Re: [PATCH v2 05/11] pci: use helper for safer setting of driver_override

[Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>]

On 25/02/2022 00:52, Bjorn Helgaas wrote:
> On Thu, Feb 24, 2022 at 08:49:15AM +0100, Krzysztof Kozlowski wrote:
>> On 23/02/2022 22:51, Bjorn Helgaas wrote:
>>> In subject, to match drivers/pci/ convention, do something like:
>>>
>>>   PCI: Use driver_set_override() instead of open-coding
>>>
>>> On Wed, Feb 23, 2022 at 08:13:04PM +0100, Krzysztof Kozlowski wrote:
>>>> Use a helper for seting driver_override to reduce amount of duplicated
>>>> code.
>>>> @@ -567,31 +567,15 @@ static ssize_t driver_override_store(struct device *dev,
>>>>  				     const char *buf, size_t count)
>>>>  {
>>>>  	struct pci_dev *pdev = to_pci_dev(dev);
>>>> -	char *driver_override, *old, *cp;
>>>> +	int ret;
>>>>  
>>>>  	/* We need to keep extra room for a newline */
>>>>  	if (count >= (PAGE_SIZE - 1))
>>>>  		return -EINVAL;
>>>
>>> This check makes no sense in the new function.  Michael alluded to
>>> this as well.
>>
>> I am not sure if I got your comment properly. You mean here:
>> 1. Move this check to driver_set_override()?
>> 2. Remove the check entirely?
> 
> I was mistaken about the purpose of the comment and the check.  I
> thought it had to do with *this* function, and this function doesn't
> add a newline, and there's no obvious connection with PAGE_SIZE.
> 
> But looking closer, I think the "extra room for a newline" is really
> to make sure that *driver_override_show()* can add a newline and have
> it still fit within the PAGE_SIZE sysfs limit.
> 
> Most driver_override_*() functions have the same comment, so maybe
> this was obvious to everybody except me :)  I do see that spi.c adds
> "when displaying value" at the end, which helps a lot.
> 
> Sorry for the wild goose chase.

I think I will move this check anyway to driver_set_override() helper,
because there is no particular benefit to have duplicated all over. The
helper will receive "count" argument so can perform all checks.


Best regards,
Krzysztof