linux-kernel - Re: associating miscdevice with inode

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Message-ID: <20100204111337.0c474c94@lxorguk.ukuu.org.uk>
Date:	Thu, 4 Feb 2010 11:13:37 +0000
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	vb@...e.com
Cc:	linux-kernel@...r.kernel.org
Subject: Re: associating miscdevice with inode

On Wed, 3 Feb 2010 22:24:46 -0800
vb@...e.com wrote:

> guys,
> 
> say I have a misc device driver which instantiates several devices.
> When a file operation on this device is invoked, I need to be able to
> figure out which device is being accessed. All available information
> are
> 
> struct inode and struct file. Is there a way to find the address of
> the miscdevice structure passed to misc_register() when this device
> was created?

Not really. If you have a single misc device which each open creates a
new context of some sort then use filp->private_data to store your own
cotntext pointer.

Misc doesn't expect people to be registering lots of devices - its for
one offs and weirdnesses. You could I guess work backwards from

	minor = iminor(inode);

and see which of your miscdevs has c->minor == minor.

If you have more than a couple of instances being put into misc you
should probably register an anonymous device major/minor range instead
and go direct.

Alan
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