/*
* linux/kernel/printk.c
*
* Copyright (C) 1991, 1992 Linus Torvalds
*
* Modified to make sys_syslog() more flexible: added commands to
* return the last 4k of kernel messages, regardless of whether
* they‘ve been read or not. Added option to suppress kernel printk‘s
* to the console. Added hook for sending the console messages
* elsewhere, in preparation for a serial line console (someday).
* Ted Ts‘o, 2/11/93.
*/
#include <stdarg.h>
#include <asm/segment.h>
#include <asm/system.h>
#include <linux/errno.h>
#include <linux/sched.h>
#include <linux/kernel.h>
#define LOG_BUF_LEN 4096
static char buf[1024];
extern int vsprintf(char * buf, const char * fmt, va_list args);
extern void console_print(const char *);
#define DEFAULT_MESSAGE_LOGLEVEL 7 /* KERN_DEBUG */
#define DEFAULT_CONSOLE_LOGLEVEL 7 /* anything more serious than KERN_DEBUG */
unsigned long log_size = 0;
struct wait_queue * log_wait = NULL;
int console_loglevel = DEFAULT_CONSOLE_LOGLEVEL;
static void (*console_print_proc)(const char *) = 0;
static char log_buf[LOG_BUF_LEN];
static unsigned long log_start = 0;
static unsigned long logged_chars = 0;
/*
* Commands to sys_syslog:
*
* 0 -- Close the log. Currently a NOP. 关闭日志，当前不处理
* 1 -- Open the log. Currently a NOP. 打开日中
* 2 -- Read from the log. 从日志中读取
* 3 -- Read up to the last 4k of messages in the ring buffer. 在环形缓冲区中读取最近的4K消息
* 4 -- Read and clear last 4k of messages in the ring buffer 在环形缓冲区中读取并清空最近的4K消息
* 5 -- Clear ring buffer. 清空环形缓冲区
* 6 -- Disable printk‘s to console 禁制输出消息到控制台
* 7 -- Enable printk‘s to console 使消息输出到控制台
* 8 -- Set level of messages printed to console 设置消息的级别
*/
//系统日志
asmlinkage int sys_syslog(int type, char * buf, int len)
{
unsigned long i, j, count;
int do_clear = 0;
char c;
int error;
//权限检测
if ((type != 3) && !suser())
return -EPERM;
switch (type) {
case 0: /* Close log */
return 0;
case 1: /* Open log */
return 0;
case 2: /* Read from log */
if (!buf || len < 0)
return -EINVAL;
if (!len)
return 0;
//对指定位置进行写权限验证
error = verify_area(VERIFY_WRITE,buf,len);
if (error)
return error;
cli();
//
while (!log_size) {
if (current->signal & ~current->blocked) {
sti();
return -ERESTARTSYS;
}
interruptible_sleep_on(&log_wait);
}
i = 0;
while (log_size && i < len) {
//计算位置
c = *((char *) log_buf+log_start);
log_start++;
log_size--;
log_start &= LOG_BUF_LEN-1;
//开中断
sti();
//写入缓冲区
put_fs_byte(c,buf);
buf++;
i++;
//关中断
cli();
}
sti();
return i;
case 4: /* Read/clear last kernel messages */
do_clear = 1;
/* FALL THRU */
case 3: /* Read last kernel messages */
if (!buf || len < 0)//校验后读取数据，并清空
return -EINVAL;
if (!len)
return 0;
error = verify_area(VERIFY_WRITE,buf,len);
if (error)
return error;
count = len;
if (count > LOG_BUF_LEN)
count = LOG_BUF_LEN;
if (count > logged_chars)
count = logged_chars;
j = log_start + log_size - count;
for (i = 0; i < count; i++) {
c = *((char *) log_buf+(j++ & (LOG_BUF_LEN-1)));
put_fs_byte(c, buf++);
}
if (do_clear)
logged_chars = 0;
return i;
case 5: /* Clear ring buffer */
logged_chars = 0;
return 0;
case 6: /* Disable logging to console */
console_loglevel = 1; /* only panic messages shown */
return 0;
case 7: /* Enable logging to console */
console_loglevel = DEFAULT_CONSOLE_LOGLEVEL;
return 0;
case 8:
if (len < 0 || len > 8)
return -EINVAL;
console_loglevel = len;
return 0;
}
return -EINVAL;
}
//输出
asmlinkage int printk(const char *fmt, ...)
{
va_list args;
int i;
char *msg, *p, *buf_end;
static char msg_level = -1;
long flags;
save_flags(flags);
cli();
va_start(args, fmt);
i = vsprintf(buf + 3, fmt, args); /* hopefully i < sizeof(buf)-4 */
buf_end = buf + 3 + i;
va_end(args);
for (p = buf + 3; p < buf_end; p++) {
msg = p;
//确定日志级别
if (msg_level < 0) {
if (
p[0] != ‘<‘ ||
p[1] < ‘0‘ ||
p[1] > ‘7‘ ||
p[2] != ‘>‘
) {
p -= 3;
p[0] = ‘<‘;
p[1] = DEFAULT_MESSAGE_LOGLEVEL - 1 + ‘0‘;
p[2] = ‘>‘;
} else
msg += 3;
msg_level = p[1] - ‘0‘;
}
//循环拷贝日志内容
for (; p < buf_end; p++) {
log_buf[(log_start+log_size) & (LOG_BUF_LEN-1)] = *p;
if (log_size < LOG_BUF_LEN)
log_size++;
else
log_start++;
logged_chars++;
if (*p == ‘\n‘)
break;
}
//输出到控制台
if (msg_level < console_loglevel && console_print_proc) {
char tmp = p[1];
p[1] = ‘\0‘;
(*console_print_proc)(msg);
p[1] = tmp;
}
if (*p == ‘\n‘)
msg_level = -1;
}
restore_flags(flags);
wake_up_interruptible(&log_wait);
return i;
}
/*
* The console driver calls this routine during kernel initialization
* to register the console printing procedure with printk() and to
* print any messages that were printed by the kernel before the
* console driver was initialized.
*/
//注册控制台输出,参数为函数指针
void register_console(void (*proc)(const char *))
{
int i,j;
int p = log_start;
char buf[16];
char msg_level = -1;
char *q;
//挂接回调函数
console_print_proc = proc;
//
for (i=0,j=0; i < log_size; i++) {
buf[j++] = log_buf[p];
p++; p &= LOG_BUF_LEN-1;
if (buf[j-1] != ‘\n‘ && i < log_size - 1 && j < sizeof(buf)-1)
continue;
buf[j] = 0;
q = buf;
if (msg_level < 0) {
msg_level = buf[1] - ‘0‘;
q = buf + 3;
}
if (msg_level < console_loglevel)
(*proc)(q);
if (buf[j-1] == ‘\n‘)
msg_level = -1;
j = 0;
}
}
kernel/printk.c