linux-kernel - Re: [PATCH 1/6] driver-core : add class iteration api

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Message-Id: <200801212224.18149.david-b@pacbell.net>
Date:	Mon, 21 Jan 2008 22:24:17 -0800
From:	David Brownell <david-b@...bell.net>
To:	Dave Young <hidave.darkstar@...il.com>
Cc:	Greg KH <gregkh@...e.de>, stefanr@...6.in-berlin.de,
	James.Bottomley@...senpartnership.com, a.zummo@...ertech.it,
	peterz@...radead.org, cbou@...l.ru, linux-kernel@...r.kernel.org,
	stern@...land.harvard.edu, dwmw2@...radead.org,
	davem@...emloft.net, jarkao2@...il.com
Subject: Re: [PATCH 1/6] driver-core : add class iteration api

On Monday 21 January 2008, Dave Young wrote:
>  
> +/**
> + *	class_for_each_device - device iterator
> + *	@class:	the class we're iterating
> + *	@data: data for the callback
> + *	@fn: function to be called for each device
> + *
> + *	Iterate over @class's list of devices, and call @fn for each,
> + *	passing it @data.
> + *
> + *	We check the return of @fn each time. If it returns anything
> + *	other than 0, we break out and return that value.

I have a suggestion for better documentation, which
applies to all these utilities:


> + */
> +int class_for_each_device(struct class *class, void *data,
> +			   int (*fn)(struct device *, void *))
> +{
> +	struct device *dev;
> +	int error = 0;
> +
> +	if (!class)
> +		return -EINVAL;
> +	down(&class->sem);
> +	list_for_each_entry(dev, &class->devices, node) {
> +		dev = get_device(dev);
> +		if (dev) {
> +			error = fn(dev, data);

This is called with class->sem held.  So fn() has a
constraint to not re-acquire that ... else it'd be
self-deadlocking.  I'd like to see docs at least
mention that; calls to add or remove class members
would be verboten, for example, which isn't an issue
with most other driver model iterators.


> +			put_device(dev);
> +		} else
> +			error = -ENODEV;
> +		if (error)
> +			break;
> +	}
> +	up(&class->sem);
> +
> +	return error;
> +}
> +EXPORT_SYMBOL_GPL(class_for_each_device);
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