linux-kernel - Re: [RFC][PATCH] fs: configfs: programmatically create config groups

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Date:	Mon, 26 Nov 2012 17:30:25 +0100
From:	Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To:	Andrzej Pietrasiewicz <andrzej.p@...sung.com>
CC:	linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
	Kyungmin Park <kyungmin.park@...sung.com>,
	Felipe Balbi <balbi@...com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Joel Becker <jlbec@...lplan.org>,
	Marek Szyprowski <m.szyprowski@...sung.com>,
	Michal Nazarewicz <mina86@...a86.com>
Subject: Re: [RFC][PATCH] fs: configfs: programmatically create config groups

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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