Re: [PATCH] gpiolib: check if gpio_desc pointer is error or NULL

[Ben Dooks <ben.dooks@codethink.co.uk>]

On 19/03/14 02:48, Alexandre Courbot wrote:
> On Tue, Mar 18, 2014 at 7:41 PM, Ben Dooks <ben.dooks@codethink.co.uk> wrote:
>> Some of the gpiod_ calls take a pointer to a gpio_desc as their
>> argument but only check to see if it is NULL to validate the
>> input.
>>
>> Calls such as devm_gpiod_get() return an error-pointer if they
>> fail, so doing the following will not work:
>>
>>          gpio = devm_gpiod_get(...);
>>          gpiod_direction_output(gpio, 0);
>>
>> The sequence produces an OOPS like:
>>
>>          Unable to handle kernel paging request at virtual address fffffffe
>>
>> Change all calls that check for !desc to use IS_ERR_OR_NULL() to
>> avoid these issues.
>
> This change is certainly correct from a semantics point of view. Maybe
> I'd argue that the burden is on the caller to check that gpiod_get()
> returns a valid GPIO descriptor, but having extra security doesn't
> hurt. However my problem with this change in its current form is that
> it will hide such forgetfulnesses by making functions like
> gpiod_get_value() fail silently instead of triggering a oops.

On the other hand, it means that we do not have to keep checking
the validity of the pointer in the caller.

> Could you make sure that any call of a gpiolib function on a non-valid
> descriptor raises at least a message in the console, and while you are
> at it harmonize the way these messages are output? Right now we are
> using pr_debug(), pr_warn() or WARN_ON() depending on the location. I
> would say that using an invalid GPIO descriptor is offending enough
> that it should trigger a stack dump at every attempt.

-- 
Ben Dooks				http://www.codethink.co.uk/
Senior Engineer				Codethink - Providing Genius