Subject: Re: [PATCH 3/4] of: Convert to using %pOFn instead of device_node.name

From: Thierry Reding <[email-masked]>
Date: Mon, 10 Sep 2018 11:06:25 +0200

On Fri, Sep 07, 2018 at 05:30:23PM -0700, Joe Perches wrote:
> On Fri, 2018-09-07 at 14:29 +0200, Thierry Reding wrote:
> > On Tue, Aug 28, 2018 at 10:52:53AM -0500, Rob Herring wrote:
> > > In preparation to remove the node name pointer from struct device_node,
> > > convert printf users to use the %pOFn format specifier.
> > > 
> > > Cc: Frank Rowand <[email-masked]>
> > > Cc: Andrew Lunn <[email-masked]>
> > > Cc: Florian Fainelli <[email-masked]>
> > > Cc: [email-masked]
> > > Cc: [email-masked]
> > > Signed-off-by: Rob Herring <[email-masked]>
> > > ---
> > >  drivers/of/device.c   |  4 ++--
> > >  drivers/of/of_mdio.c  | 12 ++++++------
> > >  drivers/of/of_numa.c  |  4 ++--
> > >  drivers/of/overlay.c  |  4 ++--
> > >  drivers/of/platform.c |  8 ++++----
> > >  drivers/of/unittest.c | 12 ++++++------
> > >  6 files changed, 22 insertions(+), 22 deletions(-)
> > > 
> > > diff --git a/drivers/of/device.c b/drivers/of/device.c
> > > index 5957cd4fa262..daa075d87317 100644
> > > --- a/drivers/of/device.c
> > > +++ b/drivers/of/device.c
> > > @@ -219,7 +219,7 @@ static ssize_t of_device_get_modalias(struct device *dev, char *str, ssize_t len
> > >  		return -ENODEV;
> > >  
> > >  	/* Name & Type */
> > > -	csize = snprintf(str, len, "of:N%sT%s", dev->of_node->name,
> > > +	csize = snprintf(str, len, "of:N%pOFnT%s", dev->of_node,
> > >  			 dev->of_node->type);
> > >  	tsize = csize;
> > >  	len -= csize;
> > 
> > This seems to cause the modalias to be improperly constructed. As a
> > consequence, automatic module loading at boot time is now broken. I
> > think the reason why this fails is because vsnprintf() will skip all
> > alpha-numeric characters after a call to pointer(). Presumably this
> > is meant to be a generic way of skipping whatever specifiers we throw
> > at it.
> > 
> > Unfortunately for the case of OF modaliases, this means that the 'T'
> > character gets eaten, so we end up with something like this:
> > 
> > 	# udevadm info /sys/bus/platform/devices/54200000.dc
> > 	[...]
> > 	E: MODALIAS=of:Ndc<NULL>Cnvidia,tegra124-dc
> > 	[...]
> > 
> > instead of this:
> > 
> > 	# udevadm info /sys/bus/platform/devices/54200000.dc
> > 	[...]
> > 	E: MODALIAS=of:NdcT<NULL>Cnvidia,tegra124-dc
> > 	[...]
> > 
> > Everything is back to normal if I revert this patch. However, since
> > that's obviously not what we want, I think perhaps what we need is a
> > way for pointer() (and its implementations) to report back how many
> > characters in the format string it consumed so that we can support
> > these kinds of back-to-back strings.
> > 
> > If nobody else has the time I can look into coding up a fix, but in the
> > meantime it might be best to back this one out until we can handle the
> > OF modalias format string.
> 
> Or just use 2 consecutive snprintf calls
> 
> 	csize = snprintf(str, len, "of:N%pOFn", dev->of_node);
> 	csize += snprintf(str + csize, len - csize, "T%s",
> 			  dev->of_node->type);

Yeah, that's what I ended up doing. Rob came up with another alternative
which is to output the 'T' via %c, which also works around the issue.

Thierry