有一些内核变量（例如tcp_frto）可以通过使用类似sysctl net.ipv4.tcp_frtoor的命令从用户空间访问cat /proc/sys/net/ipv4/tcp_frto。
它可以从 bash 命令行读取和轻松更改。但是我想从我正在编写的内核模块中更改它们。
如何从模块中读取和写入这些变量？
（Linux源代码用于sysctl_tcp_frto访问tcp.h文件中声明的这个变量。也许可以导出变量名然后可以被模块找到，但我不想更改源并再次编译它）。我正在尝试制作可加载内核模块（LKM），而无需每次都编译源代码。
Unless a Linux kernel variable is made global (using EXPORT_SYMBOL or one of its variants) it cannot be read outside its scope.
As there is an alternate means to access tcp_frto using the procfs, you can use VFS functions to do the same from within a Linux kernel module as shown in these sample code snippets.
How this works and why it is generally NOT a good idea (unless except for debugging) is described in detail in this article.