issues dealing with kobjects

[arrao@cdac.in (Raghavendra)]

On Friday 20 June 2014 11:31 AM, Raghavendra wrote:
> Hello all,
>
> I am facing a small issue dealing with kobjects.
> I am writing a simple i2c driver for which I would like to export a few
> sysfs attributes(files).
> The files are many, so I've decided to pack them into a directory in
> sysfs (inside the i2c device) and so I thought of kobjects.
>
> My private data struture is something like this :
> struct my_private {
>       struct i2c_client *client;
>       ...
>       struct kobject kobj;
> };
>
> In my probe function, I am doing something like this :
> int my_probe(struct i2c_client *client, ...)
> {
>       struct my_private *dev;
>
>       dev = devm_kzalloc(...);
>       pr_info("%x", dev);                    /* The address that I got is
> : 0xdbf94210 */
>
>       ....
>
>       /* Init. and add kboject */
>       kobject_init(&dev->kobj, client->dev.kobj.ktype);
>       kobject_add(&dev->kobj, &client->dev.kobj, "my_dir");
>
>       /* Export sysfs group */
>       sysfs_create_group(&dev->kobj, &my_attr_grp);
>
>       ....
> }
>
> My show function for one of the attribute is something like this :
> ssize_t show(struct kobject *kobj, ... )
> {
>       struct my_private *dev = container_of(kobj, struct my_private, kobj);
>       pr_info("%x", dev);                    /* The address that I got is
> : 0xdbf94208 */
>
>       ....
> }
>
> I tried to probe and remove the device mutilple times. Every time I am
> getting a difference of 2bytes for the 'dev'
> pointer between probe and show functions.
>
> Can anyone explain me where am I going wrong or is there any better way
> to create directories in sysfs?
> I am building this module against 3.13.2 kernel.
>
> Thank you.
> Raghavendra.
>
>
>
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I guess I've solved the issue. Now the code looks something like this :

struct my_private {
      struct i2c_client *client;
      ...
      struct kobject *kobj;	/* Converted variable to ptr */
};

int my_probe(struct i2c_client *client, ...)
{
      struct my_private *dev;

      dev = devm_kzalloc(...);
  
      ....
	
/* Replaced with kobject_init and kobject_add calls */
  dev->kobj = kobject_create_and_add("my_dir", &client->dev.kobj);	

      /* Export sysfs group */
      sysfs_create_group(dev->kobj, &my_attr_grp);

      ....
}

ssize_t show(struct kobject *kobj, ... )
{
	struct device *i2cdev = kobj_to_dev(kobj->parent);
	struct i2c_client *client = to_i2c_client(i2cdev);
	struct my_private *dev = i2c_get_clientdata(client);

  ....
}

This approach worked, but there's a lot of redundancy in the show() function, just to obtain the pointer to the private data.
I would be glad if anyone suggested any better approach to create and manage sysfs directories and attribute groups.

Thank you,
Raghavendra

  






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disclosure, dissemination, forwarding, printing or copying of this email
is strictly prohibited and appropriate legal action will be taken.
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