网络内核阅读笔记

Linux2.4网络内核源代码阅读笔记

应用层网络接口

#include<sys/types.h>

#include<sys/socket.h>

intsocket（intfamily,inttype,intprotocol）

/东服务器与客户端都调用socket。来建立socket*/

其中：（1）family指明套节字协议族,其值包括:

AF_UNIX（UNIX内部协议族）

AF_INET（Internet协议族）

AF_NS（XeroxNs协议，TCP/IP编程取该值）

AF_IMPLINK（IMP链接层）

（2）type指明套接字类型,取值有:

SOCK_STREAM（流套接字）

SOCK_DGRAM（数据报套接字）

SOCK_RAW（原始套接字）

SOCK_SEQPACKET（定序分组套接字）

股情况卜.，前两个参数的组合的可以决定所使用的协议，这时第三个参数被置为0，如果第一个参数为AFJNET

第：个参数选SOCK_STREAM,则使用的协议为TCP；第.个参数选SOCK_DGRAM,则使用的协议为UDP：

当第：个参数选SOCK_RAW时，使用的协议为IP。值得指出的是并不是所有的族和类型的组合都是合法的,

具体请查阅相关资料。该系统调用若成功则返一个类似文件描述符，称为套接口描述字，可以像文件描述符

那样用read和write对其进行I/O操作。当一个进程使用完该软插座时，需用close（＜描述符〉）关闭。

intbind（intsocketfd,structsockaddrjn*localaddr,sizeof（structsockaddrjn））

/*服务器端Bind系统调用*/

其中：

（1）第一个参数socketfd是前步socket。系统调用返回的套节字描述符。

（2）笫二个参数被捆向本地地址的一种结构,该结构在sys/netinet/in.h中定义:

structsockaddr_in{

shortsin_family;/*socket。系统调用的协议族如AF_INET*/

u_shortsin_port;/*网络字节次序形式的端口号码*/

structin_addrsin_addr;/*网络字节次序形式的网络地址*/

charsin_zero[8];

）：

/'一台机器上的每一个网络程序都使用一个各自独立的网络端口号。如telnet使用23端口

ftp使用21端口，我们在写程序的时候，可以通过调用getservbyname。函数从etc/services

辉文件中得到端口号,也可以使用htons（intportnum）函数k转换为网络字节次序

来得到，有些版本的unix规定1024以卜一端口只能被超级用户使用，普通用户只能使用

1025-32767之间的端I」号,网络地址可以由gethostbyname（char*hostname）函数得到

（该函数与getservbyname（）一样都是以网络字节次序形式返回所有在他们结构中的数据），

参数hostname为etc/hosts文件中某个网络地址所对应的机器名，该函数返回一个类型为

hostent的结构体指针，该结构体hostent在netdb.h

*/

structhostent{

char*h_name;

char**h_aliases;

inth_addrtype;

inth」ength;/*地址长度*/

char**h_addr_list;

井defineh_addrh_addr_list[O];/*地址*/

}：

(3)笫：个参数为第.个结构参数的长度，如果调用成功，bind返回0,否则将返回一1并设置errno。

intlisten(intsockedfd,intbacklog)

/*面向连接的服务器端系统调用listen,表示服务器愿意接受连接*/

它通常是在socket。和bind。调用后，在accept。调用前执行。第二个参数指定accept

调用时系统可以等待多少个连接请求o

intnewsocket=accept(intsocketfd,structsockaddrjn*peer,int*addlen);

/*服务器调用accept,以等待客户机调用connect进行连接。*/

调用等待队列中的第一个连接请求，并建立一个与socketfd一样特征的套接字。

如果没有等待的连接请求，此调用阻塞调用者一直到连接请求到达。

连接成功后，该accept。调用将把对端的地址结构和地址长度放到到参数peer和addlen中，

如果服务器端对客户端的地址信息不感兴趣，这两个参数可以用0代替。

intconnect(intsocketfd,structsockaddrjn*servsaddr,intaddrlen)

/*客户端调用connect。与服务器建立连接*/

客户端取得套接字描述符后，用该connect。调用建立。服务器的连接，

参数socketfd为socket。调用返回的套接字描述符，第和第1个参数是指向想要连接的

目的地址的结构和地址长度。调用成功返回0,否则将返回一1并设置errno.

/*通过建立的socket发送和接收数据*/

一旦建立连接，就可以通过调用read()和write像普通文件一样向网络上发送和接收数据。

intread(intsockfd,char*buff,intnbytes)

Read。有三个参数：一个是套接字描述符，个为数据将被加入的数据缓冲区，还仃一个整数指明要要接受的数据的长度，

Read。返Ml实际接收到的了节数，出错返回-1,遇到文件尾则返回0。

intwrite(intsockfd,char*buff,intnbytes)

Write。有三个参数：•个是套接字描述符，个为指向需要发送的数据的缓冲区，还有一个整数为要写入到文件中的字节个数,

它返回实际写入的字」数，出错返回-10

intsend(intsockfd,char*buff,intnbytes,intflags);

intrecv(intsockfd,char*buff,intnbytes,intflags);

也可以调用send和recv来对套节字进行读写，其调用与基本的read和write系统调用相似，只是多了一个发送方式参数flags，

intsendto(intsockfd,char*buff,intnbytes,intflags,structsockaddr*to,intaddrlen);

intrecvfrom(intsockfd,char*buff,intnbytes,intflags,structsockaddr*from,intaddrlen);

对于使用无连接协议的服务器程序和客户端程序的流程,

客户端程序并不和服务器程序建迂连接,它是通过使用服务器地址作为参数的sendto()系统调用，

发送一个数据报给服务器的。同样，服务器并不接受客户端的连接，而是川recvfrom()调用等待从客户端来的数据。

这些调用与标准的系统调用read()^11write。相似。

这些调用需要附加的参数.Flag参数可以是。或者下列常数：

MSG_OOB接受或发送绑定外的数据

MSG_PEEK监视进入信息

MSG_DONTROUTE绕过路由

intclose(socketfd)

/*退出程序时，应按正常方式关闭套节字号

Socket及协议管理层

include\linux\fs.h

描述：ljsocket相关的文件系统部分结构体

Structinode

structinode{

structIist_headi_hash;

structlist_headUist;

structlist_headi_dentry;

structlist_headi_dirty_buffers;

structlist_headi_dirty_data_buffers;

unsignedlongLino;

atomic_ti_count;

kdev_ti_dev;

umode_ti_mode;

nlink_ti.nlink;

uid_tLuid;

gid_ti_gid;

kdev_ti_rdev;

lofOi_size;

time_ti_atime;

i_mtime;

time_ti_ctime;

unsignedinti_blkbits;

unsignedlongi_blksize;

unsignedlongi_blocks;

unsignedlongi_version;

structsemaphorei_sem;

structsemaphorei_zombie;

structinode_operations*i_op;

structfile_operations*i_fop;/*former->i_op->default_file_ops*/

structsuper_block*i_sb;

wait_queue_head_ti_wait;

structfile_lock*i_flock;

structaddress_space*i_mapping;

structaddress_spacei_data;

structdquot*i_dquot[MAXQUOTAS];

/*Thesethreeshouldprobablybeaunion*/

structlist_headi_devices;

structpipe_inode_info*i_pipe;

structblock_device*i_bdev;

structchar_device*i_cdev;

unsignedlongi_dnotify_mask;/*Directorynotifyevents*/

structdnotify_struct*i_dnotify;/*fordirectorynotifications*/

unsignedlongi_state;

unsignedintijlags;

unsignedchari_sock;

atomic_ti_writecount;

unsignedinti_attr_flags;

_u32Lgeneration;

union{

structminix_inode_infominix__i;

structext2_inode_infoext2_i;

structext3_inode_infoext3_i;

structhpfs_inode_infohpfs_i;

structntfs_inode_infontfs_i;

structmsdos_inode_infomsdos_i；

structumsdos_inode_infbumsdos_i;

structiso_inode_infoisofis_i;

structnfs_inode_infonfs_i;

structsysv_inode_infosysv_i;

structaffs_inode_infoaffs_i;

structufs_inode_infoufs_i;

structefs_inode_infoefs_i;

structromfs_inode_inforomfs_i;

structshmem_inode_infbshmem_i

structcoda_inode_infocoda_i;

structsmb_inode_infosmbfs_i;

structhfs_inode_infohfs_i;

structadfs_inode_infoadfs_i;

structqnx4_inode_infbqnx4_i;

structreiserfs_inode_inforeiserfs_i;

structbfs_inode_infobfs_i;

structudf_inode_infoudU；

structncp_inode_infoncpfs_i;

structproc_inode_infoproc_i;

structsocketsocket_i;

structusbdev_inode_infousbdev_i

structjffis2_inode_infojffs2_i;

void*generic_ip;

}u;

);

structfile

structfile{

structlist_headfjist;

structdentry*f_dentry;

structvfsmount*Cvfsmnt;

structfileoperations*f,op；

atomic_tf_count;

unsignedintLflags;

mode_tf_mode;

lofLtf_pos;

unsignedlongJreada,匚ramax,Jraend,匚ralen,Lrawin;

structfbwn__structf_owner;

unsignedintLuid,fLgid;

intCerror;

unsignedlongCversion;

/*neededforttydriver,andmaybeothers*/

void*private_data;

/*preallocatedhelperkiobuftospeedupO_DIRECT*/

structkiobuf*Mobuf;

longCiobuf_lock;

)；

structfile_operations

/*

*NOTE:

*read,write,polkfsync,readv,writevcanbecalled

*withoutthebigkernellockheldinallfilesystems.

*/

structfile_operations{

structmodule"owner;

loff_t(*llseek)(structfile*,loff_t,int);

ssize_t(*read)(structfile*,char*,size_t,lofLt*);

ssize_t(*write)(structfile*,constchar*,size_t,lofO*)；

int(*readdir)(structfile*,void*,filldir_t);

unsignedint(*poH)(structfile*,structpoll_table_struct*);

int(*ioctl)(structinode*,structfile*,unsignedint,unsignedlong);

int(*mmap)(structfile*,structvm_area_struct*);

int(*open)(structinode*,structfile*);

int(*flush)(structfile*);

int(*release)(structinode*,structfile*);

int(*fsync)(structfile*,structdentry*,intdatasync);

int(*fasync)(int,structfile*,int);

int(*lock)(structfile*,int,structfile_lock*);

ssize_t(*readv)(structfile*,conststructiovec*,unsignedlong,lofO*);

ssize_t(*writev)(structfile*,conststructiovec*,unsignedlong,lofLt*)；

ssize_t(*sendpage)(structfile*,stmctpage*,int,size_t,loffLt*,int);

unsignedlong(*get_unmapped_area)(structfile*,unsignedlong,unsignedlong,unsigned

long,unsignedlong);

)；

include\linux\skbuff.h

structsk_buff_head

structsk_buff_head{

/*Thesetwomembersmustbefirst.*/

structsk_buff*next;

structsk_buff*prev;

―u32qlen;

spinlock_tlock;

);

structsk_buff

structsk_buff{

/*Thesetwomembersmustbefirst.*/

structsk_buff*next;/*Nextbufferinlist*/

structsk_buff*prev;/*Previousbufferinlist*/

structsk_bufLhead*list;/*Listweareon*/

structsock*sk;/*Socketweareownedby*/

structtimevalstamp;/*Timewearrived*/

structnet_device*dev;/*Devicewearrivedon/areleavingby*1

/*Transportlayerheader传输层头部结构体*/

union

(

structtcphdr*th;

structudphdr*uh;

structicmphdr*icmph;

structigmphdr*igmph;

structiphdr*ipiph;

structspxhdr*spxh;

unsignedchar*raw;

}h;

/*Networklayerheader网络层头部结构体*/

union

(

structiphdr*iph;

structipv6hdr*ipv6h;

structarphdr*arph;

structipxhdr*ipxh;

unsignedchar*raw;

}nh;

/*Linklayerheader数据链路层头部结构体*/

union

(

structethhdr*ethemet;

unsignedchar*raw;

}mac;

/*该数据报的传输路由信息结构体*/

structdst_entry*dst;

*Thisisthecontrolbuffer.Itisfreetouseforevery

*layer.Pleaseputyourprivatevariablesthere.Ifyou

*wanttokeepthemacrosslayersyouhavetodoaskb_clone()

*first.ThisisownedbywhoeverhastheskbqueuedATM.

*1

/*这个字符数组是一个控制缓冲区，每一层都可以自由使用。

请把你的私有变量存放在这儿。如果你想要这个数组的数据

在每一层都可以使用，那么你必须调用skb_clone()函数。

*/

charcb(48];

unsignedintlen;/*Lengthofactualdata整个数据报的实际长度*/

unsignedintdata_len;

unsignedintcsum;/*Checksum*/

unsignedchar_unused,/*Deadfield,maybereused*/

cloned,/*headmaybecloned(checkrefcnttobesure).*/

pkt_type,/*Packetclass*/

ip_summed;/*DriverfedusanIPchecksum*/

_u32priority;/*Packetqueueingpriority*/

atomic_tusers;/*Usercount-seedatagram.c,tcp.c*/

unsignedshortprotocol;/*Packetprotocolfromdriver.*1

unsignedshortsecurity;/*Securitylevelofpacket列

unsignedinttruesize;/*Buffersize整个缓冲区的大小*/

unsignedchar*head;/*Headofbuffer缓冲区起始地址*/

unsignedchar*data;/*Dataheadpointer协议数据报的起始地址*/

unsignedchar*tail;/*Tailpointer协议数据报尾地址*/

unsignedchar*end;/*Endpointer整个缓冲区的尾地址*/

void(*destructor)(structsk_buff*);/*Destructfunction*/

#ifdefCONFIG_NETFILTER

/*Canbeusedforcommunicationbetweenhooks.*/

unsignedlongnfmark;

/*Cacheinfo*/

_u32nfcache;

/*Associatedconnection,ifany*/

structnfLct_info*nfct;

#ifdefCONFIG_NETFIETER_DEBUG

unsignedintnCdebug;

#endif

#endif/*CONFIGNETFILTER*/

#ifdefined(CONF!G_HIPPI)

union{

—u32ifield;

}private;

#endif

#ifdefCONFIG_NET_SCHED

―u32tc_index;/*trafficcontrolindex*/

#endif

)；

include\net\sock.h

structinet_opt

structinet_opt{

intttl;/*TTLsetting*/

inttos;/*TOS*/

unsignedcmsg_flags;

structip_options*opt;

unsignedcharhdrincl;/*Includeheaders?*1

_u8/*MulticastingTTL*/

_u8mc_loop;/*Loopback*/

unsignedrecverr:1,

freebind:1;

_ul6id；1*IDcounterforDFpkts*/

_u8pmtudisc;

intmc_index;/*Multicastdeviceindex*/

_u32mc_addr;

structip_mc_socklist/*Grouparray*/

)；

structtcp_opt

描述：Linux_2.4.1网络套接字内部包含了一个由tcp_opt结构

组成的共计420个字节的传输控制块

structtcp_opt{

inttcp_header_len;/*Bytesoftcpheadertosend*/

/*

*Headerpredictionflags

*0x5?10«16+snd_wndinnetbyteorder

*/

,u32pred_flags;

*RFC793variablesbytheirpropernames.Thismeansyoucan

*readthecodeandthespecsidebyside(andlaugh...)

*SeeRFC793andRFC1122.TheRFCwritestheseincapitals.

*/

_u32rcv_nxt;/*Whatwewanttoreceivenext*/

_u32snd_nxt;/*Nextsequencewesend*/

_u32snd_una;/*Firstbytewewantanackfor*/

_u32snd_sml;/*Lastbyteofthemostrecentlytransmittedsmallpacket*/

_u32rcv_tstamp;/*timestampoflastreceivedACK(forkeepalives)*/

_u32Isndtime;/*timestampoflastsentdatapacket(forrestartwindow)*/

/*DelayedACKcontroldata*/

struct{

一u8pending;/*ACKispending*/

一u8quick;/*Schedulednumberofquickacks*/

_u8pingpong;/*Thesessionisinteractive*/

_u8blocked;/*DelayedACKwasblockedbysocketlock*/

_u32ato;/*Predictedtickofsoftclock*/

unsignedlongtimeout;/*Currentlyscheduledtimeout*/

_u32Ircvtime;/*timestampoflastreceiveddatapacket*/

—u16last_seg_size;/*Sizeoflastincomingsegment*/

—ul6rcv_mss;/*MSSusedfordelayedACKdecisions*1

}ack;

/*Datafordirectcopytouser*/

struct{

structskbuffheadprequeue;

structtask__struct*task;

structiovec*iov;

intmemory;

intlen;

}ucopy;

—u32snd_wl1;/*Sequenceforwindowupdate*/

—u32snd_wnd;/*Thewindowweexpecttoreceive*/

―u32max_window;/*Maximalwindoweverseenfrompeer*/

_u32pmtu_cookie;/*Lastpmtuseenbysocket*/

_ul6mss_cache;/*Cachedeffectivemss,notincludingSACKS*/

_u!6mss_clamp;/*Maximalmss,negotiatedatconnectionsetup*/

—ul6ext_header_len;/*Networkprotocoloverhead(IP/IPv6options)*/

_u8ca_state;/*Stateoffast-retransmitmachine*/

一u8retransmits;/*NumberofunrecoveredRTOtimeouts.*/

_u8reordering;/*Packetreorderingmetric.*/

一u8queue_shrunk;/*Writequeuehasbeenshrunkrecently.*/

一u8defer_accept;/*Userwaitsforsomedataafteraccept()*/

/*RTTmeasurement*/

_u8backoff;/*backoff*/

_u32srtt;/*smothedroundtriptime«3*/

_u32mdev;/*mediumdeviation*/

_u32mdev_max;/*maximalmdevforthelastrttperiod*/

_u32rttvar;/*smoothedmdev_max*/

_u32rtt_seq;/*sequencenumbertoupdaterttvar*/

_u32rto;/*retransmittimeout*/

_u32packets_out:/*Packetswhichare"inflight"*/

_u32left_out;/*Packetswhichleavednetwork*/

_u32retrans_out;/*Retransmittedpacketsout*/

*Slowstartandcongestioncontrol(seealsoNagle,andKam&Partridge)

*/

—u32snd_ssthresh;/*Slowstartsizethreshold*/

―u32snd_cwnd;/*Sendingcongestionwindow*/

_ul6snd_cwnd_cnt;/*Linearincreasecounter*/

_ul6snd_cwnd_clamp;/*Donotallowsnd_cwndtogrowabovethis*/

_u32snd_cwnd_used;

―u32snd_cwnd_stamp;

/*Twocommonlyusedtimersinbothsenderandreceiverpaths.*/

unsignedlongtimeout;

structtimer_listretransmit_timer;/*Resend(noack)*/

structtimerjistdelack_timer;/*Ackdelay*/

/*out_of_order_queue用于接收无序得tcp包*/

structsk_bufLheadout_oLorder_queue;/*Outofordersegmentsgohere*/

/*OperationswhichareAF_INET{4,6}specific*/

structtcp_func^af_specific;

structsk_buff*send_head;/*Frontofstufftotransmit*/

structpage*sndmsg_page;/*Cachedpageforsendmsg*/

u32sndmsg_off;/*Cachedoffsetforsendmsg*/

—u32rcv_wnd;/*Currentreceiverwindow*/

—u32rcv_wup;/*rcv_nxtonlastwindowupdatesent*/

—u32write_seq;/*Tail(+1)ofdataheldintcpsendbuffer

_u32pushed_seq;/*Lastpushedseq,requiredtotalktowindows*/

―u32copied_seq;/*Headofyetunreaddata*/

Optionsreceived(usuallyonlastpacket,someonlyonSYNpackets).

*/

chartstamp_ok,/*TIMESTAMPseenonSYNpacket*/

wscale_ok,/*WscaleseenonSYNpacket*/

sack_ok;/*SACKseenonSYNpacket*/

charsaw_tstamp;/*SawTIMESTAMPonlastpacket*/

_u8snd_wscale;/*Windowscalingreceivedfromsender*/

一u8rcv_wscale;/*Windowscalingtosendtoreceiver*/

一u8nonagle;/*DisableNaglealgorithm?*/

_u8keepalive_probes;/*numofallowedkeepaliveprobes*/

PAWS/RTTMdata*/

_u32rcv_tsval;/*Timestampvalue*/

―u32rcv_tsecr;/*Timestampechoreply*/

_u32ts_recent;/*Timestamptoechonext*/

longts_recent_stamp;/*Timewestoredts_recent(foraging)*1

SACKsdata*/

_u16user_mss;/*mssrequestedbyuserinioctl*/

_u8dsack;/*D-SACKisscheduled*/

_u8eff_sacks;/*SizeofSACKarraytosendwithnextpacket*/

structtcp_sack_blockduplicate_sack[1];/*D-SACKblock*/

structtcp_sack_blockselective_acks[4];/*TheSACKSthemselves*/

―u32window_clamp;/*Maximalwindowtoadvertise*/

―u32rcv_ssthresh;/*Currentwindowclamp*/

一u8probes_out;/*unanswered0windowprobes*/

一u8num_sacks;/*NumberofSACKblocks*/

—ul6advmss;/*AdvertisedMSS*/

_u8syn_retries;/*numofallowedsynretries*/

_u8ecn_flags;/*ECNstatusbits.*/

_ul6prior_ssthresh;/*ssthreshsavedatrecoverystart*/

―u32lost_out;/*Lostpackets*/

―u32sacked_out;/*SACK'dpackets*/

―u32fackets_out;/*FACK'dpackets*/

―u32high_seq;/*snd_nxtatonsetofcongestion*/

―u32retrans_stamp;/*Timestampofthelastretransmit,

*alsousedinSYN-SENTtorememberstampof

*thefirstSYN.*/

―u32undo_marker;/*trackingretransstartedhere.*/

intundo_retrans;/*numberofundoableretransmissions.*/

_u32urg_seq;/*Seqofreceivedurgentpointer*/

一u!6urg_data;/*SavedoctetofOOBdataandcontrolflags*/

_u8pending;/*Scheduledtimerevent*/

_u8urg_mode;/*Inurgentmode*/

_u32snd_up;/*Urgentpointer*/

/*Thesyn_wait_lockisnecessaryonlytoavoidtcp_get_infohaving

*tograbthemainlocksockwhilebrowsingthelisteninghash

*(otherwiseit'sdeadlockprone).

*Thislockisacquiredinreadmodeonlyfromtcp_get_info()and

*it'sacquiredinwritemode_only_fromcodethatisactively

*changingthesyn_wait_queue.Allreadersthatareholding

*themastersocklockdon'tneedtograbthislockinreadmode

*tooasthesyn_wait_queuewritesarealwaysprotectedfrom

*themainsocklock.

*/

rwlock_tsyn_wait_lock;

structtcplistenopt*listen_opt;

/*FIFOofestablishedchildren*/

structopen_request^acceptjqueue;

structopenjrequest^acceptjqueueJail;

intwrite_pending;/*Awritetosocketwaitstostart.*1

unsignedintkeepalive_time;/*timebeforekeepalivetakesplace*/

unsignedintkeepalive_intvl;/*timeintervalbetweenkeepaliveprobes*/

intlinger2;

unsignedlonglast_synq_overflow;

)；

structsock

structsock{

/*Socketdemultiplexcomparisonsonincomingpackets.*/

_u32daddr;/*ForeignIPv4addr*/

_u32rcv_saddr;/*BoundlocalIPv4addr*/

—u!6dport;/*Destinationport*/

unsignedshortnum;/*Localport*/

intbound_dev_if;/*Bounddeviceindexif!=0*/

/*Mainhashlinkageforvariousprotocollookuptables.*/

structsock*next;

structsock**pprev;

structsock*bind_next;

structsock**bind_pprev;

volatileunsignedcharstate,/*Connectionstate*/

zapped;/*Inax25&ipxmeansnotlinked*/

_ul6sport;/*Sourceport*/

unsignedshortfamily;/*Addressfamily*/

unsignedcharreuse;/*SO_REUSEADDRsetting*/

unsignedcharshutdown;

atomic_trefcnt;/*Referencecount*/

socket_lock_tlock;/*Synchronizer...*/

/*接收缓冲区字节长度*/

intrcvbuf;/*Sizeofreceivebufferinbytes*/

wait_queue_head_t*sleep;/*Sockwaitqueue*/

structdst_entry*dst_cache;/*Destinationcache*/

rwlock_tdst_lock;

/*接收队列已经提交的字节数*/

atomic_trmem_alloc;/*Receivequeuebytescommitted*/

/*接收的数据报的队列号

structsk_buff_headreceive_queue;/*Incomingpackets*/

/*发送队列已提交的字节数*/

atomic_twniem_alloc;/*Transmitqueuebytescommitted*/

/*发送数据报的队列*/

structsk_bufL_headwrile_queue;/*Packetsendingqueue*/

atomic_tomem_alloc;/*nonis"option"or"other"*/

intwmem_queued;/*Persistentqueuesize*/

intfbrward_alloc;/*Spaceallocatedforward.*/

—u32saddr;/*Sendingsource*/

unsignedintallocation;/*Allocationmode*/

/*发送缓冲区的字节长度刃

intsndbuf;/*Sizeofsendbufferinbytes*/

structsock*prev;

/*Notallarevolatile,butsomeare,sowemightaswellsaytheyallare.

*XXXMakethisaflagword-DaveM

*/

volatilechardead,

done,

urginline,

keepopen,

linger,

destroy,

no_check,

broadcast,

bsdism;

unsignedchardebug;

unsignedcharrcvtstamp;

unsignedcharuse_write_queue;

unsignedcharuserlocks;

/*Holeof3bytes.Trytopack.*/

introute_caps;

intproc;

unsignedlonglingertime;

inthashent;

structsock*pair;

/*Thebacklogqueueisspecial,itisalwaysusedwith

*theper-socketspinlockheldandrequireslowlatency

*access.Thereforewespecialcaseit'simplementation.

*/

/*backlog是一个队列，用于将该sock接收到的skb但是不能被及时处理的skb连接成

一个链表。

*/

struct{

structsk_buff*head;

structsk_buff

}backlog;

rwlock_tcallback_lock;

/*Errorqueue,rarelyused.*/

structsk_bufLheaderror_queue;

/*

sk结构的操作指针prot注册为与具体协议相关的

操作函数集structproto,实现了在协议上的抽象。

UDP协议为udp_prot»TCP为tcp_proto

*/

/*指定协议簇的内部的协议处理函数，它是套接口层与传输层之间的一个接口,

提供如bind,accept,close等操作*/

structproto*prot:

#ifdefined(CONFIG_IPV6)IIdefined(CONFIG_IPV6_MODULE)

union{

structipv6_pinfoaf_inet6;

}net_pinfo;

#endif

union{

structtcpoptaf_tcp;/*TCP传输控制结构*/

#ifdefined(CONFIGJNET)IIdefined(CONFIG_INET_MODULE)

structraw_opttp_raw4;

#endif

#ifdefined(CONFIG」PV6)IIdefined(CONFIG_IPV6_MODULE)

structraw6_opttp_raw;

#endif/*CONFIG_IPV6*/

#ifdefined(CONHG_SPX)IIdefined(CONFIG_SPX_MODULE)

structspx_optaCspx;

#endif/*CONFIG_SPX*/

}tp_pinfo；r-传输协议控制块联合结构*1

interr,err_soft;/*Softholdserrorsthatdon't

causefailurebutarethecause

ofapersistentfailurenotjust

,timedout'*/

/*表示当前的监听队列*/

unsignedshortack_backlog;

/*表示最大的监听队列*/

unsignedshortmax_ack_backlog;

u32priority;

unsignedshorttype;

unsignedcharlocalroute;/*Routelocallyonly*/

unsignedcharprotocol;

structucredpeercred;

rcvlowat;

rcvtimeo;

sndtimeo;

#ifdefCONFIG.FILTER

/*SocketFilteringInstructions*/

structsk_filter*filter;

#endif/*CONFIG_FILTER*/

/*Thisiswherealltheprivate(optional)areasthatdon't

*overlapwilleventuallylive.

*/

union{

void*destruct_hook;

structunix_optafLunix;

#ifdefined(CONFIG」NET)IIdefined(CONFIG」NET_MODULE)

structinetoptaMnet;

#endif

#ifdefined(CONFIG_ATALK)IIdefined(CONFIG_ATALK_MODULE)

structatalk_sockaflat;

#endif

#ifdefined(CONFIG_IPX)IIdefined(CONFIG_IPX_MODULE)

structipx_opta匚ipx;

#endif

#ifdefined(CONFIG_DECNET)IIdefined(CONFIG_DECNET_MODULE)

structdn_scpdn;

#endif

#ifdefined(CONFIG_PACKET)IIdefined(CONFIG_PACKET_MODULE)

structpacket_opt*af_packet;

#endif

#ifdefined(CONFIG_X25)IIdefi