linux-kernel - Re: [PATCH 2/4] arch/arm/mach-at91/clock.c: Add missing IS

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Date:	Tue, 25 Jan 2011 12:18:40 +0100 (CET)
From:	Julia Lawall <julia@...u.dk>
To:	walter harms <wharms@....de>
Cc:	Russell King - ARM Linux <linux@....linux.org.uk>,
	Vasiliy Kulikov <segooon@...il.com>,
	Ryan Mallon <ryan@...ewatersys.com>,
	kernel-janitors@...r.kernel.org,
	Nicolas Ferre <nicolas.ferre@...el.com>,
	Jean-Christophe PLAGNIOL-VILLARD <plagnioj@...osoft.com>,
	Andrew Victor <linux@...im.org.za>,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/4] arch/arm/mach-at91/clock.c: Add missing IS_ERR test

On Tue, 25 Jan 2011, walter harms wrote:

> 
> 
> Am 25.01.2011 11:43, schrieb Russell King - ARM Linux:
> > On Tue, Jan 25, 2011 at 11:33:16AM +0100, walter harms wrote:
> >> Would it be more easy to return NULL in the error case of clk_get() instead
> >> of ERR_PTR(-ENOENT) ?
> >>
> >> So the default could be return NULL and an architecture depending solution
> >> replacing that.
> > 
> > That's not how the API is defined.  The API defines error-pointers to be
> > errors, everything should be considered valid.  Please don't go down the
> > route of doing something architecturally different from that.
> > 
> > What if, say, you couldn't return the struct clk because maybe it could
> > only be controlled by one user?  Returning an EBUSY error pointer would
> > indicate this condition.  What if the module providing the struct clk
> > hasn't finished initializing - that's another reason for EBUSY rather
> > than ENOENT.
> > 
> > Error codes are useful to describe why something failed.  NULL pointers
> > can't do that.
> > 
> 
> On Mon, 24 Jan 2011, Vasiliy Kulikov wrote:
> > 
> ...
> > clk_get() is defined per-architecture, sometimes it is NULL only.
> >
> 
> So these is a bug ? They should return -ENOENT ?
> 
> The interessting question is: what to do with an error ?
> 
> Obviously some architecture can live with NULL, so it is not an critical
> error. An the patch shows a code that is simply a return, not even the
> user is informed that something did not work as expected.
> 
> From that point of view i would like question if it is useful to have
> a "detailed" error instead of just returning NULL.

Somewhat unrelatedly, I often run into code where error handling code is 
needed, but not present, and the function returns void, so nothing is 
provided for propagating the error further.  I generally consider these 
cases to be beyond my expertise to fix...

julia
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