nginx的error log代码分析

[vislee]

概述

error log 记录了nginx系统日志，区别于业务日志。 封装成ngx_errlog_module模块，代码在文件core/ngx_log.h|c中。 ngx_errlog_module 属于核心模块NGX_CORE_MODULE，提供了error_log配置指令。

代码分析

涉及到的结构体：

// 封装打开的文件结构体 定义在core/ngx_conf_file.h 文件中
struct ngx_open_file_s {
    ngx_fd_t              fd;        // 打开的文件描述符
    ngx_str_t             name;

    void                (*flush)(ngx_open_file_t *file, ngx_log_t *log);
    void                 *data;
};

struct ngx_log_s {
    ngx_uint_t           log_level;   // 错误日志等级
    ngx_open_file_t     *file;        // 打开的文件描述结构体

    // 链接的个数下标
    ngx_atomic_uint_t    connection;

    time_t               disk_full_time;

    ngx_log_handler_pt   handler;
    void                *data;

    // 写回调ngx_syslog_writer
    ngx_log_writer_pt    writer;
    // ngx_syslog_peer_t
    void                *wdata;

    /*
     * we declare "action" as "char *" because the actions are usually
     * the static strings and in the "u_char *" case we have to override
     * their types all the time
     */

    char                *action;

    // 形成一个链表
    ngx_log_t           *next;
};

ngx_log.c文件中定义了两个静态变量，static限制了变量的作用域和保存范围。

static ngx_log_t        ngx_log;
static ngx_open_file_t  ngx_log_file;

通过ngx_error_log函数解析error_log配置指令。

涉及到的函数：

ngx_log_t *ngx_log_init(u_char *prefix);   // 初始化定义的静态日志文件结构体
void ngx_log_error_core(ngx_uint_t level, ngx_log_t *log, ngx_err_t err, const char *fmt, ...);  // 
ngx_int_t ngx_log_open_default(ngx_cycle_t *cycle);  // 没有配置error log，则打开默认error log

static char *
ngx_error_log(ngx_conf_t *cf, ngx_command_t *cmd, void *conf)
{
    ngx_log_t  *dummy;

    dummy = &cf->cycle->new_log;

    return ngx_log_set_log(cf, &dummy);
}


char *
ngx_log_set_log(ngx_conf_t *cf, ngx_log_t **head)
{
    ngx_log_t          *new_log;
    ngx_str_t          *value, name;
    ngx_syslog_peer_t  *peer;

    if (*head != NULL && (*head)->log_level == 0) {
        new_log = *head;

    } else {

        new_log = ngx_pcalloc(cf->pool, sizeof(ngx_log_t));
        if (new_log == NULL) {
            return NGX_CONF_ERROR;
        }

        if (*head == NULL) {
            *head = new_log;
        }
    }

    value = cf->args->elts;

    if (ngx_strcmp(value[1].data, "stderr") == 0) {
        ngx_str_null(&name);
        cf->cycle->log_use_stderr = 1;

        new_log->file = ngx_conf_open_file(cf->cycle, &name);
        if (new_log->file == NULL) {
            return NGX_CONF_ERROR;
        }

    } else if (ngx_strncmp(value[1].data, "memory:", 7) == 0) {

#if (NGX_DEBUG)
        size_t                 size, needed;
        ngx_pool_cleanup_t    *cln;
        ngx_log_memory_buf_t  *buf;

        value[1].len -= 7;
        value[1].data += 7;

        needed = sizeof("MEMLOG  :" NGX_LINEFEED)
                 + cf->conf_file->file.name.len
                 + NGX_SIZE_T_LEN
                 + NGX_INT_T_LEN
                 + NGX_MAX_ERROR_STR;

        size = ngx_parse_size(&value[1]);

        if (size == (size_t) NGX_ERROR || size < needed) {
            ngx_conf_log_error(NGX_LOG_EMERG, cf, 0,
                               "invalid buffer size \"%V\"", &value[1]);
            return NGX_CONF_ERROR;
        }

        buf = ngx_pcalloc(cf->pool, sizeof(ngx_log_memory_buf_t));
        if (buf == NULL) {
            return NGX_CONF_ERROR;
        }

        buf->start = ngx_pnalloc(cf->pool, size);
        if (buf->start == NULL) {
            return NGX_CONF_ERROR;
        }

        buf->end = buf->start + size;

        buf->pos = ngx_slprintf(buf->start, buf->end, "MEMLOG %uz %V:%ui%N",
                                size, &cf->conf_file->file.name,
                                cf->conf_file->line);

        ngx_memset(buf->pos, ' ', buf->end - buf->pos);

        cln = ngx_pool_cleanup_add(cf->pool, 0);
        if (cln == NULL) {
            return NGX_CONF_ERROR;
        }

        cln->data = new_log;
        cln->handler = ngx_log_memory_cleanup;

        new_log->writer = ngx_log_memory_writer;
        new_log->wdata = buf;

#else
        ngx_conf_log_error(NGX_LOG_EMERG, cf, 0,
                           "nginx was built without debug support");
        return NGX_CONF_ERROR;
#endif

    } else if (ngx_strncmp(value[1].data, "syslog:", 7) == 0) {
        peer = ngx_pcalloc(cf->pool, sizeof(ngx_syslog_peer_t));
        if (peer == NULL) {
            return NGX_CONF_ERROR;
        }

        if (ngx_syslog_process_conf(cf, peer) != NGX_CONF_OK) {
            return NGX_CONF_ERROR;
        }

        new_log->writer = ngx_syslog_writer;
        new_log->wdata = peer;

    } else {
        new_log->file = ngx_conf_open_file(cf->cycle, &value[1]);
        if (new_log->file == NULL) {
            return NGX_CONF_ERROR;
        }
    }

    if (ngx_log_set_levels(cf, new_log) != NGX_CONF_OK) {
        return NGX_CONF_ERROR;
    }

    if (*head != new_log) {
        ngx_log_insert(*head, new_log);
    }

    return NGX_CONF_OK;
}


void
ngx_log_error_core(ngx_uint_t level, ngx_log_t *log, ngx_err_t err,
    const char *fmt, va_list args)
{
    u_char      *p, *last, *msg;
    ssize_t      n;
    ngx_uint_t   wrote_stderr, debug_connection;
    u_char       errstr[NGX_MAX_ERROR_STR];

    // 2k的buffer
    last = errstr + NGX_MAX_ERROR_STR;
    // 日期时间
    p = ngx_cpymem(errstr, ngx_cached_err_log_time.data,
                   ngx_cached_err_log_time.len);
    // 日志等级
    p = ngx_slprintf(p, last, " [%V] ", &err_levels[level]);

    /* pid#tid */
    p = ngx_slprintf(p, last, "%P#" NGX_TID_T_FMT ": ",
                    ngx_log_pid, ngx_log_tid);

    if (log->connection) {
        p = ngx_slprintf(p, last, "*%uA ", log->connection);
    }

    msg = p;    // 真正的错误消息的开始

    // 错误消息
    p = ngx_vslprintf(p, last, fmt, args);


    if (err) {
        // 发生错误，会展示系统错误
        p = ngx_log_errno(p, last, err);
    }

    if (level != NGX_LOG_DEBUG && log->handler) {
        p = log->handler(log, p, last - p);
    }

    if (p > last - NGX_LINEFEED_SIZE) {
        p = last - NGX_LINEFEED_SIZE;
    }

    // 添加回车换行
    ngx_linefeed(p);

    wrote_stderr = 0;
    debug_connection = (log->log_level & NGX_LOG_DEBUG_CONNECTION) != 0;

    while (log) {

        if (log->log_level < level && !debug_connection) {
            break;
        }

        if (log->writer) {
            log->writer(log, level, errstr, p - errstr);
            goto next;
        }

        if (ngx_time() == log->disk_full_time) {

            goto next;
        }

        n = ngx_write_fd(log->file->fd, errstr, p - errstr);

        if (n == -1 && ngx_errno == NGX_ENOSPC) {
            log->disk_full_time = ngx_time();
        }

        if (log->file->fd == ngx_stderr) {
            wrote_stderr = 1;
        }

    next:

        log = log->next;
    }

    if (!ngx_use_stderr
        || level > NGX_LOG_WARN
        || wrote_stderr)
    {
        return;
    }

    // 需要向标准错误输出日志
    // 用“nginx:[等级]”替换掉开始的“时间 [等级] tid#pid 等

    msg -= (7 + err_levels[level].len + 3);

    (void) ngx_sprintf(msg, "nginx: [%V] ", &err_levels[level]);

    (void) ngx_write_console(ngx_stderr, msg, p - msg);
}