linux-kernel - Re: [patch 12/21] perfmon2 minimal: sysfs interface

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Message-ID: <7c86c4470806131531n4b24bc4dmc22d4b2277e75f24@mail.gmail.com>
Date:	Sat, 14 Jun 2008 00:31:43 +0200
From:	"stephane eranian" <eranian@...glemail.com>
To:	"Greg KH" <greg@...ah.com>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: [patch 12/21] perfmon2 minimal: sysfs interface

Greg,



On Fri, Jun 13, 2008 at 5:53 AM, Greg KH <greg@...ah.com> wrote:
> On Thu, Jun 12, 2008 at 02:54:15PM +0200, stephane eranian wrote:
>>
>> In any case, let me know if there are still things that must be
>> changed/simplified in my file.
>
> This looks much better.  I wonder if you could use the "default" kobject
> attributes, which might allow you to remove some of your show/store
> wrappers, but in general, it's much better than before.
>
Well, I wondered about that myself, but I think I am missing one piece.
The difference between some of the show/store functions and others
is that if you look closely, you see that some make reference to global
structures, e.g., pfm_controls, or call out to routines in others modules.
For those, I have switched to the default attribute. But the other show/store
functions need to access the particular object where the kobj is embedded.
And for that, it seems you need to glue function:

#define to_pmu(n) container_of(n, struct pfm_pmu_config, kobj)

static ssize_t pfm_pmu_attr_show(struct kobject *kobj,
                struct attribute *attr, char *buf)
{
        struct pfm_pmu_config *pmu = to_pmu(kobj);
        struct pfm_attribute *attribute = to_attr(attr);
        return attribute->show ? attribute->show(pmu, attribute, buf) : -EIO;
}

which basically calls the container_of() routine..

Yet, I get the feeling that is the show routein gets the same kobj,
then I could as well do the
to_pmu() there. And the attr (use the the strcmp()) would be the default.

If you tell me this is the way to go, I will certainly be happy to
make the change and remove even
more code!


Thanks.
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