On Thu, Jun 03, 2021 at 04:17:41PM -0500, Bjorn Helgaas wrote:
> 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.
>
> What's the reason for this change? The above tells me what it *does*,
> but not *why* or whether it affects users.
>
> Is this to avoid trying to print a NULL pointer as %s? Do we print
> "(null)" or something in that case now? I assume sprintf() doesn't
> actually oops. If we change what appears in sysfs, we should mention
> that here. And maybe consider whether there's any chance of breaking
> user code that might know what to do with "(null)" but not with an
> empty string.
>
> There are six other driver_override_show() methods. Five don't check
> the ->driver_override pointer at all; one (spi.c) checks like this:
>
> len = snprintf(buf, PAGE_SIZE, "%s\n", spi->driver_override ? : "");
>
> Do the others need similar fixes? Most of them still use sprintf()
> also.
I can't remember if there's a reason for holding device_lock() around
this. Of the seven: amba, platform, vmbus, pci, s390, and spi hold
it, while fsl-mc does not.
Since we're only reading a single scalar, I don't see the reason for
device_lock(). If we do need it, it would be nice to have a brief
comment explaining why. Obviously not an issue with this patch :)
> > Signed-off-by: Krzysztof Wilczyński <kw@xxxxxxxxx>
> > Reviewed-by: Logan Gunthorpe <logang@xxxxxxxxxxxx>
> > ---
> > 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
> >
