linux-kernel - Re: [PATCH v1 1/1] Input: icn8505 - Utilize acpi_get_subsystem

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Date:   Tue, 6 Sep 2022 12:01:37 -0700
From:   Dmitry Torokhov <dmitry.torokhov@...il.com>
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc:     linux-input@...r.kernel.org, linux-kernel@...r.kernel.org,
        Hans de Goede <hdegoede@...hat.com>
Subject: Re: [PATCH v1 1/1] Input: icn8505 - Utilize acpi_get_subsystem_id()

On Tue, Sep 06, 2022 at 03:54:06PM +0300, Andy Shevchenko wrote:
> On Mon, Sep 05, 2022 at 12:35:42PM -0700, Dmitry Torokhov wrote:
> > On Mon, Sep 05, 2022 at 08:20:01PM +0300, Andy Shevchenko wrote:
> 
> ...
> 
> > > +	subsys = acpi_get_subsystem_id(ACPI_HANDLE(dev));
> > > +	if (IS_ERR(subsys) && PTR_ERR(subsys) != -ENODATA)
> > > +		return PTR_ERR(subsys);
> > > +
> > > +	if (IS_ERR(subsys) && PTR_ERR(subsys) == -ENODATA)
> > > +		subsys = kstrdup_const("unknown", GFP_KERNEL);
> > 
> > Do we really need kstrdup_const() here? This makes me wonder if we need
> > to also have error handling here, and if we going to tip some automated
> > tools by not having it. Why can't we simply assign the constant here
> > (and continue using kfree_const() below)?
> 
> Which makes code inconsistent. But okay, no big deal.

To me the *_const() APIs are needed when the code does not really know
if it deals with a const/read-only object or not. If we know for sure we
are dealing with a const/read-only object, we can skip allocation and
freeing, so I do not see any inconsistencies.

> 
> > I think this is the case where PTR_ERR_OR_ZERO() might help avoid
> > multiple IS_ERR/PTR_ERR:
> > 
> > 	subsys = acpi_get_subsystem_id(ACPI_HANDLE(dev));
> > 	error = PTR_ERR_OR_ZERO(subsys);
> > 	if (error == -ENODATA)
> > 		subsys = "unknown";
> > 	else if (error)
> > 		return error;
> 
> Would it matter? The generated code will be the same in both cases, no?

No, in the end I think the optimizer will reduce both variants to the
same thing. I do find mine a bit more compact and thus easier to read,
but I will not insist.

Thanks.

-- 
Dmitry