linux-kernel - Re: [PATCH RFC 02/15 v5] gpio: Add sysfs support to block GPIO API

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Date:	Fri, 19 Oct 2012 12:35:31 +0200
From:	Linus Walleij <linus.walleij@...aro.org>
To:	Roland Stigge <stigge@...com.de>,
	Greg KH <gregkh@...uxfoundation.org>,
	Grant Likely <grant.likely@...retlab.ca>
Cc:	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	w.sang@...gutronix.de, jbe@...gutronix.de, plagnioj@...osoft.com,
	highguy@...il.com, broonie@...nsource.wolfsonmicro.com,
	daniel-gl@....net, rmallon@...il.com
Subject: Re: [PATCH RFC 02/15 v5] gpio: Add sysfs support to block GPIO API

On Thu, Oct 18, 2012 at 12:07 PM, Roland Stigge <stigge@...com.de> wrote:
> On 10/17/2012 09:05 PM, Greg KH wrote:
>>>
>>> +    if (value != exported) {
>>> +            if (value)
>>> +                    status = gpio_block_value_export(block);
>>> +            else
>>> +                    status = gpio_block_value_unexport(block);
>>
>> That looks like a recipie for disaster.  Why do you allow userspace to
>> do this?
>
> Exporting for gpio blocks is done as follows: writing "1" to the
> "exported" _device_ attribute of the gpio block creates the "values"
> attribute and at the same time requests the whole block (including all
> of its gpios) as "sysfs".

To me it reads like Greg's comment is basically pinpointing a flaw
in Brownell's initial design of gpio sysfs: that new sysfs files are
created and destroyed by writing into sysfs */export files from
userspace?

See commit: d8f388d8dc8d4f36539dd37c1fff62cc404ea0fc

The block GPIO stuff is just following that design pattern.

Yours,
Linus Walleij
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