linux-kernel - RE: [RFC 0/2] USB gadget

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Date:	Tue, 10 Jul 2012 10:54:44 +0200
From:	Andrzej Pietrasiewicz <andrzej.p@...sung.com>
To:	'Joel Becker' <jlbec@...lplan.org>
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>,
	'Sebastian Andrzej Siewior' <bigeasy@...utronix.de>,
	Marek Szyprowski <m.szyprowski@...sung.com>,
	'Alan Stern' <stern@...land.harvard.edu>
Subject: RE: [RFC 0/2] USB gadget - configfs

Dear Joel,

Thank you for your review.

@Sebastian, Alan, Felipe: Thank you, too.

On Monday, July 02, 2012 11:09 AM Joel Becker wrote:

<snip>

> 
> > As a prerequisite it adds an operation to configfs. The operation allows
> > checking if it is ok to remove a pseudo directory corresponding to a
> > configfs item/group.
> 
> 	I NAK'd that patch because you should be using
> configfs_depend_item().  If you have trouble with that, let's talk.
> 

Now I see the configfs_depend_item() is the way to go. I am in doubt,
though, so could you please throw some light on it? Here is why:
As an example I did a quick-and-dirty port of f_mass_storage to the new,
configfs-based approach. The business logic of this function is that
once a lun is opened, it must not be changed (deleted, in particular)
until it is closed. The moment the lun is opened is defined by a write
to a configfs "file" attribute of a lun config item:

               +-/lunX
               |  |
               |  +-file
               |  |
               |  +-nofua
               |  |
               |  +-removable
               |  |
               |  +-ro

So, the config item corresponding to the lun becomes depended on during
the write file operation, the same with undepend. Can this be expressed
with configfs_depend/undepend_item()? Your code in fs/configfs/dir.c
contains a warning not to call the configfs_depend_item()
from a configfs callback.
In this case, is store_attribute a configfs callback?

Thanks,

Andrzej

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