Re: [PATCH v6 5/6] PCI/sysfs: Only show value when driver_override is not NULL

From: Bjorn Helgaas <helgaas@kernel.org>
To: "Krzysztof Wilczyński" <kw@linux.com>
Cc: Bjorn Helgaas <bhelgaas@google.com>,
	Logan Gunthorpe <logang@deltatee.com>,
	Joe Perches <joe@perches.com>,
	Oliver O'Halloran <oohall@gmail.com>,
	Michael Ellerman <mpe@ellerman.id.au>,
	Benjamin Herrenschmidt <benh@kernel.crashing.org>,
	Paul Mackerras <paulus@samba.org>,
	Tyrel Datwyler <tyreld@linux.ibm.com>,
	Russell Currey <ruscur@russell.cc>,
	Kurt Schwemmer <kurt.schwemmer@microsemi.com>,
	Vidya Sagar <vidyas@nvidia.com>,
	Xiongfeng Wang <wangxiongfeng2@huawei.com>,
	linux-pci@vger.kernel.org,
	Alex Williamson <alex.williamson@redhat.com>
Subject: Re: [PATCH v6 5/6] PCI/sysfs: Only show value when driver_override is not NULL
Date: Thu, 3 Jun 2021 18:23:34 -0500	[thread overview]
Message-ID: <20210603232334.GA2153375@bjorn-Precision-5520> (raw)
In-Reply-To: <20210603000112.703037-6-kw@linux.com>

[+cc Alex, FYI]

On Thu, Jun 03, 2021 at 12:01:11AM +0000, Krzysztof Wilczyński wrote:
> Only expose the value of the "driver_override" variable through the
> corresponding sysfs object when a value is actually set.

This changes the attribute contents from "(null)" to an empty
(zero-length) file when no driver override has been set.

There are a few other driver_override_show() functions.  Most don't
check the pointer so they'll show "(null)".  One (spi.c) checks and
shows an empty string ("", file containing a single NULL character)
instead of an empty (zero-length) file.

> Signed-off-by: Krzysztof Wilczyński <kw@linux.com>
> Reviewed-by: Logan Gunthorpe <logang@deltatee.com>
> ---
>  drivers/pci/pci-sysfs.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/pci/pci-sysfs.c b/drivers/pci/pci-sysfs.c
> index 5d63df7c1820..4e9f582ca10f 100644
> --- a/drivers/pci/pci-sysfs.c
> +++ b/drivers/pci/pci-sysfs.c
> @@ -580,10 +580,11 @@ static ssize_t driver_override_show(struct device *dev,
>  				    struct device_attribute *attr, char *buf)
>  {
>  	struct pci_dev *pdev = to_pci_dev(dev);
> -	ssize_t len;
> +	ssize_t len = 0;
>  
>  	device_lock(dev);
> -	len = sysfs_emit(buf, "%s\n", pdev->driver_override);
> +	if (pdev->driver_override)
> +		len = sysfs_emit(buf, "%s\n", pdev->driver_override);
>  	device_unlock(dev);
>  	return len;
>  }
> -- 
> 2.31.1
> 