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Date: Mon, 26 Nov 2012 17:30:25 +0100
From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
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To: Andrzej Pietrasiewicz <andrzej.p@samsung.com>
CC: linux-usb@vger.kernel.org, linux-kernel@vger.kernel.org,
        Kyungmin Park <kyungmin.park@samsung.com>, Felipe Balbi <balbi@ti.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Joel Becker <jlbec@evilplan.org>,
        Marek Szyprowski <m.szyprowski@samsung.com>,
        Michal Nazarewicz <mina86@mina86.com>
Subject: Re: [RFC][PATCH] fs: configfs: programmatically create config groups
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On 11/26/2012 09:35 AM, Andrzej Pietrasiewicz wrote:
> In some parts of the kernel (e.g. planned configfs integration into usb
> gadget) there is a need to programmatically create config groups
> (directories) but it would be preferable to disallow creating them by
> the user. This is more or less what default_groups used to be for.
> But e.g. in the mass storage gadget, after storing the number of
> luns (logical units) into some configfs attribute, the corresponding lun#
> directories should be created, their number is not known up front so
> default_groups are no good for this.
>
> Example:
>
> $ echo 3>  /cfg/..../mass_storage/luns
>
> causes
>
> /cfg/....../mass_storage/lun0
> /cfg/....../mass_storage/lun1
> /cfg/....../mass_storage/lun2

I though we did not want the luns file but instead use

mkdir /cfg/....../mass_storage/lun0
mkdir /cfg/....../mass_storage/lun1

directly.

> to be created. Yet
>
> $ mkdir /cfg/..../mass_storage/<any name>
>
> should not be allowed.
>
> With create_group exported it is very easily achieved: make_group and make_item
> are set to NULL in mass_storage's config_group, yet the kernel can
> create_groups at will.
>
> I kindly ask for comments. In particular, I would like to discuss
> if this is the right approach. A counterpart to remove config groups
> is also required. It is not implemented in this patch, though. What are
> your opinions?

Could you please at the tcm gadget? This is a mass storage gadget using
target as backend and target is using configfs. Here is a snippet how
you setup it:

|mkdir -p $FABRIC/naa.6001405c3214b06a/tpgt_1
|mkdir $FABRIC/naa.6001405c3214b06a/tpgt_1/lun/lun_0
|mkdir $FABRIC/naa.6001405c3214b06a/tpgt_1/lun/lun_1

So you setup two luns without this patch. Would that work for you?

Sebastian
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