从内核代码的其他部分访问/proc fs变量 [英] Access /proc fs variable from other parts of Kernel code

问题描述

我正在尝试获取一个用户级程序，以通过/proc与内核进行通信.

I'm trying to get a user-level program to communicate with the kernel via /proc.

我按照 tldp 上的说明进行操作，并成功地创建一个自定义proc文件，并使用 insmod 动态加载它，然后从用户区读取(cat)并写入(echo)该proc文件.

I followed the instructions on tldp, and was successfully able to create a custom proc file, load it dynamically with insmod and read (cat) and write (echo) to the proc file from userland.

现在我的问题是，如何从内核的另一部分(例如系统调用基础结构)访问/proc变量(它是字节缓冲区)?由于自定义proc文件是动态加载和链接的，因此如何从静态编译的内核代码中引用它?

Now my question is how do I access the /proc variable (it's a byte buffer) from within another part of the kernel, say the system call infrastructure? Since the custom proc file is dynamically loaded and linked, how can I reference it from statically compiled kernel code?

系统规格:在Mac Pro Fusion 13(2009)上的VMWare Fusion中运行的Ubuntu 10.10.

System specs: Ubuntu 10.10 running in VMWare Fusion on a MacBook Pro 13" (2009).

相关代码(根据要求)-

Pertinent code (by request) -

procfile.c

procfile.c

//This function is called when the module is loaded
int init_module()
{
    /* create the /proc file */

    EXPORT_SYMBOL(procfs_buffer);
    EXPORT_SYMBOL(procfs_buffer_size);
...
...
}

get_procvariable.c(在内核的另一部分)

get_procvariable.c (In another part of the kernel)

//The buffer used to store character for this module
extern char * procfs_buffer;

//The size of the buffer
extern unsigned long procfs_buffer_size;

int get_procvariable(void)
{
.. do something
return procfs_buffer; // LD Error: Undefined reference
}

如果您需要更多详细信息，请在评论中让我知道.预先感谢.

Do let me know in the comments, if you need further details. Thanks in advance.

推荐答案

回答了我自己的问题，并从上面的答案中得到了一些提示:

Answered my own question, taking a few hints from the answers above:

我缺少的关键是我需要在内核本身内声明一个变量(例如int kernel_var = 0;)(而不是在procfs开销模块内声明，因为我之前做错了).之后，使用EXPORT_SYMBOL将其导出，然后将其添加到全局模块符号表中，最后将其作为extern变量包含在开销procfs模块中.

The key thing I was missing was that I needed to declare a variable (say int kernel_var = 0;) within the kernel itself (and not within the procfs overhead module, as I had incorrectly done before). Thereafter export this with EXPORT_SYMBOL, which adds it to the global module symbol table and finally include it in the overhead procfs module as an extern variable.

因此，本质上来说，开销变量已经存在于内核中，我只是使用procfs模块将其作为外部变量引用并修改其值.

So essentially the overhead variable already exists within the kernel and I'm simply using the procfs module to reference it as an extern variable and modify its value.

我对这个假设进行了编码，它就像一个魅力.

I coded out this hypothesis and it worked like a charm.

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