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

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Message-ID: <AANLkTikseiXY0zZ7AsyJgUXrqWsbjCgHqCabeg_SdWzZ@mail.gmail.com>
Date:	Thu, 29 Jul 2010 16:22:50 +0200
From:	Kay Sievers <kay.sievers@...y.org>
To:	Milan Broz <mbroz@...hat.com>
Cc:	util-linux-ng@...r.kernel.org, linux-kernel@...r.kernel.org,
	kzak@...hat.com, axboe@...nel.dk
Subject: Re: [PATCH] loop: add some basic read-only sysfs attributes

On Thu, Jul 29, 2010 at 16:06, Milan Broz <mbroz@...hat.com> wrote:
> On 07/29/2010 03:47 PM, Kay Sievers wrote:
>> On Thu, Jul 29, 2010 at 15:33, Milan Broz <mbroz@...hat.com> wrote:
>>> Create /sys/block/loopX/loop directory and provide these attributes:
>>>  - backing_file
>>>  - autoclear
>>>  - offset
>>>  - sizelimit
>>>
>>> To be used in util-linux-ng (and possibly elsewhere like udev rules)
>>> where code need to get loop attributes from kernel (and not store
>>> duplicate info in userspace).
>>
>> Isn't it that the loop attributes are created _after_ the loopdev is
>> registered? That would make it hard to use these attributes from udev,
>> as the event is already running while they are created.
>
> First 8 loop devices are registered always (without backing file),
> so you have wait for change event initiated from fd set ioctl anyway...
> (backing file attribute is empty in that case)

Ah, so we are sure, we always get a 'change' event, and before that,
none of these values are ever useful to read? I mean, there will not
be attributes that are interesting during an 'add' event?

Kay
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