网络数据发送流程

为了了解TOE，以TCP协议为例子。

以arm平台为例.首先看一下系统调用过程。
系统调用的时候会触发软中断，通过swi指令跳转到指定的入口函数。软中断属于arm异常模式的一种。在linux-.3.4 中，异常向量表的定义在entry-armv.S：

include “calls.S”

    .globl  __vectors_start
__vectors_start:
 ARM(   swi SYS_ERROR0  )
 THUMB( svc #0      )
 THUMB( nop         )
    W(b)    vector_und + stubs_offset
    W(ldr)  pc, .LCvswi + stubs_offset  
    /* ldr vector_swi+stubs_offset*/
    W(b)    vector_pabt + stubs_offset
    W(b)    vector_dabt + stubs_offset
    W(b)    vector_addrexcptn + stubs_offset
    W(b)    vector_irq + stubs_offset
    W(b)    vector_fiq + stubs_offset

    .globl  __vectors_end
__vectors_end:

其中

.LCvswi:
    .word   vector_swi

    .globl  __stubs_end

ENTRY(vector_swi)
    sub sp, sp, #S_FRAME_SIZE
    stmia   sp, {r0 - r12}          @ Calling r0 - r12
 ARM(   add r8, sp, #S_PC       )
 ARM(   stmdb   r8, {sp, lr}^       )   @ Calling sp, lr
 THUMB( mov r8, sp          )
 THUMB( store_user_sp_lr r8, r10, S_SP  )   @ calling sp, lr
    mrs r8, spsr            @ called from non-FIQ mode, so ok.
    str lr, [sp, #S_PC]         @ Save calling PC
    str r8, [sp, #S_PSR]        @ Save CPSR
    str r0, [sp, #S_OLD_R0]     @ Save OLD_R0
    zero_fp
    adr **tbl**, sys_call_table     @ load syscall table pointer

    ldrcc   pc, [tbl, scno, lsl #2]     @ call sys_* routine//查找入口函数表

其中

ENTRY(sys_call_table)
#include "calls.S"

adr tbl, sys_call_table 这句话就把calls.S中的内容都读入到tbl表中，然后根据scno查找入口函数：
calls.S：

/*
 *  linux/arch/arm/kernel/calls.S
 *
 *  Copyright (C) 1995-2005 Russell King
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 as
 * published by the Free Software Foundation.
 *
 *  This file is included thrice in entry-common.S
 */
/* 0 */     CALL(sys_restart_syscall)
        CALL(sys_exit)
        CALL(sys_fork_wrapper)
        CALL(sys_read)
        CALL(sys_write)
/* 5 */     CALL(sys_open)
        CALL(sys_close)
        CALL(sys_ni_syscall)        /* was sys_waitpid */
        CALL(sys_creat)
        CALL(sys_link)
/* 10 */    CALL(sys_unlink)
        CALL(sys_execve_wrapper)
        CALL(sys_chdir)
        CALL(OBSOLETE(sys_time))    /* used by libc4 */
        CALL(sys_mknod)
/* 15 */    CALL(sys_chmod)
        CALL(sys_lchown16)
        CALL(sys_ni_syscall)        /* was sys_break */
        CALL(sys_ni_syscall)        /* was sys_stat */
        CALL(sys_lseek)
/* 20 */    CALL(sys_getpid)
        CALL(sys_mount)
        CALL(OBSOLETE(sys_oldumount))   /* used by libc4 */
        CALL(sys_setuid16)
        CALL(sys_getuid16)
/* 25 */    CALL(OBSOLETE(sys_stime))
        CALL(sys_ptrace)
        CALL(OBSOLETE(sys_alarm))   /* used by libc4 */
        CALL(sys_ni_syscall)        /* was sys_fstat */
        CALL(sys_pause)
/* 30 */    CALL(OBSOLETE(sys_utime))   /* used by libc4 */
        CALL(sys_ni_syscall)        /* was sys_stty */
        CALL(sys_ni_syscall)        /* was sys_getty */
        CALL(sys_access)
        CALL(sys_nice)
/* 35 */    CALL(sys_ni_syscall)        /* was sys_ftime */
        CALL(sys_sync)
        CALL(sys_kill)
        CALL(sys_rename)
        CALL(sys_mkdir)
/* 40 */    CALL(sys_rmdir)
        CALL(sys_dup)
        CALL(sys_pipe)
        CALL(sys_times)
        CALL(sys_ni_syscall)        /* was sys_prof */
/* 45 */    CALL(sys_brk)
        CALL(sys_setgid16)
        CALL(sys_getgid16)
        CALL(sys_ni_syscall)        /* was sys_signal */
        CALL(sys_geteuid16)
/* 50 */    CALL(sys_getegid16)
        CALL(sys_acct)
        CALL(sys_umount)
        CALL(sys_ni_syscall)        /* was sys_lock */
        CALL(sys_ioctl)
/* 55 */    CALL(sys_fcntl)
        CALL(sys_ni_syscall)        /* was sys_mpx */
        CALL(sys_setpgid)
        CALL(sys_ni_syscall)        /* was sys_ulimit */
        CALL(sys_ni_syscall)        /* was sys_olduname */
/* 60 */    CALL(sys_umask)
        CALL(sys_chroot)
        CALL(sys_ustat)
        CALL(sys_dup2)
        CALL(sys_getppid)
/* 65 */    CALL(sys_getpgrp)
        CALL(sys_setsid)
        CALL(sys_sigaction)
        CALL(sys_ni_syscall)        /* was sys_sgetmask */
        CALL(sys_ni_syscall)        /* was sys_ssetmask */
/* 70 */    CALL(sys_setreuid16)
        CALL(sys_setregid16)
        CALL(sys_sigsuspend)
        CALL(sys_sigpending)
        CALL(sys_sethostname)
/* 75 */    CALL(sys_setrlimit)
        CALL(OBSOLETE(sys_old_getrlimit)) /* used by libc4 */
        CALL(sys_getrusage)
        CALL(sys_gettimeofday)
        CALL(sys_settimeofday)
/* 80 */    CALL(sys_getgroups16)
        CALL(sys_setgroups16)
        CALL(OBSOLETE(sys_old_select))  /* used by libc4 */
        CALL(sys_symlink)
        CALL(sys_ni_syscall)        /* was sys_lstat */
/* 85 */    CALL(sys_readlink)
        CALL(sys_uselib)
        CALL(sys_swapon)
        CALL(sys_reboot)
        CALL(OBSOLETE(sys_old_readdir)) /* used by libc4 */
/* 90 */    CALL(OBSOLETE(sys_old_mmap))    /* used by libc4 */
        CALL(sys_munmap)
        CALL(sys_truncate)
        CALL(sys_ftruncate)
        CALL(sys_fchmod)
/* 95 */    CALL(sys_fchown16)
        CALL(sys_getpriority)
        CALL(sys_setpriority)
        CALL(sys_ni_syscall)        /* was sys_profil */
        CALL(sys_statfs)
/* 100 */   CALL(sys_fstatfs)
        CALL(sys_ni_syscall)        /* sys_ioperm */
        CALL(OBSOLETE(ABI(sys_socketcall, sys_oabi_socketcall)))
        CALL(sys_syslog)
        CALL(sys_setitimer)
/* 105 */   CALL(sys_getitimer)
        CALL(sys_newstat)
        CALL(sys_newlstat)
        CALL(sys_newfstat)
        CALL(sys_ni_syscall)        /* was sys_uname */
/* 110 */   CALL(sys_ni_syscall)        /* was sys_iopl */
        CALL(sys_vhangup)
        CALL(sys_ni_syscall)
        CALL(OBSOLETE(sys_syscall)) /* call a syscall */
        CALL(sys_wait4)
/* 115 */   CALL(sys_swapoff)
        CALL(sys_sysinfo)
        CALL(OBSOLETE(ABI(sys_ipc, sys_oabi_ipc)))
        CALL(sys_fsync)
        CALL(sys_sigreturn_wrapper)
/* 120 */   CALL(sys_clone_wrapper)
        CALL(sys_setdomainname)
        CALL(sys_newuname)
        CALL(sys_ni_syscall)        /* modify_ldt */
        CALL(sys_adjtimex)
/* 125 */   CALL(sys_mprotect)
        CALL(sys_sigprocmask)
        CALL(sys_ni_syscall)        /* was sys_create_module */
        CALL(sys_init_module)
        CALL(sys_delete_module)
/* 130 */   CALL(sys_ni_syscall)        /* was sys_get_kernel_syms */
        CALL(sys_quotactl)
        CALL(sys_getpgid)
        CALL(sys_fchdir)
        CALL(sys_bdflush)
/* 135 */   CALL(sys_sysfs)
        CALL(sys_personality)
        CALL(sys_ni_syscall)        /* reserved for afs_syscall */
        CALL(sys_setfsuid16)
        CALL(sys_setfsgid16)
/* 140 */   CALL(sys_llseek)
        CALL(sys_getdents)
        CALL(sys_select)
        CALL(sys_flock)
        CALL(sys_msync)
/* 145 */   CALL(sys_readv)
        CALL(sys_writev)
        CALL(sys_getsid)
        CALL(sys_fdatasync)
        CALL(sys_sysctl)
/* 150 */   CALL(sys_mlock)
        CALL(sys_munlock)
        CALL(sys_mlockall)
        CALL(sys_munlockall)
        CALL(sys_sched_setparam)
/* 155 */   CALL(sys_sched_getparam)
        CALL(sys_sched_setscheduler)
        CALL(sys_sched_getscheduler)
        CALL(sys_sched_yield)
        CALL(sys_sched_get_priority_max)
/* 160 */   CALL(sys_sched_get_priority_min)
        CALL(sys_sched_rr_get_interval)
        CALL(sys_nanosleep)
        CALL(sys_mremap)
        CALL(sys_setresuid16)
/* 165 */   CALL(sys_getresuid16)
        CALL(sys_ni_syscall)        /* vm86 */
        CALL(sys_ni_syscall)        /* was sys_query_module */
        CALL(sys_poll)
        CALL(sys_ni_syscall)        /* was nfsservctl */
/* 170 */   CALL(sys_setresgid16)
        CALL(sys_getresgid16)
        CALL(sys_prctl)
        CALL(sys_rt_sigreturn_wrapper)
        CALL(sys_rt_sigaction)
/* 175 */   CALL(sys_rt_sigprocmask)
        CALL(sys_rt_sigpending)
        CALL(sys_rt_sigtimedwait)
        CALL(sys_rt_sigqueueinfo)
        CALL(sys_rt_sigsuspend)
/* 180 */   CALL(ABI(sys_pread64, sys_oabi_pread64))
        CALL(ABI(sys_pwrite64, sys_oabi_pwrite64))
        CALL(sys_chown16)
        CALL(sys_getcwd)
        CALL(sys_capget)
/* 185 */   CALL(sys_capset)
        CALL(sys_sigaltstack_wrapper)
        CALL(sys_sendfile)
        CALL(sys_ni_syscall)        /* getpmsg */
        CALL(sys_ni_syscall)        /* putpmsg */
/* 190 */   CALL(sys_vfork_wrapper)
        CALL(sys_getrlimit)
        CALL(sys_mmap2)
        CALL(ABI(sys_truncate64, sys_oabi_truncate64))
        CALL(ABI(sys_ftruncate64, sys_oabi_ftruncate64))
/* 195 */   CALL(ABI(sys_stat64, sys_oabi_stat64))
        CALL(ABI(sys_lstat64, sys_oabi_lstat64))
        CALL(ABI(sys_fstat64, sys_oabi_fstat64))
        CALL(sys_lchown)
        CALL(sys_getuid)
/* 200 */   CALL(sys_getgid)
        CALL(sys_geteuid)
        CALL(sys_getegid)
        CALL(sys_setreuid)
        CALL(sys_setregid)
/* 205 */   CALL(sys_getgroups)
        CALL(sys_setgroups)
        CALL(sys_fchown)
        CALL(sys_setresuid)
        CALL(sys_getresuid)
/* 210 */   CALL(sys_setresgid)
        CALL(sys_getresgid)
        CALL(sys_chown)
        CALL(sys_setuid)
        CALL(sys_setgid)
/* 215 */   CALL(sys_setfsuid)
        CALL(sys_setfsgid)
        CALL(sys_getdents64)
        CALL(sys_pivot_root)
        CALL(sys_mincore)
/* 220 */   CALL(sys_madvise)
        CALL(ABI(sys_fcntl64, sys_oabi_fcntl64))
        CALL(sys_ni_syscall) /* TUX */
        CALL(sys_ni_syscall)
        CALL(sys_gettid)
/* 225 */   CALL(ABI(sys_readahead, sys_oabi_readahead))
        CALL(sys_setxattr)
        CALL(sys_lsetxattr)
        CALL(sys_fsetxattr)
        CALL(sys_getxattr)
/* 230 */   CALL(sys_lgetxattr)
        CALL(sys_fgetxattr)
        CALL(sys_listxattr)
        CALL(sys_llistxattr)
        CALL(sys_flistxattr)
/* 235 */   CALL(sys_removexattr)
        CALL(sys_lremovexattr)
        CALL(sys_fremovexattr)
        CALL(sys_tkill)
        CALL(sys_sendfile64)
/* 240 */   CALL(sys_futex)
        CALL(sys_sched_setaffinity)
        CALL(sys_sched_getaffinity)
        CALL(sys_io_setup)
        CALL(sys_io_destroy)
/* 245 */   CALL(sys_io_getevents)
        CALL(sys_io_submit)
        CALL(sys_io_cancel)
        CALL(sys_exit_group)
        CALL(sys_lookup_dcookie)
/* 250 */   CALL(sys_epoll_create)
        CALL(ABI(sys_epoll_ctl, sys_oabi_epoll_ctl))
        CALL(ABI(sys_epoll_wait, sys_oabi_epoll_wait))
        CALL(sys_remap_file_pages)
        CALL(sys_ni_syscall)    /* sys_set_thread_area */
/* 255 */   CALL(sys_ni_syscall)    /* sys_get_thread_area */
        CALL(sys_set_tid_address)
        CALL(sys_timer_create)
        CALL(sys_timer_settime)
        CALL(sys_timer_gettime)
/* 260 */   CALL(sys_timer_getoverrun)
        CALL(sys_timer_delete)
        CALL(sys_clock_settime)
        CALL(sys_clock_gettime)
        CALL(sys_clock_getres)
/* 265 */   CALL(sys_clock_nanosleep)
        CALL(sys_statfs64_wrapper)
        CALL(sys_fstatfs64_wrapper)
        CALL(sys_tgkill)
        CALL(sys_utimes)
/* 270 */   CALL(sys_arm_fadvise64_64)
        CALL(sys_pciconfig_iobase)
        CALL(sys_pciconfig_read)
        CALL(sys_pciconfig_write)
        CALL(sys_mq_open)
/* 275 */   CALL(sys_mq_unlink)
        CALL(sys_mq_timedsend)
        CALL(sys_mq_timedreceive)
        CALL(sys_mq_notify)
        CALL(sys_mq_getsetattr)
/* 280 */   CALL(sys_waitid)
        CALL(sys_socket)
        CALL(ABI(sys_bind, sys_oabi_bind))
        CALL(ABI(sys_connect, sys_oabi_connect))
        CALL(sys_listen)
/* 285 */   CALL(sys_accept)
        CALL(sys_getsockname)
        CALL(sys_getpeername)
        CALL(sys_socketpair)
        CALL(sys_send)
/* 290 */   CALL(ABI(sys_sendto, sys_oabi_sendto))
        CALL(sys_recv)
        CALL(sys_recvfrom)
        CALL(sys_shutdown)
        CALL(sys_setsockopt)
/* 295 */   CALL(sys_getsockopt)
        CALL(ABI(sys_sendmsg, sys_oabi_sendmsg))
        CALL(sys_recvmsg)
        CALL(ABI(sys_semop, sys_oabi_semop))
        CALL(sys_semget)
/* 300 */   CALL(sys_semctl)
        CALL(sys_msgsnd)
        CALL(sys_msgrcv)
        CALL(sys_msgget)
        CALL(sys_msgctl)
/* 305 */   CALL(sys_shmat)
        CALL(sys_shmdt)
        CALL(sys_shmget)
        CALL(sys_shmctl)
        CALL(sys_add_key)
/* 310 */   CALL(sys_request_key)
        CALL(sys_keyctl)
        CALL(ABI(sys_semtimedop, sys_oabi_semtimedop))
/* vserver */   CALL(sys_ni_syscall)
        CALL(sys_ioprio_set)
/* 315 */   CALL(sys_ioprio_get)
        CALL(sys_inotify_init)
        CALL(sys_inotify_add_watch)
        CALL(sys_inotify_rm_watch)
        CALL(sys_mbind)
/* 320 */   CALL(sys_get_mempolicy)
        CALL(sys_set_mempolicy)
        CALL(sys_openat)
        CALL(sys_mkdirat)
        CALL(sys_mknodat)
/* 325 */   CALL(sys_fchownat)
        CALL(sys_futimesat)
        CALL(ABI(sys_fstatat64,  sys_oabi_fstatat64))
        CALL(sys_unlinkat)
        CALL(sys_renameat)
/* 330 */   CALL(sys_linkat)
        CALL(sys_symlinkat)
        CALL(sys_readlinkat)
        CALL(sys_fchmodat)
        CALL(sys_faccessat)
/* 335 */   CALL(sys_pselect6)
        CALL(sys_ppoll)
        CALL(sys_unshare)
        CALL(sys_set_robust_list)
        CALL(sys_get_robust_list)
/* 340 */   CALL(sys_splice)
        CALL(sys_sync_file_range2)
        CALL(sys_tee)
        CALL(sys_vmsplice)
        CALL(sys_move_pages)
/* 345 */   CALL(sys_getcpu)
        CALL(sys_epoll_pwait)
        CALL(sys_kexec_load)
        CALL(sys_utimensat)
        CALL(sys_signalfd)
/* 350 */   CALL(sys_timerfd_create)
        CALL(sys_eventfd)
        CALL(sys_fallocate)
        CALL(sys_timerfd_settime)
        CALL(sys_timerfd_gettime)
/* 355 */   CALL(sys_signalfd4)
        CALL(sys_eventfd2)
        CALL(sys_epoll_create1)
        CALL(sys_dup3)
        CALL(sys_pipe2)
/* 360 */   CALL(sys_inotify_init1)
        CALL(sys_preadv)
        CALL(sys_pwritev)
        CALL(sys_rt_tgsigqueueinfo)
        CALL(sys_perf_event_open)
/* 365 */   CALL(sys_recvmmsg)
        CALL(sys_accept4)
        CALL(sys_fanotify_init)
        CALL(sys_fanotify_mark)
        CALL(sys_prlimit64)
/* 370 */   CALL(sys_name_to_handle_at)
        CALL(sys_open_by_handle_at)
        CALL(sys_clock_adjtime)
        CALL(sys_syncfs)
        CALL(sys_sendmmsg)
/* 375 */   CALL(sys_setns)
        CALL(sys_process_vm_readv)
        CALL(sys_process_vm_writev)
#ifndef syscalls_counted
.equ syscalls_padding, ((NR_syscalls + 3) & ~3) - NR_syscalls
#define syscalls_counted
#endif
.rept syscalls_padding
        CALL(sys_ni_syscall)
.endr

比如，我们用户程序执行了socket，最终就是调用到这里的sys_socket.
CALL(sys_socket)
sys_socket定义在 net/core.c

SYSCALL_DEFINE3(socket, int, family, int, type, int, protocol)
{
    int retval;
    struct socket *sock;
    int flags;

    /* Check the SOCK_* constants for consistency.  */
    BUILD_BUG_ON(SOCK_CLOEXEC != O_CLOEXEC);
    BUILD_BUG_ON((SOCK_MAX | SOCK_TYPE_MASK) != SOCK_TYPE_MASK);
    BUILD_BUG_ON(SOCK_CLOEXEC & SOCK_TYPE_MASK);
    BUILD_BUG_ON(SOCK_NONBLOCK & SOCK_TYPE_MASK);

    flags = type & ~SOCK_TYPE_MASK;
    if (flags & ~(SOCK_CLOEXEC | SOCK_NONBLOCK))
        return -EINVAL;
    type &= SOCK_TYPE_MASK;

    if (SOCK_NONBLOCK != O_NONBLOCK && (flags & SOCK_NONBLOCK))
        flags = (flags & ~SOCK_NONBLOCK) | O_NONBLOCK;

    retval = sock_create(family, type, protocol, &sock);
    if (retval < 0)
        goto out;

    retval = sock_map_fd(sock, flags & (O_CLOEXEC | O_NONBLOCK));
    if (retval < 0)
        goto out_release;

out:
    /* It may be already another descriptor 8) Not kernel problem. net_rx_ation */
    return retval;

out_release:
    sock_release(sock);
    return retval;
}

其他系统调用过程，与之类似。

下面看看网络相关的系统调用吧
socket->sys_socket
sys_socket–>sock_create(family, type, protocol, &sock);
—> retval = sock_map_fd(sock, flags & (O_CLOEXEC | O_NONBLOCK));
其中
sock_create最终就会调用到对应的协议簇的create，如PF_INET，将会执行net_families[PF_INET]的creat函数。