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

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Date:	Mon, 26 Nov 2012 18:06:40 +0100
From:	Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To:	Michal Nazarewicz <mina86@...a86.com>
CC:	Andrzej Pietrasiewicz <andrzej.p@...sung.com>,
	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>
Subject: Re: [RFC][PATCH] fs: configfs: programmatically create config groups

On 11/26/2012 05:56 PM, Michal Nazarewicz wrote:
>> 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
>
> On Mon, Nov 26 2012, Sebastian Andrzej Siewior wrote:
>> I though we did not want the luns file but instead use
>>
>> mkdir /cfg/....../mass_storage/lun0
>> mkdir /cfg/....../mass_storage/lun1
>>
>> directly.
>
> I think that's suboptimal, and we can do better.  There are too many
> corner cases (ie. what if user does “mkdir lun7” without the previous
> luns?), it adds complexity to the kernel (ie. parsing of the name), and
> the thing is overly complicated for user (“echo 5>  nluns” is much nicer
> than having to create 5 directories).

Wouldn't say that. It may adds complexity on another level. The target
subsystem has the same problem with adding luns and there seems nothing
wrong with having lun3 and 4 and leaving 0 and 1 unsued.
With the tcm gadget I get:

|scsi 0:0:0:2: Direct-Access     LIO-ORG  RAMDISK-MCP      4.0  PQ: 0 
ANSI: 5
|scsi 0:0:0:3: Direct-Access     LIO-ORG  FILEIO           4.0  PQ: 0 
ANSI: 5

You notice :2 and :3 instead :0 and :1. While should be there something
wrong with this?

Sebastian
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