linux-kernel - Re: drivers/base/core.c: about device_find

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Date:	Mon, 15 Apr 2013 10:51:29 +0200
From:	Federico Vaga <federico.vaga@...il.com>
To:	Lars-Peter Clausen <lars@...afoo.de>
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	linux-kernel@...r.kernel.org,
	Cornelia Huck <cornelia.huck@...ibm.com>,
	Greg Kroah-Hartman <gregkh@...e.de>,
	Alessandro Rubini <rubini@...dd.com>
Subject: Re: drivers/base/core.c: about device_find_child() function

Hi Lars,

> Considering that there seems to be a common pattern here where the caller
> only wants to know if the device exists, but is not really interested in the
> device itself, how about adding a helper function for this?

It was my first thought when I opened this thread. But now I'm convinced that 
device_for_each_child() is the best choice (maybe I'm wrong).

device_for_each_child() allow you to perform an operation of each child of a 
device: look for a specific child, do something on every children, retrieve a 
specific group of children, etc.

I think that an helper for this case will be a perfect duplication of 
device_for_each_child() with a different name and comment (borrowed from 
device_find_child()). Maybe, a macro to assign a different name to this 
function:

/*
 * [...]
 * The callback should return 0 if the device doesn't match and non-zero
 * if it does
 * [...]
 */
#define device_has_child(parent, data, match) device_for_each_child(parent, 
data, match)

But, is it useful? It can be a suggestion to developers to prefer 
device_for_each_child() instead of device_find_child() when (s)he is 
interested only about the child existence. So, (s)he does not need to 
put_device(). But I think that is not a strong argumentation, and later in 
time someone will propose his own special use of device_for_each_child().

I think that device_for_each_child() is generic enough to cover this problem.

-- 
Federico Vaga
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