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

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Date:	Tue, 25 Jan 2011 12:12:45 +0100
From:	walter harms <wharms@....de>
To:	Russell King - ARM Linux <linux@....linux.org.uk>
CC:	Julia Lawall <julia@...u.dk>, 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



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.

just my 2 cents,
re,
 wh
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