TCP 相关实验
理解 listen 的第二个参数
- 基于刚才封装的 TcpSocket 实现以下测试代码
- 对于服务器, listen 的第二个参数设置为 1, 并且不调用 accept
- 测试代码链接
test_server.cc
c
#include "tcp_socket.hpp"
int main(int argc, char* argv[]) {
if (argc != 3) {
printf("Usage ./test_server [ip] [port]\n");
return 1;
}
TcpSocket sock;
bool ret = sock.Bind(argv[1], atoi(argv[2]));
if (!ret) {
return 1;
}
ret = sock.Listen(2);
if (!ret) {
return 1;
}
// 客户端不进行 accept
while (1) {
sleep(1);
}
return 0;
}test_client.cc
c
#include "tcp_socket.hpp"
int main(int argc, char* argv[]) {
if (argc != 3) {
printf("Usage ./test_client [ip] [port]\n");
return 1;
}
TcpSocket sock;
bool ret = sock.Connect(argv[1], atoi(argv[2]));
if (ret) {
printf("connect ok\n");
} else {
printf("connect failed\n");
}
while (1) {
sleep(1);
}
return 0;
}此时启动 3 个客户端同时连接服务器, 用 netstat 查看服务器状态, 一切正常.
但是启动第四个客户端时, 发现服务器对于第四个连接的状态存在问题了
tcp 3 0 0.0.0.0:9090 0.0.0.0:* LISTEN 9084/./test_server
tcp 0 0 127.0.0.1:9090 127.0.0.1:48178 SYN_RECV -
tcp 0 0 127.0.0.1:9090 127.0.0.1:48176 ESTABLISHED -
tcp 0 0 127.0.0.1:48178 127.0.0.1:9090 ESTABLISHED 9140/./test_client
tcp 0 0 127.0.0.1:48174 127.0.0.1:9090 ESTABLISHED 9087/./test_client
tcp 0 0 127.0.0.1:48176 127.0.0.1:9090 ESTABLISHED 9088/./test_client
tcp 0 0 127.0.0.1:48172 127.0.0.1:9090 ESTABLISHED 9086/./test_client
tcp 0 0 127.0.0.1:9090 127.0.0.1:48174 ESTABLISHED -
tcp 0 0 127.0.0.1:9090 127.0.0.1:48172 ESTABLISHED -客户端状态正常, 但是服务器端出现了 SYN_RECV 状态, 而不是 ESTABLISHED 状态
这是因为, Linux 内核协议栈为一个 tcp 连接管理使用两个队列:
- 半连接队列 (用来保存处于 SYN_SENT 和 SYN_RECV 状态的请求)
- 全连接队列 (accpetd 队列) (用来保存处于 established 状态, 但是应用层没有调用 accept 取走的请求)
而全连接队列的长度会受到 listen 第二个参数的影响.
全连接队列满了的时候, 就无法继续让当前连接的状态进入 established 状态了.
这个队列的长度通过上述实验可知, 是 listen 的第二个参数 + 1.
使用 TCP dump 进行抓包，分析 TCP 过程
我们代码中故意在 close(sockfd)那里留了一个问题
TCPDump 是一款强大的网络分析工具, 主要用于捕获和分析网络上传输的数据包。
安装 tcpdump
tcpdump 通常已经预装在大多数 Linux 发行版中。如果没有安装, 可以使用包管理器进行安装。例如 Ubuntu, 可以使用以下命令安装:
bash
sudo apt - get update
sudo apt - get install tcpdump在 Red Hat 或 CentOS 系统中, 可以使用以下命令:
bash
sudo yum install tcpdump常见使用
- 捕获所有网络接口上的 TCP 报文
使用以下命令可以捕获所有网络接口上传输的 TCP 报文:
bash
$ sudo tcpdump -i any tcp注意: -i any 指定捕获所有网络接口上的数据包, tcp 指定捕获 TCP 协议的数据, -i 可以理解为 interface 的意思
- 捕获指定网络接口上的 TCP 报文
如果你只想捕获某个特定网络接口 (如 eth0) 上的 TCP 报文, 可以使用以下命令:
bash
$ sudo tcpdump -i eth0 tcpeth0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
inet 172.18.45.153 netmask 255.255.192.0 broadcast 172.18.63.255
inet6 fe80::216:3eff:fe03:059b prefixlen 64 scopeid 0x20<link>
ether 00:16:3e:03:95:9b txqueuelen 1000 (Ethernet)
RX packets 34378927 bytes 6954263239 (6.9 GB)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 34274797 bytes 6954263239 (6.9 GB)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0- 捕获特定源或目的 IP 地址的 TCP 报文
使用 host 关键字可以指定源或目的 IP 地址。例如, 要捕获源 IP 地址为 192.168.1.100 的 TCP 报文, 可以使用以下命令:
bash
$ sudo tcpdump src host 192.168.1.100 and tcp要捕获目的 IP 地址为 192.168.1.200 的 TCP 报文, 可以使用以下命令:
bash
$ sudo tcpdump dst host 192.168.1.200 and tcp同时指定源和目的 IP 地址, 可以使用 and 关键字连接两个条件:
bash
$ sudo tcpdump src host 192.168.1.100 and dst host 192.168.1.200 and tcp- 捕获特定端口的 TCP 报文
使用 port 关键字可以指定端口号。例如, 要捕获端口号为 80 的 TCP 报文 (通常是 HTTP 请求), 可以使用以下命令:
bash
$ sudo tcpdump port 80 and tcp- 保存捕获的数据包到文件
使用 -w 选项可以将捕获的数据包保存到文件中, 以便后续分析。例如:
bash
$ sudo tcpdump -i eth0 port 80 -w data.pcap这将把捕获到的 HTTP 流量保存到名为 data.pcap 的文件中。
- 了解: pcap 后缀的文件通常与 PCAP (Packet Capture) 文件格式相关, 这是一种用于捕获网络数据包的文件格式
- 从文件中读取数据包进行分析
使用 -r 选项可以从文件中读取数据包进行分析。例如:
bash
tcpdump -r data.pcap这将读取 data.pcap 文件中的数据包并进行分析。
注意事项
- 使用 tcpdump 时, 请确保你有足够的权限来捕获网络接口上的数据。通常, 你需要以 root 用户身份运行 tcpdump。
- 使用 tcpdump 的时候, 有些主机名会被云服务器解释成为随机的主机名, 如果不想要, 就用-n 选项
- 主机观察三次握手的第三次握手, 不占序号
socket源码分析
c
struct socket {
socket_state state;
unsigned long flags;
const struct proto_ops *ops;
struct fasync_struct *fasync_list;
struct file *file;
struct sock *sk;
wait_queue_head_t wait;
short type;
};我们知道。在Linux系统下，一切皆文件。所以socket是如何与文件描述符相关联的？
c
struct task_struct {
volatile long state; /* -1 unrunnable, 0 runnable, >0 stopped */
void *stack;
atomic_t usage;
unsigned int flags; /* per process flags, defined below */
unsigned int ptrace;
int lock_depth; /* BKL lock depth */
#ifdef CONFIG_SMP
#ifdef __ARCH_WANT_UNLOCKED_CTXSW
int oncpu;
#endif
#endif
int prio, static_prio, normal_prio;
const struct sched_class *sched_class;
struct sched_entity se;
struct sched_rt_entity rt;
#ifdef CONFIG_PREEMPT_NOTIFIERS
/* list of struct preempt_notifier: */
struct hlist_head preempt_notifiers;
#endif
/*
* fpu_counter contains the number of consecutive context switches
* that the FPU is used. If this is over a threshold, the lazy fpu
* saving becomes unlazy to save the trap. This is an unsigned char
* so that after 256 times the counter wraps and the behavior turns
* lazy again; this to deal with bursty apps that only use FPU for
* a short time
*/
unsigned char fpu_counter;
s8 oomkilladj; /* OOM kill score adjustment (bit shift). */
#ifdef CONFIG_BLK_DEV_IO_TRACE
unsigned int btrace_seq;
#endif
unsigned int policy;
cpumask_t cpus_allowed;
#ifdef CONFIG_PREEMPT_RCU
int rcu_read_lock_nesting;
int rcu_flipctr_idx;
#endif /* #ifdef CONFIG_PREEMPT_RCU */
#if defined(CONFIG_SCHEDSTATS) || defined(CONFIG_TASK_DELAY_ACCT)
struct sched_info sched_info;
#endif
struct list_head tasks;
/*
* ptrace_list/ptrace_children forms the list of my children
* that were stolen by a ptracer.
*/
struct list_head ptrace_children;
struct list_head ptrace_list;
struct mm_struct *mm, *active_mm;
/* task state */
struct linux_binfmt *binfmt;
int exit_state;
int exit_code, exit_signal;
int pdeath_signal; /* The signal sent when the parent dies */
/* ??? */
unsigned int personality;
unsigned did_exec:1;
pid_t pid;
pid_t tgid;
#ifdef CONFIG_CC_STACKPROTECTOR
/* Canary value for the -fstack-protector gcc feature */
unsigned long stack_canary;
#endif
/*
* pointers to (original) parent process, youngest child, younger sibling,
* older sibling, respectively. (p->father can be replaced with
* p->parent->pid)
*/
struct task_struct *real_parent; /* real parent process (when being debugged) */
struct task_struct *parent; /* parent process */
/*
* children/sibling forms the list of my children plus the
* tasks I'm ptracing.
*/
struct list_head children; /* list of my children */
struct list_head sibling; /* linkage in my parent's children list */
struct task_struct *group_leader; /* threadgroup leader */
/* PID/PID hash table linkage. */
struct pid_link pids[PIDTYPE_MAX];
struct list_head thread_group;
struct completion *vfork_done; /* for vfork() */
int __user *set_child_tid; /* CLONE_CHILD_SETTID */
int __user *clear_child_tid; /* CLONE_CHILD_CLEARTID */
unsigned int rt_priority;
cputime_t utime, stime, utimescaled, stimescaled;
cputime_t gtime;
cputime_t prev_utime, prev_stime;
unsigned long nvcsw, nivcsw; /* context switch counts */
struct timespec start_time; /* monotonic time */
struct timespec real_start_time; /* boot based time */
/* mm fault and swap info: this can arguably be seen as either mm-specific or thread-specific */
unsigned long min_flt, maj_flt;
cputime_t it_prof_expires, it_virt_expires;
unsigned long long it_sched_expires;
struct list_head cpu_timers[3];
/* process credentials */
uid_t uid,euid,suid,fsuid;
gid_t gid,egid,sgid,fsgid;
struct group_info *group_info;
kernel_cap_t cap_effective, cap_inheritable, cap_permitted, cap_bset;
unsigned securebits;
struct user_struct *user;
#ifdef CONFIG_KEYS
struct key *request_key_auth; /* assumed request_key authority */
struct key *thread_keyring; /* keyring private to this thread */
unsigned char jit_keyring; /* default keyring to attach requested keys to */
#endif
char comm[TASK_COMM_LEN]; /* executable name excluding path
- access with [gs]et_task_comm (which lock
it with task_lock())
- initialized normally by flush_old_exec */
/* file system info */
int link_count, total_link_count;
#ifdef CONFIG_SYSVIPC
/* ipc stuff */
struct sysv_sem sysvsem;
#endif
#ifdef CONFIG_DETECT_SOFTLOCKUP
/* hung task detection */
unsigned long last_switch_timestamp;
unsigned long last_switch_count;
#endif
/* CPU-specific state of this task */
struct thread_struct thread;
/* filesystem information */
struct fs_struct *fs;
/* open file information */
struct files_struct *files; //重点！！！！！
/* namespaces */
struct nsproxy *nsproxy;
/* signal handlers */
struct signal_struct *signal;
struct sighand_struct *sighand;
sigset_t blocked, real_blocked;
sigset_t saved_sigmask; /* restored if set_restore_sigmask() was used */
struct sigpending pending;
unsigned long sas_ss_sp;
size_t sas_ss_size;
int (*notifier)(void *priv);
void *notifier_data;
sigset_t *notifier_mask;
#ifdef CONFIG_SECURITY
void *security;
#endif
struct audit_context *audit_context;
#ifdef CONFIG_AUDITSYSCALL
uid_t loginuid;
unsigned int sessionid;
#endif
seccomp_t seccomp;
/* Thread group tracking */
u32 parent_exec_id;
u32 self_exec_id;
/* Protection of (de-)allocation: mm, files, fs, tty, keyrings */
spinlock_t alloc_lock;
/* Protection of the PI data structures: */
spinlock_t pi_lock;
#ifdef CONFIG_RT_MUTEXES
/* PI waiters blocked on a rt_mutex held by this task */
struct plist_head pi_waiters;
/* Deadlock detection and priority inheritance handling */
struct rt_mutex_waiter *pi_blocked_on;
#endif
#ifdef CONFIG_DEBUG_MUTEXES
/* mutex deadlock detection */
struct mutex_waiter *blocked_on;
#endif
#ifdef CONFIG_TRACE_IRQFLAGS
unsigned int irq_events;
int hardirqs_enabled;
unsigned long hardirq_enable_ip;
unsigned int hardirq_enable_event;
unsigned long hardirq_disable_ip;
unsigned int hardirq_disable_event;
int softirqs_enabled;
unsigned long softirq_disable_ip;
unsigned int softirq_disable_event;
unsigned long softirq_enable_ip;
unsigned int softirq_enable_event;
int hardirq_context;
int softirq_context;
#endif
#ifdef CONFIG_LOCKDEP
# define MAX_LOCK_DEPTH 48UL
u64 curr_chain_key;
int lockdep_depth;
struct held_lock held_locks[MAX_LOCK_DEPTH];
unsigned int lockdep_recursion;
#endif
/* journalling filesystem info */
void *journal_info;
/* stacked block device info */
struct bio *bio_list, **bio_tail;
/* VM state */
struct reclaim_state *reclaim_state;
struct backing_dev_info *backing_dev_info;
struct io_context *io_context;
unsigned long ptrace_message;
siginfo_t *last_siginfo; /* For ptrace use. */
#ifdef CONFIG_TASK_XACCT
/* i/o counters(bytes read/written, #syscalls */
u64 rchar, wchar, syscr, syscw;
#endif
struct task_io_accounting ioac;
#if defined(CONFIG_TASK_XACCT)
u64 acct_rss_mem1; /* accumulated rss usage */
u64 acct_vm_mem1; /* accumulated virtual memory usage */
cputime_t acct_stimexpd;/* stime since last update */
#endif
#ifdef CONFIG_NUMA
struct mempolicy *mempolicy;
short il_next;
#endif
#ifdef CONFIG_CPUSETS
nodemask_t mems_allowed;
int cpuset_mems_generation;
int cpuset_mem_spread_rotor;
#endif
#ifdef CONFIG_CGROUPS
/* Control Group info protected by css_set_lock */
struct css_set *cgroups;
/* cg_list protected by css_set_lock and tsk->alloc_lock */
struct list_head cg_list;
#endif
#ifdef CONFIG_FUTEX
struct robust_list_head __user *robust_list;
#ifdef CONFIG_COMPAT
struct compat_robust_list_head __user *compat_robust_list;
#endif
struct list_head pi_state_list;
struct futex_pi_state *pi_state_cache;
#endif
atomic_t fs_excl; /* holding fs exclusive resources */
struct rcu_head rcu;
/*
* cache last used pipe for splice
*/
struct pipe_inode_info *splice_pipe;
#ifdef CONFIG_TASK_DELAY_ACCT
struct task_delay_info *delays;
#endif
#ifdef CONFIG_FAULT_INJECTION
int make_it_fail;
#endif
struct prop_local_single dirties;
#ifdef CONFIG_LATENCYTOP
int latency_record_count;
struct latency_record latency_record[LT_SAVECOUNT];
#endif
};
/*
* Priority of a process goes from 0..MAX_PRIO-1, valid RT
* priority is 0..MAX_RT_PRIO-1, and SCHED_NORMAL/SCHED_BATCH
* tasks are in the range MAX_RT_PRIO..MAX_PRIO-1. Priority
* values are inverted: lower p->prio value means higher priority.
*
* The MAX_USER_RT_PRIO value allows the actual maximum
* RT priority to be separate from the value exported to
* user-space. This allows kernel threads to set their
* priority to a value higher than any user task. Note:
* MAX_RT_PRIO must not be smaller than MAX_USER_RT_PRIO.
*/
c
struct files_struct {
/*
* read mostly part
*/
atomic_t count;
struct fdtable *fdt;
struct fdtable fdtab;
/*
* written part on a separate cache line in SMP
*/
spinlock_t file_lock ____cacheline_aligned_in_smp;
int next_fd;
struct embedded_fd_set close_on_exec_init;
struct embedded_fd_set open_fds_init;
struct file * fd_array[NR_OPEN_DEFAULT];
};
c
struct file {
/*
* fu_list becomes invalid after file_free is called and queued via
* fu_rcuhead for RCU freeing
*/
union {
struct list_head fu_list;
struct rcu_head fu_rcuhead;
} f_u;
struct path f_path;
#define f_dentry f_path.dentry
#define f_vfsmnt f_path.mnt
const struct file_operations *f_op;
atomic_t f_count;
unsigned int f_flags;
mode_t f_mode;
loff_t f_pos;
struct fown_struct f_owner;
unsigned int f_uid, f_gid;
struct file_ra_state f_ra;
u64 f_version;
#ifdef CONFIG_SECURITY
void *f_security;
#endif
/* needed for tty driver, and maybe others */
void *private_data; //重点！！！！
#ifdef CONFIG_EPOLL
/* Used by fs/eventpoll.c to link all the hooks to this file */
struct list_head f_ep_links;
spinlock_t f_ep_lock;
#endif /* #ifdef CONFIG_EPOLL */
struct address_space *f_mapping;
#ifdef CONFIG_DEBUG_WRITECOUNT
unsigned long f_mnt_write_state;
#endif
};struct file 中成员void*private_data; ，将会指向struct socket；同时struct socket中的struct file *file同时也会指向管理他的文件描述符。
cpp
struct tcp_sock {
/* inet_connection_sock has to be the first member of tcp_sock */
struct inet_connection_sock inet_conn; //重点！！！！！
u16 tcp_header_len; /* Bytes of tcp header to send */
u16 xmit_size_goal; /* Goal for segmenting output packets */
/*
* Header prediction flags
* 0x5?10 << 16 + snd_wnd in net byte order
*/
__be32 pred_flags;
/*
* 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 */
u32 copied_seq; /* Head of yet unread data */
u32 rcv_wup; /* rcv_nxt on last window update sent */
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) */
/* Data for direct copy to user */
struct {
struct sk_buff_head prequeue;
struct task_struct *task;
struct iovec *iov;
int memory;
int len;
#ifdef CONFIG_NET_DMA
/* members for async copy */
struct dma_chan *dma_chan;
int wakeup;
struct dma_pinned_list *pinned_list;
dma_cookie_t dma_cookie;
#endif
} ucopy;
u32 snd_wl1; /* Sequence for window update */
u32 snd_wnd; /* The window we expect to receive */
u32 max_window; /* Maximal window ever seen from peer */
u32 mss_cache; /* Cached effective mss, not including SACKS */
u32 window_clamp; /* Maximal window to advertise */
u32 rcv_ssthresh; /* Current window clamp */
u32 frto_highmark; /* snd_nxt when RTO occurred */
u8 reordering; /* Packet reordering metric. */
u8 frto_counter; /* Number of new acks after RTO */
u8 nonagle; /* Disable Nagle algorithm? */
u8 keepalive_probes; /* num of allowed keep alive probes */
/* RTT measurement */
u32 srtt; /* smoothed round trip time << 3 */
u32 mdev; /* medium deviation */
u32 mdev_max; /* maximal mdev for the last rtt period */
u32 rttvar; /* smoothed mdev_max */
u32 rtt_seq; /* sequence number to update rttvar */
u32 packets_out; /* Packets which are "in flight" */
u32 retrans_out; /* Retransmitted packets out */
/*
* 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;
struct sk_buff_head out_of_order_queue; /* Out of order segments go here */
u32 rcv_wnd; /* Current receiver window */
u32 write_seq; /* Tail(+1) of data held in tcp send buffer */
u32 pushed_seq; /* Last pushed seq, required to talk to windows */
/* SACKs data */
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; /* highest skb with SACK received
* (validity guaranteed only if
* sacked_out > 0)
*/
/* 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;
int lost_cnt_hint;
int retransmit_cnt_hint;
u32 lost_retrans_low; /* Sent seq after any rxmit (lowest) */
u16 advmss; /* Advertised MSS */
u32 prior_ssthresh; /* ssthresh saved at recovery start */
u32 lost_out; /* Lost packets */
u32 sacked_out; /* SACK'd packets */
u32 fackets_out; /* FACK'd packets */
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; /* tracking retrans started here. */
int undo_retrans; /* number of undoable retransmissions. */
u32 urg_seq; /* Seq of received urgent pointer */
u16 urg_data; /* Saved octet of OOB data and control flags */
u8 urg_mode; /* In urgent mode */
u8 ecn_flags; /* ECN status bits. */
u32 snd_up; /* Urgent pointer */
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 */
unsigned int keepalive_intvl; /* time interval between keep alive probes */
int linger2;
unsigned long last_synq_overflow;
u32 tso_deferred;
/* 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;
#ifdef CONFIG_TCP_MD5SIG
/* TCP AF-Specific parts; only used by MD5 Signature support so far */
struct tcp_sock_af_ops *af_specific;
/* TCP MD5 Signagure Option information */
struct tcp_md5sig_info *md5sig_info;
#endif
};inet_connection_sock中request_sock_queue，既是全连接队列
cpp
struct inet_connection_sock {
/* inet_sock has to be the first member! */
struct inet_sock icsk_inet;
struct request_sock_queue icsk_accept_queue;
struct inet_bind_bucket *icsk_bind_hash;
unsigned long icsk_timeout;
struct timer_list icsk_retransmit_timer;
struct timer_list icsk_delack_timer;
__u32 icsk_rto;
__u32 icsk_pmtu_cookie;
const struct tcp_congestion_ops *icsk_ca_ops;
const struct inet_connection_sock_af_ops *icsk_af_ops;
unsigned int (*icsk_sync_mss)(struct sock *sk, u32 pmtu);
__u8 icsk_ca_state;
__u8 icsk_retransmits;
__u8 icsk_pending;
__u8 icsk_backoff;
__u8 icsk_syn_retries;
__u8 icsk_probes_out;
__u16 icsk_ext_hdr_len;
struct {
__u8 pending; /* ACK is pending */
__u8 quick; /* Scheduled number of quick acks */
__u8 pingpong; /* The session is interactive */
__u8 blocked; /* Delayed ACK was blocked by socket lock */
__u32 ato; /* Predicted tick of soft clock */
unsigned long timeout; /* Currently scheduled timeout */
__u32 lrcvtime; /* timestamp of last received data packet */
__u16 last_seg_size; /* Size of last incoming segment */
__u16 rcv_mss; /* MSS used for delayed ACK decisions */
} icsk_ack;
struct {
int enabled;
/* Range of MTUs to search */
int search_high;
int search_low;
/* Information on the current probe. */
int probe_size;
} icsk_mtup;
u32 icsk_ca_priv[16];
#define ICSK_CA_PRIV_SIZE (16 * sizeof(u32))
};inet_sock首个成员struct sock sk
cpp
struct inet_sock {
/* sk and pinet6 has to be the first two members of inet_sock */
struct sock sk;
#if defined(CONFIG_IPV6) || defined(CONFIG_IPV6_MODULE)
struct ipv6_pinfo *pinet6;
#endif
/* Socket demultiplex comparisons on incoming packets. */
__be32 daddr;
__be32 rcv_saddr;
__be16 dport;
__u16 num;
__be32 saddr;
__s16 uc_ttl;
__u16 cmsg_flags;
struct ip_options *opt;
__be16 sport;
__u16 id;
__u8 tos;
__u8 mc_ttl;
__u8 pmtudisc;
__u8 recverr:1,
is_icsk:1,
freebind:1,
hdrincl:1,
mc_loop:1;
int mc_index;
__be32 mc_addr;
struct ip_mc_socklist *mc_list;
struct {
unsigned int flags;
unsigned int fragsize;
struct ip_options *opt;
struct dst_entry *dst;
int length; /* Total length of all frames */
__be32 addr;
struct flowi fl;
} cork;
};