linux-kernel - Re: [PATCH v6 3/4] of: overlay: add per overlay sysfs attributes

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Date:	Thu, 22 Oct 2015 19:15:43 +0300
From:	Pantelis Antoniou <pantelis.antoniou@...sulko.com>
To:	Rob Herring <robherring2@...il.com>
Cc:	Frank Rowand <frowand.list@...il.com>,
	Matt Porter <mporter@...sulko.com>,
	Koen Kooi <koen@...inion.thruhere.net>,
	Guenter Roeck <linux@...ck-us.net>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-api@...r.kernel.org" <linux-api@...r.kernel.org>
Subject: Re: [PATCH v6 3/4] of: overlay: add per overlay sysfs attributes

Hi Rob,

> On Oct 22, 2015, at 00:52 , Rob Herring <robherring2@...il.com> wrote:
> 
> On Wed, Oct 21, 2015 at 2:37 PM, Pantelis Antoniou
> <pantelis.antoniou@...sulko.com> wrote:
>> Hi Rob,
>> 
>>> On Oct 21, 2015, at 00:54 , Rob Herring <robherring2@...il.com> wrote:
>>> 
>>> On Tue, Oct 20, 2015 at 4:11 PM, Pantelis Antoniou
>>> <pantelis.antoniou@...sulko.com> wrote:
>>>> Hi Rob,
>>>> 
>>>>> On Oct 21, 2015, at 00:04 , Rob Herring <robherring2@...il.com> wrote:
>>>>> 
>>>>> On Tue, Oct 20, 2015 at 2:13 PM, Pantelis Antoniou
>>>>> <pantelis.antoniou@...sulko.com> wrote:
>>>>>> * A per overlay can_remove sysfs attribute that reports whether
>>>>>> the overlay can be removed or not due to another overlapping overlay.
>>>>>> 
>>>>>> * A target sysfs attribute listing the target of each fragment,
>>>>>> in a group named after the name of the fragment.
>>> 
>>> [...]
>>> 
>>>>>> @@ -255,6 +278,17 @@ err_fail:
>>>>>>      return -EINVAL;
>>>>>> }
>>>>>> 
>>>>>> +static ssize_t target_show(struct kobject *kobj,
>>>>>> +               struct fragment_attribute *fattr, char *buf)
>>>>>> +{
>>>>>> +       struct of_overlay_info *ovinfo = fattr->ovinfo;
>>>>>> +
>>>>>> +       return snprintf(buf, PAGE_SIZE, "%s\n",
>>>>>> +                       of_node_full_name(ovinfo->target));
>>>>> 
>>>>> This can be a link to the node itself, can't it?
>>>>> 
>>>> 
>>>> Yes. Do you want it like this?
>>> 
>>> Yes, hence the suggestion. Unless you see some reason why not.
>>> 
>> 
>> Nope, can’t be done. The sysfs API only allows linking one kobj to another.
>> The kobj is the overlay but the target is in the fragment attribute group.
> 
> Can't we make the fragments kobj's as well?
> 

We could, but it break the mental model of what a kobj should represent.
An overlay is an object which can be address, a fragment is never directly
exposed.

TBH a link attribute is indeed better than a path attribute, but marginally so.
It’s not worth the trouble IMO.
 
> Rob

Regards

— Pantelis

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