发信人: arira(大天使)
整理人: qiaoqian(2001-12-31 00:01:56), 站内信件
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主题：《Linux内核模块编程指南》(十)
发信人: kevintz()
整理人: kevintz(2000-06-24 00:42:52), 站内信件
《Linux内核模块编程指南》
《Linux Kernel Module Programming Guide》
作者：Ori Pomerantz 中译者：谭志([email protected])
译者注：
1、LKMPG是一本免费的书，英文版的发行和修改遵从GPL version 2的许可。为了
节省时间，我只翻译了其中的大部分的大意，或者说这只是我学习中的一些中文
笔记吧，不能算是严格上的翻译，但我认为这已经足够了。本文也允许免费发布
，但发布前请和我联系，但不要把本文用于商业目的。鉴于本人的水平，文章中
难免有错误，请大家不吝指正。
2、本文中的例子在Linux(kernel version 2.2.10)上调试通过。你用的Linux必
须支持内核模块的加载，如果不支持，请在编译内核时选上内核模块的支持或升
级你的内核到一个支持内核模块的版本。
第十章 替换printk's
在刚开始的时候，我提到过X和内核模块编程不要混用的问题。这在内核模块
开发时是正确的。但实际使用上你想能够发信息到运行调用这个模块的程序所在
的终端上。这在内核模块释放以后能够标识错误时就显得很重要了。因为内核模
块被很多进程调用，不同的进程有不同的终端。
实现方法是使用current(一个指向当前运行任务的指针)来取得任务的tty结
构体，然后从tty结构体里找到写字符串到tty的函数指针。
/* printk.c - send textual output to the tty you're
* running on, regardless of whether it's passed
* through X11, telnet, etc. */
/* Copyright (C) 1998 by Ori Pomerantz */
/* The necessary header files */
/* Standard in kernel modules */
#include <linux/kernel.h> /* We're doing kernel work */
#include <linux/module.h> /* Specifically, a module */
/* Deal with CONFIG_MODVERSIONS */
#if CONFIG_MODVERSIONS==1
#define MODVERSIONS
#include <linux/modversions.h>
#endif
/* Necessary here */
#include <linux/sched.h> /* For current */
#include <linux/tty.h> /* For the tty declarations */
/* Print the string to the appropriate tty, the one
* the current task uses */
void print_string(char *str)
{
struct tty_struct *my_tty;
/* The tty for the current task */
my_tty = current->tty;
/* If my_tty is NULL, it means that the current task
* has no tty you can print to (this is possible, for
* example, if it's a daemon). In this case, there's
* nothing we can do. */
if (my_tty != NULL) {
/* my_tty->driver is a struct which holds the tty's
* functions, one of which (write) is used to
* write strings to the tty. It can be used to take
* a string either from the user's memory segment
* or the kernel's memory segment.
*
* The function's first parameter is the tty to
* write to, because the same function would
* normally be used for all tty's of a certain type.
* The second parameter controls whether the
* function receives a string from kernel memory
* (false, 0) or from user memory (true, non zero).
* The third parameter is a pointer to a string,
* and the fourth parameter is the length of
* the string.
*/
(*(my_tty->driver).write)(
my_tty, /* The tty itself */
0, /* We don't take the string from user space */
str, /* String */
strlen(str)); /* Length */
/* ttys were originally hardware devices, which
* (usually) adhered strictly to the ASCII standard.
* According to ASCII, to move to a new line you
* need two characters, a carriage return and a
* line feed. In Unix, on the other hand, the
* ASCII line feed is used for both purposes - so
* we can't just use \n, because it wouldn't have
* a carriage return and the next line will
* start at the column right
* after the line feed.
*
* BTW, this is the reason why the text file
* format is different between Unix and Windows.
* In CP/M and its derivatives, such as MS-DOS and
* Windows, the ASCII standard was strictly
* adhered to, and therefore a new line requires
* both a line feed and a carriage return.
*/
(*(my_tty->driver).write)(
my_tty,
0,
"\015\012",
2);
}
}
/* Module initialization and cleanup ****************** */
/* Initialize the module - register the proc file */
int init_module()
{
print_string("Module Inserted");
return 0;
}
/* Cleanup - unregister our file from /proc */
void cleanup_module()
{
print_string("Module Removed");
}
kevintz注：
有了这个print_string函数调试就方便多了，但它没有printk可变参数的功能，
这是它最大的缺点。下面是我写的一个可接收可变参数的版本。大家可以试试。
static char buff[1024]; /*buffer print_string to write*/
spinlock_t console_lock;
void print_string(const char *fmt, ...)
{
va_list args;
int i;
struct tty_struct *my_tty;
long flags;
spin_lock_irqsave(&console_lock, flags);
/* The tty for the current task */
va_start(args, fmt);
i=vsprintf(buff, fmt, args);
buff[i]=0;
va_end(args);
my_tty = current->tty;
/* If my_tty is NULL, it means that the current task
* has no tty you can print to (this is possible, for
* example, if it's a daemon). In this case, there's
* nothing we can do. */
if (my_tty != NULL) {
(*(my_tty->driver).write)(
my_tty, /* The tty itself */
0, /* We don't take the string from user space */
buff, /* String */
strlen(buff)); /* Length */
(*(my_tty->driver).write)(
my_tty,
0,
"\015\012",
2);
}
spin_unlock_irqrestore(&console_lock, flags);
}
--
那一刹那，我开始用心去看这个世界，所有的事物真的可以看得前
所未有的那么清楚……
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