linux设备驱动模型一三基础结构之示例
前面我们了解了设备驱动模型的三个基本结构，以及它们的相关操作函数，这里我们以实例来看一下它们的用法。
首先定义一个内嵌的kobject结构：
struct test_container {
int member;
struct kobject kobj;
};
定义了一个kobject和一个member成员，主要就是嵌套了kobject结构。
struct test_container *con1, *con2, *con3; struct kset *test_kset; struct kobj_type test_type;
定义了三个test_container变量，一个kset，一个kobj_type.
struct attribute name_attr = {
.name = "name",
.mode = 0666,
};
struct attribute val_attr = {
.name = "member",
.mode = 0666,
};
struct attribute *test_attrs[] = {
&name_attr,
&val_attr,
NULL,
};
定义了两个属性变量，name和member，以及它们的访问权限，最后把它们都放到一个属性数组中。这里要注意的是属性数组中的最后一项为NULL.
ssize_t test_show(struct kobject *kobj, struct attribute *attr, char *buffer)
{
struct test_container *obj = container_of(kobj, struct test_container, kobj);
ssize_t count = 0;
if (strcmp(attr->name, "name") == 0) {
count = sprintf(buffer, "%s\n", kobject_name(kobj));
} else if (strcmp(attr->name, "member") == 0) {
count = sprintf(buffer, "%d\n", obj->member);
}
return count;
}
ssize_t test_store(struct kobject *kobj, struct attribute *attr, const char *buffer, size_t size)
{
struct test_container *obj = container_of(kobj, struct test_container, kobj);
if (strcmp(attr->name, "member") == 0) {
sscanf(buffer, "%d", &obj->member);
}
return size;
}
struct sysfs_ops test_sysfsops = {
.show = test_show,
.store = test_store,
};
定义文件读写函数，并赋值到sysfs_ops结构的变量test_sysfsops中。
void obj_release(struct kobject *kobj)
{
struct test_container *obj = container_of(kobj, struct test_container, kobj);
printk(KERN_INFO "obj_release,name is: %s\n", kobject_name(&obj->kobj));
kfree(obj);
}
当konject释放的时候调用。
static int __init testkset_init(void)
{
printk(KERN_WARNING "test_init\n");
test_kset = kset_create_and_add("test_kset", NULL, NULL);
if (!test_kset) {
return -ENOMEM;
}
con1 = kzalloc(sizeof(struct test_container), GFP_KERNEL);
if (!con1) {
kset_unregister(test_kset);
return -ENOMEM;
}
con1->member = 1;
con2 = kzalloc(sizeof(struct test_container), GFP_KERNEL);
if (!con2) {
kset_unregister(test_kset);
kfree(con1);
return -ENOMEM;
}
con2->member = 2;
con3 = kzalloc(sizeof(struct test_container), GFP_KERNEL);
if (!con3) {
kset_unregister(test_kset);
kfree(con1);
kfree(con2);
return -ENOMEM;
}
con3->member = 3;
con1->kobj.kset = test_kset;
con2->kobj.kset = test_kset;
con3->kobj.kset = test_kset;
test_type.release = obj_release;
test_type.default_attrs = test_attrs;
test_type.sysfs_ops = &test_sysfsops;
kobject_init_and_add(&con1->kobj, &test_type, NULL, "con1");
kobject_init_and_add(&con2->kobj, &test_type, &con1->kobj, "con2");
kobject_init_and_add(&con3->kobj, &test_type, NULL, "con3");
return 0;
}
这里主要进行kset，kobject的初始化操作，对于kset，直接调用kset_create_and_add初始化并添加到体系结构中，而对于 kobject,首先是赋值，然后设置kset，最后调用kobject_init_and_add添加到体系结构。这里还对这个ktype进行了赋值，进行了属性的相关设置 。
static void __exit testkset_exit(void)
{
printk(KERN_INFO "test_kset_exit\n");
kobject_del(&con1->kobj);
kobject_put(&con1->kobj);
kobject_del(&con2->kobj);
kobject_put(&con2->kobj);
kobject_del(&con3->kobj);
kobject_put(&con3->kobj);
kset_unregister(test_kset);
return;
}kobject_del的作用是把kobject从设备模型的那棵树里摘掉，同时sysfs里相应的目录也会删除。这里需要指出的是，释放的顺序应该是先子对象，后父对象。因为kobject_init_and_add和kobject_add这两个函数会调用kobject_get来增加父对象的引用计数，所以kobject_del需要调用kobject_put来减少父对象的引用计数。在本例中，如果先通过kobject_put来释放obj1，那kobject_del(&obj2->kobj)就会出现内存错误。
这个示例构建了一个如下的架构：
相关的/sys目录结构及属性操作：
root@leaves-desktop:/home/leaves/Test/ldm/ldm2# insmod ldm2.ko root@leaves-desktop:/home/leaves/Test/ldm/ldm2# ll /sys total 4 drwxr-xr-x 13 root root 0 May 15 14:39 ./ drwxr-xr-x 26 root root 4096 Mar 14 14:28 ../ drwxr-xr-x 2 root root 0 May 15 14:39 block/ drwxr-xr-x 22 root root 0 May 15 14:39 bus/ drwxr-xr-x 45 root root 0 May 15 14:39 class/ drwxr-xr-x 4 root root 0 May 15 14:39 dev/ drwxr-xr-x 14 root root 0 May 15 14:39 devices/ drwxr-xr-x 4 root root 0 May 15 14:39 firmware/ drwxr-xr-x 6 root root 0 May 15 14:39 fs/ drwxr-xr-x 7 root root 0 May 15 14:39 kernel/ drwxr-xr-x 105 root root 0 May 15 14:39 module/ drwxr-xr-x 2 root root 0 May 15 14:39 power/ drwxr-xr-x 4 root root 0 May 15 14:43 test_kset/ root@leaves-desktop:/home/leaves/Test/ldm/ldm2# ll /sys/test_kset/ total 0 drwxr-xr-x 4 root root 0 May 15 14:43 ./ drwxr-xr-x 13 root root 0 May 15 14:39 ../ drwxr-xr-x 3 root root 0 May 15 14:43 con1/ drwxr-xr-x 2 root root 0 May 15 14:43 con3/ root@leaves-desktop:/home/leaves/Test/ldm/ldm2# ll /sys/test_kset/con con1/ con3/ root@leaves-desktop:/home/leaves/Test/ldm/ldm2# ll /sys/test_kset/con con1/ con3/ root@leaves-desktop:/home/leaves/Test/ldm/ldm2# ll /sys/test_kset/con1/ total 0 drwxr-xr-x 3 root root 0 May 15 14:43 ./ drwxr-xr-x 4 root root 0 May 15 14:43 ../ drwxr-xr-x 2 root root 0 May 15 14:43 con2/ -rw-rw-rw- 1 root root 4096 May 15 14:43 member -rw-rw-rw- 1 root root 4096 May 15 14:43 name root@leaves-desktop:/home/leaves/Test/ldm/ldm2# cat /sys/test_kset/con1/member 1 root@leaves-desktop:/home/leaves/Test/ldm/ldm2# cat /sys/test_kset/con1/name con1 root@leaves-desktop:/home/leaves/Test/ldm/ldm2# ll /sys/test_kset/con1/con2/ total 0 drwxr-xr-x 2 root root 0 May 15 14:43 ./ drwxr-xr-x 3 root root 0 May 15 14:43 ../ -rw-rw-rw- 1 root root 4096 May 15 14:44 member -rw-rw-rw- 1 root root 4096 May 15 14:44 name root@leaves-desktop:/home/leaves/Test/ldm/ldm2# cat /sys/test_kset/con con1/ con3/ root@leaves-desktop:/home/leaves/Test/ldm/ldm2# cat /sys/test_kset/con1/con2/member 2 root@leaves-desktop:/home/leaves/Test/ldm/ldm2# echo 4 /sys/test_kset/con1/member 4 /sys/test_kset/con1/member root@leaves-desktop:/home/leaves/Test/ldm/ldm2# cat /sys/test_kset/con1/member 1 root@leaves-desktop:/home/leaves/Test/ldm/ldm2# echo 4 > /sys/test_kset/con1/member root@leaves-desktop:/home/leaves/Test/ldm/ldm2# cat /sys/test_kset/con1/member 4 root@leaves-desktop:/home/leaves/Test/ldm/ldm2# rmmod ldm2.ko root@leaves-desktop:/home/leaves/Test/ldm/ldm2#
上面的case中，我们介绍到如何使用default attribute。Default attribute使用很方便，但不够灵活。比如上面的那个例子，name和val这两个attribute使用同一个show/store函数来访问，如果attribute非常多，show/store函数里的分支就会很凌乱。
为了解决这个问题，我们可以参考内核提供的kobj_attribute。在内核里，kobj_attibute是这样定义的：
static ssize_t kobj_attr_show(struct kobject *kobj, struct attribute *attr,
char *buf)
{
struct kobj_attribute *kattr;
ssize_t ret = -EIO;
kattr = container_of(attr, struct kobj_attribute, attr);
if (kattr->show)
ret = kattr->show(kobj, kattr, buf);
return ret;
}
static ssize_t kobj_attr_store(struct kobject *kobj, struct attribute *attr,
const char *buf, size_t count)
{
struct kobj_attribute *kattr;
ssize_t ret = -EIO;
kattr = container_of(attr, struct kobj_attribute, attr);
if (kattr->store)
ret = kattr->store(kobj, kattr, buf, count);
return ret;
}
const struct sysfs_ops kobj_sysfs_ops = {
.show = kobj_attr_show,
.store = kobj_attr_store,
};
static void dynamic_kobj_release(struct kobject *kobj)
{
pr_debug("kobject: (%p): %s\n", kobj, __func__);
kfree(kobj);
}
static struct kobj_type dynamic_kobj_ktype = {
.release = dynamic_kobj_release,
.sysfs_ops = &kobj_sysfs_ops,
};
kobj_attribute是内核提供给我们的一种更加灵活的处理attribute的方式，但是它还不够。只有当我们使用kobject_create来创建kobject时，使用kobj_attribute才比较方便，但大部分情况下，我们是把kobject内嵌到自己的结构里，此时就无法直接使用内核提供的dynamic_kobj_ktype，因此，我们需要创建自己的kobj_attribute。
struct my_attribute {
struct attribute attr;
ssize_t (*show)(struct my_kobj *obj,
struct my_attribute *attr, char *buf);
ssize_t (*store)(struct my_kobj *obj,
struct my_attribute *attr, const char *buf, size_t count);
};
在my_attribute里，我们的show/store直接操作my_kobj，这样更加方便。
参考Linux内核，kobj_type里的sysfs_ops这样定义：
static ssize_t my_attr_show(struct kobject *kobj, struct attribute *attr,
char *buf)
{
struct my_attribute *my_attr;
ssize_t ret = -EIO;
my_attr = container_of(attr, struct my_attribute, attr);
if (my_attr->show)
ret = my_attr->show(container_of(kobj, struct my_kobj, kobj),
my_attr, buf);
return ret;
}
static ssize_t my_attr_store(struct kobject *kobj, struct attribute *attr,
const char *buf, size_t count)
{
struct my_attribute *my_attr;
ssize_t ret = -EIO;
my_attr = container_of(attr, struct my_attribute, attr);
if (my_attr->store)
ret = my_attr->store(container_of(kobj, struct my_kobj, kobj),
my_attr, buf, count);
return ret;
}
下面就可以分别对name和val两个attribute定义自己的show/store。name这个attribute是只读的，只要为它定义show即可。
ssize_t name_show(struct my_kobj *obj, struct my_attribute *attr, char *buffer)
{
return sprintf(buffer, "%s\n", kobject_name(&obj->kobj));
}
ssize_t val_show(struct my_kobj *obj, struct my_attribute *attr, char *buffer)
{
return sprintf(buffer, "%d\n", obj->val);
}
ssize_t val_store(struct my_kobj *obj, struct my_attribute *attr,
const char *buffer, size_t size)
{
sscanf(buffer, "%d", &obj->val);
return size;
}
接下来，利用内核提供的宏__ATTR来初始化my_attribute，并建立attribute数组。
struct my_attribute name_attribute =
__ATTR(name, 0444, name_show, NULL);
struct my_attribute val_attribute =
__ATTR(val, 0666, val_show, val_store);
struct attribute *my_attrs[] = {
&name_attribute.attr,
&val_attribute.attr,
NULL,
};
其中，宏__ATTR的定义如下：
#define __ATTR(_name,_mode,_show,_store) { \
.attr = {.name = __stringify(_name), .mode = _mode }, \
.show = _show, \
.store = _store, \
}在module_init里，我们调用sysfs_create_files来把attribute增加到sysfs中。
retval = sysfs_create_files(&obj->kobj,
(const struct attribute **)my_attrs);
if (retval) {
// ...
}在kobject对应的目录里，还可以创建子目录，Linux内核里是用attribute_group来实现。在本例中，我们可以这么做：
struct attribute_group my_group = {
.name = "mygroup",
.attrs = my_attrs,
};然后在module_init里调用sysfs_create_group来添加。
retval = sysfs_create_group(&obj->kobj, &my_group);
if (retval) {
// ...
}
本例创建的attribute_group中包含的attribute也是my_attrs，所以在子目录mygroup下的文件和mykobj目录下的文件完全一致。 最后我们得到的目录结构是这样的。
mykobj/ |-- mygroup | |-- name | `-- val |-- name `-- val
总结：
kobj、kset对应着sys目录下面的一个个文件夹，而ktype反映的是sys目录下面的文件及操作其show 和store的方法
测试代码：
http://download.csdn.net/detail/new_abc/4312872