netdev - Re: [patch 4/4] mISDN: misc timerdev fixes

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Message-ID: <20080923120029.GA14012@pingi.kke.suse.de>
Date:	Tue, 23 Sep 2008 14:00:30 +0200
From:	Karsten Keil <kkeil@...e.de>
To:	Christoph Hellwig <hch@...radead.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>, kkeil@...e.de,
	netdev@...r.kernel.org, andi@...stfloor.org, ak@...ux.intel.com
Subject: Re: [patch 4/4] mISDN: misc timerdev fixes

On Tue, Sep 23, 2008 at 07:45:34AM -0400, Christoph Hellwig wrote:
> On Tue, Sep 23, 2008 at 04:30:05AM -0700, Andrew Morton wrote:
> > so.. this?
> 
> Much better.
> 
> > --- a/drivers/isdn/mISDN/timerdev.c~misdn-misc-timerdev-fixes-fix
> > +++ a/drivers/isdn/mISDN/timerdev.c
> > @@ -61,7 +61,7 @@ mISDN_open(struct inode *ino, struct fil
> >  	init_waitqueue_head(&dev->wait);
> >  	filep->private_data = dev;
> >  	__module_get(THIS_MODULE);
> > -	return 0;
> > +	return nonseekable_open(ino, filep);
> 
> But this also shows that mISDN is kinda stuck in a different century.
> Doing __module_get(THIS_MODULE) at the end of ->open is utterly racy,
> it really needs to set a owner field in file_operations and rip this
> cruft out.
> 
> Btw, can anyone explain WTF this timerdev module is doing?  It's not
> using any functionality from the rest of mISDN, it's not exporting
> any functionality to it either but just provides a really awkward way
> to expose dumb timers to userspace.  What does it provide that the
> normal timer syscalls can't provide?

This version only makes the programing of upper ISDN layers easier,
you only need to watch /dev/mISDNtimer together with the sockets in one
select call.
The next version will have a option to synchronise the timer with
the ISDN hardware clock which would avoid additional jitter if you need to
bridge channels in software.

-- 
Karsten Keil
SuSE Labs
ISDN and VOIP development
SUSE LINUX Products GmbH, Maxfeldstr.5 90409 Nuernberg, GF: Markus Rex, HRB 16746 (AG Nuernberg)
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