ) {ret = -eexist;}} set_bit (__link_state_present, &dev->state); //set the status of the network device; List_netdevice (dev); //to call the network device into the appropriate namespace;} Export_symbol (Register_netdev);             

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3. Unregister a network device structure:

void unregister_netdev(struct net_device *dev);EXPORT_SYMBOL(unregister_netdev);

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4. Set the MAC address of a network device:

int dev_set_mac_address(struct net_device *dev,                     struct sockaddr *sa);EXPORT_SYMBOL(dev_set_mac_address);

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5. Set the maximum transmission unit for a network device:

int dev_set_mtu(struct net_device *dev, int new_mtu);EXPORT_SYMBOL(dev_set_mtu);

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6. Change the flag identifier of a network device:

int dev_change_flags(struct net_device *dev, unsigend flags);EXPORT_SYMBOL(dev_change_flags);

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7. Obtain a flag identifier for a network device:

unsigned dev_get_flags(struct net_device *dev);EXPORT_SYMBOL(dev_get_flags);

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8. Add a unicast MAC address to the network device when the network device uses a unicast MAC address when sending the unicast

int dev_unicast_add(struct net_device *dev, void *addr);EXPORT_SYMBOL(dev_unicast_add);

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9. Remove the unicast MAC address from the network device:

int dev_unicast_delete(struct net_device *dev, void *addr);EXPORT_SYMBOL(dev_unicast_delete);

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10. Add a device address to the network device:

int dev_addr_add(struct net_device *dev, unsigned char *addr,                  unsigned char addr_type)EXPORT_SYMBOL(dev_addr_add);addr_type : address type;

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11. Remove a device address from the network device:

int dev_addr_del(struct net_device *dev, unsigend char *addr,                  unsigned char addr_type);EXPORT_SYMBOL(dev_addr_del);

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12. Set the interface for the network device to promiscuous mode:

 int dev_set_promiscuity(struct net_device *dev, int inc); EXPORT_SYMBOL(dev_set_promiscuity);

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When the INC > 0 sets the network device to promiscuous mode;
When inc = 0 sets the network device to normal mode;
When the INC < 0 will remove the promiscuous mode of the network device;

13. Set the interface for the network device to Allmulticast mode:

 int dev_set_allmulti(struct net_device *dev, int inc); EXPORT_SYMBOL(dev_set_allmulti); inc 含义同上；

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14. When assigning a device name to a network device, first check if the name is valid:

 int dev_valid_name(const char *name); EXPORT_SYMBOL(dev_valid_name);

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Return:
1: the expression is valid;
0: the expression is invalid;

15. Obtain the device structure of the network device via the device's MAC address and device type:

  struct net_device *dev_getbyhwaddr(struct net *net,              unsigned short type, char *hwaddr); EXPORT_SYMBOL(dev_getbyhwaddr);

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NET: Network namespace;
Type:media type of device;
Hwaddr:hardware address;
Through MEMCMP (dev->dev_addr, HWADDR, Dev->addr_len) to achieve;

16. Obtain the network device structure through the interface index value of the network device:

 struct net_device *dev_get_by_index(struct net *net, int ifindex); EXPORT_SYMBOL(dev_get_by_index);

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17. Obtain the network device structure through the device name of the network device:

struct net_device *dev_get_by_name(struct net *net, const char *name);  EXPORT_SYMBOL(dev_get_by_name);

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All the functions described above are located in/NET/CORE/DEV.C;

This article is reproduced from http://weiguozhihui.blog.51cto.com/3060615/1584894

struct Net_device network equipment structure body detailed