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

Bjorn Helgaas
2022-02-24T23:52:14Z

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@lists.infradead.org
> >> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
>
>
> Best regards,
> Krzysztof
>
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