Network Driver in Linux 2.4

Presentation on theme: "Network Driver in Linux 2.4"— Presentation transcript:

1 Network Driver in Linux 2.4
潘仁義 CCU COMM

2 Overview Auto Configuration I/O access Byte ordering
Address translation Bus cycles Bus Direct Memory Access Power management Operating System Device Driver framework Timer management Memory management Race condition handling (SMP) CPU/Memory cache consistency Device operations Interrupt handling

3 Outline Driver framework Device operation Driver example
Linux network drivers Device operation RTL8139 programming Driver example A piece of code for 93C46 series EEPROM, 93C46 64 x 16 bits, 93C x 16 bits pci_skeleton.c (for RTL8139)

4 Linux network driver framework Connecting to the Kernel (1/2)
Module_loading struct net_device snull_dev = { init : snull_init, }; //初始化函式 if((result = register_netdev(snull_dev)))) printk(“error”); 呼叫前, 先設定name 為“eth%d”, 以便其配置 “ethX” 函式內部會呼叫 devinit() snull_init( ) Probe function Called when register_netdev() Usually avoid registering I/O and IRQ, delay until devopen() time To fill in the “dev” strcuture ether_setup(dev), 會將正確的ARP相關作業方法設定好 設定私有資料結構 “priv”; 網路介面生命期與系統一樣長, 可放統計資料 Module_unloading kfree(priv); unregister_netdev (snull_dev);

5 Linux network driver framework Connecting to the Kernel (2/2)
struct net_device { char name[IFNAMSIZ]; // eth%d unsigned long base_addr, unsigned char irq; unsigned char broadcast[], dev_addr[MAX_ADDR_LEN]; unsigned short flags; // IFF_UP, IFF_PROMISC, IFF_ALLMULTI Function pointers: (*init) 初始化 (*open) 開啟介面 (*stop) 停用介面 (*do_ioctl)() (*tx_timeout) 逾時處理 (*get_stats) 結算統計資訊 (*hard_start_xmit) 送出封包 (*set_multicast_list) 群播及flag變動處理 unsigned long trans_start, last_rx; // for watchdog and power management struct dev_mc_list *mc_list; // multicast address list

6 Linux network driver framework Opening and closing
在介面傳輸封包之前，必須先以ifconfig開啟介面，並賦予IP位址 ifconfig設定IP位址給介面時： ioctl(SIOCSIFADDR)設定軟體位址給介面 ioctl(SIOCSIFFLAGS)要求驅動程式開啟、關閉介面觸動open及stop open() 設法取得必要的系統資源(佔領IRQ, IObase, buffer) 要求介面硬體起動 讀出MAC, 複製到 devdev_addr (也可作在init或probe時) 將devdev_addr設定至介面MAC暫存器中 stop() 停止介面硬體 歸還系統資源

7 Linux network driver framework Packet transmission: 當核心需要送出資料封包時
將資料排入出境封包佇列(outgoing queue) 呼叫作業方法 hard_start_transmit(struct sk_buff *skb, struct net_device *dev) 僅將封包交付網卡。網卡後續會再將封包傳送至網路(例如RTL8139) Spinlock_t xmit_lock; 只有在返回後才有可能再被呼叫 實務上，於返回之後，網路卡仍忙著傳輸剛交付的封包。 網卡緩衝區小，滿了必須讓核心知道，不接收新的傳輸要求。 netif_stop_queue()與netif_wake_queue(),netif_start_queue() 註: 還有Carrier loss detection/Watchdog 的 netif_carrier_on/off() 跟Hot-plugging/power management 的 netif_device_attach/detach() 核心經手的每一封包，都是包裝成一個struct sk_buff socket buffer 指向sk_buff的指標，通常取名為skb skbdata指向即將被送出的封包 skblen是該封包的長度，單位是octet

8 Linux network driver framework Transmission queuing model
If ( present && carrier_ok && queue_stopped && ( jiffies – trans_start ) > watchdog_timeo ) Then Call tx_timeout( ) 更新統計，並設定使能繼續送封包 Linux network driver framework Transmission queuing model Present? netif_device_attach() netif_device_detach() Packets go to the LAN Packets from OS Queue stopped ? netif_start_queue() netif_wake_queue() netif_stop_queue() Carrier ok ? netif_carrer_on() netif_carrer_off()

9 Linux network driver framework Packet reception
封包接收事件通常是從網路硬體觸發中斷開始 多半寫在interrupt handler 配置一個sk_buff，並交給核心內部的網路子系統 Interrupt-based 較 polling方式有效率 Example: snull_rx() skb = dev_alloc_skb(len+2); // 採用GFP_ATOMIC,可在ISR中用 skb_reserve(skb, 2); // 16 byte align the IP field memcpy(skb_put(skb, len), receive_packet, len); //skb_put()參考sk_buff 填寫相關資訊 skbdev = dev; skbprotocol = eth_type_trans(skb, dev); skbip_summed = CHECKSUM_UNNECESSARY; /* 不必檢查 */ CHECKSUM_HW(硬體算了)/NONE(待算,預設)/UNNECESSARY(不算) netif_rx(skb); // 交給核心內部的網路子系統

10 Linux network driver framework The interrupt handler
Interrupt happen when A new packet has arrived Transmission of an outgoing packet is completed Something happened: PCI bus error, cable length change, time out Interrupt status register (ISR) Packet reception Pass to the kernel Packet transmission is completed Reset the transmit buffer of the interface Statistics

11 Linux network driver framework The socket buffers (struct sk_buff)
head data tail len end struct sk_buff *dev_alloc_skb(len) 配置 payload headroom tailroom void dev_kfree_skb(struct sk_buff *)釋放 An empty sk_buff void skb_reserve(skb, len)保留前頭空間 unsigned char *skb_put(skb, len)附加資料 unsigned char*skb_push(skb, len)前置資料 unsigned char *skb_pull(skb, len)前抽資料

12 Linux network driver framework Setup receive mode and multicast accept list
Unicast, broadcast (all 1), multicast (bit0==1) Receive all, receive all multicast, receive a list of multicast address Transmit multicast frames is the same as unicast Receive multicast frames Hardware filtering for a list of multicast addresses void (*set_multicast_list)(dev) 要接收的群播位址清單或是dev->flags有改變, 會被核心呼叫 struct dev_mc_list *mc_list; // int mc_count 串列所有dev必須接收的所有群播位址 IFF_PROMISC 設立則進入『混雜模式』(全收) IFF_ALLMULTI 收進所有群播封包

13 Outline Driver framework Device operation Driver example
Linux network drivers Device operation RTL8139 programming Driver example A piece of code for 93C46 series EEPROM, 93C46 64 x 16 bits, 93C x 16 bits pci_skeleton.c (for RTL8139)

14 RTL8139 block diagram

15 Device operation RTL8139(A/B) programming
Packet transmission 4 transmit descriptors in round-robin Transmit FIFO and Early Transmit Packet reception Ring buffer in a physical continuous memory Receive FIFO and FIFO Threshold Hardware initialization Command register (0x37) Reset (4) / Transmit Enable (2) / Receive Enable (3) / Buffer empty (0) Transmit (Tx) Configuration Register (0x40~0x43) Interframe Gap time (螃蟹卡) (25~24) Receive (Rx) Configuration Register (0x44~0x47) Rx FIFO threshold (15~13) Accept Broadcast (3) / Multicast (2) / All (0, Promiscuous mode) packet Rx buffer length (12~11) Interrupt Mask Register (0x3C~0x3D) Software initialization (TxDescriptor and Ring buffer)

16 RTL8139 Packet transmission Transmit descriptor
Transmit start address (TSAD0-3) The physical address of packet The packet must be in a continuous physical memory Transmit status(TSD0-3) TOK(15R) Set to 1 indicates packet transmission was completed successfully and no transmit underrun (14R) has occurred OWN(13R/W) Set to 1 when the Tx DMA operation of this descriptor was completed The driver must set this bit to 0 when the “Size” is written Size(12~0R/W) The total size in bytes of the data in this descriptor Early Tx Threshold(21~16R/W) When the byte count in the Tx FIFO reaches this, the transmit happens. From to in unit of 32 bytes ( = 8 bytes)

17 RTL8139 Packet transmission Process of transmitting a packet
copy the packet to a physically continuous buffer in memory Write the functioning descriptor Address, Size, Early transmit threshold, Clear OWN bit (this starts PCI operation) As TxFIFO meet threshold, the chip start to move from FIFO to line When the whole packet is moved to FIFO, the OWN bit is set to 1 When the whole packet is moved to line, the TOK(TSD) is set to 1 If TOK(IMR) is set, then TOK(ISR) is set and a interrupt is triggered Interrupt service routine called, driver should clear TOK(ISR)

18 Packet reception Ring buffer
Data goes to RxFIFO coming from line Move to the buffer when early receive threshold is meet. Ring buffer physical continuous CBR (0x3A~3B R) the Current address of data moved to Buffer CAPR (0x38~39 R/W) the pointer keeps Current Address of Pkt having been read Status of receiving a packet stored in front of the packet (packet header)

19 Packet reception The Packet Header (32 bits, i.e. 4 bytes)
Bit 31~16: rx_size, including 4 bytes CRC in the tail pkt_size = rx_size - 4

20 Packet reception Process of packet receive in detail
Data received from line is stored in the receive FIFO When Early Receive Threshold is meet, data is moved from FIFO to Receive Buffer After the whole packet is moved from FIFO to Receive Buffer, the receive packet header (receive status and packet length) is written in front of the packet. CBA is updated to the end of the packet. 4 byte alignment CMD (BufferEmpty) is clear and ISR(ROK) is set. ISR routine called and then driver clear ISR(ROK) and update CAPR cur_rx = (cur_rx + rx_size ) & ~3; NETDRV_W16_F (RxBufPtr, cur_rx - 16); Packet header Avoid overflow

21 Outline Driver framework Device operation Driver example
Linux network drivers Device operation RTL8139 programming Driver example A piece of code for 93C46 series EEPROM, 93C46 64 x 16 bits, 93C x 16 bits pci_skeleton.c (for RTL8139)

22 EEPROM 93C46 operations 93C46 Command Register (0x50 R/W)

23 A piece code for EEPROM 93C46
addr_len = read_eeprom (ioaddr, 0, 8) == 0x8129 ? 8 : 6; for (i = 0; i < 3; i++) ((u16 *) (dev->dev_addr))[i] = le16_to_cpu (read_eeprom (ioaddr, i + 7, addr_len)); /* Shift the read command bits out. */ for (i = 4 + addr_len; i >= 0; i--) { int dataval = (read_cmd & (1 << i)) ? EE_DATA_WRITE : 0; writeb (EE_ENB | dataval, ee_addr); eeprom_delay (); writeb (EE_ENB | dataval | EE_SHIFT_CLK, ee_addr); } writeb (EE_ENB, ee_addr); for (i = 16; i > 0; i--) { writeb (EE_ENB | EE_SHIFT_CLK, ee_addr); retval = (retval << 1) | ((readb (ee_addr) & EE_DATA_READ) ? 1 : 0); /* Terminate the EEPROM access. */ writeb (~EE_CS, ee_addr); return retval; #define EE_SHIFT_CLK 0x04 /* EEPROM shift clock. */ #define EE_CS x08 /* EEPROM chip select. */ #define EE_DATA_WRITE 0x02 /* EEPROM chip data in. */ #define EE_DATA_READ 0x01 /* EEPROM chip data out. */ #define EE_ENB (0x80 | EE_CS) #define eeprom_delay() readl(ee_addr) /* EEPROM commands include the alway-set leading bit */ #define EE_WRITE_CMD (5) #define EE_READ_CMD (6) #define EE_ERASE_CMD (7) static int __devinit read_eeprom ( void *ioaddr, int location, int addr_len) { int i; unsigned retval = 0; void *ee_addr = ioaddr + Cfg9346; int read_cmd = location | (EE_READ_CMD << addr_len); writeb (EE_ENB & ~EE_CS, ee_addr); writeb (EE_ENB, ee_addr); eeprom_delay ();

24 Outline Driver framework Device operation Driver example
Linux network drivers Device operation RTL8139 programming Driver example A piece of code for 93C46 series EEPROM, 93C46 64 x 16 bits, 93C x 16 bits pci_skeleton.c (for RTL8139)

25 #include<> of the RTL8139
barrier() printk() byteorder.h module_init() module_exit() spinlock.h config.h MOD_* MODULE_*() Operating System Definitions of I/O port read/write and ioremap() module.h init.h kernel.h delay.h PCI BUS udelay() definition asm/io.h pci-skeleton.c crc32.h 給multicast算ether_crc() pci.h 被間接引入 sched.h (irq, jiffies,capable) slab.h time.h spinlock.h asm/atomic.h skbuff.h PCI defines and prototypes pci_alloc_consistent() pci_resource_*() pci_request_regions() pci_set_master() pci_read_config_word()(err) Network Device mii.h etherdevice.h netdevice.h Definitions for struct net_device register_netdev() netif_*() skbuff.h Definitions for Ethernet eth_type_trans() alloc_ethdev() Definitions for MII_ADVERTISE, MII_LPA ADVERTISE_FULL, LPA_100FULL…

26 Driver structure of the RTL8139
pci_module_init() / pci_unregister_driver() static struct pci_driver netdrv_pci_driver = { name: "netdrv", id_table: netdrv_pci_tbl, probe: netdrv_init_one, remove: netdrv_remove_one, #ifdef CONFIG_PM suspend: netdrv_suspend, resume: netdrv_resume, static struct pci_device_id netdrv_pci_tbl[] __devinitdata = { {0x10ec, 0x8139, PCI_ANY_ID, PCI_ANY_ID, 0, 0, RTL8139 }, MODULE_DEVICE_TABLE (pci, netdrv_pci_tbl); driver_data (Private, Sq# here) pci_device_id

27 PCI device probe function netdrv_init_one()
Linux invoke when probing netdrv_init_one() call netdrv_init_board() to get net_device dev, void *ioaddr Initial net_device dev Set up dev_addr[], irq, base_addr Set up method: dev->open, dev->hard_start_transmit, dev->stop, dev->get_stats, dev->set_multicast_list, dev->do_ioctl, dev->tx_timeout struct pci_dev *pdev, struct pci_device_id *ent netdrv_init_board() dev = alloc_etherdev(sizeof()) pci_enable_device (pdev); pci_request_regions (pdev, “pci-sk"); pci_set_master (pdev); mmio_start = pci_resource_start (pdev, 1); ioaddr = ioremap (mmio_start, len); Soft reset the chip. NETDRV_W8 (ChipCmd, (NETDRV_R8 (ChipCmd) & ChipCmdClear) | CmdReset); identify chip attached to board register_netdev (dev); // ethX 登記I/O port and memory

28 NETDRV_W?() /* write MMIO register, with flush */
/* Flush avoids rtl8139 bug w/ posted MMIO writes */ #define NETDRV_W8_F(reg, val8) do { writeb ((val8), ioaddr + (reg)); readb (ioaddr + (reg)); } while (0) #define NETDRV_W16_F(reg, val16) do { writew ((val16), ioaddr + (reg)); readw (ioaddr + (reg)); } while (0) #define NETDRV_W32_F(reg, val32) do { writel ((val32), ioaddr + (reg)); readl (ioaddr + (reg)); } while (0) #define NETDRV_W8 NETDRV_W8_F #define NETDRV_W16 NETDRV_W16_F #define NETDRV_W32 NETDRV_W32_F #define NETDRV_R8(reg) readb (ioaddr + (reg)) #define NETDRV_R16(reg) readw (ioaddr + (reg)) #define NETDRV_R32(reg) ((unsigned long) readl (ioaddr + (reg)))

29 Device methods dev->open int netdrv_open (struct net_device *dev);
dev->hard_start_transmit int netdrv_start_xmit (struct sk_buff *skb, struct net_device *dev); dev->stop int netdrv_close (…); dev->get_stats struct net_device_stats * netdrv_get_stats (struct net_device *); dev->set_multicast_list void netdrv_set_rx_mode (…); dev->do_ioctl int netdrv_ioctl (struct net_device *dev, struct ifreq *rq, int cmd); dev->tx_timeout void netdrv_tx_timeout (struct net_device *dev);

30 Up up…… netdrv_open() netdrv_open()
Soft reset the chip /* Restore our idea of the MAC address. */ NETDRV_W32_F (MAC0 + 0, cpu_to_le32 (*(u32 *) (dev->dev_addr + 0))); NETDRV_W32_F (MAC0 + 4, cpu_to_le32 (*(u32 *) (dev->dev_addr + 4))); NETDRV_W8_F (ChipCmd, (NETDRV_R8 (ChipCmd) & ChipCmdClear) | CmdRxEnb | CmdTxEnb); Setting RxConfig and TxConfig NETDRV_W32_F (RxBuf, tp->rx_ring_dma); init Tx buffer DMA addresses netdrv_set_rx_mode (dev); NETDRV_W16_F (IntrMask, netdrv_intr_mask); netif_start_queue (dev); netdrv_hw_start (dev) netdrv_open() request_irq (dev->irq, netdrv_interrupt, SA_SHIRQ, dev->name, dev) tx_bufs = pci_alloc_consistent(pdev, TXBUFLEN, &tx_bufs_dma); rx_ring = pci_alloc_consistent(pdev, RXBUFLEN, &rx_ring_dma); netdrv_init_ring (dev); netdrv_hw_start (dev); Set the timer to check for link beat

31 Setup receive mode and multicast hashtable (
Setup receive mode and multicast hashtable (*set_multicast_list)() netdrv_set_rx_mode() if (flags & IFF_PROMISC) AcceptBroadcast | AcceptMulticast | AcceptMyPhys | AcceptAllPhy mc_filter[1] = mc_filter[0] = 0xffffffff else if ((mc_count > multicast_filter_limit) || (flags & IFF_ALLMULTI)) AcceptBroadcast | AcceptMulticast | AcceptMyPhys else mclist[0].dmi_addr mclist[1].dmi_addr mclist[2].dmi_addr ether_crc() 31 30 29 28 27 26 25...0 63 62 1

32 Transmit a packet netdrv_start_xmit()
if (skb->len < ETH_ZLEN) skb = skb_padto(skb, ETH_ZLEN); entry = atomic_read (&cur_tx) % NUM_TX_DESC; tx_info[entry].skb = skb; memcpy (tx_buf[entry], skb->data, skb->len); NETDRV_W32 (TxStatus[entry], tx_flag | skb->len); dev->trans_start = jiffies; atomic_inc (&cur_tx); if ((atomic_read (&cur_tx) - atomic_read (&dirty_tx)) >= NUM_TX_DESC) netif_stop_queue (dev); dirty_tx 1 2 3 cur_tx

33 Interrupt handling netdrv_interrupt()
spin_lock (&tp->lock); status = NETDRV_R16 (IntrStatus); NETDRV_W16_F (IntrStatus, status); // Acknowledge Spec says, “The ISR bits are always set to 1 if the condition is present. ” Spec says, “Reading the ISR clears all. Writing to the ISR has no effect.” if (status & (PCIErr | PCSTimeout | RxUnderrun | RxOverflow |RxFIFOOver | TxErr | RxErr)) netdrv_weird_interrupt (dev, tp, ioaddr, status, link_changed); if (RxOK | RxUnderrun | RxOverflow | RxFIFOOver) netdrv_rx_interrupt (dev, tp, ioaddr); if (status & (TxOK | TxErr)) netdrv_tx_interrupt (dev, tp, ioaddr); spin_unlock (&tp->lock); ISR 1 1 1 1 1 IMR 1 1 1 Interrupt

34 Interrupt handling netdrv_tx_interrupt(dev, tp, ioaddr)
dirty_tx = atomic_read (&tp->dirty_tx); cur_tx = atomic_read (&tp->cur_tx); tx_left = cur_tx - dirty_tx; while (tx_left > 0) { int entry = dirty_tx % NUM_TX_DESC; int txstatus = NETDRV_R32 (TxStatus[entry]); if (!(txstatus & (TxStatOK | TxUnderrun | TxAborted))) break; /* It still hasn't been Txed */ if (txstatus & (TxOutOfWindow | TxAborted)) { /* There was an major error, log it. */ tp->stats.tx_errors++; } else { if (txstatus & TxUnderrun) /* Add 64 to the Tx FIFO threshold. */ tp->tx_flag += 0x ; tp->stats.tx_bytes += txstatus & 0x7ff; tp->stats.tx_packets++; } dev_kfree_skb_irq (tp->tx_info[entry].skb); tp->tx_info[entry].skb = NULL; dirty_tx++; if (netif_queue_stopped (dev)) netif_wake_queue (dev); atomic_set (&tp->dirty_tx, dirty_tx);

35 Interrupt handling Packet reception netdrv_rx_interrupt (dev,tp, ioaddr)
rx_ring = tp->rx_ring; cur_rx = tp->cur_rx; while ((NETDRV_R8 (ChipCmd) & RxBufEmpty) == 0) { ring_offset = cur_rx % RX_BUF_LEN; rx_status = le32_to_cpu (*(u32 *) (rx_ring + ring_offset)); rx_size = rx_status >> 16; pkt_size = rx_size - 4; skb = dev_alloc_skb (pkt_size + 2); skb->dev = dev; skb_reserve (skb, 2); /* 16 byte align the IP fields. */ eth_copy_and_sum (skb, &rx_ring[ring_offset + 4], pkt_size, 0); skb_put (skb, pkt_size); skb->protocol = eth_type_trans (skb, dev); netif_rx (skb); dev->last_rx = jiffies; tp->stats.rx_bytes += pkt_size; tp->stats.rx_packets++; cur_rx = (cur_rx + rx_size ) & ~3; NETDRV_W16_F (RxBufPtr, cur_rx - 16); } tp->cur_rx = cur_rx; Status packet CRC

36 Backup slide

37 How snull is designed ? Ping 看看…

38 14.3 詳解net_device結構 初次研究網路驅動程式的讀者可以略過本節,因為就算不了解它,也不會妨礙你的入門學習.
逐一描述每個欄位的意義與用途,參考性質,不需強記. 此結構可分為兩大部分:開放與隱藏. 開放-此結構宣告為靜態結構,可以預先設定初值的欄位. 隱藏-剩餘欄位,主要提供核心內部的網路層使用.

39 14.3.1 開放欄位(1/2) char name[IFNAMESIZ] 裝置名稱 unsigned long rmem_end;
unsigned long rmem_start; unsigned long mem_end; unsigned long mem_start; 裝置的公共記憶體範圍,rmem是接收區的範圍,mem是傳送區的範圍. unsigned long base_addr; 網路卡I/O基底位址 unsigned char irq; 裝置使用的中斷編號

40 14.3.1 開放欄位(2/2) unsigned char if_port; 若網卡有多個連接埠,此欄代表正在使用的的那個連接埠.
unsigned char dma; 分配給網路裝置的DMA通道. unsigned long state; 裝置的狀態,驅程不直接操作這些旗標,而是透過一組工具函式來改變或取得. struct net_device *next; 指向全域鏈結串列裡的下一個裝置,驅程不應該接觸到. int (*init)(struct net_device *dev); 指向初始函式的指標.

41 14.3.2 隱藏欄位 這些欄位大致可分成三大類: 第一類 提供網路介面資訊(ifconfig). 第二類 輔助驅動程式(核心用不到).
第三類 裝置作業方法,是kernel-driver介面的一部分. 其後說明上述欄位,並非表示在此結構的實際排列順序.

42 14.3.2.1 界面資訊欄位(1/5) 設定網路介面的資訊性欄位 (driver/net/net_init.c)
void ether_setup(struct net_device *dev); void fddi_setup(struct net_device *dev); void hippi_setup(struct net_device *dev); void ltalk_setup(struct net_device *dev); void tr_setup(struct net_device *dev); void fc_setup(struct net_device *dev); 這六類已經涵括所有能夠找到的網路技術,若有更新奇的玩意兒,就只好老老實實自己填寫下面的欄位了.

43 14.3.2.1 界面資訊欄位(2/5) unsigned short hard_header_len;
硬體標頭長度,計算單位是octet. 對於Ethernet值為14 unsigned mtu; 傳輸單位上限.對於Ethernet值為1500 octets unsigned long tx_queue_len; 傳輸佇列可容納的訊框長度上限. ether_setup()設為100 unsigned short type; 介面硬體型態. 提供ARP判斷介面支援何種硬體位址

44 14.3.2.1 界面資訊欄位(3/5) unsigned char addr_len; 硬體位址(MAC)長度.
unsigned char broadcast[MAX_ADDR_LEN]; 廣播位址. unsigned char dev_addr[MAX_ADDR_LEN]; 硬體位址. 以Ethernet而言,硬體位址長度為6 octets,廣播位址是6個連續0xff, ether_setup()能正確地填寫這兩值,但MAC位址則須靠驅動程式自己填寫.

45 14.3.2.1 界面資訊欄位(4/5) unsigned short flags;
介面旗標.flags是一個位元遮罩,<linux/if.h>定義了一系列代表各種位元值的IFF_符號(InterFace Flags),有效的旗標包括: IFF_UP 介面運作狀態.對驅程唯讀,只有核心能變更. IFF_BROADCAST 介面是否具備廣播能力. IFF_DEBUG 除錯模式.驅程用此控制printk的囉唆程度 IFF_LOOPBACK 只有loopback介面才能設立此旗標. IFF_POINTOPOINT 點對點介面. IFF_NOARP 是否支援ARP.

46 14.3.2.1 界面資訊欄位(5/5) IFF_PROMISC 啟動混雜模式. IFF_MULTICAST 介面是否具備群播能力.
IFF_ALLMULTI 要求介面收下所有群播封包. IFF_MASTER 負載平衡. 驅程不需理會. IFF_SLAVE 負載平衡. 驅程不需理會. IFF_PORTSEL 支援具備切換傳媒能力的網卡. IFF_AUTOMEDIA 同上,多了自動. IFF_DYNAMIC 介面的硬體位址可以被改變.撥接裝置. IFF_RUNNING 與IFF_UP相同,只為了保持BSD相容性. IFF_NOTRAILERS Linux並未使用.為了BSD相容性

47 網路介面的作業方法(1/4) 大致可分成基本與額外兩組,你的驅程必須提供基本作業方法,網路介面才有用.額外作業方法是屬於比較高階的功能,並不嚴格要求一定要具備. 以下為基本作業方法: int (*open)(struct net_device *dev); 開啟介面 int (*stop)(struct net_device *dev); 停用介面 int (*hard_start_xmit) (struct sk_buff *skb, struct net_device *dev); 要求硬體開始送出一個封包 int (*hard_header) (struct sk_buff *skb, struct net_device *dev, unsigned short type, void *daddr, void *saddr, unsigned len); 負責建構硬體標頭

48 14.3.2.2 網路介面的作業方法(2/4) int (*rebuild_header)(struct sk_buff *skb);
負責在傳輸封包之前重建硬體標頭. 2.4改用hard_header void (*tx_timeout)(struct net_device *dev); 若無法在一段合理時間內完成封包傳輸,則會呼叫此作業方法. struct net_device_stats *(*get_stats)(struct net_device *dev); 每當應用程式需介面統計資訊時,就會觸動此作業方法. int (*set_config)(struct net_device *dev, struct ifmap *map); 更改介面的硬體組態.

49 14.3.2.2 網路介面的作業方法(3/4) 以下為額外作業方法:
int (*do_ioctl)(struct net_device *dev, struct ifreq *ifr, int cmd); 執行特殊的ioctl命令. void (*set_multicast_list)(struct net_device *dev); 每當裝置的群播名單或flags位元遮罩有任何變動時,就會觸發此作業方法. int (*set_mac_address)(struct net_device *dev, void *addr); 若你的網卡提供改變硬體位址的能力,則可以實作此作業方法.

50 網路介面的作業方法(4/4) int (*change_mtu)(struct net_device *dev, int new_mtu); 當介面MTU有所變更時,由此作業方法負責相關動作. int (*header_cache) (struct neighbour *neigh, struct hh_cache *hh); 將ARP查詢的結果填寫到hh_cache結構. int (*header_cache_update) (struct hh_cache *hh, struct net_device *dev, unsigned char *haddr); MAC位址備改變時,修正hh_cache結構裡的目標位址. int (*hard_header_parse) (struct sk_buff *skb, unsigned char *haddr); 從skb取出來源位址,然後複製到haddr所指的緩衝區.

51 14.3.2.3 工具欄位(1/2) unsigned long trans_start; 開始傳輸的系統時刻.
unsigned long last_rx; 最近一次收到完整封包的系統時刻. int watchdog_timeo; 網路子系統斷定傳輸逾期的最短時間間隔. void *priv; 地位相當於filp->private_data. struct dev_mc_list *mc_list; int mc_count; 這兩個欄位用來處理群播傳輸. mc_count是mc_list的節點個數.

52 14.3.2.3 工具欄位(2/2) spinlock_t xmit_lock;
保護驅程的hard_start_xmit,避免它被同時多次重複呼叫. int xmit_lock_owner; 代表目前有多少個CPU取得了xmit_lock的擁有權. struct module *owner; 擁有本網路裝置結構的模組.用來維護模組的用量計次.

53 14.12 統計資訊 Struct net_device_stats裡面重要欄位 unsigned long tx_packets;
unsigned long rx_packets; unsigned long tx_bytes; unsigned long rx_bytes; unsigned long tx_errors; unsigned long rx_errors; unsigned long tx_dropped; unsigned long rx_dropped; unsigned long collisions; unsigned long multicast;

54 封包處理流程

55 IPtable