linux-kernel - Re: [PATCH 1/7] driver-core : add class iteration api

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Date:	Mon, 14 Jan 2008 09:32:47 +0800
From:	"Dave Young" <hidave.darkstar@...il.com>
To:	"Stefan Richter" <stefanr@...6.in-berlin.de>
Cc:	"Greg KH" <gregkh@...e.de>, James.Bottomley@...senpartnership.com,
	a.zummo@...ertech.it, peterz@...radead.org, cbou@...l.ru,
	linux-kernel@...r.kernel.org,
	"David Brownell" <david-b@...bell.net>, krh@...hat.com,
	stern@...land.harvard.edu, dwmw2@...radead.org,
	davem@...emloft.net, jarkao2@...il.com
Subject: Re: [PATCH 1/7] driver-core : add class iteration api

On Jan 12, 2008 6:50 PM, Stefan Richter <stefanr@...6.in-berlin.de> wrote:
> Dave Young wrote:
> > Add the following class iteration functions for driver use:
>
> Thanks Dave.  I will check the ieee1394 part in detail later.
>
> ...
> > +/**
> > + * class_find_device - device iterator for locating a particular device
> > + * @class: the class we're iterating
> > + * @data: data for the match function
> > + * @match: function to check device
> > + *
> > + * This is similar to the class_for_each_dev() function above, but it
> > + * returns a reference to a device that is 'found' for later use, as
> > + * determined by the @match callback.
>
> Maybe add "Drop the reference with put_device() after use." for the
> really slow driver programmers like me?

Sounds good, thanks.

>
> > + *
> > + * The callback should return 0 if the device doesn't match and non-zero
> > + * if it does.  If the callback returns non-zero, this function will
> > + * return to the caller and not iterate over any more devices.
> > + */
> > +struct device *class_find_device(struct class *class, void *data,
> > +                                int (*match)(struct device *, void *))
> > +{
>
> A general comment on the linux/device.h API (not a direct comment on
> your patch):
>
> The match argument in bus_find_device(), driver_find_device(),
> device_find_child(), class_find_device(), class_find_child() could be
> changed to
>
>         bool (*match)(struct device *, void *)).
>
> Then the semantics are IMO a little bit clearer.  Ditto for the
> dr_match_t type and the struct bus_type.match member.

Yes, from semantics side it's better.
But IMHO int is good as well, although it need a little bit more
understanding of the api.

>
> I don't know though whether the churn of doing such a change everywhere
> would be justified by the result.
>
>
> A comment on patch 2/7...6/7:
>
> You can bring most or all of the various __match implementations into a
> slightly terser but IMO easy to read form, like this:
>
>  static int __match_ne(struct device *dev, void *data)
>  {
>         struct unit_directory *ud;
>         struct node_entry *ne = (struct node_entry *)data;
>
>         ud = container_of(dev, struct unit_directory, unit_dev);
> -       if (ud->ne == ne)
> -               return 1;
> -       return 0;
> +       return ud->ne == ne;
>  }
>
> Here it is also easy to see that readability would improve if the return
> type was bool rather than int.

Ok, thanks.

> --
> Stefan Richter
> -=====-==--- ---= -==--
> http://arcgraph.de/sr/
>
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