Confusion in kobjects

Confusion in kobjects

[Vikram Narayanan]

The kernel doc (kobject.txt) says that

"No structure should EVER have more than one kobject embedded within it.
 If it does, the reference counting for the object is sure to be messed
 up and incorrect, and your code will be buggy.  So do not do this. "

But in the file drivers/uio/uio.c, a structure has two such kobjects.

struct uio_device {
         struct module           *owner;
         struct device           *dev;
         int                     minor;
         atomic_t                event;
         struct fasync_struct    *async_queue;
         wait_queue_head_t       wait;
         int                     vma_count;
         struct uio_info         *info;
         struct kobject          *map_dir;
         struct kobject          *portio_dir;
 };

So, What is the exception for this structure? Is this right? If yes,
can someone explain why it is right, and where should we use it?

Thanks,
Vikram

Confusion in kobjects

[Greg KH]

On Wed, May 04, 2011 at 07:26:44PM +0530, Vikram Narayanan wrote:
> The kernel doc (kobject.txt) says that
> 
> "No structure should EVER have more than one kobject embedded within it.
>  If it does, the reference counting for the object is sure to be messed
>  up and incorrect, and your code will be buggy.  So do not do this. "
> 
> But in the file drivers/uio/uio.c, a structure has two such kobjects.
> 
> struct uio_device {
>          struct module           *owner;
>          struct device           *dev;
>          int                     minor;
>          atomic_t                event;
>          struct fasync_struct    *async_queue;
>          wait_queue_head_t       wait;
>          int                     vma_count;
>          struct uio_info         *info;
>          struct kobject          *map_dir;
>          struct kobject          *portio_dir;
>  };
> 
> So, What is the exception for this structure? Is this right? If yes,
> can someone explain why it is right, and where should we use it?

There are not more than one kobject _IN_ the structure.  It merely
has pointers to more than one kobject (three actually), which is fine to
do.

Hope this helps,

greg k-h

Confusion in kobjects

[Vikram Narayanan]

> On Wed, May 04, 2011 at 07:26:44PM +0530, Vikram Narayanan wrote:
>> The kernel doc (kobject.txt) says that
>>
>> "No structure should EVER have more than one kobject embedded within it.
>> ?If it does, the reference counting for the object is sure to be messed
>> ?up and incorrect, and your code will be buggy. ?So do not do this. "
>>
>> But in the file drivers/uio/uio.c, a structure has two such kobjects.
>>
>> struct uio_device {
>> ? ? ? ? ?struct module ? ? ? ? ? *owner;
>> ? ? ? ? ?struct device ? ? ? ? ? *dev;
>> ? ? ? ? ?int ? ? ? ? ? ? ? ? ? ? minor;
>> ? ? ? ? ?atomic_t ? ? ? ? ? ? ? ?event;
>> ? ? ? ? ?struct fasync_struct ? ?*async_queue;
>> ? ? ? ? ?wait_queue_head_t ? ? ? wait;
>> ? ? ? ? ?int ? ? ? ? ? ? ? ? ? ? vma_count;
>> ? ? ? ? ?struct uio_info ? ? ? ? *info;
>> ? ? ? ? ?struct kobject ? ? ? ? ?*map_dir;
>> ? ? ? ? ?struct kobject ? ? ? ? ?*portio_dir;
>> ?};
>>
>> So, What is the exception for this structure? Is this right? If yes,
>> can someone explain why it is right, and where should we use it?
>
> There are not more than one kobject _IN_ the structure. ?It merely
> has pointers to more than one kobject (three actually), which is fine to
> do.
Thanks for the clarification. Think I have to go for an eye checkup ;)

Thanks,
Vikram