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

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Message-ID: <20100729145827.GB1981@nb.net.home>
Date:	Thu, 29 Jul 2010 16:58:27 +0200
From:	Karel Zak <kzak@...hat.com>
To:	Kay Sievers <kay.sievers@...y.org>
Cc:	Milan Broz <mbroz@...hat.com>, util-linux-ng@...r.kernel.org,
	linux-kernel@...r.kernel.org, axboe@...nel.dk
Subject: Re: [PATCH] loop: add some basic read-only sysfs attributes

On Thu, Jul 29, 2010 at 04:22:50PM +0200, Kay Sievers wrote:
> 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?

I think the patch does not change the current behavior. It exports
details about loopdevs to userspace by /sys. This is the primary goal
of the patch.

    Karel

-- 
 Karel Zak  <kzak@...hat.com>
 http://karelzak.blogspot.com
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