TCP/IP研究-TCB
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TCB结构中各变量统计
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2006-11-20 |
Kevin |
First Draft |
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TCB结构取自kernel 2.6.16.27,
RX : 变量只被”接收”模块访问
TX : 变量只被”发送”模块访问
Timer : 变量只被”超时处理”模块访问
RX, TX : 变量只被”接收/发送”模块访问
RX, Timer : 变量只被”接收/超时处理”模块访问
TX, Timer : 变量只被”发送/超时处理”模块访问
RX, TX, Timer : 变量只被”接收/发送/超时处理”模块访问
struct tcp_sock {
/* inet_connection_sock has to be the first member of tcp_sock */
struct inet_connection_sock inet_conn;
int tcp_header_len; /* Bytes of tcp header to send */ // RX, TX
/*
* Header prediction flags
* 0x5?10 << 16 + snd_wnd in net byte order
*/
__u32 pred_flags; // RX, TX
/*
* 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 */ // RX, TX
__u32 snd_nxt; /* Next sequence we send */ // RX, TX
__u32 snd_una; /* First byte we want an ack for */ // RX, TX
__u32 snd_sml; /* Last byte of the most recently transmitted small packet */ // TX
__u32 rcv_tstamp; /* timestamp of last received ACK (for keepalives) */ // Timer
__u32 lsndtime; /* timestamp of last sent data packet (for restart window) */ // RX, TX, Timer
/* Data for direct copy to user */
struct {
struct sk_buff_head prequeue;
struct task_struct *task;
struct iovec *iov;
int memory;
int len;
} ucopy; // RX, Timer
__u32 snd_wl1; /* Sequence for window update */ // RX
__u32 snd_wnd; /* The window we expect to receive */ // RX, TX, Timer
__u32 max_window; /* Maximal window ever seen from peer */ // RX, TX
__u32 mss_cache; /* Cached effective mss, not including SACKS */ // RX, TX
__u16 xmit_size_goal; /* Goal for segmenting output packets */ // TX
/* XXX Two bytes hole, try to pack */
__u32 window_clamp; /* Maximal window to advertise */ // RX, TX
__u32 rcv_ssthresh; /* Current window clamp */ // RX, TX
__u32 frto_highmark; /* snd_nxt when RTO occurred */ // RX
__u8 reordering; /* Packet reordering metric. */ // RX
__u8 frto_counter; /* Number of new acks after RTO */ // RX
__u8 nonagle; /* Disable Nagle algorithm? */ // TX
__u8 keepalive_probes; /* num of allowed keep alive probes */ // Timer
/* RTT measurement */
__u32 srtt; /* smoothed round trip time << 3 */ // RX, TX
__u32 mdev; /* medium deviation */ // RX
__u32 mdev_max; /* maximal mdev for the last rtt period */ // RX
__u32 rttvar; /* smoothed mdev_max */ // RX
__u32 rtt_seq; /* sequence number to update rttvar */ // RX
__u32 packets_out; /* Packets which are "in flight" */ // RX, TX, Timer
__u32 left_out; /* Packets which leaved network */ // RX, TX
__u32 retrans_out; /* Retransmitted packets out */ // RX, TX
/*
* Options received (usually on last packet, some only on SYN packets).
*/
struct tcp_options_received rx_opt; // RX, TX
/*
* Slow start and congestion control (see also Nagle, and Karn & Partridge)
*/
__u32 snd_ssthresh; /* Slow start size threshold */ // RX, TX
__u32 snd_cwnd; /* Sending congestion window */ // RX, TX
__u16 snd_cwnd_cnt; /* Linear increase counter */ // RX
__u16 snd_cwnd_clamp; /* Do not allow snd_cwnd to grow above this */ // RX
__u32 snd_cwnd_used; // RX, TX
__u32 snd_cwnd_stamp; // RX, TX
struct sk_buff_head out_of_order_queue; /* Out of order segments go here */
__u32 rcv_wnd; /* Current receiver window */ // RX, TX
__u32 rcv_wup; /* rcv_nxt on last window update sent */ // RX, TX
__u32 write_seq; /* Tail(+1) of data held in tcp send buffer */ // RX, TX
__u32 pushed_seq; /* Last pushed seq, required to talk to windows */ // TX
__u32 copied_seq; /* Head of yet unread data */ // RX, TX
/* SACKs data */
struct tcp_sack_block duplicate_sack[1]; /* D-SACK block */ // RX, TX
struct tcp_sack_block selective_acks[4]; /* The SACKS themselves*/ // RX, TX
struct tcp_sack_block recv_sack_cache[4]; // RX
/* from STCP, retrans queue hinting */
struct sk_buff* lost_skb_hint;
struct sk_buff *scoreboard_skb_hint;
struct sk_buff *retransmit_skb_hint;
struct sk_buff *forward_skb_hint;
struct sk_buff *fastpath_skb_hint;
int fastpath_cnt_hint; // RX
int lost_cnt_hint; // RX
int retransmit_cnt_hint; // TX
int forward_cnt_hint; // TX
__u16 advmss; /* Advertised MSS */ // RX, TX
__u16 prior_ssthresh; /* ssthresh saved at recovery start */ // RX, TX
__u32 lost_out; /* Lost packets */ // RX, TX
__u32 sacked_out; /* SACK‘d packets */ // RX, TX
__u32 fackets_out; /* FACK‘d packets */ // RX, TX
__u32 high_seq; /* snd_nxt at onset of congestion */ // RX, TX
__u32 retrans_stamp; /* Timestamp of the last retransmit, // RX, TX
* also used in SYN-SENT to remember stamp of
* the first SYN. */
__u32 undo_marker; /* tracking retrans started here. */ // RX, TX
int undo_retrans; /* number of undoable retransmissions. */ // RX, TX
__u32 urg_seq; /* Seq of received urgent pointer */ // RX
__u16 urg_data; /* Saved octet of OOB data and control flags */ // RX
__u8 urg_mode; /* In urgent mode */ // RX, TX
__u8 ecn_flags; /* ECN status bits. */ // RX
__u32 snd_up; /* Urgent pointer */ // RX, TX
__u32 total_retrans; /* Total retransmits for entire connection */
__u32 bytes_acked; /* Appropriate Byte Counting - RFC3465 */
unsigned int keepalive_time; /* time before keep alive takes place */ // RX, Timer
unsigned int keepalive_intvl; /* time interval between keep alive probes */ // Timer
int linger2; // RX, Timer
unsigned long last_synq_overflow;
/* Receiver side RTT estimation */
struct {
__u32 rtt;
__u32 seq;
__u32 time;
} rcv_rtt_est; // RX
/* Receiver queue space */
struct {
int space;
__u32 seq;
__u32 time;
} rcvq_space; // RX
}
可见,TCB结构中大多数变量都会被”发送”,”接收”模块同时修改, 不可能以下理想情况: ”发送”模块访问一部分标量,”接收”模块
访问一部分变量,互不冲突.
所以, 在设计中必须解决多TCB结构的竞争访问问题.
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