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

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Date:	Tue, 22 Jan 2008 14:30:27 +0800
From:	"Dave Young" <hidave.darkstar@...il.com>
To:	"David Brownell" <david-b@...bell.net>
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 Jan 22, 2008 2:24 PM, David Brownell <david-b@...bell.net> wrote:
> 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.

Very good comment, thanks david.  I will update after a while.

>
>
>
> > +                     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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