module_param和module_param_named定义在<linux/moduleparam.h>文件：
/**
* module_param - typesafe helper for a module/cmdline parameter
* @value: the variable to alter, and exposed parameter name.
* @type: the type of the parameter
* @perm: visibility in sysfs.
*
* @value becomes the module parameter, or (prefixed by KBUILD_MODNAME and a
* ".") the kernel commandline parameter. Note that - is changed to _, so
* the user can use "foo-bar=1" even for variable "foo_bar".
*
* @perm is 0 if the the variable is not to appear in sysfs, or 0444
* for world-readable, 0644 for root-writable, etc. Note that if it
* is writable, you may need to use kparam_block_sysfs_write() around
* accesses (esp. charp, which can be kfreed when it changes).
*
* The @type is simply pasted to refer to a param_ops_##type and a
* param_check_##type: for convenience many standard types are provided but
* you can create your own by defining those variables.
*
* Standard types are:
* byte, short, ushort, int, uint, long, ulong
* charp: a character pointer
* bool: a bool, values 0/1, y/n, Y/N.
* invbool: the above, only sense-reversed (N = true).
*/
#define module_param(name, type, perm) \
module_param_named(name, name, type, perm)
/**
* module_param_named - typesafe helper for a renamed module/cmdline parameter
* @name: a valid C identifier which is the parameter name.
* @value: the actual lvalue to alter.
* @type: the type of the parameter
* @perm: visibility in sysfs.
*
* Usually it's a good idea to have variable names and user-exposed names the
* same, but that's harder if the variable must be non-static or is inside a
* structure. This allows exposure under a different name.
*/
#define module_param_named(name, value, type, perm) \
param_check_##type(name, &(value)); \
module_param_cb(name, ¶m_ops_##type, &value, perm); \
__MODULE_PARM_TYPE(name, #type)
module_param用来定义一个模块参数，type指定类型（int，bool等等），perm指定用户访问权限，取值如下（<linux/stat.h>）：
#define S_IRWXU 00700
#define S_IRUSR 00400
#define S_IWUSR 00200
#define S_IXUSR 00100
#define S_IRWXG 00070
#define S_IRGRP 00040
#define S_IWGRP 00020
#define S_IXGRP 00010
#define S_IRWXO 00007
#define S_IROTH 00004
#define S_IWOTH 00002
#define S_IXOTH 00001
#define S_IRWXUGO (S_IRWXU|S_IRWXG|S_IRWXO)
#define S_IALLUGO (S_ISUID|S_ISGID|S_ISVTX|S_IRWXUGO)
#define S_IRUGO (S_IRUSR|S_IRGRP|S_IROTH)
#define S_IWUGO (S_IWUSR|S_IWGRP|S_IWOTH)
#define S_IXUGO (S_IXUSR|S_IXGRP|S_IXOTH)
module_param_named则是为变量取一个可读性更好的名字。
以ktap源码为例：
int kp_max_loop_count = 100000;
module_param_named(max_loop_count, kp_max_loop_count, int, S_IRUGO | S_IWUSR);
MODULE_PARM_DESC(max_loop_count, "max loop execution count");
加载ktapvm模块，读取kp_max_loop_count的值：
[root@Linux ~]# cat /sys/module/ktapvm/parameters/max_loop_count
100000
[root@Linux ~]# ls -lt /sys/module/ktapvm/parameters/max_loop_count
-rw-r--r--. 1 root root 4096 Oct 22 22:51 /sys/module/ktapvm/parameters/max_loop_count
可以看到kp_max_loop_count变量在/sys/module/ktapvm/parameters文件夹下的名字是max_loop_count，值是100000，只有root用户拥有写权限。可以通过修改这个文件达到改变kp_max_loop_count变量的目的：
[root@Linux ~]# echo 200000 > /sys/module/ktapvm/parameters/max_loop_count
[root@Linux ~]# cat /sys/module/ktapvm/parameters/max_loop_count
200000
MODULE_PARM_DESC用来定义参数的描述信息，使用modinfo命令可以查看：
[root@Linux ~]# modinfo ktapvm.ko
.....
parm: max_loop_count:max loop execution count (int)参考资料：
Everything You Wanted to Know About Module Parameters。
