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

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Message-ID: <51691053.7060707@metafoo.de>
Date:	Sat, 13 Apr 2013 09:59:15 +0200
From:	Lars-Peter Clausen <lars@...afoo.de>
To:	Federico Vaga <federico.vaga@...il.com>
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

On 04/12/2013 02:09 PM, Federico Vaga wrote:
> [...]
> 
> [**] (argumentation based, obviously, on my limited understanding)
> 
> These drivers work like this:
> 
> 	child = device_find_child(parent, data, match_function);
> 	if (child) {
> 		put_device(child);		
> 		<do something unrelated with child> 
> 	}
> 
> In these cases we do not need to get_device(). But we need to know if there 
> is a child that match a rule. It can also "disapper" after the
> put_device(child) but the driver continues on its way because it does not
> use the child. For example virtio_rpmsg_bus.c:
> 
> 	/* make sure a similar channel doesn't already exist */
> 	tmp = device_find_child(dev, chinfo, rpmsg_channel_match);
> 	if (tmp) {
> 		/* decrement the matched device's refcount back */
> 		put_device(tmp);
> 		dev_err(dev, "channel %s:%x:%x already exist\n",
> 				chinfo->name, chinfo->src, chinfo->dst);
> 		return NULL;
> 	}

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?

- Lars
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