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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