linux-kernel - Re: [Question: Drivers/base/core.c] Why dev->init_name = NULL in device

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Message-ID: <CADYu30_o7rzERKEDe=eZiONp6n1ktMWPydMnXQjDeLrDFQh+vg@mail.gmail.com>
Date:	Sat, 2 Aug 2014 03:54:32 +0530
From:	Aniroop Mathur <aniroop.mathur@...il.com>
To:	Greg KH <gregkh@...uxfoundation.org>
Cc:	linux-kernel@...r.kernel.org, linux-hotplug@...r.kernel.org
Subject: Re: [Question: Drivers/base/core.c] Why dev->init_name = NULL in
 device_add function ?

On Sat, Aug 2, 2014 at 12:53 AM, Greg KH <gregkh@...uxfoundation.org> wrote:
> On Fri, Aug 01, 2014 at 10:43:23PM +0530, Aniroop Mathur wrote:
>> Dear Mr. Greg Kroah-Hartman and Linux Community,
>> Greetings of the day !! :)
>>
>> I am Aniroop Mathur working on Linux Kernel for last two years.
>> I am stuck at one point and could not find the solution over internet.
>> I posted on linuxquestions.org too.
>> So I need your help and suggestion for it.
>>
>> Can you please help in answering my query as below:
>>
>> =====================================================
>> In function device_add of /drivers/base/core.c file, it is mentioned:
>> /*
>> * for statically allocated devices, which should all be converted
>> * some day, we need to initialize the name. We prevent reading back
>> * the name, and force the use of dev_name()
>> */
>> if (dev->init_name) {
>> dev_set_name(dev, "%s", dev->init_name);
>> dev->init_name = NULL;
>> }
>>
>>
>> Except forcing the use of dev_name to read device name,
>> Is there any other reason to make init_name as NULL ?
>
> Why would you want init_name to not be NULL?
>

Currently in kernel, we cannot set name of event node.

If dev->init_name is not set as NULL in device_add(),
then I can easily set name of event node in evdev_dev.c
file as below:

if(dev->init_name) {
      sprintf(dev->init_name, "event_%s", dev->init_name);
}
error = device_add(&evdev->dev);

And in some input device driver code, I will use like below:
dev->init_name = "accelerometer";
input_register_device(dev);

So, overall output will be
/dev/input/event<x> --> /dev/input/event_accelerometer
sys/class/input/input<x> --> sys/class/input/accelerometer

In short, input and event node names are set just by
adding one line, which i found quite efficient.
There is other way also to set name of event node but
it involves using extra variable and little more code,
So I am looking for best solution possible. :)

>> And if it is not made NULL, is there any problem or side-effect ?
>
> Yes, people would start to use it thinking it was the real name of the
> device, when it might not be.
>

As the name itself nicely suggests, it is just a initial name.
It may not be the final name as developer can change the name
using dev_set_name. Also dev_name api is available to get
final/current name of the device.

Thanks and Regards,
Aniroop Mathur
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