linux-kernel - Re: Allow setting of number of raw devices as a module parameter

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Message-ID: <20110502211141.GA14889@quack.suse.cz>
Date:	Mon, 2 May 2011 23:11:41 +0200
From:	Jan Kara <jack@...e.cz>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	Jan Kara <jack@...e.cz>, LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: Allow setting of number of raw devices as a module parameter

On Mon 02-05-11 21:44:31, Arnd Bergmann wrote:
> On Monday 02 May 2011, Jan Kara wrote:
> > On Sat 30-04-11 14:15:02, Arnd Bergmann wrote:
> > > On Friday 29 April 2011 00:24:29 Jan Kara wrote:
> > > > Allow setting of maximal number of raw devices as a module parameter. This
> > > > requires changing of static array into a vmalloced one (the array is going to
> > > > be too large for kmalloc).
> > > > 
> > > > Signed-off-by: Jan Kara <jack@...e.cz>
> > > 
> > > Why don't you get rid of the global raw_devices array instead?
> > > 
> > > I suppose if you embed the struct cdev in raw_device_data and
> > > register it during RAW_SETBIND separately for each raw device
> > > instead of globally at raw_init time, you can support any number
> > > of devices while making the code smaller and simpler. I suppose
> > > you can even remove the raw_mutex then.
> >   OK, I see. This might be a reasonable option. I'd then use kobj_lookup()
> > to find my structure where I need it instead of array indexing, right? 
> > I have really zero experience with writing device drivers so I'm asking
> > simple questions :).
> 
> The character device layer uses kobj_lookup internally when opening
> the device. When you are inside the driver, you can access it through
> file->f_path.dentry->d_inode->i_cdev, from where you go to your own data
> structure using container_of.
  OK, but if I don't have the inode of the character device (like in
RAW_GETBIND case)?

								Honza
-- 
Jan Kara <jack@...e.cz>
SUSE Labs, CR
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