Nginx日志详解

Nginx日志系统由两条指令开启error_log、access_log

error_log  logs/error.log debug;

http {
    ...
    access_log  logs/access.log  main;
    ...
}

具体配置可以参考error_log跟access_log

首先来看一下关于日志的几个宏定义

filename:log.h
#if (NGX_HAVE_C99_VARIADIC_MACROS)

#define NGX_HAVE_VARIADIC_MACROS  1

#define ngx_log_error(level, log, ...)                                        
    if ((log)->log_level >= level) ngx_log_error_core(level, log, __VA_ARGS__)

void ngx_log_error_core(ngx_uint_t level, ngx_log_t *log, ngx_err_t err,
    const char *fmt, ...);

#define ngx_log_debug(level, log, ...)                                        
    if ((log)->log_level & level)                                             
        ngx_log_error_core(NGX_LOG_DEBUG, log, __VA_ARGS__)



#elif (NGX_HAVE_GCC_VARIADIC_MACROS)

#define NGX_HAVE_VARIADIC_MACROS  1

#define ngx_log_error(level, log, args...)                                    
    if ((log)->log_level >= level) ngx_log_error_core(level, log, args)

void ngx_log_error_core(ngx_uint_t level, ngx_log_t *log, ngx_err_t err,
    const char *fmt, ...);

#define ngx_log_debug(level, log, args...)                                    
    if ((log)->log_level & level)                                             
        ngx_log_error_core(NGX_LOG_DEBUG, log, args)



#else 

#define NGX_HAVE_VARIADIC_MACROS  0

void ngx_cdecl ngx_log_error(ngx_uint_t level, ngx_log_t *log, ngx_err_t err,
    const char *fmt, ...);
void ngx_log_error_core(ngx_uint_t level, ngx_log_t *log, ngx_err_t err,
    const char *fmt, va_list args);
void ngx_cdecl ngx_log_debug_core(ngx_log_t *log, ngx_err_t err,
    const char *fmt, ...);


#endif 

从上面的定义可以看出，实现日志功能的核心在于ngx_log_error_core函数，接下来我们就来看看这个函数的实现

#if (NGX_HAVE_VARIADIC_MACROS)

void
ngx_log_error_core(ngx_uint_t level, ngx_log_t *log, ngx_err_t err,
    const char *fmt, ...)

#else

void
ngx_log_error_core(ngx_uint_t level, ngx_log_t *log, ngx_err_t err,
    const char *fmt, va_list args)

#endif
{
#if (NGX_HAVE_VARIADIC_MACROS)
    va_list      args;
#endif
    u_char      *p, *last, *msg;
    ssize_t      n;
    ngx_uint_t   wrote_stderr, debug_connection;
    u_char       errstr[NGX_MAX_ERROR_STR];

    last = errstr + NGX_MAX_ERROR_STR;

    p = ngx_cpymem(errstr, ngx_cached_err_log_time.data,
                   ngx_cached_err_log_time.len);

    p = ngx_slprintf(p, last, " [%V] ", &err_levels[level]);

    
    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;

#if (NGX_HAVE_VARIADIC_MACROS)

    va_start(args, fmt);
    p = ngx_vslprintf(p, last, fmt, args);
    va_end(args);

#else

    p = ngx_vslprintf(p, last, fmt, args);

#endif

    if (err) {
        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;
    }

    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;
    }

    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);
}

1. 从代码中可以看出，nginx的作者对于变参处理还是很细心的，把各种情况都考虑到了，在处理好变参定义之后，就开始初始化字符串格式：

p = ngx_cpymem(errstr, ngx_cached_err_log_time.data,
ngx_cached_err_log_time.len);

p = ngx_slprintf(p, last, " [%V] ", &err_levels[level]);

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);
}

2. 处理变参参数，将变参的值复制到日志串中：

#if (NGX_HAVE_VARIADIC_MACROS)

    va_start(args, fmt);
    p = ngx_vslprintf(p, last, fmt, args);
    va_end(args);

#else

    p = ngx_vslprintf(p, last, fmt, args);

#endif

3. 处理错误号跟换行：

if (err) {
    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;
}
ngx_linefeed(p);

4. 最后就是将日志串输出到文件或者标准错误流