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Date: Sat, 13 Apr 2013 09:59:15 +0200
From: Lars-Peter Clausen <lars@metafoo.de>
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To: Federico Vaga <federico.vaga@gmail.com>
CC: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        linux-kernel@vger.kernel.org, Cornelia Huck <cornelia.huck@de.ibm.com>,
        Greg Kroah-Hartman <gregkh@suse.de>,
        Alessandro Rubini <rubini@gnudd.com>
Subject: Re: drivers/base/core.c: about device_find_child() function
References: <3798489.yISokZugC2@harkonnen> <20130411134844.GA3489@kroah.com> <2849474.HO2K6X9Bdi@harkonnen>
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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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