Re: [PATCH v3 07/39] fs: char_dev: introduce cd_acquire function to acquire cdev

[Dongsheng Yang <yangds.fnst@cn.fujitsu.com>]

On 09/16/2015 04:16 PM, Jan Kara wrote:
> On Tue 15-09-15 17:02:02, Dongsheng Yang wrote:
>> cd_acquire() works like bd_acquire() to get cdev by an inode,
>> this commit is a preparation for lookup_cdev().
>>
>> Signed-off-by: Dongsheng Yang <yangds.fnst@cn.fujitsu.com>
>
> Two comments below.
>
>> ---
>>   fs/char_dev.c | 35 +++++++++++++++++++++++++++++++++++
>>   1 file changed, 35 insertions(+)
>>
>> diff --git a/fs/char_dev.c b/fs/char_dev.c
>> index ea06a3d..e818faa 100644
>> --- a/fs/char_dev.c
>> +++ b/fs/char_dev.c
>> @@ -439,6 +439,41 @@ static int exact_lock(dev_t dev, void *data)
>>   	return cdev_get(p) ? 0 : -1;
>>   }
>>
>> +struct cdev *cd_acquire(struct inode *inode)
>> +{
>> +	struct cdev *cdev;
>> +	struct cdev *new = NULL;
>> +
>> +	spin_lock(&cdev_lock);
>> +	cdev = inode->i_cdev;
>> +	if (!cdev) {
>> +		struct kobject *kobj;
>> +		int idx;
>
> Empty line here please to separate variable declarations from the code.

Yes,
>
>> +		spin_unlock(&cdev_lock);
>> +		kobj = kobj_lookup(cdev_map, inode->i_rdev, &idx);
>> +		if (!kobj) {
>> +			cdev = NULL;
>> +			goto out;
>> +		}
>> +		new = container_of(kobj, struct cdev, kobj);
>> +		spin_lock(&cdev_lock);
>> +		/* Check i_cdev again in case somebody beat us to it while
>> +		   we dropped the lock. */
>> +		cdev = inode->i_cdev;
>> +		if (!cdev) {
>> +			inode->i_cdev = cdev = new;
>> +			list_add(&inode->i_devices, &cdev->list);
>> +		}
>
> I think you need to put 'new' in case you didn't use it, don't you?

Oh, yes, I forgot it. will update it.

Thanx
Yang
>
>> +	}
>> +
>> +	if (!cdev_get(cdev))
>> +		cdev = NULL;
>> +	spin_unlock(&cdev_lock);
>> +
>> +out:
>> +	return cdev;
>> +}
>> +
>>   /**
>>    * cdev_add() - add a char device to the system
>>    * @p: the cdev structure for the device
>
> 								Honza
>