linux-kernel - Re: [PATCH v2 05/11] pci: use helper for safer setting of driver

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Date:   Fri, 25 Feb 2022 11:13:41 -0600
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Krzysztof Kozlowski <krzysztof.kozlowski@...onical.com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Stuart Yoder <stuyoder@...il.com>,
        Laurentiu Tudor <laurentiu.tudor@....com>,
        Abel Vesa <abel.vesa@....com>, Shawn Guo <shawnguo@...nel.org>,
        Sascha Hauer <s.hauer@...gutronix.de>,
        Fabio Estevam <festevam@...il.com>,
        "K. Y. Srinivasan" <kys@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        Wei Liu <wei.liu@...nel.org>, Dexuan Cui <decui@...rosoft.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Mathieu Poirier <mathieu.poirier@...aro.org>,
        Vineeth Vijayan <vneethv@...ux.ibm.com>,
        Peter Oberparleiter <oberpar@...ux.ibm.com>,
        Heiko Carstens <hca@...ux.ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Alexander Gordeev <agordeev@...ux.ibm.com>,
        Christian Borntraeger <borntraeger@...ux.ibm.com>,
        Sven Schnelle <svens@...ux.ibm.com>,
        Andy Gross <agross@...nel.org>,
        Srinivas Kandagatla <srinivas.kandagatla@...aro.org>,
        Mark Brown <broonie@...nel.org>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Jason Wang <jasowang@...hat.com>, linux-kernel@...r.kernel.org,
        linux-clk@...r.kernel.org, NXP Linux Team <linux-imx@....com>,
        linux-arm-kernel@...ts.infradead.org, linux-hyperv@...r.kernel.org,
        linux-pci@...r.kernel.org, linux-remoteproc@...r.kernel.org,
        linux-s390@...r.kernel.org, linux-arm-msm@...r.kernel.org,
        alsa-devel@...a-project.org, linux-spi@...r.kernel.org,
        virtualization@...ts.linux-foundation.org,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Rasmus Villemoes <linux@...musvillemoes.dk>
Subject: Re: [PATCH v2 05/11] pci: use helper for safer setting of
 driver_override

On Fri, Feb 25, 2022 at 10:36:20AM +0100, Krzysztof Kozlowski wrote:
> 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.

Thanks, I think that would be good!

Bjorn