linux设备：device

原文地址：http://blog.chinaunix.net/uid-24631445-id-3420457.html

简述struct device相关的东西。

类似于bus_type，kobject是嵌入在struct device中的。

而且device也有device_attribute。

用struct device声明一个设备，然后用device_register函数来注册，完后用device_unregister注销设备。

用struct device_attribute定义设备属性，或用DEVICE_ATTR宏来定义，对属性文件的处理使用

device_create_file函数和device_remove_file函数。

这里以platform_bus_init()函数来为例来介绍设备注册的过程。

platform_bus_init是在设备初始化过程中调用的函数，对应于目录/sys/devices/platform。

1：struct device

这个结构体比较复杂。

struct device {
    struct device        *parent;

    struct device_private    *p;

    struct kobject kobj;
    const char        *init_name; /* initial name of the device */
    struct device_type    *type;
    struct semaphore    sem;    /* semaphore 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 */
    struct dev_pm_info    power;
#ifdef CONFIG_NUMA
    int        numa_node;    /* NUMA node this device is close to */
#endif
    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. */

    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 */
    /* arch specific additions */
    struct dev_archdata    archdata;

    dev_t            devt;    /* dev_t, creates the sysfs "dev" */

    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 driver_private {
    struct kobject kobj;
    struct klist klist_devices;
    struct klist_node knode_bus;
    struct module_kobject *mkobj;
    struct device_driver *driver;
};

platform_bus的定义如下：

struct device platform_bus = {
    .init_name = "platform",
};

在platform_bus_init(void)中调用了“error = device_register(&platform_bus);”下面主要分析device_register函数

2：device_register(struct device *)

int device_register(struct device *dev)
{
    device_initialize(dev);
    return device_add(dev);
}

意外的只有两句，先初始化设备，然后add设备。

3：device_initialize(struct device *)

void device_initialize(struct device *dev)
{
    /* 先初始化dev->kobj */
    dev->kobj.kset = devices_kset;
    kobject_init(&dev->kobj, &device_ktype);

    /* 初始化其他部分 */
    INIT_LIST_HEAD(&dev->dma_pools);
    init_MUTEX(&dev->sem);
    spin_lock_init(&dev->devres_lock);
    INIT_LIST_HEAD(&dev->devres_head);
    device_init_wakeup(dev, 0);
    device_pm_init(dev);
    set_dev_node(dev, -1);
}

那么前两句将dev->kobj的kset初始化为devices_kset, ktype初始化为device_ktype。

devices_kset是在函数devices_init中初始化的，

devices_kset = kset_create_and_add("devices", &device_uevent_ops, NULL);

device_ktype的定义如下：

static struct kobj_type device_ktype = {
    .release    = device_release,
    .sysfs_ops    = &dev_sysfs_ops,
};

/* 先尝试dev->release,在尝试dev->type->release,最后尝试dev->class->dev_release */

static void device_release(struct kobject *kobj)

static struct sysfs_ops dev_sysfs_ops = {
    .show    = dev_attr_show,
    .store    = dev_attr_store,
};

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 = to_dev(kobj);
    ssize_t ret = -EIO;

    if (dev_attr->show)
        ret = dev_attr->show(dev, dev_attr, buf);
    ...
}

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 = to_dev(kobj);
    ssize_t ret = -EIO;

    if (dev_attr->store)
        ret = dev_attr->store(dev, dev_attr, buf, count);
    return ret;
}

可见device_ktype与bus_ktype类似。对show和store函数的调用最终还是要调用device_attribute中指定的show与store函数。

4：device_add(struct *dev)

核心函数，该函数比较复杂。

int device_add(struct device *dev)
{
    struct device *parent = NULL;
    struct class_interface *class_intf;
    int error = -EINVAL;

    /* 调用了kobject_get(&dev->kobj) */
    dev = get_device(dev);
    if (!dev)
        goto done;

    if (!dev->p) {
        /* 分配了一个device_private对象，并初始化dev->p->klist_children */
        error = device_private_init(dev);
        if (error)
            goto done;
    }

    /* 对platform_bus变量来说，这里将dev->kobj.name设成"platform" */
    if (dev->init_name) {
        dev_set_name(dev, "%s", dev->init_name);
        dev->init_name = NULL;
    }

    if (!dev_name(dev))
        goto name_error;

    pr_debug("device: '%s': %s\n", dev_name(dev), __func__);
    /* platform_bus->parent为NULL, setup_parent函数用于设定dev->kobj.parent的值*/

    parent = get_device(dev->parent);
    setup_parent(dev, parent);

    /* use parent numa_node */
    if (parent)
        set_dev_node(dev, dev_to_node(parent));

    /* first, register with generic layer. */
    /* we require the name to be set before, and pass NULL */
    /* 调用kobject_add将dev->kobj加入设备模型，这里parent为NULL，因此此处将
       dev->kobj加入了devices_kset, 并将dev->kobj.parent = devices_kset->kobj */
    error = kobject_add(&dev->kobj, dev->kobj.parent, NULL);
    if (error)
        goto Error;

    /* notify platform of device entry */
    if (platform_notify)
        platform_notify(dev);

    /* 创建属性文件，即uevent文件 （在注册pci_bus_type时也有它）*/
    error = device_create_file(dev, &uevent_attr);
    if (error)
        goto attrError;

    if (MAJOR(dev->devt)) {
        error = device_create_file(dev, &devt_attr);
        if (error)
            goto ueventattrError;

        error = device_create_sys_dev_entry(dev);
        if (error)
            goto devtattrError;

        devtmpfs_create_node(dev);
    }
    /* 对于platform_bus变量来说，下面的函数均无作用（是我选的device不好，有点特殊）*/
    error = device_add_class_symlinks(dev);
    if (error)
        goto SymlinkError;
    error = device_add_attrs(dev);
    if (error)
        goto AttrsError;
    error = bus_add_device(dev);
    if (error)
        goto BusError;
    error = dpm_sysfs_add(dev);
    if (error)
        goto DPMError;
    device_pm_add(dev);

    /* Notify clients of device addition. This call must come
     * after dpm_sysf_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);
    bus_probe_device(dev);
    if (parent)
        klist_add_tail(&dev->p->knode_parent,
             &parent->p->klist_children);

    if (dev->class) {
        mutex_lock(&dev->class->p->class_mutex);
        /* tie the class to the device */
        klist_add_tail(&dev->knode_class,
             &dev->class->p->class_devices);

        /* notify any interfaces that the device is here */
        list_for_each_entry(class_intf,
                 &dev->class->p->class_interfaces, node)
            if (class_intf->add_dev)
                class_intf->add_dev(dev, class_intf);
        mutex_unlock(&dev->class->p->class_mutex);
    }
done:
    put_device(dev);
    return error;
/* 下面都是错误处理相关的代码，已省略 */
.........
}

好吧，这个platform_bus的例子不太好，该变量太特殊，并没有具体的设备，因此device_add函数里很多函数没有用到。

通常在device_register之前需要设置好device对象的parent, bus_id, bus和release成员，但platform_bus仅设定了init_name，

可见对platform_bus的注册主要就是调用kobject_add函数在/sys/devices目录下创建个platform目录。

！！！需补充例子...

待续...