linux-kernel - Re: [PATCH v2] loop: add some basic read-only sysfs attributes

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Message-ID: <AANLkTik7DZ6-4UOTZnJiFJ5c19wGd4ko4Kc6zE7UMG8U@mail.gmail.com>
Date:	Fri, 30 Jul 2010 16:34:43 +0200
From:	Kay Sievers <kay.sievers@...y.org>
To:	Milan Broz <mbroz@...hat.com>
Cc:	Karel Zak <kzak@...hat.com>, util-linux-ng@...r.kernel.org,
	linux-kernel@...r.kernel.org, axboe@...nel.dk
Subject: Re: [PATCH v2] loop: add some basic read-only sysfs attributes

On Fri, Jul 30, 2010 at 16:22, Milan Broz <mbroz@...hat.com> wrote:
> On 07/30/2010 06:36 AM, Kay Sievers wrote:
>
>> Alternatively, these attributes could be created and removed/created
>> with the ioctl, and before the 'change' event, only if there is an
>> active backing file, but I would expect the attribute group at the
>> device to work just fine.
> I have no idea how you can add attribute group before add_disk() which
> initializes kobj (it ends with BUG_ON in internal_create_group
> - because !kobj->sd). Perhaps I missed something?

Attribute groups handle the creation of a kobject (subdir) for you,
you only supply a name to the group. Without a name, they will put all
the attributes in the root of the device.

The 'struct device' has a member **groups, and that can have a list of
attribute groups assigned. You assign them before you register the
device, and the core will take care of everything.

> Anyway, second approach works - now is loop attributes available only
> when loop is configured and before CHANGE uevent is sent.
>
> Ok with that?

Sounds good, nothing to complain from a sysfs timing perspective.

Now you have do decide if you prefer that over the attribute group
approach. :) The code with attribute groups, instead of custom kobject
stuff, might be a bit easier to understand.

Thanks,
Kay
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