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

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Date:	Mon, 20 Aug 2012 10:53:42 +0200
From:	Andrzej Pietrasiewicz <andrzej.p@...sung.com>
To:	'Joel Becker' <jlbec@...lplan.org>,
	'Sebastian Andrzej Siewior' <bigeasy@...utronix.de>
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>,
	Marek Szyprowski <m.szyprowski@...sung.com>,
	'Alan Stern' <stern@...land.harvard.edu>
Subject: RE: [RFC 0/2] USB gadget - configfs

Hello Joel,

Thanks for your reply.

On Monday, August 20, 2012 8:00 AM Joel Becker wrote:
> 
> 	I think what you want here is a symlink.  Create a directory
> high in the tree called 'ready' or 'available', and when you want to
> lock the device in place, symlink it into that directory.  This will pin
> the item.  You can also make use of the ->allow_link() and ->drop_link()
> callbacks to prevent symlinking an item until it is fully configured,
> and prevent unlinking an item that is in use.
> 
>   $ ln -s /cfg/usb-function-gadget/G1/C1/F1/f_mass_storage/lun0 \
>         /cfg/usb-function-gadget/ready/
> 

Is using the userspace program "ln" the way you suggest doing it? Or just
a suggestion about what should be the link target and the link name?

If links are to be created from userspace then some other process can race
us and rmdir "lun0" before ln is called, can't it?

And a question to you as the creator of configfs: is using symlinks to
prevent config item deletion their intended purpose? How do you like it?

Thanks,

Andrzej


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