转载:https://www.cnblogs.com/sctb/...
1. 编译运行
代码从如下链接获得:
https://github.com/torvalds/l...
编写 Makefile 文件:
obj-m += configfs_sample.o
all:
make -C /lib/modules/$(shell uname -r)/build M=$(PWD) modules
clean:
make -C /lib/modules/$(shell uname -r)/build M=$(PWD) clean
编译生成内核模块:
make
ls -l
-rwxr--r-- 1 abin abin 10K Oct 27 16:58 configfs_sample.c?
-rw-rw-r-- 1 abin abin 13K Oct 29 11:16 configfs_sample.ko
-rw-rw-r-- 1 abin abin 603 Oct 29 11:16 configfs_sample.mod.c
-rw-rw-r-- 1 abin abin 2.6K Oct 29 11:16 configfs_sample.mod.o
-rw-rw-r-- 1 abin abin 12K Oct 29 11:16 configfs_sample.o
-rw-rw-r-- 1 abin abin 166 Oct 29 11:16 Makefile
-rw-rw-r-- 1 abin abin 92 Oct 29 11:16 modules.order
-rw-rw-r-- 1 abin abin 0 Oct 29 11:16 Module.symvers
其中,configfs_sample.ko
使编译好的内核模块,使用如下命令加载该模块:
sudo modprobe configfs_sample.ko
如果出现如下错误:
modprobe: FATAL: Module configfs_sample.ko not found in directory /lib/modules/4.15.0-117-generic
将 configfs_sample.ko 拷贝进 /lib/modules/4.15.0-117-generic 再次尝试。
查看 configfs_sample.ko 内核模块是否已经挂载:
lsmod | grep configfs_sample
configfs_sample 16384 0
查看 configfs 根目录:
ls -l /sys/kernel/config/
total 0
drwxr-xr-x 2 root root 0 Oct 29 11:32 01-childless
drwxr-xr-x 2 root root 0 Oct 29 11:32 02-simple-children
drwxr-xr-x 2 root root 0 Oct 29 11:32 03-group-children
如需卸载模块,使用如下命令:
sudo modprobe -r configfs_sample.ko
2. 代码理解
为了理解代码,我们首先整理一下 configfs 中的层级结构:
内核模块初始化入口:
module_init(configfs_example_init);
configfs_example_init(void)
函数:
/*
* 此处是configfs_subsystem结构体数组,分别对应示例中的三个configfs子系统
*/
static struct configfs_subsystem *example_subsys[] = {
&childless_subsys.subsys,
&simple_children_subsys,
&group_children_subsys,
NULL,
};
static int __init configfs_example_init(void)
{
int ret;
int i;
struct configfs_subsystem *subsys; //configfs子系统
for (i = 0; example_subsys[i]; i++) {
subsys = example_subsys[i];
config_group_init(&subsys->su_group); //初始化 group
mutex_init(&subsys->su_mutex); //初始化 mutex
ret = configfs_register_subsystem(subsys); //注册 subsystem
if (ret) {
printk(KERN_ERR "Error %d while registering subsystem %s\n", ret, subsys->su_group.cg_item.ci_namebuf);
goto out_unregister;
}
}
return 0;
out_unregister:
for (i--; i >= 0; i--)
configfs_unregister_subsystem(example_subsys[i]);
return ret;
}
程序的主要逻辑是通过 struct configfs_subsystem 结构体传递给 configfs 的,下面分别对3个示例进行分析。
2.1 示例01-childless
变量 childless_subsys 的内容:
struct childless {
struct configfs_subsystem subsys;
int showme;
int storeme;
};
static struct childless childless_subsys = {
.subsys = {
.su_group = {
.cg_item = {
.ci_namebuf = "01-childless",
.ci_type = &childless_type, //struct config_item_type,定义操作、属性等
},
},
},
};
childless_type 变量如下:
static const struct config_item_type childless_type = {
.ct_attrs = childless_attrs, //configfs_attribute,只定义了属性,没有定义对item和group操作
.ct_owner = THIS_MODULE,
};
childless_attrs 是一个数组,以 NULL 结尾。以下定义了三个属性,在 configfs 中,将表现为3个文件:
static struct configfs_attribute *childless_attrs[] = {
&childless_attr_showme,
&childless_attr_storeme,
&childless_attr_description,
NULL,
};
childless_attr_showme,childless_attr_storeme 和 childless_attr_description 三个属性是通过以下函数创建的:
CONFIGFS_ATTR_RO(childless_, showme); //需要定义childless_showme_show()函数
CONFIGFS_ATTR(childless_, storeme); //需要定义childless_storeme_show()和childless_storeme_store()函数
CONFIGFS_ATTR_RO(childless_, description); //需要定义childless_description_show()函数
创建属性的函数有3个,在 linux/configfs.h 中:
#define CONFIGFS_ATTR(_pfx, _name) \
static struct configfs_attribute _pfx##attr_##_name = { \
.ca_name = __stringify(_name), \
.ca_mode = S_IRUGO | S_IWUSR, \
.ca_owner = THIS_MODULE, \
.show = _pfx##_name##_show, \
.store = _pfx##_name##_store, \
}
#define CONFIGFS_ATTR_RO(_pfx, _name) \
static struct configfs_attribute _pfx##attr_##_name = { \
.ca_name = __stringify(_name), \
.ca_mode = S_IRUGO, \
.ca_owner = THIS_MODULE, \
.show = _pfx##_name##_show, \
}
#define CONFIGFS_ATTR_WO(_pfx, _name) \
static struct configfs_attribute _pfx##attr_##_name = { \
.ca_name = __stringify(_name), \
.ca_mode = S_IWUSR, \
.ca_owner = THIS_MODULE, \
.store = _pfx##_name##_store, \
}
可以看到,这三个宏定义函数可以根据传入的参数定义不同的结构体变量,变量名为:_pfx_attr_name,同时也会定义相应的 show 和 store 函数名。
CONFIGFS_ATTR(_pfx, _name) 需要定义 show 和 store 函数,相应的函数名分别为:_pfx_name_show 和 _pfx_name_store;
CONFIGFS_ATTR_RO(_pfx, _name)只需要定义 show 函数;
CONFIGFS_ATTR_WO(_pfx, _name) 只需要定义 store 函数。
childless_showme_show(),childless_storeme_show(),childless_storeme_store()和childless_description_show()的定义如下:
/*
* 传入item,得到该item所在的childless结构体
*/
static inline struct childless *to_childless(struct config_item *item)
{
return item ? container_of(to_configfs_subsystem(to_config_group(item)), struct childless, subsys) : NULL;
}
//childless_showme_show函数的实现,根据item找到结构体struct childless,输出childless->showme,然后将childless->showme加1
static ssize_t childless_showme_show(struct config_item *item, char *page)
{
struct childless *childless = to_childless(item);
ssize_t pos;
pos = sprintf(page, "%d\n", childless->showme);
childless->showme++;
return pos;
}
//childless_storeme_show函数实现,输出结构体struct childless成员storeme的值
static ssize_t childless_storeme_show(struct config_item *item, char *page)
{
return sprintf(page, "%d\n", to_childless(item)->storeme);
}
//childless_storeme_store函数实现,接受从文件系统输入的值,保存在struct childless成员storeme中
static ssize_t childless_storeme_store(struct config_item *item, const char *page, size_t count)
{
struct childless *childless = to_childless(item);
unsigned long tmp;
char *p = (char *) page;
tmp = simple_strtoul(p, &p, 10); //将字符串转化为10进制数字,类型为unsigned long
if (!p || (*p && (*p != '\n')))
return -EINVAL;
if (tmp > INT_MAX)
return -ERANGE;
childless->storeme = tmp;
return count;
}
//childless_description_show函数实现,向page中填充内容
static ssize_t childless_description_show(struct config_item *item, char *page)
{
return sprintf(page,
"[01-childless]\n"
"\n"
"The childless subsystem is the simplest possible subsystem in\n"
"configfs. It does not support the creation of child config_items.\n"
"It only has a few attributes. In fact, it isn't much different\n"
"than a directory in /proc.\n");
}
根据我的理解,page指向一块内存空间,这块空间接收来自文件系统的数据,同时,负责将configfs中的内容输出给文件系统。
showme 文件运行效果:
cat showme
1
cat showme
2
storeme 文件运行效果:
cat storeme
0
echo 1111 > storeme
cat storeme
1111
2.2 示例02-simple-children
simple_children_subsys 变量的内容:
struct simple_children {
struct config_group group;
};
static struct configfs_subsystem simple_children_subsys = {
.su_group = {
.cg_item = {
.ci_namebuf = "02-simple-children",
.ci_type = &simple_children_type,
},
},
};
simple_children_type 内容:
static const struct config_item_type simple_children_type = {
.ct_item_ops = &simple_children_item_ops, //item的操作
.ct_group_ops = &simple_children_group_ops, //group的操作
.ct_attrs = simple_children_attrs, //属性,和01相同
.ct_owner = THIS_MODULE,
};
可以看到,与01示例相比,02-siimple-chiildren 不光定义了 ct_attrs,还定义了 ct_item_ops 和 ct_group_ops。先看看赋值给 ct_attrs 的变量 simple_children_attrs:
static struct configfs_attribute *simple_children_attrs[] = {
&simple_children_attr_description, //属性,configfs中表示为文件
NULL,
};
simple_children_attrs 定义对象的属性,在 configfs 中表示为文件。simple_children_attr_description 是通过宏函数创建的:
CONFIGFS_ATTR_RO(simple_children_, description);
在 CONFIGFS_ATTR_RO 宏函数中会使用 show 函数,定义如下:
static ssize_t simple_children_description_show(struct config_item *item, char *page)
{
return sprintf(page,
"[02-simple-children]\n"
"\n"
"This subsystem allows the creation of child config_items. These\n"
"items have only one attribute that is readable and writeable.\n");
}
此处和01示例没什么区别,主要看 ct_item_ops 和 ct_group_ops。simple_children_item_ops 的定义如下:
static struct configfs_item_operations simple_children_item_ops = {
.release = simple_children_release, //实现release函数
};
simple_children_item_ops 是 struct configfs_item_operations 类型,也很简单,只定义了 release 函数,simple_children_release 函数定义如下:
static void simple_children_release(struct config_item *item)
{
kfree(to_simple_children(item)); //将item转换为simple_children结构体并释放内核分配的内存
}
simple_children_group_ops 的定义如下:
static struct configfs_group_operations simple_children_group_ops = {
.make_item = simple_children_make_item,
};
simple_children_group_ops 也很简单,只实现了 make_item 函数。simple_children_make_item 如下:
/*
* 传入item,得到该item所在的simple_children结构体
*/
static inline struct simple_children *to_simple_children(struct config_item *item)
{
return item ? container_of(to_config_group(item), struct simple_children, group) : NULL;
}
static struct config_item *simple_children_make_item(struct config_group *group, const char *name)
{
struct simple_child *simple_child;
simple_child = kzalloc(sizeof(struct simple_child), GFP_KERNEL); //为simple_child分配内存
if (!simple_child)
return ERR_PTR(-ENOMEM);
config_item_init_type_name(&simple_child->item, name, &simple_child_type); //创建新的item时,使用config_item_init_type_name初始化,simple_child_type是子item使用的config_item_type结构体
simple_child->storeme = 0; //将simple_child的storeme设置为0
return &simple_child->item;
}
simple_child_type定义如下:
struct simple_child {
struct config_item item;
int storeme;
};
static const struct config_item_type simple_child_type = {
.ct_item_ops = &simple_child_item_ops,
.ct_attrs = simple_child_attrs,
.ct_owner = THIS_MODULE,
};
同上,定义了 ct_attrs 和 ct_item_ops,没有定义 ct_item_ops,simple_child_attrs变量定义如下:
CONFIGFS_ATTR(simple_child_, storeme);
static struct configfs_attribute *simple_child_attrs[] = {
&simple_child_attr_storeme,
NULL,
};
需要定义 show 和 store 函数:
static inline struct simple_child *to_simple_child(struct config_item *item)
{
return item ? container_of(item, struct simple_child, item) : NULL;
}
/*
* 子item的show函数,将item转换为simple_child结构体并输出storeme的值
*/
static ssize_t simple_child_storeme_show(struct config_item *item, char *page)
{
return sprintf(page, "%d\n", to_simple_child(item)->storeme);
}
/*
* 子item的store函数,将从文件系统输入的值保存在simple_child->storeme中
*/
static ssize_t simple_child_storeme_store(struct config_item *item, const char *page, size_t count)
{
struct simple_child *simple_child = to_simple_child(item);
unsigned long tmp;
char *p = (char *) page;
tmp = simple_strtoul(p, &p, 10); //将字符串转换为10进制数字
if (!p || (*p && (*p != '\n')))
return -EINVAL;
if (tmp > INT_MAX)
return -ERANGE;
simple_child->storeme = tmp;
return count;
}
运行效果:
make child
ls
child description
cd child
ls -l
total 0
-rw-r--r-- 1 root root 4096 Nov 3 21:57 storeme
child 文件夹中的 store 文件是自动创建的,这是因为定义了 make_item 函数,初始化 item 时 simple_child_type 变量的作用。
cat storeme
0
echo 2222 > storeme
cat storeme
2222
2.3 示例03-group-children
group_children_subsys变量的内容为:
static struct configfs_subsystem group_children_subsys = {
.su_group = {
.cg_item = {
.ci_namebuf = "03-group-children",
.ci_type = &group_children_type,
},
},
};
group_children_type 的定义如下:
static const struct config_item_type group_children_type = {
.ct_group_ops = &group_children_group_ops,
.ct_attrs = group_children_attrs,
.ct_owner = THIS_MODULE,
};
可以看到,和示例02相比,此处没有定义对 item 的操作,只定义了对 group 的操作。先看 group_children_attrs 的定义:
CONFIGFS_ATTR_RO(group_children_, description);
static struct configfs_attribute *group_children_attrs[] = {
&group_children_attr_description,
NULL,
};
同样,使用 CONFIGFS_ATTR_RO 宏定义函数需要先定义好 show 函数:
static ssize_t group_children_description_show(struct config_item *item, char *page)
{
return sprintf(page,
"[03-group-children]\n"
"\n"
"This subsystem allows the creation of child config_groups. These\n"
"groups are like the subsystem simple-children.\n");
}
此处和示例01和02都一样,下面是示例03的重点:
static struct config_group *group_children_make_group( struct config_group *group, const char *name)
{
struct simple_children *simple_children; //此处使用的struct simple_children结构体是示例02中定义的结构体
simple_children = kzalloc(sizeof(struct simple_children), GFP_KERNEL); //分配内存
if (!simple_children)
return ERR_PTR(-ENOMEM);
config_group_init_type_name(&simple_children->group, name, &simple_children_type); //初始化group,simple_children_type也是示例02中定义的
return &simple_children->group;
}
这段代码负责创建group,初始化group时使用 simple_children_type变量,该变量是 struct config_item_type 类型,其中定义的内容就是实例02的内容。
在configfs中的表现为:在 03-group-children 下创建的每个目录,都相当于加载内核模快时创建的 02-simple-children 目录。
运行效果:
mkdir group
ls
description group
cd group
ls -l
total 0
-r--r--r-- 1 root root 4096 Nov 3 22:20 description
cat description
[02-simple-children]
This subsystem allows the creation of child config_items. These
items have only one attribute that is readable and writeable.
到这里可以看到,在示例03创建的目录等同于 02-simple-children 目录,下面的操作的示例02效果一样。
mkdir group_child
ls
description group_child
cd group_child
ls
storeme
cat storeme
0
echo 3333 > storeme
cat storeme
3333
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