1、前言
Linux内核中有大量的驱动，而这些驱动往往具有类似的结构，根据面向对象的思想，可以将共同的部分提取为父类，而这个父类就是kobject，kobject结构体中包含了大量设备的必须信息，而三大类设备驱动都需要包含这个kobject结构，运用面向对象的思想来看问题，也就是继承来自kobject，一个kobject对象往往就对应sysfs中的一个目录，kobject是组成设备模型的基本结构，kobject需要处理的基本任务有如下：
（1）对象的引用计数
当一个内核对象被创建时，不可能知道对象的存活时间，跟踪该对象的的生命周期的一个方法就是使用引用计数，当内核中没有代码持有该对象的引用时，说明该对象可以被销毁了；
（2）sysfs表述
一个kobject对象往往对应sysfs中的一个目录，kobject被用来与内核交互并创建它的sysfs可见表述；
（3）数据结构关联
从整体上看，设备模型是一个友好而复杂的数据结构，通过kobject对象实现了大量的连接而构成了一个多层次的体系结构；
（4）热拔插事件处理
当系统中的硬件被热插拔时，在kobject子系统的控制下，将产生事件以通知用户空间。
2、kobject以及相关结构体
Linux内核源码中对kobject结构体的定义在include/linux/kobject.h文件中，实现在lib/kobjet.c，struct kobject结构体的定义如下所示：
struct kobject {
const char *name;
struct list_head entry;
struct kobject *parent;
struct kset *kset;
struct kobj_type *ktype;
struct kernfs_node *sd; /* sysfs directory entry */
struct kref kref;
#ifdef CONFIG_DEBUG_KOBJECT_RELEASE
struct delayed_work release;
#endif
unsigned int state_initialized:;
unsigned int state_in_sysfs:;
unsigned int state_add_uevent_sent:;
unsigned int state_remove_uevent_sent:;
unsigned int uevent_suppress:;
};结构体常用成员解释：
name：表示kobject对象的名字，对应sysfs下的一个目录；
entry：在kobject中嵌入双向链表list_head结构；
parent：指向当前kobject父对象的指针；
kset：表示当前kobject对象所属的集合；
ktype：表示当前kobject对象所属类型；
sd：用于VFS文件系统的目录项，是设备与文件之间的桥梁，sysfs中的符号链接就是通过kernfs_node内的联合体实现的；
kref：是对kobject的引用计数，当引用计数为0时，就回调之前注册的release函数释放该对象；
state_initialized:1：初始化的标志位，在对象被初始化时置位，用于表示对象已被初始化；
state_in_sysfs:1：表示kobject对象在sysfs中的状态，在对应目录中被创建则置1，否则为0；
state_add_uevent_sent:1：添加设备的uevent事件是否发送标志，添加设备时会向用户空间发送uevent事件，请求新增设备；
state_remove_uevent_sent:1：删除设备的uevent事件是否发送标志，删除设备时会向用户空间发送uevent事件，请求卸载设备。
struct kobj_type定义了kobject的类型，该结构体既有操作的函数，也有默认的公共属性，该结构体定义如下：
struct kobj_type {
void (*release)(struct kobject *kobj);
const struct sysfs_ops *sysfs_ops;
struct attribute **default_attrs;
const struct kobj_ns_type_operations *(*child_ns_type)(struct kobject *kobj);
const void *(*namespace)(struct kobject *kobj);
void (*get_ownership)(struct kobject *kobj, kuid_t *uid, kgid_t *gid);
};结构体常用成员解释：
release：函数指针，当引用计数为0时，在kobject释放时调用；
sysfs_ops：定义了读写属性文件时调用的函数；
default_attrs：定义了这类kobject默认属性，指向attribute数组的指针。
struct sysfs_ops结构体是用于实现属性的的函数操作集，其定义如下所示：
struct sysfs_ops {
ssize_t (*show)(struct kobject *, struct attribute *, char *);
ssize_t (*store)(struct kobject *, struct attribute *, const char *, size_t);
};show：函数用于读取一个属性到用户空间，函数的第一个参数是要读取的kobject指针，它对应要读的目录，第二个参数是要读的属性，第三个参数存放读到的属性的缓冲区，当函数调用成功后，返回实际读取的数据长度；
store：函数用于将属性写入到内核，函数第一个参数是与写相关的kobject指针，它对应要写的目录，第二个参数是要写的属性，第三个参数是要写入的数据，第四个参数是要写入的参数长度，这个长度不能超过PAGESIZE个字节大小，只有当拥有属性写权限时，才能调用store()函数。
struct attribute定义了kobject的属性，该结构体定义如下：
struct attribute {
const char *name;
umode_t mode;
#ifdef CONFIG_DEBUG_LOCK_ALLOC
bool ignore_lockdep:;
struct lock_class_key *key;
struct lock_class_key skey;
#endif
};常用结构体成员解释：
name：属性文件的名称，属性文件将在kobject的sysfs目录中显示；
mode：属性文件的读写权限。
struct kset可以看成是在kobject上的拓展，它包含了一个kobject的链表，可以方便地表示sysfs中目录与子目录的关系，该结构体定义如下：
/**
* struct kset - a set of kobjects of a specific type, belonging to a specific subsystem.
*
* A kset defines a group of kobjects. They can be individually
* different "types" but overall these kobjects all want to be grouped
* together and operated on in the same manner. ksets are used to
* define the attribute callbacks and other common events that happen to
* a kobject.
*
* @list: the list of all kobjects for this kset
* @list_lock: a lock for iterating over the kobjects
* @kobj: the embedded kobject for this kset (recursion, isn't it fun...)
* @uevent_ops: the set of uevent operations for this kset. These are
* called whenever a kobject has something happen to it so that the kset
* can add new environment variables, or filter out the uevents if so
* desired.
*/
struct kset {
struct list_head list;
spinlock_t list_lock;
struct kobject kobj;
const struct kset_uevent_ops *uevent_ops;
};
结构体常用成员解释：
list：用来挂在链表上的结构，包含在一个kset的所有kobject构成了一个双向循坏链表，list_head是这个链表的头部，这个链表用来连接第一个和最后一个kobject对象，第一个kobject使用entry连接kset集合以及第二个kobject对象，第二个kobject对象使用entry连接第一个kobject对象和第三个kobject对象，最终形成一个kobject对象的链表；
list_lock：用于迭代kobjects的锁；
kobj：归属于该kset的所有的kobject的共有parent，这个parent就是体现内核设备组织结构的关键，同时，kset的引用计数就是内嵌的kobject对象的引用计数；
uevent_ops：此kset的uevent操作函数集。
struct kobj_attribute是kobject在attribute上的拓展，添加了专门读写kobject_attribute属性的函数，结构体定义如下：
struct kobj_attribute {
struct attribute attr;
ssize_t (*show)(struct kobject *kobj, struct kobj_attribute *attr,
char *buf);
ssize_t (*store)(struct kobject *kobj, struct kobj_attribute *attr,
const char *buf, size_t count);
};结构体成员解释：
attr：kobject的公共属性，包括名称和读写权限；
show：函数指针，用于读取属性到用户空间；
store：函数指针，用于用户空间写属性到内核。
注意：无论是kobjec还是kset（说到底是kset内部的kobject），都提供了使用kobj_attribute的快速创建方法。
3、kobject实现操作
在Linux内核中提供了一系列kobject的实现方法，接下来，进行简要分析：
/*
* populate_dir - populate directory with attributes.
* @kobj: object we're working on.
*
* Most subsystems have a set of default attributes that are associated
* with an object that registers with them. This is a helper called during
* object registration that loops through the default attributes of the
* subsystem and creates attributes files for them in sysfs.
*/
static int populate_dir(struct kobject *kobj)
{
struct kobj_type *t = get_ktype(kobj);
struct attribute *attr;
int error = ;
int i; if (t && t->default_attrs) {
for (i = ; (attr = t->default_attrs[i]) != NULL; i++) {
error = sysfs_create_file(kobj, attr);//在sysfs目录创建属性文件
if (error)
break;
}
}
return error;
} static int create_dir(struct kobject *kobj)
{
const struct kobj_ns_type_operations *ops;
int error; error = sysfs_create_dir_ns(kobj, kobject_namespace(kobj));//创建sysfs目录
if (error)
return error; error = populate_dir(kobj);//在sysfs目录中填充属性文件
if (error) {
sysfs_remove_dir(kobj);
return error;
} /*
* @kobj->sd may be deleted by an ancestor going away. Hold an
* extra reference so that it stays until @kobj is gone.
*/
sysfs_get(kobj->sd);//引用计数加1 /*
* If @kobj has ns_ops, its children need to be filtered based on
* their namespace tags. Enable namespace support on @kobj->sd.
*/
ops = kobj_child_ns_ops(kobj);
if (ops) {
BUG_ON(ops->type <= KOBJ_NS_TYPE_NONE);
BUG_ON(ops->type >= KOBJ_NS_TYPES);
BUG_ON(!kobj_ns_type_registered(ops->type)); sysfs_enable_ns(kobj->sd);
} return ;
}
上面两个函数中，create_dir()用于在sysfs中创建kobj相应的目录，populate_dir()创建kobj中默认属性对应的文件，create_dir()函数就是调用populate_dir()实现的。
static int get_kobj_path_length(struct kobject *kobj)
{
int length = ;
struct kobject *parent = kobj; /* walk up the ancestors until we hit the one pointing to the
* root.
* Add 1 to strlen for leading '/' of each level.
*/
do {
if (kobject_name(parent) == NULL)
return ;
length += strlen(kobject_name(parent)) + ;
parent = parent->parent;
} while (parent);
return length;
} static void fill_kobj_path(struct kobject *kobj, char *path, int length)
{
struct kobject *parent; --length;
for (parent = kobj; parent; parent = parent->parent) {
int cur = strlen(kobject_name(parent));
/* back up enough to print this name with '/' */
length -= cur;
strncpy(path + length, kobject_name(parent), cur);
*(path + --length) = '/';
} pr_debug("kobject: '%s' (%p): %s: path = '%s'\n", kobject_name(kobj),
kobj, __func__, path);
} /**
* kobject_get_path - generate and return the path associated with a given kobj and kset pair.
*
* @kobj: kobject in question, with which to build the path
* @gfp_mask: the allocation type used to allocate the path
*
* The result must be freed by the caller with kfree().
*/
char *kobject_get_path(struct kobject *kobj, gfp_t gfp_mask)
{
char *path;
int len; len = get_kobj_path_length(kobj);
if (len == )
return NULL;
path = kzalloc(len, gfp_mask);
if (!path)
return NULL;
fill_kobj_path(kobj, path, len); return path;
}
在上面的三个函数中，前面两个函数是内部函数，get_kobj_path_length()函数用于获得kobj路径名的长度，fill_kobj_path()函数用于将kobj路径名填充到path缓冲区，然后将指针返回，kobject_get_path()函数就是调用这两个函数进行实现的。
/* add the kobject to its kset's list */
static void kobj_kset_join(struct kobject *kobj)
{
if (!kobj->kset)
return; kset_get(kobj->kset);//引用计数加1
spin_lock(&kobj->kset->list_lock);
list_add_tail(&kobj->entry, &kobj->kset->list);//在链表尾部插入节点
spin_unlock(&kobj->kset->list_lock);
} /* remove the kobject from its kset's list */
static void kobj_kset_leave(struct kobject *kobj)
{
if (!kobj->kset)
return; spin_lock(&kobj->kset->list_lock);
list_del_init(&kobj->entry);//链表删除节点
spin_unlock(&kobj->kset->list_lock);
kset_put(kobj->kset);//引用计数减1
}
上面两个函数的功能是相对的，kobj_kset_join()用于将kobj加入到kobj->kset的链表中，kobj_kset_leave()用于将kobj从kobj->kset的链表中删除。
static void kobject_init_internal(struct kobject *kobj)
{
if (!kobj)
return;
kref_init(&kobj->kref);//引用计数初始化
INIT_LIST_HEAD(&kobj->entry);//链表初始化
kobj->state_in_sysfs = ;
kobj->state_add_uevent_sent = ;
kobj->state_remove_uevent_sent = ;
kobj->state_initialized = ;
} static int kobject_add_internal(struct kobject *kobj)
{
int error = ;
struct kobject *parent; if (!kobj)
return -ENOENT; if (!kobj->name || !kobj->name[]) {
WARN(, "kobject: (%p): attempted to be registered with empty "
"name!\n", kobj);
return -EINVAL;
} parent = kobject_get(kobj->parent);//父kobject引用计数加1 /* join kset if set, use it as parent if we do not already have one */
if (kobj->kset) {
if (!parent)
parent = kobject_get(&kobj->kset->kobj);
kobj_kset_join(kobj);
kobj->parent = parent;//设置kobject的parent指针
} pr_debug("kobject: '%s' (%p): %s: parent: '%s', set: '%s'\n",
kobject_name(kobj), kobj, __func__,
parent ? kobject_name(parent) : "<NULL>",
kobj->kset ? kobject_name(&kobj->kset->kobj) : "<NULL>"); error = create_dir(kobj);//在sysfs中创建目录
if (error) {
kobj_kset_leave(kobj);
kobject_put(parent);
kobj->parent = NULL; /* be noisy on error issues */
if (error == -EEXIST)
pr_err("%s failed for %s with -EEXIST, don't try to register things with the same name in the same directory.\n",
__func__, kobject_name(kobj));
else
pr_err("%s failed for %s (error: %d parent: %s)\n",
__func__, kobject_name(kobj), error,
parent ? kobject_name(parent) : "'none'");
} else
kobj->state_in_sysfs = ; return error;
}
kobject_init_internal()函数用来初始化kobj，kobject_add_internal()函数用来将kobj加入已有的结构中去，这两个函数有密切的联系，在kobject结构体中有很多变量，但是重要的只有两个，一个是kset，一个是parent，这两个变量表示了kobject在整个体系中的位置，决不能自行决定，需要外部参与设置，kobject的创建过程分为init和add两个阶段。kobject_init_internal()把一些结构体变量进行初始化后，等外界设置了parent和kset后，再调用kobject_add_internal()把kobject添加到适当的位置，并创建相应的sysfs目录及文件。
/**
* kobject_set_name_vargs - Set the name of an kobject
* @kobj: struct kobject to set the name of
* @fmt: format string used to build the name
* @vargs: vargs to format the string.
*/
int kobject_set_name_vargs(struct kobject *kobj, const char *fmt,
va_list vargs)
{
const char *s; if (kobj->name && !fmt)
return ; s = kvasprintf_const(GFP_KERNEL, fmt, vargs);
if (!s)
return -ENOMEM; /*
* ewww... some of these buggers have '/' in the name ... If
* that's the case, we need to make sure we have an actual
* allocated copy to modify, since kvasprintf_const may have
* returned something from .rodata.
*/
if (strchr(s, '/')) {
char *t; t = kstrdup(s, GFP_KERNEL);
kfree_const(s);
if (!t)
return -ENOMEM;
strreplace(t, '/', '!');
s = t;
}
kfree_const(kobj->name);
kobj->name = s; return ;
} /**
* kobject_set_name - Set the name of a kobject
* @kobj: struct kobject to set the name of
* @fmt: format string used to build the name
*
* This sets the name of the kobject. If you have already added the
* kobject to the system, you must call kobject_rename() in order to
* change the name of the kobject.
*/
int kobject_set_name(struct kobject *kobj, const char *fmt, ...)
{
va_list vargs;
int retval; va_start(vargs, fmt);
retval = kobject_set_name_vargs(kobj, fmt, vargs);
va_end(vargs); return retval;
}
kobject_set_name()函数的作用是设置kobj的名称，它通过调用kobject_set_name_vargs()来实现，需要注意的时，kobject_set_name()仅限于kobject添加到体系之前使用，因为该函数只是修改了名字，并未通知到用户空间。
/**
* kobject_init - initialize a kobject structure
* @kobj: pointer to the kobject to initialize
* @ktype: pointer to the ktype for this kobject.
*
* This function will properly initialize a kobject such that it can then
* be passed to the kobject_add() call.
*
* After this function is called, the kobject MUST be cleaned up by a call
* to kobject_put(), not by a call to kfree directly to ensure that all of
* the memory is cleaned up properly.
*/
void kobject_init(struct kobject *kobj, struct kobj_type *ktype)
{
char *err_str; if (!kobj) {
err_str = "invalid kobject pointer!";
goto error;
}
if (!ktype) {
err_str = "must have a ktype to be initialized properly!\n";
goto error;
}
if (kobj->state_initialized) {
/* do not error out as sometimes we can recover */
printk(KERN_ERR "kobject (%p): tried to init an initialized "
"object, something is seriously wrong.\n", kobj);
dump_stack();
} kobject_init_internal(kobj);
kobj->ktype = ktype;
return; error:
printk(KERN_ERR "kobject (%p): %s\n", kobj, err_str);
dump_stack();
}
kobject_init()函数就是调用了kobject_init_internal()函数进行一些结构体变量初始化，然后又设置了ktype结构体成员，ktype的作用是管理一些默认属性。
static int kobject_add_varg(struct kobject *kobj,
struct kobject *parent,
const char *fmt, va_list vargs)
{
int retval; retval = kobject_set_name_vargs(kobj, fmt, vargs);
if (retval) {
printk(KERN_ERR "kobject: can not set name properly!\n");
return retval;
}
kobj->parent = parent;
return kobject_add_internal(kobj);
} /**
* kobject_add - the main kobject add function
* @kobj: the kobject to add
* @parent: pointer to the parent of the kobject.
* @fmt: format to name the kobject with.
*
* The kobject name is set and added to the kobject hierarchy in this
* function.
*
* If @parent is set, then the parent of the @kobj will be set to it.
* If @parent is NULL, then the parent of the @kobj will be set to the
* kobject associated with the kset assigned to this kobject. If no kset
* is assigned to the kobject, then the kobject will be located in the
* root of the sysfs tree.
*
* If this function returns an error, kobject_put() must be called to
* properly clean up the memory associated with the object.
* Under no instance should the kobject that is passed to this function
* be directly freed with a call to kfree(), that can leak memory.
*
* Note, no "add" uevent will be created with this call, the caller should set
* up all of the necessary sysfs files for the object and then call
* kobject_uevent() with the UEVENT_ADD parameter to ensure that
* userspace is properly notified of this kobject's creation.
*/
int kobject_add(struct kobject *kobj, struct kobject *parent,
const char *fmt, ...)
{
va_list args;
int retval; if (!kobj)
return -EINVAL; if (!kobj->state_initialized) {
printk(KERN_ERR "kobject '%s' (%p): tried to add an "
"uninitialized object, something is seriously wrong.\n",
kobject_name(kobj), kobj);
dump_stack();
return -EINVAL;
}
va_start(args, fmt);
retval = kobject_add_varg(kobj, parent, fmt, args);
va_end(args); return retval;
}
kobject_add()函数用于将kobj添加到体系中去，但是该函数还有一个附加的功能，设置kobj的名字，parent作为参数被传进来。
/**
* kobject_init_and_add - initialize a kobject structure and add it to the kobject hierarchy
* @kobj: pointer to the kobject to initialize
* @ktype: pointer to the ktype for this kobject.
* @parent: pointer to the parent of this kobject.
* @fmt: the name of the kobject.
*
* This function combines the call to kobject_init() and
* kobject_add(). The same type of error handling after a call to
* kobject_add() and kobject lifetime rules are the same here.
*/
int kobject_init_and_add(struct kobject *kobj, struct kobj_type *ktype,
struct kobject *parent, const char *fmt, ...)
{
va_list args;
int retval; kobject_init(kobj, ktype); va_start(args, fmt);
retval = kobject_add_varg(kobj, parent, fmt, args);
va_end(args); return retval;
}
kobject_init_and_add()其实是kobjec_init()和kobject_add()的合并，将kobject初始化后并添加到kobject的层次结构中去。
/**
* kobject_rename - change the name of an object
* @kobj: object in question.
* @new_name: object's new name
*
* It is the responsibility of the caller to provide mutual
* exclusion between two different calls of kobject_rename
* on the same kobject and to ensure that new_name is valid and
* won't conflict with other kobjects.
*/
int kobject_rename(struct kobject *kobj, const char *new_name)
{
int error = ;
const char *devpath = NULL;
const char *dup_name = NULL, *name;
char *devpath_string = NULL;
char *envp[]; kobj = kobject_get(kobj);
if (!kobj)
return -EINVAL;
if (!kobj->parent)
return -EINVAL; devpath = kobject_get_path(kobj, GFP_KERNEL);
if (!devpath) {
error = -ENOMEM;
goto out;
}
devpath_string = kmalloc(strlen(devpath) + , GFP_KERNEL);
if (!devpath_string) {
error = -ENOMEM;
goto out;
}
sprintf(devpath_string, "DEVPATH_OLD=%s", devpath);
envp[] = devpath_string;
envp[] = NULL; name = dup_name = kstrdup_const(new_name, GFP_KERNEL);
if (!name) {
error = -ENOMEM;
goto out;
} error = sysfs_rename_dir_ns(kobj, new_name, kobject_namespace(kobj));
if (error)
goto out; /* Install the new kobject name */
dup_name = kobj->name;
kobj->name = name; /* This function is mostly/only used for network interface.
* Some hotplug package track interfaces by their name and
* therefore want to know when the name is changed by the user. */
kobject_uevent_env(kobj, KOBJ_MOVE, envp); out:
kfree_const(dup_name);
kfree(devpath_string);
kfree(devpath);
kobject_put(kobj); return error;
}
kobject_rename()函数实现的功能为，当kobj已经添加到系统后，可以使用此函数调用实现更改kobject的名字，它除了能完成kobject_set_name()的功能以外，还向用户空间通知这一消息。
/**
* kobject_move - move object to another parent
* @kobj: object in question.
* @new_parent: object's new parent (can be NULL)
*/
int kobject_move(struct kobject *kobj, struct kobject *new_parent)
{
int error;
struct kobject *old_parent;
const char *devpath = NULL;
char *devpath_string = NULL;
char *envp[]; kobj = kobject_get(kobj);
if (!kobj)
return -EINVAL;
new_parent = kobject_get(new_parent);
if (!new_parent) {
if (kobj->kset)
new_parent = kobject_get(&kobj->kset->kobj);
} /* old object path */
devpath = kobject_get_path(kobj, GFP_KERNEL);
if (!devpath) {
error = -ENOMEM;
goto out;
}
devpath_string = kmalloc(strlen(devpath) + , GFP_KERNEL);
if (!devpath_string) {
error = -ENOMEM;
goto out;
}
sprintf(devpath_string, "DEVPATH_OLD=%s", devpath);
envp[] = devpath_string;
envp[] = NULL;
error = sysfs_move_dir_ns(kobj, new_parent, kobject_namespace(kobj));
if (error)
goto out;
old_parent = kobj->parent;
kobj->parent = new_parent;
new_parent = NULL;
kobject_put(old_parent);
kobject_uevent_env(kobj, KOBJ_MOVE, envp);
out:
kobject_put(new_parent);
kobject_put(kobj);
kfree(devpath_string);
kfree(devpath);
return error;
}
kobjec_move()函数实现的功能是在kobj添加到系统后，调用此函数能将kobj移动到新的parent下，同时会通知用户空间。
/**
* kobject_del - unlink kobject from hierarchy.
* @kobj: object.
*/
void kobject_del(struct kobject *kobj)
{
struct kernfs_node *sd; if (!kobj)
return; sd = kobj->sd;
sysfs_remove_dir(kobj);
sysfs_put(sd); kobj->state_in_sysfs = ;
kobj_kset_leave(kobj);
kobject_put(kobj->parent);
kobj->parent = NULL;
}
kobject_del()函数用于将kobj从系统中删除，和kobject_add()是相对的操作。
/**
* kobject_get - increment refcount for object.
* @kobj: object.
*/
struct kobject *kobject_get(struct kobject *kobj)
{
if (kobj) {
if (!kobj->state_initialized)
WARN(, KERN_WARNING "kobject: '%s' (%p): is not "
"initialized, yet kobject_get() is being "
"called.\n", kobject_name(kobj), kobj);
kref_get(&kobj->kref);
}
return kobj;
}
/*
* kobject_cleanup - free kobject resources.
* @kobj: object to cleanup
*/
static void kobject_cleanup(struct kobject *kobj)
{
struct kobj_type *t = get_ktype(kobj);
const char *name = kobj->name; pr_debug("kobject: '%s' (%p): %s, parent %p\n",
kobject_name(kobj), kobj, __func__, kobj->parent); if (t && !t->release)
pr_debug("kobject: '%s' (%p): does not have a release() "
"function, it is broken and must be fixed.\n",
kobject_name(kobj), kobj); /* send "remove" if the caller did not do it but sent "add" */
if (kobj->state_add_uevent_sent && !kobj->state_remove_uevent_sent) {
pr_debug("kobject: '%s' (%p): auto cleanup 'remove' event\n",
kobject_name(kobj), kobj);
kobject_uevent(kobj, KOBJ_REMOVE);
} /* remove from sysfs if the caller did not do it */
if (kobj->state_in_sysfs) {
pr_debug("kobject: '%s' (%p): auto cleanup kobject_del\n",
kobject_name(kobj), kobj);
kobject_del(kobj);
} if (t && t->release) {
pr_debug("kobject: '%s' (%p): calling ktype release\n",
kobject_name(kobj), kobj);
t->release(kobj);
} /* free name if we allocated it */
if (name) {
pr_debug("kobject: '%s': free name\n", name);
kfree_const(name);
}
} #ifdef CONFIG_DEBUG_KOBJECT_RELEASE
static void kobject_delayed_cleanup(struct work_struct *work)
{
kobject_cleanup(container_of(to_delayed_work(work),
struct kobject, release));
}
#endif static void kobject_release(struct kref *kref)
{
struct kobject *kobj = container_of(kref, struct kobject, kref);
#ifdef CONFIG_DEBUG_KOBJECT_RELEASE
unsigned long delay = HZ + HZ * (get_random_int() & 0x3);
pr_info("kobject: '%s' (%p): %s, parent %p (delayed %ld)\n",
kobject_name(kobj), kobj, __func__, kobj->parent, delay);
INIT_DELAYED_WORK(&kobj->release, kobject_delayed_cleanup); schedule_delayed_work(&kobj->release, delay);
#else
kobject_cleanup(kobj);
#endif
} /**
* kobject_put - decrement refcount for object.
* @kobj: object.
*
* Decrement the refcount, and if 0, call kobject_cleanup().
*/
void kobject_put(struct kobject *kobj)
{
if (kobj) {
if (!kobj->state_initialized)
WARN(, KERN_WARNING "kobject: '%s' (%p): is not "
"initialized, yet kobject_put() is being "
"called.\n", kobject_name(kobj), kobj);
kref_put(&kobj->kref, kobject_release);
}
}
kobject_get()和kobject_put()函数完成的是kobject的引用计数功能，kobject_put()函数在当引用计数为0时，撤销整个kobject的存在：向用户空间发送REMOVE信息，从sysfs中删除相应的目录，并调用ktype中定义的release函数，并释放name所占用的空间。kobject_cleanup()函数用来释放kobject创建时所分配的资源。
上述提到到API接口，基本上概括了kobject从创建到删除，包括kobject的名字修改、位置修改以及引用计数的变动等功能。但是，kobject的创建仍然比较麻烦，因为ktype需要自己去实现，下面是Linux内核中为kobject提供的一种快速创建的方法：
首先是kobject的属性文件的读写函数定义：
/* default kobject attribute operations */
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,
};
然后是，kobject的释放函数，以及kobj_type结构体变量的定义，如下：
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,
};
这是Linux内核里面为kobject自身提供的一种kobj_type，名称叫做dynamic_kobj_type，它并没有提供默认的属性，但是提供了release函数和访问属性的方法。
/**
* kobject_create - create a struct kobject dynamically
*
* This function creates a kobject structure dynamically and sets it up
* to be a "dynamic" kobject with a default release function set up.
*
* If the kobject was not able to be created, NULL will be returned.
* The kobject structure returned from here must be cleaned up with a
* call to kobject_put() and not kfree(), as kobject_init() has
* already been called on this structure.
*/
struct kobject *kobject_create(void)
{
struct kobject *kobj; kobj = kzalloc(sizeof(*kobj), GFP_KERNEL);
if (!kobj)
return NULL; kobject_init(kobj, &dynamic_kobj_ktype);
return kobj;
} /**
* kobject_create_and_add - create a struct kobject dynamically and register it with sysfs
*
* @name: the name for the kobject
* @parent: the parent kobject of this kobject, if any.
*
* This function creates a kobject structure dynamically and registers it
* with sysfs. When you are finished with this structure, call
* kobject_put() and the structure will be dynamically freed when
* it is no longer being used.
*
* If the kobject was not able to be created, NULL will be returned.
*/
struct kobject *kobject_create_and_add(const char *name, struct kobject *parent)
{
struct kobject *kobj;
int retval; kobj = kobject_create();
if (!kobj)
return NULL; retval = kobject_add(kobj, parent, "%s", name);
if (retval) {
printk(KERN_WARNING "%s: kobject_add error: %d\n",
__func__, retval);
kobject_put(kobj);
kobj = NULL;
}
return kobj;
}
在kobject_create()和kobject_create_add()函数中，使用了dynamic_kobj_ktype这个结构体变量，这是一种很好的偷懒方式，因为release()函数会释放掉kobj，所以这里的kobj必须是动态创建的，这里的kobject_create()和kobject_init()相对，kobject_create_and_add()和kobject_init_and_add()相对。需要注意的是，这里创建的kobject无法嵌入到其它结构，是独立存在的，所以用到的地方很少。
/**
* kset_init - initialize a kset for use
* @k: kset
*/
void kset_init(struct kset *k)
{
kobject_init_internal(&k->kobj);
INIT_LIST_HEAD(&k->list);
spin_lock_init(&k->list_lock);
}
kset_init()函数用于将kset结构体初始化，和kobject初始化类似。
/**
* kset_register - initialize and add a kset.
* @k: kset.
*/
int kset_register(struct kset *k)
{
int err; if (!k)
return -EINVAL; kset_init(k);
err = kobject_add_internal(&k->kobj);
if (err)
return err;
kobject_uevent(&k->kobj, KOBJ_ADD);
return ;
}
kset_register()函数用来初始化并添加到kset，函数比较简单，它负责将kset中的kobject添加到系统，并向用户空间发布KOBJ_ADD消息，所以在调用之前，需要先设置好k->kobj.name、k->kobj.parent和k->kobj.kset这些成员。
/**
* kset_unregister - remove a kset.
* @k: kset.
*/
void kset_unregister(struct kset *k)
{
if (!k)
return;
kobject_del(&k->kobj);
kobject_put(&k->kobj);
}
kset_unregister()和kset_register()函数功能是相对的，用于移除kset，并减少引用计数。
/**
* kset_find_obj - search for object in kset.
* @kset: kset we're looking in.
* @name: object's name.
*
* Lock kset via @kset->subsys, and iterate over @kset->list,
* looking for a matching kobject. If matching object is found
* take a reference and return the object.
*/
struct kobject *kset_find_obj(struct kset *kset, const char *name)
{
struct kobject *k;
struct kobject *ret = NULL; spin_lock(&kset->list_lock); list_for_each_entry(k, &kset->list, entry) {
if (kobject_name(k) && !strcmp(kobject_name(k), name)) {
ret = kobject_get_unless_zero(k);
break;
}
} spin_unlock(&kset->list_lock);
return ret;
}
kset_find_obj()函数功能为通过从kset的链表中寻找名为name的kobject，实现了链表的遍历。
与kobject类似，kset也提供看一种kobj_type，名称为kset_ktype，实现如下：
static void kset_release(struct kobject *kobj)
{
struct kset *kset = container_of(kobj, struct kset, kobj);
pr_debug("kobject: '%s' (%p): %s\n",
kobject_name(kobj), kobj, __func__);
kfree(kset);
} void kset_get_ownership(struct kobject *kobj, kuid_t *uid, kgid_t *gid)
{
if (kobj->parent)
kobject_get_ownership(kobj->parent, uid, gid);
} static struct kobj_type kset_ktype = {
.sysfs_ops = &kobj_sysfs_ops,
.release = kset_release,
.get_ownership = kset_get_ownership,
}; /**
* kset_create - create a struct kset dynamically
*
* @name: the name for the kset
* @uevent_ops: a struct kset_uevent_ops for the kset
* @parent_kobj: the parent kobject of this kset, if any.
*
* This function creates a kset structure dynamically. This structure can
* then be registered with the system and show up in sysfs with a call to
* kset_register(). When you are finished with this structure, if
* kset_register() has been called, call kset_unregister() and the
* structure will be dynamically freed when it is no longer being used.
*
* If the kset was not able to be created, NULL will be returned.
*/
static struct kset *kset_create(const char *name,
const struct kset_uevent_ops *uevent_ops,
struct kobject *parent_kobj)
{
struct kset *kset;
int retval; kset = kzalloc(sizeof(*kset), GFP_KERNEL);
if (!kset)
return NULL;
retval = kobject_set_name(&kset->kobj, "%s", name);
if (retval) {
kfree(kset);
return NULL;
}
kset->uevent_ops = uevent_ops;
kset->kobj.parent = parent_kobj; /*
* The kobject of this kset will have a type of kset_ktype and belong to
* no kset itself. That way we can properly free it when it is
* finished being used.
*/
kset->kobj.ktype = &kset_ktype;
kset->kobj.kset = NULL; return kset;
} /**
* kset_create_and_add - create a struct kset dynamically and add it to sysfs
*
* @name: the name for the kset
* @uevent_ops: a struct kset_uevent_ops for the kset
* @parent_kobj: the parent kobject of this kset, if any.
*
* This function creates a kset structure dynamically and registers it
* with sysfs. When you are finished with this structure, call
* kset_unregister() and the structure will be dynamically freed when it
* is no longer being used.
*
* If the kset was not able to be created, NULL will be returned.
*/
struct kset *kset_create_and_add(const char *name,
const struct kset_uevent_ops *uevent_ops,
struct kobject *parent_kobj)
{
struct kset *kset;
int error; kset = kset_create(name, uevent_ops, parent_kobj);
if (!kset)
return NULL;
error = kset_register(kset);
if (error) {
kfree(kset);
return NULL;
}
return kset;
}
kset_create()和kset_create_and_add()就是使用kset_type来快速创建kset的函数，当需要在sysfs中创建单纯的目录时，可以使用这两个函数进行创建。
static inline struct kset *to_kset(struct kobject *kobj)
{
return kobj ? container_of(kobj, struct kset, kobj) : NULL;
} static inline struct kset *kset_get(struct kset *k)
{
return k ? to_kset(kobject_get(&k->kobj)) : NULL;
} static inline void kset_put(struct kset *k)
{
kobject_put(&k->kobj);
} static inline struct kobj_type *get_ktype(struct kobject *kobj)
{
return kobj->ktype;
}
上面这些函数是在kobject.h文件里面的内联函数，to_kset()函数通过kobj的指针获取kset结构体的首地址，kset_get()和kset_put()为引用计数操作，get_ktype()函数用于获取kobject的ktype类型。
4、 kobject的层次结构
内核用kobject结构将各个对象连接起来组成一个分层的结构体系，从而与模型化的子系统相匹配。kobject结构体中的parent指针成员、kset指针成员和链表list_head实现了kobject的层次结构，parent指针最重要的用途是在sysfs分层结构中定位对象，下图是一个简单的kobject、kset的分层结构图：
5、小节
本文主要对kobject结构体以及相关的结构体以及Linux内核提供的相关API做了简要介绍，kobject结构体和设备驱动模型和sysfs的实现密切相关，必须深刻理解。
参考：
https://blog.csdn.net/yuanmengliang/article/details/52700529
https://blog.csdn.net/qb_2008/article/details/6846779
https://www.cnblogs.com/xiaojiang1025/p/6193959.html
《LINUX设备驱动程序（第三版）》