tcp_sock_struct

tcp_sock结构分析

位置：include/linux/tcp.h

基础机构

struct tcp_sock {
/* inet_connection_sock has to be the first member of tcp_sock */
struct inet_connection_sock inet_conn;
u16 tcp_header_len; /* Bytes of tcp header to send      */
u16 gso_segs;   /* Max number of segs per GSO packet    *//**  Header prediction flags*  0x5?10 << 16 + snd_wnd in net byte order*  预判标志，判定是否走快速处理路径*/
__be32  pred_flags;//都是序列号
/**  RFC793 variables by their proper names. This means you can*  read the code and the spec side by side (and laugh ...)*  See RFC793 and RFC1122. The RFC writes these in capitals.*/
u32 rcv_nxt;    /* What we want to receive next  下一个期望收到的序号   */
u32 copied_seq; /* Head of yet unread data，未读数据开头的序列号      */
u32 rcv_wup;    /* rcv_nxt on last window update sent，窗口更新就是发送ACK，ACK序号有新的变化(snd_una会移动)。发送ACK后就更新成rcv_nxt  */
u32 snd_nxt;    /* Next sequence we send        */u32 snd_una;    /* First byte we want an ack for    */
u32 snd_sml;    /* Last byte of the most recently transmitted small packet */
u32 rcv_tstamp; /* timestamp of last received ACK (for keepalives) */
u32 lsndtime;   /* timestamp of last sent data packet (for restart window) */u32 tsoffset;   /* timestamp offset */struct list_head tsq_node; /* anchor in tsq_tasklet.head list */
unsigned long   tsq_flags;/* Data for direct copy to user */
struct {struct sk_buff_head prequeue;struct task_struct  *task;struct msghdr       *msg;int         memory;int         len;
} ucopy;u32 snd_wl1;    /* Sequence for window update窗口更新的ACK序号 */
u32 snd_wnd;    /* The window we expect to receive，接到对方ACK后，tcphdr中window字段  */
u32 max_window; /* Maximal window ever seen from peer，snd_wnd的最大值  */
u32 mss_cache;  /* Cached effective mss, not including SACKS */u32 window_clamp;   /* Maximal window to advertise      */
u32 rcv_ssthresh;   /* Current window clamp         */u16 advmss;     /* Advertised MSS           */
u8  unused;
u8  nonagle     : 4,/* Disable Nagle algorithm?             */thin_lto    : 1,/* Use linear timeouts for thin streams */thin_dupack : 1,/* Fast retransmit on first dupack      */repair      : 1,frto        : 1;/* F-RTO (RFC5682) activated in CA_Loss */
u8  repair_queue;
u8  do_early_retrans:1,/* Enable RFC5827 early-retransmit  */syn_data:1, /* SYN includes data */syn_fastopen:1, /* SYN includes Fast Open option */syn_data_acked:1,/* data in SYN is acked by SYN-ACK */is_cwnd_limited:1;/* forward progress limited by snd_cwnd? */
u32 tlp_high_seq;   /* snd_nxt at the time of TLP retransmit. */
/* RTT measurement */
u32 srtt_us;    /* smoothed round trip time << 3 in usecs */
u32 mdev_us;    /* medium deviation         */
u32 mdev_max_us;    /* maximal mdev for the last rtt period */
u32 rttvar_us;  /* smoothed mdev_max            */
u32 rtt_seq;    /* sequence number to update rttvar */u32 packets_out;    /* Packets which are "in flight"， SND.NXT-SND.UNA   */
u32 retrans_out;    /* Retransmitted packets out        */
u32 max_packets_out;  /* max packets_out in last window */
u32 max_packets_seq;  /* right edge of max_packets_out flight */u16 urg_data;   /* Saved octet of OOB data and control flags */
u8  ecn_flags;  /* ECN status bits.         */
u8  keepalive_probes; /* num of allowed keep alive probes   */
u32 reordering; /* Packet reordering metric.        */
u32 snd_up;     /* Urgent pointer       *//**  Options received (usually on last packet, some only on SYN packets).*/
struct tcp_options_received rx_opt;/**  Slow start and congestion control (see also Nagle, and Karn & Partridge)*/
u32 snd_ssthresh;   /* Slow start size threshold        */
u32 snd_cwnd;   /* Sending congestion window        */
u32 snd_cwnd_cnt;   /* Linear increase counter      */
u32 snd_cwnd_clamp; /* Do not allow snd_cwnd to grow above this */
u32 snd_cwnd_used;
u32 snd_cwnd_stamp;
u32 prior_cwnd; /* Congestion window at start of Recovery. */
u32 prr_delivered;  /* Number of newly delivered packets to* receiver in Recovery. */
u32 prr_out;    /* Total number of pkts sent during Recovery. */u32 rcv_wnd;    /* Current receiver window      */
u32 write_seq;  /* Tail(+1) of data held in tcp send buffer */
u32 notsent_lowat;  /* TCP_NOTSENT_LOWAT */
u32 pushed_seq; /* Last pushed seq, required to talk to windows */
u32 lost_out;   /* Lost packets  在网络上丢失的段       */
u32 sacked_out; /* SACK'd packets 发送在网络上，乱序的段？但是没有被ack  */
u32 fackets_out;    /* FACK'd packets 被acked包总数？          */
u32 tso_deferred;/* from STCP, retrans queue hinting */
struct sk_buff* lost_skb_hint;
struct sk_buff *retransmit_skb_hint;/* OOO(out of order) segments go in this list. Note that socket lock must be held,* as we do not use sk_buff_head lock.*/
//乱序队列
struct sk_buff_head out_of_order_queue;/* SACKs data, these 2 need to be together (see tcp_options_write) */
struct tcp_sack_block duplicate_sack[1]; /* D-SACK block */
struct tcp_sack_block selective_acks[4]; /* The SACKS themselves*/struct tcp_sack_block recv_sack_cache[4];struct sk_buff *highest_sack;   /* skb just after the highest* skb with SACKed bit set* (validity guaranteed only if* sacked_out > 0)*/
int     lost_cnt_hint;
u32     retransmit_high;    /* L-bits may be on up to this seqno */u32 lost_retrans_low;   /* Sent seq after any rxmit (lowest) */u32 prior_ssthresh; /* ssthresh saved at recovery start */
u32 high_seq;   /* snd_nxt at onset of congestion   */u32 retrans_stamp;  /* Timestamp of the last retransmit,* also used in SYN-SENT to remember stamp of* the first SYN. */
u32 undo_marker;    /* snd_una upon a new recovery episode. */
int undo_retrans;   /* number of undoable retransmissions. */
u32 total_retrans;  /* Total retransmits for entire connection */u32 urg_seq;    /* Seq of received urgent pointer */
unsigned int        keepalive_time;   /* time before keep alive takes place */
unsigned int        keepalive_intvl;  /* time interval between keep alive probes */int         linger2;/* Receiver side RTT estimation */
struct {u32 rtt;u32 seq;u32 time;
} rcv_rtt_est;/* Receiver queue space */
struct {int space;u32 seq;u32 time;
} rcvq_space;/* TCP-specific MTU probe information. */
struct {u32       probe_seq_start;u32       probe_seq_end;
} mtu_probe;
u32 mtu_info; /* We received an ICMP_FRAG_NEEDED / ICMPV6_PKT_TOOBIG* while socket was owned by user.*/#ifdef CONFIG_TCP_MD5SIG
/* TCP AF-Specific parts; only used by MD5 Signature support so far */
const struct tcp_sock_af_ops    *af_specific;/* TCP MD5 Signature Option information */
struct tcp_md5sig_info  __rcu *md5sig_info;
#endif/* TCP fastopen related information */
struct tcp_fastopen_request *fastopen_req;
/* fastopen_rsk points to request_sock that resulted in this big* socket. Used to retransmit SYNACKs etc.*/
struct request_sock *fastopen_rsk;
};

tcp选项

struct tcp_options_received {/*  PAWS/RTTM data  */long    ts_recent_stamp;/* Time we stored ts_recent (for aging) */u32 ts_recent;  /* Time stamp to echo next      */u32 rcv_tsval;  /* Time stamp value                 */u32 rcv_tsecr;  /* Time stamp echo reply            */u16     saw_tstamp : 1, /* Saw TIMESTAMP on last packet     */tstamp_ok : 1,  /* TIMESTAMP seen on SYN packet  在连接建立阶段打开tstamp选项   */dsack : 1,  /* D-SACK is scheduled          */wscale_ok : 1,  /* Wscale seen on SYN packet        */sack_ok : 4,    /* SACK seen on SYN packet      */snd_wscale : 4, /* Window scaling received from sender  */rcv_wscale : 4; /* Window scaling to send to receiver   */u8  cookie_plus:6,  /* bytes in authenticator/cookie option */cookie_out_never:1,cookie_in_always:1;u8  num_sacks;  /* Number of SACK blocks SACK块的个数       */u16 user_mss;   /* mss requested by user in ioctl，用户通过设置TCP_MAXSEG得到的值  */u16 mss_clamp;  /* Maximal mss, negotiated at connection setup,连接建立过程中，SYN包的tcp选项得到的 */
};

tcp_skb_cb

此结构主要是实现TCP的每一个要发送的Segment保存的信息，
此信息占用的内存结构是sk_buff中的cb字段。/* This is what the send packet queuing engine uses to pass* TCP per-packet control information to the transmission code.* We also store the host-order sequence numbers in here too.* This is 44 bytes if IPV6 is enabled.* If this grows please adjust skbuff.h:skbuff->cb[xxx] size appropriately.*/
struct tcp_skb_cb {union {struct inet_skb_parm    h4;
#if IS_ENABLED(CONFIG_IPV6)struct inet6_skb_parm   h6;
#endif} header;   /* For incoming frames      */__u32       seq;        /* Starting sequence number tcphdr里带的发送序号 */__u32       end_seq;    /* SEQ + FIN + SYN + datalen 因为FIN，SYN都占一个字节的序号    */__u32       when;       /* used to compute rtt's 保存发送的时间戳    */__u8        tcp_flags;  /* TCP header flags. (tcp[13]) TCPhdr中的标记 */__u8        sacked;     /* State flags for SACK/FACK.  sack标记，貌似还记录sack块相对于tcphdr尾端(20字节)的偏移量？ */
#define TCPCB_SACKED_ACKED  0x01    /* SKB ACK'd by a SACK block    */
#define TCPCB_SACKED_RETRANS    0x02    /* SKB retransmitted        */
#define TCPCB_LOST      0x04    /* SKB is lost          */
#define TCPCB_TAGBITS       0x07    /* All tag bits         */__u8        ip_dsfield; /* IPv4 tos or IPv6 dsfield *//* 1 byte hole */
#define TCPCB_EVER_RETRANS  0x80    /* Ever retransmitted frame */
#define TCPCB_RETRANS       (TCPCB_SACKED_RETRANS|TCPCB_EVER_RETRANS)__u32       ack_seq;    /* Sequence number ACK'd  TCPhdr里带的ack sequence  */
};

tcp_sock_struct

tcp_sock结构分析

基础机构

tcp选项

tcp_skb_cb

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