nginx源码分析—处理继承的sockets

作者：阿波
链接：http://blog.csdn.net/livelylittlefish/article/details/7277607

Content

0.序

1.侦听结构

2. ngx_add_inherited_sockets()分析

3. ngx_set_inherited_sockets()分析

4.小结

0.序

本文将着重分析初始化过程中如何处理继承的sockets。文中如无特别说明，.表示nginx-1.0.4代码目录，本文为/usr/src/nginx-1.0.4。

1.侦听结构

侦听结构较为复杂，描述如下。

file: ./src/core/ngx_connection.h

typedef struct ngx_listening_s  ngx_listening_t;

struct ngx_listening_s {
    ngx_socket_t        fd;         /* 文件描述符,即socket */

    struct sockaddr    *sockaddr;   /* socket地址 */
    socklen_t           socklen;    /* size of sockaddr */
    size_t              addr_text_max_len;
    ngx_str_t           addr_text;

    int                 type;

    int                 backlog;
    int                 rcvbuf;     /* 接收缓冲区 */
    int                 sndbuf;     /* 发送缓冲区 */

    /* handler of accepted connection */
    ngx_connection_handler_pt   handler;

    void               *servers;  /* array of ngx_http_in_addr_t, for example */

    ngx_log_t           log;
    ngx_log_t          *logp;

    size_t              pool_size;
    /* should be here because of the AcceptEx() preread */
    size_t              post_accept_buffer_size;
    /* should be here because of the deferred accept */
    ngx_msec_t          post_accept_timeout;

    ngx_listening_t    *previous;   /* 指向前一个ngx_listening_t结构 */
    ngx_connection_t   *connection;

    unsigned            open:1;
    unsigned            remain:1;
    unsigned            ignore:1;

    unsigned            bound:1;       /* already bound */
    unsigned            inherited:1;   /* inherited from previous process */
    unsigned            nonblocking_accept:1;
    unsigned            listen:1;
    unsigned            nonblocking:1;
    unsigned            shared:1;    /* shared between threads or processes */
    unsigned            addr_ntop:1;

#if (NGX_HAVE_INET6 && defined IPV6_V6ONLY)
    unsigned            ipv6only:2;
#endif

#if (NGX_HAVE_DEFERRED_ACCEPT)
    unsigned            deferred_accept:1;
    unsigned            delete_deferred:1;
    unsigned            add_deferred:1;
#ifdef SO_ACCEPTFILTER
    char               *accept_filter;
#endif
#endif
#if (NGX_HAVE_SETFIB)
    int                 setfib;
#endif

};

sizeof(ngx_listening_t)=184。结构如下图。

ngx_listening_t与ngx_connection_t之间的关系如下图。

2. ngx_add_inherited_sockets()分析

该函数通过解析环境变量NGINX_VAR="NGINX"，将其中的socket number保存至ngx_cycle.listening数组，该数组元素类型为ngx_listening_t。这些socekts在环境变量中以':'或';'隔开。

例如，为调试方便，设环境变量NGINX为如下值

# export NGINX="16000:16500:16600;"

注意：当然，后续的测试并不一定会成功，此处只是为了分析该函数。例如，可能会出现如下错误。

nginx: [crit] getsockname() of the inherited socket #16000 failed (9: Bad file descriptor)

nginx: [crit] getsockname() of the inherited socket #16500 failed (9: Bad file descriptor)

nginx: [crit] getsockname() of the inherited socket #16600 failed (9: Bad file descriptor)

/* 传入该参数的是init_cycle,调用ngx_init_cycle()后全局变量ngx_cycle会指向该结构 */
static ngx_int_t
ngx_add_inherited_sockets(ngx_cycle_t *cycle)
{
    u_char           *p, *v, *inherited;
    ngx_int_t         s;
    ngx_listening_t  *ls;

    inherited = (u_char *) getenv(NGINX_VAR);  /* NGINX_VAR为宏，值为"NGINX" */

    if (inherited == NULL) {
        return NGX_OK;
    }

    ngx_log_error(NGX_LOG_NOTICE, cycle->log, 0,
                  "using inherited sockets from \"%s\"", inherited);

    if (ngx_array_init(&cycle->listening, cycle->pool, 10,
                       sizeof(ngx_listening_t))
        != NGX_OK)  /* 初始化ngx_cycle.listening数组, 10个元素空间 */
    {
        return NGX_ERROR;
    }

    for (p = inherited, v = p; *p; p++) {
        if (*p == ':' || *p == ';') {  /* sockets以':'或者';'隔开 */
            s = ngx_atoi(v, p - v);    /* sockets是10进制正整数 */
            if (s == NGX_ERROR) {
                ngx_log_error(NGX_LOG_EMERG, cycle->log, 0,
                              "invalid socket number \"%s\" in " NGINX_VAR
                              " environment variable, ignoring the rest"
                              " of the variable", v);
                break;
            }

            /* 第一次满足该条件时v和p分别指向如下值，此时解析出s=16000 
               (gdb) p v
               $6 = (u_char *) 0x6b0139 "16000:16500:16600;"
               (gdb) p p
               $7 = (u_char *) 0x6b013e ":16500:16600;"
            */
            v = p + 1;

            ls = ngx_array_push(&cycle->listening);  /* 将合法的socket number加入该数组*/
            if (ls == NULL) {
                return NGX_ERROR;
            }

            ngx_memzero(ls, sizeof(ngx_listening_t));

            ls->fd = (ngx_socket_t) s;  /* 保存该socket至listening数组元素的fd字段 */
        }
    }

    ngx_inherited = 1;

    return ngx_set_inherited_sockets(cycle);  /* 该函数逐一设置cycle->listening数组每个元素 */
}

调试过程中，得到以下信息，供参考。

(gdb) p cycle->listening
$11 = {elts = 0x6b02a0, nelts = 3, size = 184, nalloc = 10, pool = 0x6af650}
(gdb) x/w 0x6b02a0
0x6b02a0:       16000
(gdb) x/w 0x6b0358
0x6b0358:       16500
(gdb) x/w 0x6b0410
0x6b0410:       16600

可以验证，0x6b0358-0x6b02a0=0xB8=184，0x6b0410-0x6b0358=0xB8=184。

3. ngx_set_inherited_sockets()分析

该函数从参数cycle(后续调用ngx_init_cycle()函数后全局变量ngx_cycle会指向该参数)的listening数组中逐一对每个元素(ngx_listening_t结构)进行初始化，即初始化除fd字段外的其他的字段。

因此，ngx_set_inherited_sockets()函数主要完成以下事情。

对全局变量ngx_cycle的listening数组，逐一设置该数组每个元素的以下字段

ls[i].sockaddr (调用getsockname())
ls[i].addr_text_max_len
ls[i].addr_text
ls[i].backlog
ls[i].rcvbuf (调用getsockopt())
ls[i].sndbuf (调用getsockopt())
ls[i].accept_filter
ls[i].deferred_accept

涉及到的相关系统函数调用如下。

getenv()获取环境变量，并返回指向该值字符串的指针；

getsockname()获取socket名字(地址及长度)；
getsockopt()获取socket选项；

具体请参考附录或者源代码。

4.小结

本文主要分析初始化过程中如何处理继承的sockets。

Reference

# man getenv

# mangetsockopt

# man getsockname

nginx源码分析—处理继承的sockets

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