Re: [PATCH 1/3] driver core: add probe_err log helper

From: Joe Perches <joe@perches.com>
To: Russell King - ARM Linux <linux@armlinux.org.uk>,
	Andy Shevchenko <andy.shevchenko@gmail.com>
Cc: Andrzej Hajda <a.hajda@samsung.com>,
	"Rafael J. Wysocki" <rafael@kernel.org>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Javier Martinez Canillas <javierm@redhat.com>,
	Mark Brown <broonie@kernel.org>,
	linux-arm Mailing List <linux-arm-kernel@lists.infradead.org>,
	Marek Szyprowski <m.szyprowski@samsung.com>
Subject: Re: [PATCH 1/3] driver core: add probe_err log helper
Date: Wed, 17 Oct 2018 18:45:36 -0700	[thread overview]
Message-ID: <c2c8f5186beff6bdc04cfe79292cedad20f36475.camel@perches.com> (raw)
In-Reply-To: <20181017112914.GH30658@n2100.armlinux.org.uk>

On Wed, 2018-10-17 at 12:29 +0100, Russell King - ARM Linux wrote:
> On Tue, Oct 16, 2018 at 04:55:00PM +0300, Andy Shevchenko wrote:
> > On Tue, Oct 16, 2018 at 3:55 PM Andrzej Hajda <a.hajda@samsung.com> wrote:
> > > On 16.10.2018 13:29, Andrzej Hajda wrote:
> > > > On 16.10.2018 13:01, Andy Shevchenko wrote:
> > > > > On Tue, Oct 16, 2018 at 10:22 AM Andrzej Hajda <a.hajda@samsung.com> wrote:
> > > > > > During probe every time driver gets resource it should usually check for error
> > > > > > printk some message if it is not -EPROBE_DEFER and return the error. This
> > > > > > pattern is simple but requires adding few lines after any resource acquisition
> > > > > > code, as a result it is often omited or implemented only partially.
> > > > > > probe_err helps to replace such code seqences with simple call, so code:
> > > > > >         if (err != -EPROBE_DEFER)
> > > > > >                 dev_err(dev, ...);
> > > > > >         return err;
> > > > > > becomes:
> > > > > >         return probe_err(dev, err, ...);
> > > > > > +               va_start(args, fmt);
> > > > > > +
> > > > > > +               vaf.fmt = fmt;
> > > > > > +               vaf.va = &args;
> > > > > > +
> > > > > > +               __dev_printk(KERN_ERR, dev, &vaf);
> > > > > It would be nice to print an error code as well, wouldn't it?
> > > > Hmm, on probe fail error is printed anyway (with exception of
> > > > EPROBE_DEFER, ENODEV and ENXIO):
> > > >     "probe of %s failed with error %d\n"
> > > > On the other side currently some drivers prints the error code anyway
> > > > via dev_err or similar, so I guess during conversion to probe_err it
> > > > should be removed then.
> > > > 
> > > > If we add error code to probe_err is it OK to report it this way?
> > > >     dev_err(dev, "%V, %d\n", &vaf, err);
> > > 
> > > Ups, I forgot that message passed to probe_err will contain already
> > > newline character.
> > 
> > You may consider not to pass it.
> 
> It's normal to pass the '\n', so by doing this, we create the situation
> where this function becomes the exception to the norm.  That's not a
> good idea - we will see people forget that appending '\n' should not
> be done for this particular function.
> 
> While we could add a checkpatch rule, that's hassle (extra rework).

It would not be a simple checkpatch rule with high confidence
because of pr_cont uses that may not be in the patch context.

> In I think the message would be much better formatted if we did:
> 
> 	dev_err(dev, "error %d: %V", err, &vaf);

s/%V/%pV/