原创 Linux网络设备驱动

第十六章Linux网络设备驱动

16.1、Linux网络设备驱动的结构

（1）网络协议接口层向网络协议提供统一的数据包收发接口，不论上层协议是ARP还是IP，都通过dev_queue_xmit()函数发送数据，并通过netif_rx()函数接收数据。这一层的存在使得上层协议独立于具体的设备

（2）网络设备接口层向协议接口层提供统一的用于描述具体网络设备属性和操作的结构体net_device,该结构体是设备驱动功能层中函数的容器。实际上，网络设备接口层从宏观上规划了具体操作硬件的设备驱动功能层的结构。

（3）设备器驱动各函数是网络设备接口层net_device数据结构的具体成员，是驱使网络设备上中断触发接收操作。

（4）网络设备与媒介层是完成数据包发送和接收的物理实体，包括网络适配器和具体的传输媒介，网络适配器被设备驱动功能层中的函数物理上的驱动。对于Linux系统而言，网络设备驱动和媒介都可以使虚拟的。

我们需要做的主要工作是编写设备驱动功能层相关函数以填充net_devices数据结构的内容并将net_devices注册入内核。

16.1.1、网络协议接口层

网络协议接口层最主要的功能是给上层协议提供了透明的数据包发送和接收接口。

sk_buff结构体定义在include /linux/skbuff.h文件中，含义是“套接字缓冲区”，用于在Linux网络子系统中的各层之间传递数据。、

（1）分配

static inline struct sk_buff *alloc_skb(unsigned int size,gfp_t priority)

struct sk_buff *dev_alloc_skb(unsigned int length);

分配一个套接字缓冲区和一个数据缓冲区。

（2）释放

void kfree_skb(struct sk_buff *skb)        //net/core/Skbuff.c

         ---Linux内核内部使用

#define dev_kfree_skb(a)       kfree_skb(a)        //net/core/Skbuff.c

         ---用于非中断的上下文

void dev_kfree_skb_irq(struct sk_buff *skb)   //net/core/Dev.c

         ---用于中断上下文

void dev_kfree_skb_any(struct sk_buff *skb) //net/core/Dev.c

         ---皆可

（3）变更

unsigned char *skb_put(struct sk_buff *skb, unsigned int len) //net/core/Skbuff.c

         在缓冲区尾部添加数据

unsigned char *skb_push(struct sk_buff *skb, unsigned int len) //net/core/Skbuff.c

在缓冲区开头添加数据

static inline void skb_reserve(struct sk_buff *skb, int len)  //include /linux/skbuff.h

        在缓冲区前后添加数据

16.1.2、网络设备接口层

    net_device结构体在内核中指代一个网络设备，定义在include /linux/netdeviceh文件中。

/*

 *       The DEVICE structure.

 *       Actually, this whole structure is a big mistake.  It mixes I/O

 *       data with strictly "high-level" data, and it has to know about

 *       almost every data structure used in the INET module.

 *

 *       FIXME: cleanup struct net_device such that network protocol info

 *       moves out.

 */

 

struct net_device

{

 

    /*

     * This is the first field of the "visible" part of this structure

     * (i.e. as seen by users in the "Space.c" file).  It is the name

     * the interface.

     */

    char                     name[IFNAMSIZ];

    /* device name hash chain */

    struct hlist_node name_hlist;

    /* snmp alias */

    char                    *ifalias;

 

    /*

     *   I/O specific fields

     *   FIXME: Merge these and struct ifmap into one

     */

    unsigned long             mem_end;    /* shared mem end     */

    unsigned long             mem_start;   /* shared mem start    */

    unsigned long             base_addr;    /* device I/O address */

    unsigned int        irq;         /* device IRQ number      */

 

    /*

     *   Some hardware also needs these fields, but they are not

     *   part of the usual set specified in Space.c.

     */

 

    unsigned char             if_port;  /* Selectable AUI, TP,..*/

    unsigned char             dma;             /* DMA channel         */

 

    unsigned long             state;

 

    struct list_head    dev_list;

#ifdef CONFIG_NETPOLL

    struct list_head    napi_list;

#endif

   

    /* The device initialization function. Called only once. */

    int                 (*init)(struct net_device *dev);

 

    /* ------- Fields preinitialized in Space.c finish here ------- */

 

    /* Net device features */

    unsigned long             features;

#define NETIF_F_SG          1     /* Scatter/gather IO. */

#define NETIF_F_IP_CSUM            2     /* Can checksum TCP/UDP over IPv4. */

#define NETIF_F_NO_CSUM         4     /* Does not require checksum. F.e. loopack. */

#define NETIF_F_HW_CSUM         8     /* Can checksum all the packets. */

#define NETIF_F_IPV6_CSUM       16   /* Can checksum TCP/UDP over IPV6 */

#define NETIF_F_HIGHDMA         32   /* Can DMA to high memory. */

#define NETIF_F_FRAGLIST  64   /* Scatter/gather IO. */

#define NETIF_F_HW_VLAN_TX 128 /* Transmit VLAN hw acceleration */

#define NETIF_F_HW_VLAN_RX 256 /* Receive VLAN hw acceleration */

#define NETIF_F_HW_VLAN_FILTER       512 /* Receive filtering on VLAN */

#define NETIF_F_VLAN_CHALLENGED  1024      /* Device cannot handle VLAN packets */

#define NETIF_F_GSO              2048      /* Enable software GSO. */

#define NETIF_F_LLTX            4096      /* LockLess TX - deprecated. Please */

                                /* do not use LLTX in new drivers */

#define NETIF_F_NETNS_LOCAL       8192      /* Does not change network namespaces */

#define NETIF_F_LRO              32768    /* large receive offload */

 

    /* Segmentation offload features */

#define NETIF_F_GSO_SHIFT       16

#define NETIF_F_GSO_MASK       0xffff0000

#define NETIF_F_TSO              (SKB_GSO_TCPV4 << NETIF_F_GSO_SHIFT)

#define NETIF_F_UFO              (SKB_GSO_UDP << NETIF_F_GSO_SHIFT)

#define NETIF_F_GSO_ROBUST   (SKB_GSO_DODGY << NETIF_F_GSO_SHIFT)

#define NETIF_F_TSO_ECN           (SKB_GSO_TCP_ECN << NETIF_F_GSO_SHIFT)

#define NETIF_F_TSO6            (SKB_GSO_TCPV6 << NETIF_F_GSO_SHIFT)

 

    /* List of features with software fallbacks. */

#define NETIF_F_GSO_SOFTWARE    (NETIF_F_TSO | NETIF_F_TSO_ECN | NETIF_F_TSO6)

 

 

#define NETIF_F_GEN_CSUM       (NETIF_F_NO_CSUM | NETIF_F_HW_CSUM)

#define NETIF_F_V4_CSUM          (NETIF_F_GEN_CSUM | NETIF_F_IP_CSUM)

#define NETIF_F_V6_CSUM          (NETIF_F_GEN_CSUM | NETIF_F_IPV6_CSUM)

#define NETIF_F_ALL_CSUM       (NETIF_F_V4_CSUM | NETIF_F_V6_CSUM)

 

    /*

     * If one device supports one of these features, then enable them

     * for all in netdev_increment_features.

     */

#define NETIF_F_ONE_FOR_ALL       (NETIF_F_GSO_SOFTWARE | NETIF_F_GSO_ROBUST | \

                          NETIF_F_SG | NETIF_F_HIGHDMA | \

                          NETIF_F_FRAGLIST)

 

    /* Interface index. Unique device identifier */

    int                 ifindex;

    int                 iflink;

 

 

    struct net_device_stats* (*get_stats)(struct net_device *dev);

    struct net_device_stats     stats;

 

#ifdef CONFIG_WIRELESS_EXT

    /* List of functions to handle Wireless Extensions (instead of ioctl).

     * See <net/iw_handler.h> for details. Jean II */

    const struct iw_handler_def * wireless_handlers;

    /* Instance data managed by the core of Wireless Extensions. */

    struct iw_public_data *    wireless_data;

#endif

    const struct ethtool_ops *ethtool_ops;

 

    /* Hardware header description */

    const struct header_ops *header_ops;

 

    /*

     * This marks the end of the "visible" part of the structure. All

     * fields hereafter are internal to the system, and may change at

     * will (read: may be cleaned up at will).

     */

 

 

    unsigned int        flags;     /* interface flags (a la BSD)    */

    unsigned short            gflags;

        unsigned short          priv_flags; /* Like 'flags' but invisible to userspace. */

    unsigned short            padded; /* How much padding added by alloc_netdev() */

 

    unsigned char             operstate; /* RFC2863 operstate */

    unsigned char             link_mode; /* mapping policy to operstate */

 

    unsigned              mtu;       /* interface MTU value            */

    unsigned short            type;      /* interface hardware type       */

    unsigned short            hard_header_len;       /* hardware hdr length      */

 

    /* extra head- and tailroom the hardware may need, but not in all cases

     * can this be guaranteed, especially tailroom. Some cases also use

     * LL_MAX_HEADER instead to allocate the skb.

     */

    unsigned short            needed_headroom;

    unsigned short            needed_tailroom;

 

    struct net_device *master; /* Pointer to master device of a group,

                                  * which this device is member of.

                                  */

 

    /* Interface address info. */

    unsigned char             perm_addr[MAX_ADDR_LEN]; /* permanent hw address */

    unsigned char             addr_len;      /* hardware address length      */

    unsigned short          dev_id;              /* for shared network cards */

 

    spinlock_t            addr_list_lock;

    struct dev_addr_list   *uc_list; /* Secondary unicast mac addresses */

    int                 uc_count;     /* Number of installed ucasts  */

    int                 uc_promisc;

    struct dev_addr_list   *mc_list;       /* Multicast mac addresses      */

    int                 mc_count;    /* Number of installed mcasts */

    unsigned int        promiscuity;

    unsigned int        allmulti;

 

 

    /* Protocol specific pointers */

   

#ifdef CONFIG_NET_DSA

    void                     *dsa_ptr;      /* dsa specific data */

#endif

    void                    *atalk_ptr;    /* AppleTalk link       */

    void                     *ip_ptr;  /* IPv4 specific data  */ 

    void                    *dn_ptr;        /* DECnet specific data */

    void                    *ip6_ptr;       /* IPv6 specific data */

    void                     *ec_ptr; /* Econet specific data      */

    void                     *ax25_ptr;    /* AX.25 specific data */

    struct wireless_dev    *ieee80211_ptr;   /* IEEE 802.11 specific data,

                                          assign before registering */

 

/*

 * Cache line mostly used on receive path (including eth_type_trans())

 */

    unsigned long             last_rx;  /* Time of last Rx       */

    /* Interface address info used in eth_type_trans() */

    unsigned char             dev_addr[MAX_ADDR_LEN];    /* hw address, (before bcast

                                              because most packets are unicast) */

 

    unsigned char             broadcast[MAX_ADDR_LEN];    /* hw bcast add   */

 

    struct netdev_queue   rx_queue;

 

    struct netdev_queue   *_tx ____cacheline_aligned_in_smp;

 

    /* 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;

 

    unsigned long             tx_queue_len;      /* Max frames per queue allowed */

    spinlock_t            tx_global_lock;

/*

 * One part is mostly used on xmit path (device)

 */

    void                     *priv;     /* pointer to private data   */

    int                 (*hard_start_xmit) (struct sk_buff *skb,

                                           struct net_device *dev);

    /* These may be needed for future network-power-down code. */

    unsigned long             trans_start;   /* Time (in jiffies) of last Tx    */

 

    int                 watchdog_timeo; /* used by dev_watchdog() */

    struct timer_list   watchdog_timer;

 

/*

 * refcnt is a very hot point, so align it on SMP

 */

    /* Number of references to this device */

    atomic_t              refcnt ____cacheline_aligned_in_smp;

 

    /* delayed register/unregister */

    struct list_head    todo_list;

    /* device index hash chain */

    struct hlist_node index_hlist;

 

    struct net_device *link_watch_next;

 

    /* register/unregister state machine */

    enum { NETREG_UNINITIALIZED=0,

           NETREG_REGISTERED,     /* completed register_netdevice */

           NETREG_UNREGISTERING,    /* called unregister_netdevice */

           NETREG_UNREGISTERED,      /* completed unregister todo */

           NETREG_RELEASED,         /* called free_netdev */

    } reg_state;

 

    /* Called after device is detached from network. */

    void                     (*uninit)(struct net_device *dev);

    /* Called after last user reference disappears. */

    void                     (*destructor)(struct net_device *dev);

 

    /* Pointers to interface service routines.       */

    int                 (*open)(struct net_device *dev);

    int                 (*stop)(struct net_device *dev);

#define HAVE_NETDEV_POLL

#define HAVE_CHANGE_RX_FLAGS

    void                     (*change_rx_flags)(struct net_device *dev,

                                          int flags);

#define HAVE_SET_RX_MODE

    void                     (*set_rx_mode)(struct net_device *dev);

#define HAVE_MULTICAST                 

    void                     (*set_multicast_list)(struct net_device *dev);

#define HAVE_SET_MAC_ADDR               

    int                 (*set_mac_address)(struct net_device *dev,

                                          void *addr);

#define HAVE_VALIDATE_ADDR

    int                 (*validate_addr)(struct net_device *dev);

#define HAVE_PRIVATE_IOCTL

    int                 (*do_ioctl)(struct net_device *dev,

                                    struct ifreq *ifr, int cmd);

#define HAVE_SET_CONFIG

    int                 (*set_config)(struct net_device *dev,

                                      struct ifmap *map);

#define HAVE_CHANGE_MTU

    int                 (*change_mtu)(struct net_device *dev, int new_mtu);

 

#define HAVE_TX_TIMEOUT

    void                     (*tx_timeout) (struct net_device *dev);

 

    void                     (*vlan_rx_register)(struct net_device *dev,

                                           struct vlan_group *grp);

    void                     (*vlan_rx_add_vid)(struct net_device *dev,

                                          unsigned short vid);

    void                     (*vlan_rx_kill_vid)(struct net_device *dev,

                                           unsigned short vid);

 

    int                 (*neigh_setup)(struct net_device *dev, struct neigh_parms *);

#ifdef CONFIG_NETPOLL

    struct netpoll_info      *npinfo;

#endif

#ifdef CONFIG_NET_POLL_CONTROLLER

    void                    (*poll_controller)(struct net_device *dev);

#endif

 

    u16               (*select_queue)(struct net_device *dev,

                                       struct sk_buff *skb);

 

#ifdef CONFIG_NET_NS

    /* Network namespace this network device is inside */

    struct net             *nd_net;

#endif

 

    /* mid-layer private */

    void                     *ml_priv;

 

    /* bridge stuff */

    struct net_bridge_port      *br_port;

    /* macvlan */

    struct macvlan_port   *macvlan_port;

    /* GARP */

    struct garp_port   *garp_port;

 

    /* class/net/name entry */

    struct device        dev;

    /* space for optional statistics and wireless sysfs groups */

    struct attribute_group  *sysfs_groups[3];

 

    /* rtnetlink link ops */

    const struct rtnl_link_ops *rtnl_link_ops;

 

    /* VLAN feature mask */

    unsigned long vlan_features;

 

    /* for setting kernel sock attribute on TCP connection setup */

#define GSO_MAX_SIZE         65536

    unsigned int        gso_max_size;

};

16.1.3、设备驱动功能层

net_device结构体的成员需要被设备驱动功能层得具体函数值函数赋予，对于具体的设备xxx，工程师应该编写设备驱动功能层得函数，如xxx_open()、xxx_stop（）。

16.1.4、网络设备与媒介层

网络设备与媒介层直接对应于实际的硬件设备。

16.2网络设备的注册与注销

int register_netdev(struct net_device *dev)     //net/core/dev.c

void unregister_netdev(struct net_device *dev)  //net/core/dev.c

16.3网络设备的初始化

l  进行硬件的准备工作，检查网络设备是否存在，如果存在，则检测设备所使用的硬件资源。

l  进行软件接口的准备工作，分配net_device结构体对其数据和函数指针成员赋值。

l  获得设备的私有信息指针并初始化各成员的值。如果私有信息中包括自旋量或信号量等并发或同步机制，则需要对其进行初始化。

dm9000_init_dm9000(struct net_device *dev)

16.4网络设备的打开与释放

网络设备打开工作：

l  使能设备使用的硬件资源，申请I/O区域、中断和DMA通道

l  调用Linux内核提供的netif_start_quenue()函数，激活设备发送队列。

网络设备关闭工作：

l  调用Linux内核提供的netif_stop_queue()函数，停止对设备传输包。

l  释放设备所使用的I/O区域、中断和DMA资源。

static int dm9000_open(struct net_device *dev)

16.5数据发送流程

/*

 *  Hardware start transmission.

 *  Send a packet to media from the upper layer.

 */

static int

dm9000_start_xmit(struct sk_buff *skb, struct net_device *dev)

当数据传输超时时，意味着当前的发送操作失败或硬件已陷入未知状态，此时数据包发送超时处理函数xxx_tx_timeout()。

static inline void netif_stop_queue(struct net_device *dev)

*     Allow upper layers to call the device hard_start_xmit routine.

 *   Used for flow control when transmit resources are available.

 */

static inline void netif_wake_queue(struct net_device *dev)

 

16.6数据接收流程

网络设备接收数据的主要方法是中断引发设备的中断处理函数，中断处理函数判断中断类型，如果为接收中断，则读取接收到得数据，分配sk_buff数据结构和数据缓冲区，将接收到得数据复制到数据缓冲区，并调用netif_rx()函数将sk_buff传递给上层协议。

static irqreturn_t

dm9000_interrupt(int irq, void *dev_id)

如果是NAPI兼容的设备驱动，则可以通过poll方式接收数据包。

16.7网络连接状态

* Device has detected that carrier.

 */

void netif_carrier_on(struct net_device *dev)         //net/sched/sch_generic.c

* Device has detected loss of carrier.

 */

void netif_carrier_off(struct net_device *dev)     //net/sched/sch_generic.c

通过这两个函数来改变连接状态。

* Check if carrier is present on device

 */

static inline int netif_carrier_ok(const struct net_device *dev)

//include /linux/netdevice.h

确认链路上载波信号是否存在。

 

网络设备驱动程序中可采取一定的手段来检测和报告链路状态。

*  A periodic timer routine

 *  Dynamic media sense, allocated Rx buffer...

 */

static void

dm9000_timer(unsigned long data)

16.8参数设置和统计数据

#define HAVE_SET_MAC_ADDR             

    int                 (*set_mac_address)(struct net_device *dev,void *addr);