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

[Bjorn Helgaas <helgaas@xxxxxxxxxx>]

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.

> >> -	driver_override = kstrndup(buf, count, GFP_KERNEL);
> >> -	if (!driver_override)
> >> -		return -ENOMEM;
> >> -
> >> -	cp = strchr(driver_override, '\n');
> >> -	if (cp)
> >> -		*cp = '\0';
> >> -
> >> -	device_lock(dev);
> >> -	old = pdev->driver_override;
> >> -	if (strlen(driver_override)) {
> >> -		pdev->driver_override = driver_override;
> >> -	} else {
> >> -		kfree(driver_override);
> >> -		pdev->driver_override = NULL;
> >> -	}
> >> -	device_unlock(dev);
> >> -
> >> -	kfree(old);
> >> +	ret = driver_set_override(dev, &pdev->driver_override, buf);
> >> +	if (ret)
> >> +		return ret;
> >>  
> >>  	return count;
> >>  }
> >> -- 
> >> 2.32.0
> >>
> >>
> >> _______________________________________________
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> >> linux-arm-kernel@xxxxxxxxxxxxxxxxxxx
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> 
> 
> Best regards,
> Krzysztof
> 
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