syslog

peng.1981.china

源代码分析
#include
#include
#include
#include
#include
#if 0
#include "syslog.h"
#include "pathnames.h"
#endif
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#define _PATH_LOGNAME "/dev/log"

/* 日志文件句柄
*  文件句柄是全局的，存在于整理应用程序的生命周期
*/
static int LogFile = -1;  /* fd for log */
static int connected;  /* have done connect */
static int LogStat = 0;  /* status bits, set by openlog() */
static const char *LogTag = "syslog"; /* string to tag the entry with */
static int LogFacility = LOG_USER; /* default facility code */
void
syslog(int pri, const char *fmt, ...)
{
va_list ap;
va_start(ap, fmt);
vsyslog(pri, fmt, ap);
va_end(ap);
}
void
vsyslog(pri, fmt, ap)
int pri;
const char *fmt;
va_list ap;
{
register int cnt;
register char *p;
time_t now;
int fd, saved_errno;
int result;
char tbuf[2048], fmt_cpy[1024], *stdp = (char *) 0;
saved_errno = errno;
/* see if we should just throw out this message */
/* 如果这个消息异常，则退出*/
if (!LOG_MASK(LOG_PRI(pri)) || (pri &~ (LOG_PRIMASK|LOG_FACMASK)))
  return;
  
/* 判断是否打开日志文件， 如果没有， 则打开日志 */
if (LogFile %.15s 表示消息级别以及时间 */
(void)sprintf(tbuf, "%.15s ", pri, ctime(&now) + 4);

/* 移动到字符串尾 */
for (p = tbuf; *p; ++p);
if (LogStat & LOG_PERROR)
  stdp = p;
if (LogTag) {
  /* 如果存在标签，则添加标签到字符串尾 */
  (void)strcpy(p, LogTag);
  for (; *p; ++p);
}
if (LogStat & LOG_PID) {
  /* 如果要添加进程ID,则添加进程ID到字符串尾*/
  (void)sprintf(p, "[%d]", getpid());
  for (; *p; ++p);
}
if (LogTag) {
  /* 如果存在标签, 则添加':'和空格*/
  *p++ = ':';
  *p++ = ' ';
}
/* substitute error message for %m */
/* 用错误信息替换 %m */
{
  register char ch, *t1, *t2;
  char *strerror();
  for (t1 = fmt_cpy;
       (ch = *fmt) != '\0' && t1iov_base = stdp;
  v->iov_len = cnt - (stdp - tbuf);
  ++v;
  v->iov_base = "\n";
  v->iov_len = 1;
  (void)writev(2, iov, 2);
}
/* output the message to the local logger */
/* 输出消息到本地的日志服务器 */
result = write(LogFile, tbuf, cnt + 1);
if (result == -1
     && (errno == ECONNRESET || errno == ENOTCONN || errno == ECONNREFUSED)) {
  closelog();
  openlog(LogTag, LogStat | LOG_NDELAY, LogFacility);
  result = write(LogFile, tbuf, cnt + 1);
}
if (result >= 0 || !(LogStat&LOG_CONS))
  return;
/*
  * output the message to the console; don't worry about
  * blocking, if console blocks everything will.
  */
if ((fd = open(_PATH_CONSOLE, O_WRONLY|O_NOCTTY, 0)) ') + 1;
(void)write(fd, p, cnt - (p - tbuf));
(void)close(fd);
}
#ifndef TESTING
static struct sockaddr SyslogAddr; /* AF_UNIX address of local logger */
#endif
/*
* OPENLOG -- open system log
*/
void
openlog(ident, logstat, logfac)
const char *ident;
int logstat, logfac;
{
if (ident != NULL)
  LogTag = ident;
LogStat = logstat;
#ifdef ALLOW_KERNEL_LOGGING
if ((logfac &~ LOG_FACMASK) == 0)
#else
if (logfac != 0 && (logfac &~ LOG_FACMASK) == 0)
#endif
  LogFacility = logfac;
#ifndef TESTING
if (LogFile == -1) {
  SyslogAddr.sa_family = AF_UNIX;
  strncpy(SyslogAddr.sa_data, _PATH_LOGNAME,
      sizeof(SyslogAddr.sa_data));
  if (LogStat & LOG_NDELAY) {
   LogFile = socket(AF_UNIX, SOCK_DGRAM, 0);
/*   fcntl(LogFile, F_SETFD, 1); */
  }
}
if (LogFile != -1 && !connected &&
     connect(LogFile, &SyslogAddr, sizeof(SyslogAddr.sa_family)+
   strlen(SyslogAddr.sa_data)) != -1)
#else
   LogFile = fileno(stdout);
#endif
  connected = 1;
}
/*
* CLOSELOG -- close the system log
*/
void
closelog()
{
#ifndef TESTING
(void) close(LogFile);
#endif
LogFile = -1;
connected = 0;
}
static int LogMask = 0xff;  /* mask of priorities to be logged */
/*
* SETLOGMASK -- set the log mask level
*/
int
setlogmask(pmask)
int pmask;
{
int omask;
omask = LogMask;
if (pmask != 0)
  LogMask = pmask;
return (omask);
}



本文来自ChinaUnix博客，如果查看原文请点：http://blog.chinaunix.net/u2/69931/showart_734185.html