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SubjectRe: [PATCH v2 2/2] uacce: add uacce driver
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Hi, Greg

On 2019/8/29 下午5:54, Greg Kroah-Hartman wrote:
> On Thu, Aug 29, 2019 at 05:05:13PM +0800, zhangfei wrote:
>> Hi, Greg
>>
>> On 2019/8/28 下午11:22, Greg Kroah-Hartman wrote:
>>> On Wed, Aug 28, 2019 at 09:27:56PM +0800, Zhangfei Gao wrote:
>>>> +struct uacce {
>>>> + const char *drv_name;
>>>> + const char *algs;
>>>> + const char *api_ver;
>>>> + unsigned int flags;
>>>> + unsigned long qf_pg_start[UACCE_QFRT_MAX];
>>>> + struct uacce_ops *ops;
>>>> + struct device *pdev;
>>>> + bool is_vf;
>>>> + u32 dev_id;
>>>> + struct cdev cdev;
>>>> + struct device dev;
>>>> + void *priv;
>>>> + atomic_t state;
>>>> + int prot;
>>>> + struct mutex q_lock;
>>>> + struct list_head qs;
>>>> +};
>>> At a quick glance, this problem really stood out to me. You CAN NOT
>>> have two different objects within a structure that have different
>>> lifetime rules and reference counts. You do that here with both a
>>> 'struct cdev' and a 'struct device'. Pick one or the other, but never
>>> both.
>>>
>>> I would recommend using a 'struct device' and then a 'struct cdev *'.
>>> That way you get the advantage of using the driver model properly, and
>>> then just adding your char device node pointer to "the side" which
>>> interacts with this device.
>>>
>>> Then you might want to call this "struct uacce_device" :)
>> Here the 'struct cdev' and 'struct device' have the same lifetime and
>> refcount.
> No they do not, that's impossible as refcounts are incremented from
> different places (i.e. userspace).
>
>> They are allocated with uacce when uacce_register and freed when
>> uacce_unregister.
> And that will not work.
I am sorry, could I ask more about this part.

  * This function should be used whenever the struct cdev and the
 * struct device are members of the same structure whose lifetime is
 * managed by the struct device.

From cdev_device_add comments, looks struct cdev and stuct device
can be in the same structure like uacce, and uacce is released when
put_device(device)

Also cdev_device_del do the device_del(dev) and cdev_del(cdev).

Copy:
fs/char_dev.c
/**
 * cdev_device_add() - add a char device and it's corresponding
 *      struct device, linkink
 * @dev: the device structure
 * @cdev: the cdev structure
 *
 * cdev_device_add() adds the char device represented by @cdev to the
system,
 * just as cdev_add does. It then adds @dev to the system using device_add
 * The dev_t for the char device will be taken from the struct device which
 * needs to be initialized first. This helper function correctly takes a
 * reference to the parent device so the parent will not get released until
 * all references to the cdev are released.
 *
 * This helper uses dev->devt for the device number. If it is not set
 * it will not add the cdev and it will be equivalent to device_add.
 *
 * This function should be used whenever the struct cdev and the
 * struct device are members of the same structure whose lifetime is
 * managed by the struct device.
 *
 * NOTE: Callers must assume that userspace was able to open the cdev and
 * can call cdev fops callbacks at any time, even if this function fails.
 */
int cdev_device_add(struct cdev *cdev, struct device *dev)
{
        int rc = 0;

        if (dev->devt) {
                cdev_set_parent(cdev, &dev->kobj);

                rc = cdev_add(cdev, dev->devt, 1);
                if (rc)
                        return rc;
        }

        rc = device_add(dev);
        if (rc)
                cdev_del(cdev);

        return rc;
}

Thanks

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