1、前言
Linux内核中的设备驱动模型，是建立在sysfs设备文件系统和kobject上的，由总线（bus）、设备（device）、驱动（driver）和类（class）所组成的关系结构，在底层，Linux系统中的每个设备都有一个device结构体的实例，本文将对Linux内核的device结构体以及相关结构进行简要分析。
2、device结构体
在Linux内核源码中，struct device结构体的定义在include/linux/device.h中，实现的主要方法在drivers/base/core.c文件中，device结构体的定义如下所示：
struct device {
struct device *parent;
struct device_private *p;
struct kobject kobj;
const char *init_name; /* initial name of the device */
const struct device_type *type;
struct mutex mutex; /* mutex to synchronize calls to
* its driver.
*/
struct bus_type *bus; /* type of bus device is on */
struct device_driver *driver; /* which driver has allocated this
device */
void *platform_data; /* Platform specific data, device
core doesn't touch it */
void *driver_data; /* Driver data, set and get with
dev_set/get_drvdata */
struct dev_links_info links;
struct dev_pm_info power;
struct dev_pm_domain *pm_domain;
#ifdef CONFIG_GENERIC_MSI_IRQ_DOMAIN
struct irq_domain *msi_domain;
#endif
#ifdef CONFIG_PINCTRL
struct dev_pin_info *pins;
#endif
#ifdef CONFIG_GENERIC_MSI_IRQ
struct list_head msi_list;
#endif
#ifdef CONFIG_NUMA
int numa_node; /* NUMA node this device is close to */
#endif
const struct dma_map_ops *dma_ops;
u64 *dma_mask; /* dma mask (if dma'able device) */
u64 coherent_dma_mask;/* Like dma_mask, but for
alloc_coherent mappings as
not all hardware supports
64 bit addresses for consistent
allocations such descriptors. */
unsigned long dma_pfn_offset;
struct device_dma_parameters *dma_parms;
struct list_head dma_pools; /* dma pools (if dma'ble) */
struct dma_coherent_mem *dma_mem; /* internal for coherent mem
override */
#ifdef CONFIG_DMA_CMA
struct cma *cma_area; /* contiguous memory area for dma
allocations */
#endif
/* arch specific additions */
struct dev_archdata archdata;
struct device_node *of_node; /* associated device tree node */
struct fwnode_handle *fwnode; /* firmware device node */
dev_t devt; /* dev_t, creates the sysfs "dev" */
u32 id; /* device instance */
spinlock_t devres_lock;
struct list_head devres_head;
struct klist_node knode_class;
struct class *class;
const struct attribute_group **groups; /* optional groups */
void (*release)(struct device *dev);
struct iommu_group *iommu_group;
struct iommu_fwspec *iommu_fwspec;
bool offline_disabled:;
bool offline:;
bool of_node_reused:;
};
部分结构体成员解释：
parent：指向设备的“父”设备，它所连接的设备，在大多数情况下，父设备是某种总线或主机控制器，如果该成员为NULL，则该设备为顶级设备；
p：用于保存设备驱动核心部分的私有数据；
kobj：嵌入的struct kobject对象实例；
init_name：设备的初始名称
type：设备的类型，用于标识设备类型并携带特定类型信息；
mutex：用于同步的互斥锁；
bus：该设备所处于的总线；
driver：该设备所分配的驱动程序；
platform_data：设备中特定的平台数据；
driver_data：指向驱动程序特定的私有数据；
of_node：与设备数相联系的结构体指针；
devt：用于表示设备的设备号；
devres_lock：保护设备资源的自旋锁；
devres_head：设备资源的双向链表头；
knode_class：接入class链表时所需要的klist节点；
class：指向设备所属class的指针；
groups：该设备的属性集合；
release：函数指针，当设备需要释放时调用此函数。
device结构体中有一部分成员不愿意被外界看到，所以抽象出了struct device_private这个结构体，该结构体包括了设备驱动模型内部的链接，结构体定义如下：
struct device_private {
struct klist klist_children;
struct klist_node knode_parent;
struct klist_node knode_driver;
struct klist_node knode_bus;
struct list_head deferred_probe;
struct device *device;
};
部分结构体成员解释：
klist_children：子设备的klist链表；
knode_parent：接入父设备的klist_children时所需要的klist节点；
knode_driver：接入驱动的设备链表时所需要的klist节点；
knode_bus：接入总线的设备链表时所需要的klist节点；
device：回指struct device结构体的指针。
device结构体中包含了一个struct device_type结构体的指针，用于描述设备的类型，该结构体定义如下：
struct device_type {
const char *name;
const struct attribute_group **groups;
int (*uevent)(struct device *dev, struct kobj_uevent_env *env);
char *(*devnode)(struct device *dev, umode_t *mode,
kuid_t *uid, kgid_t *gid);
void (*release)(struct device *dev);
const struct dev_pm_ops *pm;
};
该结构体功能类似于kobj_type。
还有一个设备属性结构体，名称为struct device_attribute，是对struct attribute的进一步封装，并提供了设备属性的读写函数指针，结构体定义如下：
/* interface for exporting device attributes */
struct device_attribute {
struct attribute attr;
ssize_t (*show)(struct device *dev, struct device_attribute *attr,
char *buf);
ssize_t (*store)(struct device *dev, struct device_attribute *attr,
const char *buf, size_t count);
};
其它的一些struct device结构体成员，例如archdata、dma和devres等，是一些设备特有的东西，暂时不讨论，本文主要关心设备驱动模型的基本建立。
3、device的实现
接下来对device的实现进行简单分析，实现的方法主要在文件core.c中：
int __init devices_init(void)
{
devices_kset = kset_create_and_add("devices", &device_uevent_ops, NULL);///sys/devices目录
if (!devices_kset)
return -ENOMEM;
dev_kobj = kobject_create_and_add("dev", NULL);///sys/dev目录
if (!dev_kobj)
goto dev_kobj_err;
sysfs_dev_block_kobj = kobject_create_and_add("block", dev_kobj);///sys/dev/block目录
if (!sysfs_dev_block_kobj)
goto block_kobj_err;
sysfs_dev_char_kobj = kobject_create_and_add("char", dev_kobj);///sys/dev/char目录
if (!sysfs_dev_char_kobj)
goto char_kobj_err; return ; char_kobj_err:
kobject_put(sysfs_dev_block_kobj);
block_kobj_err:
kobject_put(dev_kobj);
dev_kobj_err:
kset_unregister(devices_kset);
return -ENOMEM;
}
devices_init()函数是在设备驱动模型初始化时调用的部分初始函数，它实现的功能是建立sysfs中的devices目录和dev目录，然后在dev目录下建立block和char两个子目录，block和char目录用来存放设备号文件。
#define to_dev_attr(_attr) container_of(_attr, struct device_attribute, attr) static ssize_t dev_attr_show(struct kobject *kobj, struct attribute *attr,
char *buf)
{
struct device_attribute *dev_attr = to_dev_attr(attr);
struct device *dev = kobj_to_dev(kobj);
ssize_t ret = -EIO; if (dev_attr->show)
ret = dev_attr->show(dev, dev_attr, buf);
if (ret >= (ssize_t)PAGE_SIZE) {
print_symbol("dev_attr_show: %s returned bad count\n",
(unsigned long)dev_attr->show);
}
return ret;
} static ssize_t dev_attr_store(struct kobject *kobj, struct attribute *attr,
const char *buf, size_t count)
{
struct device_attribute *dev_attr = to_dev_attr(attr);
struct device *dev = kobj_to_dev(kobj);
ssize_t ret = -EIO; if (dev_attr->store)
ret = dev_attr->store(dev, dev_attr, buf, count);
return ret;
} static const struct sysfs_ops dev_sysfs_ops = {
.show = dev_attr_show,
.store = dev_attr_store,
};
to_dev_attr()宏定义用来获取struct device_attribute结构体的首地址，dev_sysfs_ops结构体的内容就是device注册到sysfs设备文件系统的操作函数，dev_attr_show()和dev_attr_store()函数会调用struct device_attribute结构体内的读写属性相关函数。
static void device_release(struct kobject *kobj)
{
struct device *dev = kobj_to_dev(kobj);
struct device_private *p = dev->p; /*
* Some platform devices are driven without driver attached
* and managed resources may have been acquired. Make sure
* all resources are released.
*
* Drivers still can add resources into device after device
* is deleted but alive, so release devres here to avoid
* possible memory leak.
*/
devres_release_all(dev); if (dev->release)
dev->release(dev);
else if (dev->type && dev->type->release)
dev->type->release(dev);
else if (dev->class && dev->class->dev_release)
dev->class->dev_release(dev);
else
WARN(, KERN_ERR "Device '%s' does not have a release() "
"function, it is broken and must be fixed.\n",
dev_name(dev));
kfree(p);
} static const void *device_namespace(struct kobject *kobj)
{
struct device *dev = kobj_to_dev(kobj);
const void *ns = NULL; if (dev->class && dev->class->ns_type)
ns = dev->class->namespace(dev); return ns;
} static void device_get_ownership(struct kobject *kobj, kuid_t *uid, kgid_t *gid)
{
struct device *dev = kobj_to_dev(kobj); if (dev->class && dev->class->get_ownership)
dev->class->get_ownership(dev, uid, gid);
} static struct kobj_type device_ktype = {
.release = device_release,
.sysfs_ops = &dev_sysfs_ops,
.namespace = device_namespace,
.get_ownership = device_get_ownership,
};
当struct device结构体内的实例kobject引用计数到0时会调用device_release()函数来释放掉device，函数调用时，会先通过kobj指针获取device的首地址，然后判断device下的release()是否存在，如果存在则调用，否则，依次判断device下device_type下的release()和device下class下的dev_release()函数是否存在，存在则调用，最后将device_private结构体指针指向的内存释放掉。
static int dev_uevent_filter(struct kset *kset, struct kobject *kobj)
{
struct kobj_type *ktype = get_ktype(kobj); if (ktype == &device_ktype) {
struct device *dev = kobj_to_dev(kobj);
if (dev->bus)
return ;
if (dev->class)
return ;
}
return ;
} static const char *dev_uevent_name(struct kset *kset, struct kobject *kobj)
{
struct device *dev = kobj_to_dev(kobj); if (dev->bus)
return dev->bus->name;
if (dev->class)
return dev->class->name;
return NULL;
} static int dev_uevent(struct kset *kset, struct kobject *kobj,
struct kobj_uevent_env *env)
{
struct device *dev = kobj_to_dev(kobj);
int retval = ; /* add device node properties if present */
if (MAJOR(dev->devt)) {
const char *tmp;
const char *name;
umode_t mode = ;
kuid_t uid = GLOBAL_ROOT_UID;
kgid_t gid = GLOBAL_ROOT_GID; add_uevent_var(env, "MAJOR=%u", MAJOR(dev->devt));
add_uevent_var(env, "MINOR=%u", MINOR(dev->devt));
name = device_get_devnode(dev, &mode, &uid, &gid, &tmp);
if (name) {
add_uevent_var(env, "DEVNAME=%s", name);
if (mode)
add_uevent_var(env, "DEVMODE=%#o", mode & );
if (!uid_eq(uid, GLOBAL_ROOT_UID))
add_uevent_var(env, "DEVUID=%u", from_kuid(&init_user_ns, uid));
if (!gid_eq(gid, GLOBAL_ROOT_GID))
add_uevent_var(env, "DEVGID=%u", from_kgid(&init_user_ns, gid));
kfree(tmp);
}
} if (dev->type && dev->type->name)
add_uevent_var(env, "DEVTYPE=%s", dev->type->name); if (dev->driver)
add_uevent_var(env, "DRIVER=%s", dev->driver->name); /* Add common DT information about the device */
of_device_uevent(dev, env); /* have the bus specific function add its stuff */
if (dev->bus && dev->bus->uevent) {
retval = dev->bus->uevent(dev, env);
if (retval)
pr_debug("device: '%s': %s: bus uevent() returned %d\n",
dev_name(dev), __func__, retval);
} /* have the class specific function add its stuff */
if (dev->class && dev->class->dev_uevent) {
retval = dev->class->dev_uevent(dev, env);
if (retval)
pr_debug("device: '%s': %s: class uevent() "
"returned %d\n", dev_name(dev),
__func__, retval);
} /* have the device type specific function add its stuff */
if (dev->type && dev->type->uevent) {
retval = dev->type->uevent(dev, env);
if (retval)
pr_debug("device: '%s': %s: dev_type uevent() "
"returned %d\n", dev_name(dev),
__func__, retval);
} return retval;
} static const struct kset_uevent_ops device_uevent_ops = {
.filter = dev_uevent_filter,
.name = dev_uevent_name,
.uevent = dev_uevent,
};
kset_uevent_ops结构体内的函数是用于管理kset内部的kobject的uevent操作的，其中，filter()函数用于阻止一个kobject向用户空间发送uevent，当函数的返回值为0时表示阻止，在上面的dev_uevent_filter()函数中检查了device所属的bus或者class是否存在，如果都不存在，则返回0，也就是没有发送uevent的必要了，name()函数用于覆盖kset发送给用户空间的名称，在上面的dev_uevent_name()函数选择使用device所属的bus或者class的名称，uevent()函数是在uevent将被发送到用户空间之前进行调用的，用于向uevent中增加新的环境变量。
static ssize_t uevent_show(struct device *dev, struct device_attribute *attr,
char *buf)
{
struct kobject *top_kobj;
struct kset *kset;
struct kobj_uevent_env *env = NULL;
int i;
size_t count = ;
int retval; /* search the kset, the device belongs to */
top_kobj = &dev->kobj;
while (!top_kobj->kset && top_kobj->parent)
top_kobj = top_kobj->parent;
if (!top_kobj->kset)
goto out; kset = top_kobj->kset;
if (!kset->uevent_ops || !kset->uevent_ops->uevent)
goto out; /* respect filter */
if (kset->uevent_ops && kset->uevent_ops->filter)
if (!kset->uevent_ops->filter(kset, &dev->kobj))
goto out; env = kzalloc(sizeof(struct kobj_uevent_env), GFP_KERNEL);
if (!env)
return -ENOMEM; /* let the kset specific function add its keys */
retval = kset->uevent_ops->uevent(kset, &dev->kobj, env);
if (retval)
goto out; /* copy keys to file */
for (i = ; i < env->envp_idx; i++)
count += sprintf(&buf[count], "%s\n", env->envp[i]);
out:
kfree(env);
return count;
} static ssize_t uevent_store(struct device *dev, struct device_attribute *attr,
const char *buf, size_t count)
{
if (kobject_synth_uevent(&dev->kobj, buf, count))
dev_err(dev, "uevent: failed to send synthetic uevent\n"); return count;
}
static DEVICE_ATTR_RW(uevent);
device不仅在kset中添加了对uevent的管理，还把uevent信息封装成设备的一个属性文件uevent，其权限为拥有者可读写，其中uevent_show()函数用于在用户空间显示uevent中的环境变量，uevent_store()函数则用于将uevent属性写入到内核空间。
static int device_add_attrs(struct device *dev)
{
struct class *class = dev->class;
const struct device_type *type = dev->type;
int error; if (class) {
error = device_add_groups(dev, class->dev_groups);
if (error)
return error;
} if (type) {
error = device_add_groups(dev, type->groups);
if (error)
goto err_remove_class_groups;
} error = device_add_groups(dev, dev->groups);
if (error)
goto err_remove_type_groups; if (device_supports_offline(dev) && !dev->offline_disabled) {
error = device_create_file(dev, &dev_attr_online);
if (error)
goto err_remove_dev_groups;
} return ; err_remove_dev_groups:
device_remove_groups(dev, dev->groups);
err_remove_type_groups:
if (type)
device_remove_groups(dev, type->groups);
err_remove_class_groups:
if (class)
device_remove_groups(dev, class->dev_groups); return error;
} static void device_remove_attrs(struct device *dev)
{
struct class *class = dev->class;
const struct device_type *type = dev->type; device_remove_file(dev, &dev_attr_online);
device_remove_groups(dev, dev->groups); if (type)
device_remove_groups(dev, type->groups); if (class)
device_remove_groups(dev, class->dev_groups);
}
device_add_attrs()负责device中的属性添加，包括几个部分的集合，分别是class中groups、device_type中的groups还有device本身的groups，device_remove_attrs()则是相反的操作，负责删除device的属性。
static ssize_t dev_show(struct device *dev, struct device_attribute *attr,
char *buf)
{
return print_dev_t(buf, dev->devt);
}
static DEVICE_ATTR_RO(dev);
这里定义了一个名为dev的属性文件，其权限为拥有者只能读，函数实现的功能为显示设备的设备号。
/**
* device_create_file - create sysfs attribute file for device.
* @dev: device.
* @attr: device attribute descriptor.
*/
int device_create_file(struct device *dev,
const struct device_attribute *attr)
{
int error = ; if (dev) {
WARN(((attr->attr.mode & S_IWUGO) && !attr->store),
"Attribute %s: write permission without 'store'\n",
attr->attr.name);
WARN(((attr->attr.mode & S_IRUGO) && !attr->show),
"Attribute %s: read permission without 'show'\n",
attr->attr.name);
error = sysfs_create_file(&dev->kobj, &attr->attr);
} return error;
} /**
* device_remove_file - remove sysfs attribute file.
* @dev: device.
* @attr: device attribute descriptor.
*/
void device_remove_file(struct device *dev,
const struct device_attribute *attr)
{
if (dev)
sysfs_remove_file(&dev->kobj, &attr->attr);
} /**
* device_create_bin_file - create sysfs binary attribute file for device.
* @dev: device.
* @attr: device binary attribute descriptor.
*/
int device_create_bin_file(struct device *dev,
const struct bin_attribute *attr)
{
int error = -EINVAL;
if (dev)
error = sysfs_create_bin_file(&dev->kobj, attr);
return error;
} /**
* device_remove_bin_file - remove sysfs binary attribute file
* @dev: device.
* @attr: device binary attribute descriptor.
*/
void device_remove_bin_file(struct device *dev,
const struct bin_attribute *attr)
{
if (dev)
sysfs_remove_bin_file(&dev->kobj, attr);
}
上面这些函数是对sysfs提供的API进行简单的封装，其中device_create_file()和device_remove_file()提供直接的设备属性文件管理方法，device_create_bin_file()和device_remove_bin_file()则是提供设备管理二进制文件的方法。
static void klist_children_get(struct klist_node *n)
{
struct device_private *p = to_device_private_parent(n);
struct device *dev = p->device; get_device(dev);
} static void klist_children_put(struct klist_node *n)
{
struct device_private *p = to_device_private_parent(n);
struct device *dev = p->device; put_device(dev);
}
klist_children_get()和klist_children_put()函数是当设备挂入和删除父设备的klist_children链表时调用的函数，相当于对设备的kobject引用计数的操作。
/**
* get_device - increment reference count for device.
* @dev: device.
*
* This simply forwards the call to kobject_get(), though
* we do take care to provide for the case that we get a NULL
* pointer passed in.
*/
struct device *get_device(struct device *dev)
{
return dev ? kobj_to_dev(kobject_get(&dev->kobj)) : NULL;
} /**
* put_device - decrement reference count.
* @dev: device in question.
*/
void put_device(struct device *dev)
{
/* might_sleep(); */
if (dev)
kobject_put(&dev->kobj);
}
get_device()函数和put_device()用于dev的引用计数，通过内嵌的kobject来实现，当引用计数为0时，将会调用前面分析到的device_release()函数。
void device_initialize(struct device *dev)
{
dev->kobj.kset = devices_kset;
kobject_init(&dev->kobj, &device_ktype);
INIT_LIST_HEAD(&dev->dma_pools);
mutex_init(&dev->mutex);
lockdep_set_novalidate_class(&dev->mutex);
spin_lock_init(&dev->devres_lock);
INIT_LIST_HEAD(&dev->devres_head);
device_pm_init(dev);
set_dev_node(dev, -);
#ifdef CONFIG_GENERIC_MSI_IRQ
INIT_LIST_HEAD(&dev->msi_list);
#endif
INIT_LIST_HEAD(&dev->links.consumers);
INIT_LIST_HEAD(&dev->links.suppliers);
dev->links.status = DL_DEV_NO_DRIVER;
}
device_initialize()函数是设备在sysfs中注册的第一个阶段，用于将struct device结构体进行初始化，主要是对结构体内的一些成员进行初始化，结构体内嵌的kobject下的kset配置为devices_kset，调用kobject_init()函数设置device_ktype和sysfs_ops结构中的两个函数和device_release()函数，另外还有一些特定资源需要的成员的初始化。
static struct kobject *get_device_parent(struct device *dev,
struct device *parent)
{
if (dev->class) {
struct kobject *kobj = NULL;
struct kobject *parent_kobj;
struct kobject *k; #ifdef CONFIG_BLOCK
/* block disks show up in /sys/block */
if (sysfs_deprecated && dev->class == &block_class) {
if (parent && parent->class == &block_class)
return &parent->kobj;
return &block_class.p->subsys.kobj;
}
#endif /*
* If we have no parent, we live in "virtual".
* Class-devices with a non class-device as parent, live
* in a "glue" directory to prevent namespace collisions.
*/
if (parent == NULL)
parent_kobj = virtual_device_parent(dev);
else if (parent->class && !dev->class->ns_type)
return &parent->kobj;
else
parent_kobj = &parent->kobj; mutex_lock(&gdp_mutex); /* find our class-directory at the parent and reference it */
spin_lock(&dev->class->p->glue_dirs.list_lock);
list_for_each_entry(k, &dev->class->p->glue_dirs.list, entry)
if (k->parent == parent_kobj) {
kobj = kobject_get(k);
break;
}
spin_unlock(&dev->class->p->glue_dirs.list_lock);
if (kobj) {
mutex_unlock(&gdp_mutex);
return kobj;
} /* or create a new class-directory at the parent device */
k = class_dir_create_and_add(dev->class, parent_kobj);
/* do not emit an uevent for this simple "glue" directory */
mutex_unlock(&gdp_mutex);
return k;
} /* subsystems can specify a default root directory for their devices */
if (!parent && dev->bus && dev->bus->dev_root)
return &dev->bus->dev_root->kobj; if (parent)
return &parent->kobj;
return NULL;
}
函数get_device_parent()用于获取父节点的kobject，get_device_parent()的返回值直接决定了device将被挂在哪个目录下，设备最终挂在的目录，是由多个因素综合决定的。
static int device_add_class_symlinks(struct device *dev)
{
struct device_node *of_node = dev_of_node(dev);
int error; if (of_node) {
error = sysfs_create_link(&dev->kobj, of_node_kobj(of_node), "of_node");
if (error)
dev_warn(dev, "Error %d creating of_node link\n",error);
/* An error here doesn't warrant bringing down the device */
} if (!dev->class)
return ; error = sysfs_create_link(&dev->kobj,
&dev->class->p->subsys.kobj,
"subsystem");
if (error)
goto out_devnode; if (dev->parent && device_is_not_partition(dev)) {
error = sysfs_create_link(&dev->kobj, &dev->parent->kobj,
"device");
if (error)
goto out_subsys;
} #ifdef CONFIG_BLOCK
/* /sys/block has directories and does not need symlinks */
if (sysfs_deprecated && dev->class == &block_class)
return ;
#endif /* link in the class directory pointing to the device */
error = sysfs_create_link(&dev->class->p->subsys.kobj,
&dev->kobj, dev_name(dev));
if (error)
goto out_device; return ; out_device:
sysfs_remove_link(&dev->kobj, "device"); out_subsys:
sysfs_remove_link(&dev->kobj, "subsystem");
out_devnode:
sysfs_remove_link(&dev->kobj, "of_node");
return error;
}
device_add_class_symlinks()函数用于在device和class直接添加一些软链接，在device目录下创建指向class的subsystem文件，在class目录下创建指向device的同名文件，如果device有父设备，而且device不是块设备分区时，则在device目录下创建一个指向父设备的device链接文件。
static void device_remove_class_symlinks(struct device *dev)
{
if (dev_of_node(dev))
sysfs_remove_link(&dev->kobj, "of_node"); if (!dev->class)
return; if (dev->parent && device_is_not_partition(dev))
sysfs_remove_link(&dev->kobj, "device");
sysfs_remove_link(&dev->kobj, "subsystem");
#ifdef CONFIG_BLOCK
if (sysfs_deprecated && dev->class == &block_class)
return;
#endif
sysfs_delete_link(&dev->class->p->subsys.kobj, &dev->kobj, dev_name(dev));
}
device_remove_class_symlinks()函数则是相反操作，用于删除device和class之间建立的软链接。
/**
* dev_set_name - set a device name
* @dev: device
* @fmt: format string for the device's name
*/
int dev_set_name(struct device *dev, const char *fmt, ...)
{
va_list vargs;
int err; va_start(vargs, fmt);
err = kobject_set_name_vargs(&dev->kobj, fmt, vargs);
va_end(vargs);
return err;
}
dev_set_name()函数用于设置device的名称，该函数只能在设备未注册之前使用，名称是通过dev->kobject进行管理的。
static struct kobject *device_to_dev_kobj(struct device *dev)
{
struct kobject *kobj; if (dev->class)
kobj = dev->class->dev_kobj;
else
kobj = sysfs_dev_char_kobj; return kobj;
}
该函数用于为device选择合适的/sys/dev下的kobject或者字符设备或者NULL。
#define format_dev_t(buffer, dev) \
({ \
sprintf(buffer, "%u:%u", MAJOR(dev), MINOR(dev)); \
buffer; \
}) static int device_create_sys_dev_entry(struct device *dev)
{
struct kobject *kobj = device_to_dev_kobj(dev);
int error = ;
char devt_str[]; if (kobj) {
format_dev_t(devt_str, dev->devt);
error = sysfs_create_link(kobj, &dev->kobj, devt_str);
} return error;
} static void device_remove_sys_dev_entry(struct device *dev)
{
struct kobject *kobj = device_to_dev_kobj(dev);
char devt_str[]; if (kobj) {
format_dev_t(devt_str, dev->devt);
sysfs_remove_link(kobj, devt_str);
}
}
device_create_sys_dev_entry()函数实现的功能是在/sys/dev相应的目录下创建相应设备的软链接，首先通过调用device_to_dev_kobj()函数获得父节点的kobj，然后调用sysfs_create_link()函数建立软链接，device_remove_sys_dev_entry()函数则是执行相反的操作，用于删除已经在/sys/dev下建立的软链接。
int device_private_init(struct device *dev)
{
dev->p = kzalloc(sizeof(*dev->p), GFP_KERNEL);
if (!dev->p)
return -ENOMEM;
dev->p->device = dev;
klist_init(&dev->p->klist_children, klist_children_get,
klist_children_put);
INIT_LIST_HEAD(&dev->p->deferred_probe);
return ;
}
函数device_private_init()为dev->p分配内存空间并进行初始化，该内存的空间释放是在调用device_release()函数释放设备时才会释放。
上面提到到的函数都是比较零散的函数，看起来并没有什么联系，接下来继续分析一下提供给外界的接口函数实现：
/**
* device_register - register a device with the system.
* @dev: pointer to the device structure
*
* This happens in two clean steps - initialize the device
* and add it to the system. The two steps can be called
* separately, but this is the easiest and most common.
* I.e. you should only call the two helpers separately if
* have a clearly defined need to use and refcount the device
* before it is added to the hierarchy.
*
* For more information, see the kerneldoc for device_initialize()
* and device_add().
*
* NOTE: _Never_ directly free @dev after calling this function, even
* if it returned an error! Always use put_device() to give up the
* reference initialized in this function instead.
*/
int device_register(struct device *dev)
{
device_initialize(dev);
return device_add(dev);
}
首先是device_register()函数，该函数是提供给外界注册设备的接口，该函数首先调用device_initialize()函数进行结构体的变量初始化，然后调用device_add()函数将device添加到系统中，但是需要注意的是，在调用device_register()注册device之前，有一些device结构体变量需要自己设置，其中有指明设备位置的struct device *parent、struct bus_type *bus、struct class *class等，有指明设备属性的const char *init_name、struct device_type *type、const struct attribute_group **groups、dev_t devt和release()函数等，不同的设备使用的方法不同。
接下来分析device_add()函数的实现：
/**
* device_add - add device to device hierarchy.
* @dev: device.
*
* This is part 2 of device_register(), though may be called
* separately _iff_ device_initialize() has been called separately.
*
* This adds @dev to the kobject hierarchy via kobject_add(), adds it
* to the global and sibling lists for the device, then
* adds it to the other relevant subsystems of the driver model.
*
* Do not call this routine or device_register() more than once for
* any device structure. The driver model core is not designed to work
* with devices that get unregistered and then spring back to life.
* (Among other things, it's very hard to guarantee that all references
* to the previous incarnation of @dev have been dropped.) Allocate
* and register a fresh new struct device instead.
*
* NOTE: _Never_ directly free @dev after calling this function, even
* if it returned an error! Always use put_device() to give up your
* reference instead.
*/
int device_add(struct device *dev)
{
struct device *parent;
struct kobject *kobj;
struct class_interface *class_intf;
int error = -EINVAL;
struct kobject *glue_dir = NULL; dev = get_device(dev); //增加device的引用计数
if (!dev)
goto done; if (!dev->p) {
error = device_private_init(dev); //分配和初始化dev->p
if (error)
goto done;
} /*
* for statically allocated devices, which should all be converted
* some day, we need to initialize the name. We prevent reading back
* the name, and force the use of dev_name()
*/
if (dev->init_name) {
dev_set_name(dev, "%s", dev->init_name); //设置设备的名称
dev->init_name = NULL;
} /* subsystems can specify simple device enumeration */
if (!dev_name(dev) && dev->bus && dev->bus->dev_name)
dev_set_name(dev, "%s%u", dev->bus->dev_name, dev->id); if (!dev_name(dev)) {
error = -EINVAL;
goto name_error;
} pr_debug("device: '%s': %s\n", dev_name(dev), __func__); parent = get_device(dev->parent); //增加对parent的引用计数，无parent时返回NULL
kobj = get_device_parent(dev, parent); //获取父kobject
if (IS_ERR(kobj)) {
error = PTR_ERR(kobj);
goto parent_error;
}
if (kobj)
dev->kobj.parent = kobj; //设置dev->kobj的父kobject /* use parent numa_node */
if (parent && (dev_to_node(dev) == NUMA_NO_NODE))
set_dev_node(dev, dev_to_node(parent)); /* first, register with generic layer. */
/* we require the name to be set before, and pass NULL */
error = kobject_add(&dev->kobj, dev->kobj.parent, NULL); //将device内嵌的kobj加入到kobject层次结构中
if (error) {
glue_dir = get_glue_dir(dev);
goto Error;
} /* notify platform of device entry */
if (platform_notify)
platform_notify(dev); error = device_create_file(dev, &dev_attr_uevent); //添加uevent属性文件
if (error)
goto attrError; error = device_add_class_symlinks(dev); //dev与class软链接创建
if (error)
goto SymlinkError;
error = device_add_attrs(dev); //添加属性
if (error)
goto AttrsError;
error = bus_add_device(dev); //将设备添加到总线上，创建dev与bus间的软链接
if (error)
goto BusError;
error = dpm_sysfs_add(dev); //增加dev下的power属性集合
if (error)
goto DPMError;
device_pm_add(dev); if (MAJOR(dev->devt)) { //主设备号存在
error = device_create_file(dev, &dev_attr_dev); //添加dev属性
if (error)
goto DevAttrError; error = device_create_sys_dev_entry(dev); //在/sys/dev下添加相应的软链接
if (error)
goto SysEntryError; devtmpfs_create_node(dev); //在/dev下添加相应的设备节点
} /* Notify clients of device addition. This call must come
* after dpm_sysfs_add() and before kobject_uevent().
*/
if (dev->bus)
blocking_notifier_call_chain(&dev->bus->p->bus_notifier,
BUS_NOTIFY_ADD_DEVICE, dev); kobject_uevent(&dev->kobj, KOBJ_ADD); //kobject发布KOBJ_ADD消息到用户空间
bus_probe_device(dev); //为device寻找合适的驱动
if (parent)
klist_add_tail(&dev->p->knode_parent,
&parent->p->klist_children); //如果父节点存在，将挂入到klist_children链表 if (dev->class) { //如果device所属的class存在
mutex_lock(&dev->class->p->mutex);
/* tie the class to the device */
klist_add_tail(&dev->knode_class,
&dev->class->p->klist_devices); //节点插入链表 /* notify any interfaces that the device is here */
list_for_each_entry(class_intf,
&dev->class->p->interfaces, node)
if (class_intf->add_dev)
class_intf->add_dev(dev, class_intf);
mutex_unlock(&dev->class->p->mutex);
}
done:
put_device(dev); //减少device的引用计数
return error;
SysEntryError:
if (MAJOR(dev->devt))
device_remove_file(dev, &dev_attr_dev);
DevAttrError:
device_pm_remove(dev);
dpm_sysfs_remove(dev);
DPMError:
bus_remove_device(dev);
BusError:
device_remove_attrs(dev);
AttrsError:
device_remove_class_symlinks(dev);
SymlinkError:
device_remove_file(dev, &dev_attr_uevent);
attrError:
kobject_uevent(&dev->kobj, KOBJ_REMOVE);
glue_dir = get_glue_dir(dev);
kobject_del(&dev->kobj);
Error:
cleanup_glue_dir(dev, glue_dir);
parent_error:
put_device(parent);
name_error:
kfree(dev->p);
dev->p = NULL;
goto done;
}
函数device_add()用于将dev添加到设备驱动模型中去，它先调用get_device()来增加dev的引用计数，然后调用device_private_init()进行dev->p的分配和初始化，调用dev_set_name()对dev的名字进行设置，接下来，要做的是准备将dev添加到sysfs设备文件系统中去，首先是调用get_device()增加对paren的引用计数（无论是直接挂在parent下还是通过一个类层挂在parent下都要增加parent的引用计数），然后调用get_device_parent()找到实际要加入的父kobject，并调用kobject_add()将dev->kobj加入到dev->kobj.parent的层次结构中去，接下来是完成属性和属性集合的添加，调用device_create_file()添加uevent属性文件，然后调用device_add_class_symlinks()在dev下创建一个软链接subsystem，指向相对应的class，然后继续调用device_add_attrs()添加属性和属性集合，调用bus_add_device()添加设备的总线属性，在dev与bus之间创建软链接，并将dev挂入到总线的设备链表中去，dpm_sysfs_add()用于增加dev下的power属性集合，调用device_pm_add()将设备添加到dpm_list链表中去。如果设备被分配了主设备号，调用device_create_file()添加dev属性文件，然后调用device_create_sys_dev_entry()在/sys/dev下创建相应的软链接，调用devtmpfs_create_node()在/dev下添加对应的设备节点文件。函数开始调用kobject_uevent()向用户空间发布KOBJ_ADD消息通知，并调用bus_probe_device()为设备探测寻找合适的驱动程序，如果设备有父节点的话，则把dev->p->knode_parent挂入到parent->p->klist_children链表中，如果设备有所属的class，则将dev->knode_class挂入class->p>class_devices上，并调用可能的类设备接口add_dev()函数，对于直接在bus上的设备来讲，可以调用bus_probe_device()来查找驱动程序，但是不与bus直接接触的设备，则靠class来去寻找驱动，便使用了class_interface内的add_dev()方式，函数最后调用put_device()减少在开头增加的引用计数并返回。
/**
* device_unregister - unregister device from system.
* @dev: device going away.
*
* We do this in two parts, like we do device_register(). First,
* we remove it from all the subsystems with device_del(), then
* we decrement the reference count via put_device(). If that
* is the final reference count, the device will be cleaned up
* via device_release() above. Otherwise, the structure will
* stick around until the final reference to the device is dropped.
*/
void device_unregister(struct device *dev)
{
pr_debug("device: '%s': %s\n", dev_name(dev), __func__);
device_del(dev);
put_device(dev);
}
有设备注册函数，肯定也有设备注销函数，device_unregister()函数实现的功能为将dev从系统中注销，并减少创建时产生的引用计数，当引用计数为0时，将销毁dev。
/**
* device_del - delete device from system.
* @dev: device.
*
* This is the first part of the device unregistration
* sequence. This removes the device from the lists we control
* from here, has it removed from the other driver model
* subsystems it was added to in device_add(), and removes it
* from the kobject hierarchy.
*
* NOTE: this should be called manually _iff_ device_add() was
* also called manually.
*/
void device_del(struct device *dev)
{
struct device *parent = dev->parent;
struct kobject *glue_dir = NULL;
struct class_interface *class_intf; /* Notify clients of device removal. This call must come
* before dpm_sysfs_remove().
*/
if (dev->bus)
blocking_notifier_call_chain(&dev->bus->p->bus_notifier,
BUS_NOTIFY_DEL_DEVICE, dev); dpm_sysfs_remove(dev); //将sysfs下的power属性集合移除
if (parent) //如果存在父节点
klist_del(&dev->p->knode_parent); //将设备节点从父节点链表中移除
if (MAJOR(dev->devt)) { //如果分配了主设备号
devtmpfs_delete_node(dev); //将/dev下的设备节点文件移除
device_remove_sys_dev_entry(dev); ///sys/dev下的软链接取消
device_remove_file(dev, &dev_attr_dev); //将属性文件移除
}
if (dev->class) {
device_remove_class_symlinks(dev); mutex_lock(&dev->class->p->mutex);
/* notify any interfaces that the device is now gone */
list_for_each_entry(class_intf,
&dev->class->p->interfaces, node)
if (class_intf->remove_dev)
class_intf->remove_dev(dev, class_intf);
/* remove the device from the class list */
klist_del(&dev->knode_class);
mutex_unlock(&dev->class->p->mutex);
}
device_remove_file(dev, &dev_attr_uevent); //移除uevent属性文件
device_remove_attrs(dev); //属性及属性集合移除
bus_remove_device(dev); //总线上移除设备
device_pm_remove(dev); //将dev从dpm_list中移除
driver_deferred_probe_del(dev); //驱动移除
device_remove_properties(dev);
device_links_purge(dev); /* Notify the platform of the removal, in case they
* need to do anything...
*/
if (platform_notify_remove)
platform_notify_remove(dev);
if (dev->bus)
blocking_notifier_call_chain(&dev->bus->p->bus_notifier,
BUS_NOTIFY_REMOVED_DEVICE, dev);
kobject_uevent(&dev->kobj, KOBJ_REMOVE); //kobject发布KOBJ_REMOVE消息到用户空间
glue_dir = get_glue_dir(dev);
kobject_del(&dev->kobj); //将内嵌的kobj从层次结构中移除
cleanup_glue_dir(dev, glue_dir);
put_device(parent); //父节点引用计数减1操作
}
函数device_del()是与device_add()相对的函数，device_add()将设备添加到系统中，device_del()则是将设备从系统中移除，包括了将dev从设备驱动模型的各种klist链表中进行脱离，又将dev从sysfs的各个地方创建的文件进行删除的工作。
static struct device *prev_device(struct klist_iter *i) //返回前一个设备
{
struct klist_node *n = klist_prev(i);
struct device *dev = NULL;
struct device_private *p; if (n) {
p = to_device_private_parent(n);//返回device_private结构体的首地址
dev = p->device;//将struct device结构体地址返回
}
return dev;
} static struct device *next_device(struct klist_iter *i)
{
struct klist_node *n = klist_next(i);
struct device *dev = NULL;
struct device_private *p; if (n) {
p = to_device_private_parent(n);
dev = p->device;
}
return dev;
}
内部函数prev_device()和next_device()用于device的klist的链表遍历，prev_device()将返回前一个设备，next_device()将返回下一个设备。
/**
* device_get_devnode - path of device node file
* @dev: device
* @mode: returned file access mode
* @uid: returned file owner
* @gid: returned file group
* @tmp: possibly allocated string
*
* Return the relative path of a possible device node.
* Non-default names may need to allocate a memory to compose
* a name. This memory is returned in tmp and needs to be
* freed by the caller.
*/
const char *device_get_devnode(struct device *dev,
umode_t *mode, kuid_t *uid, kgid_t *gid,
const char **tmp)
{
char *s; *tmp = NULL; /* the device type may provide a specific name */
if (dev->type && dev->type->devnode)
*tmp = dev->type->devnode(dev, mode, uid, gid);
if (*tmp)
return *tmp; /* the class may provide a specific name */
if (dev->class && dev->class->devnode)
*tmp = dev->class->devnode(dev, mode);
if (*tmp)
return *tmp; /* return name without allocation, tmp == NULL */
if (strchr(dev_name(dev), '!') == NULL)
return dev_name(dev); /* replace '!' in the name with '/' */
s = kstrdup(dev_name(dev), GFP_KERNEL);
if (!s)
return NULL;
strreplace(s, '!', '/');
return *tmp = s;
}
函数device_get_devnode()用于返回设备的路径名。
/**
* device_for_each_child - device child iterator.
* @parent: parent struct device.
* @fn: function to be called for each device.
* @data: data for the callback.
*
* Iterate over @parent's child devices, and call @fn for each,
* passing it @data.
*
* We check the return of @fn each time. If it returns anything
* other than 0, we break out and return that value.
*/
int device_for_each_child(struct device *parent, void *data,
int (*fn)(struct device *dev, void *data))
{
struct klist_iter i;
struct device *child;
int error = ; if (!parent->p)
return ; klist_iter_init(&parent->p->klist_children, &i);//迭代器初始化，从链表头开始
while ((child = next_device(&i)) && !error) //正序遍历klist_children链表
error = fn(child, data);
klist_iter_exit(&i);
return error;
} int device_for_each_child_reverse(struct device *parent, void *data,
int (*fn)(struct device *dev, void *data))
{
struct klist_iter i;
struct device *child;
int error = ; if (!parent->p)
return ; klist_iter_init(&parent->p->klist_children, &i);
while ((child = prev_device(&i)) && !error) //逆序遍历klist_children链表
error = fn(child, data);
klist_iter_exit(&i);
return error;
} struct device *device_find_child(struct device *parent, void *data,
int (*match)(struct device *dev, void *data))
{
struct klist_iter i;
struct device *child; if (!parent)
return NULL; klist_iter_init(&parent->p->klist_children, &i);
while ((child = next_device(&i)))
if (match(child, data) && get_device(child))
break;
klist_iter_exit(&i);
return child;
}
在上面的函数都是对设备链表的遍历，device_for_each_child()函数和device_for_each_child_reverse()函数对父设备下的子设备进行遍历，并都调用一个特定的函数fn()进行处理，device_find_child()函数则是查找特定的子设备，查找使用特定match()函数进行匹配。
接下来，继续分析动态创建struct device的方法，其原理和kobject和kset的动态创建类似：
static void device_create_release(struct device *dev)
{
pr_debug("device: '%s': %s\n", dev_name(dev), __func__);
kfree(dev);
} static struct device *
device_create_groups_vargs(struct class *class, struct device *parent,
dev_t devt, void *drvdata,
const struct attribute_group **groups,
const char *fmt, va_list args)
{
struct device *dev = NULL;
int retval = -ENODEV; if (class == NULL || IS_ERR(class))//判断class指针是否有效
goto error; dev = kzalloc(sizeof(*dev), GFP_KERNEL);//为dev动态分配内存
if (!dev) {
retval = -ENOMEM;
goto error;
} device_initialize(dev);//设备初始化
dev->devt = devt;
dev->class = class;
dev->parent = parent;
dev->groups = groups;
dev->release = device_create_release;
dev_set_drvdata(dev, drvdata); retval = kobject_set_name_vargs(&dev->kobj, fmt, args);//设置kobject的name
if (retval)
goto error; retval = device_add(dev);//将设备添加到sysfs层次系统
if (retval)
goto error; return dev; error:
put_device(dev);
return ERR_PTR(retval);//将异常指针返回
} /**
* device_create_vargs - creates a device and registers it with sysfs
* @class: pointer to the struct class that this device should be registered to
* @parent: pointer to the parent struct device of this new device, if any
* @devt: the dev_t for the char device to be added
* @drvdata: the data to be added to the device for callbacks
* @fmt: string for the device's name
* @args: va_list for the device's name
*
* This function can be used by char device classes. A struct device
* will be created in sysfs, registered to the specified class.
*
* A "dev" file will be created, showing the dev_t for the device, if
* the dev_t is not 0,0.
* If a pointer to a parent struct device is passed in, the newly created
* struct device will be a child of that device in sysfs.
* The pointer to the struct device will be returned from the call.
* Any further sysfs files that might be required can be created using this
* pointer.
*
* Returns &struct device pointer on success, or ERR_PTR() on error.
*
* Note: the struct class passed to this function must have previously
* been created with a call to class_create().
*/
struct device *device_create_vargs(struct class *class, struct device *parent,
dev_t devt, void *drvdata, const char *fmt,
va_list args)
{
return device_create_groups_vargs(class, parent, devt, drvdata, NULL,
fmt, args);
} struct device *device_create(struct class *class, struct device *parent,
dev_t devt, void *drvdata, const char *fmt, ...)
{
va_list vargs;
struct device *dev; va_start(vargs, fmt);
dev = device_create_vargs(class, parent, devt, drvdata, fmt, vargs);
va_end(vargs);
return dev;
} struct device *device_create_with_groups(struct class *class,
struct device *parent, dev_t devt,
void *drvdata,
const struct attribute_group **groups,
const char *fmt, ...)
{
va_list vargs;
struct device *dev; va_start(vargs, fmt);
dev = device_create_groups_vargs(class, parent, devt, drvdata, groups,
fmt, vargs);
va_end(vargs);
return dev;
}
在上面代码中，device_create_release()和device_create_groups_vargs()属于两个内部的静态函数，第一个函数用于释放device分配的内核空间，由于dev是动态分配的，而第二个函数则是用来动态创建一个device，函数首先对传入的class进行判断，然后对device进行内存分配，分配成功后就是开始调用device_initialize()对设备初始化，并手动对device的一些成员进行赋值，然后调用kobject_set_name_vargs()对device中嵌入的kobject进行名称设置，最后，则是调用device_add()函数将动态创建的device添加到sysfs层次系统，而device_create_vargs()、device_create()和device_create_with_groups()都是对device_create_groups_vargs()的进一步封装，device_create()和device_create_with_groups()的区别在于创建的时候是否要创建device的组属性文件。
static int __match_devt(struct device *dev, const void *data)
{
const dev_t *devt = data; return dev->devt == *devt;//设备号匹配
} /**
* device_destroy - removes a device that was created with device_create()
* @class: pointer to the struct class that this device was registered with
* @devt: the dev_t of the device that was previously registered
*
* This call unregisters and cleans up a device that was created with a
* call to device_create().
*/
void device_destroy(struct class *class, dev_t devt)
{
struct device *dev; dev = class_find_device(class, NULL, &devt, __match_devt);//在class下寻找设备
if (dev) {
put_device(dev);//减少引用计数
device_unregister(dev);//注销设备
}
}
device_create()用于动态创建一个设备，而device_destroy()函数则用来销毁一个device_create()创建出来的设备，__match_devt()属于内部的静态函数，用于class_find_device()函数寻找需要销毁的device，主要是通过设备号进行匹配而寻找，之所以需要使用put_device()减少引用计数，是因为使用class_find_device()中调用了get_device()增加了引用计数。
int device_rename(struct device *dev, const char *new_name)
{
struct kobject *kobj = &dev->kobj;
char *old_device_name = NULL;
int error; dev = get_device(dev);
if (!dev)
return -EINVAL; dev_dbg(dev, "renaming to %s\n", new_name); old_device_name = kstrdup(dev_name(dev), GFP_KERNEL);
if (!old_device_name) {
error = -ENOMEM;
goto out;
} if (dev->class) {
error = sysfs_rename_link_ns(&dev->class->p->subsys.kobj,
kobj, old_device_name,
new_name, kobject_namespace(kobj));
if (error)
goto out;
} error = kobject_rename(kobj, new_name);
if (error)
goto out; out:
put_device(dev); kfree(old_device_name); return error;
}
函数device_rename()是当设备在sysfs中注册后，用来改变设备的名称用的，首先改变/sys/class目录下的软链接的名称，然后使用kobject_rename()将device下嵌入的kobject进行重新命名。
/**
* device_shutdown - call ->shutdown() on each device to shutdown.
*/
void device_shutdown(void)
{
struct device *dev, *parent; spin_lock(&devices_kset->list_lock);
/*
* Walk the devices list backward, shutting down each in turn.
* Beware that device unplug events may also start pulling
* devices offline, even as the system is shutting down.
*/
while (!list_empty(&devices_kset->list)) {
dev = list_entry(devices_kset->list.prev, struct device,
kobj.entry); /*
* hold reference count of device's parent to
* prevent it from being freed because parent's
* lock is to be held
*/
parent = get_device(dev->parent);
get_device(dev);
/*
* Make sure the device is off the kset list, in the
* event that dev->*->shutdown() doesn't remove it.
*/
list_del_init(&dev->kobj.entry);
spin_unlock(&devices_kset->list_lock); /* hold lock to avoid race with probe/release */
if (parent)
device_lock(parent);
device_lock(dev); /* Don't allow any more runtime suspends */
pm_runtime_get_noresume(dev);
pm_runtime_barrier(dev); if (dev->class && dev->class->shutdown_pre) {
if (initcall_debug)
dev_info(dev, "shutdown_pre\n");
dev->class->shutdown_pre(dev);
}
if (dev->bus && dev->bus->shutdown) {
if (initcall_debug)
dev_info(dev, "shutdown\n");
dev->bus->shutdown(dev);
} else if (dev->driver && dev->driver->shutdown) {
if (initcall_debug)
dev_info(dev, "shutdown\n");
dev->driver->shutdown(dev);
} device_unlock(dev);
if (parent)
device_unlock(parent); put_device(dev);
put_device(parent); spin_lock(&devices_kset->list_lock);
}
spin_unlock(&devices_kset->list_lock);
}
函数device_shutdown()用来关闭sysfs上的每个设备，它在系统关闭时才会进行调用，在函数内，使用了devices_kset这个顶层kset，所在的目录为/sys/devices，因此，函数调用会遍历到注册的到sysfs上的每个设备，调用设备相应的总线或驱动定义的shutdown()函数，每个设备虽然可以有不同的parent，但是kset还是一样的，当在调用kobject_add()函数时，将devices_kset这个kset->kobj设置成parent，那么新添加的kobject就会挂在/sys/devices顶层目录下，例如virtual目录等。
4、小结
在内核中，struct device结构体的实现非常地复杂，它是Linux内核设备驱动模型的基础，为了适应越来越复杂的情景，以及提高设备的驱动性能，其实现将会越来越复杂，对其分析点到为止。
参考：
《LINUX设备驱动程序（第三版）》
https://blog.csdn.net/qb_2008/article/details/6847133
https://blog.csdn.net/abo8888882006/article/details/5424363
