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

From: "Krzysztof Wilczyński" <kw@linux.com>
To: Alex Williamson <alex.williamson@redhat.com>
Cc: Bjorn Helgaas <helgaas@kernel.org>,
	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
Subject: Re: [PATCH v6 5/6] PCI/sysfs: Only show value when driver_override is not NULL
Date: Fri, 4 Jun 2021 03:10:30 +0200	[thread overview]
Message-ID: <20210604011030.GA414436@rocinante.localdomain> (raw)
In-Reply-To: <20210603184759.45c51682.alex.williamson@redhat.com>

Hi Alex and Bjorn,

[...]
> > 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.
> 
> Yeah, "(null)" was the expected output in this case.  It looks like
> this might break driverctl.  Thanks,
[...]

I had a look and it does, indeed, rely on explicitly checking whether
the value is "(null)", as per:

  https://gitlab.com/driverctl/driverctl/-/blob/master/driverctl#L96-131

I think, to avoid breaking this and other userspace tools that might
rely on this, we should drop this patch.

Having said that, I would love to be able to correct the behaviour we
have at the moment, but it seems that this ship has sail, so to speak.

	Krzysztof