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

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Date:	Mon, 26 Nov 2012 09:35:09 +0100
From:	Andrzej Pietrasiewicz <andrzej.p@...sung.com>
To:	linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org
Cc:	Andrzej Pietrasiewicz <andrzej.p@...sung.com>,
	Kyungmin Park <kyungmin.park@...sung.com>,
	Felipe Balbi <balbi@...com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Joel Becker <jlbec@...lplan.org>,
	Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
	Marek Szyprowski <m.szyprowski@...sung.com>,
	Michal Nazarewicz <mina86@...a86.com>
Subject: [RFC][PATCH] fs: configfs: programmatically create config groups

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

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?

Andrzej Pietrasiewicz (1):
  fs: configfs: allow other kernel parts to programmatically create
    config groups

 fs/configfs/dir.c        |    5 +++--
 include/linux/configfs.h |    2 ++
 2 files changed, 5 insertions(+), 2 deletions(-)

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