linux-kernel - Re: [PATCH] generic_nvram: Turn nvram

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Date:	Mon, 12 Oct 2009 00:40:36 +0200
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Arnd Bergmann <arndbergmann@...glemail.com>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	LKML <linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...e.hu>,
	John Kacur <jkacur@...hat.com>,
	Sven-Thorsten Dietrich <sven@...bigcorporation.com>,
	Jonathan Corbet <corbet@....net>,
	Alessio Igor Bogani <abogani@...ware.it>,
	Alan Cox <alan@...rguk.ukuu.org.uk>
Subject: Re: [PATCH] generic_nvram: Turn nvram_ioctl into an unlocked ioctl

On Mon, Oct 12, 2009 at 12:25:05AM +0200, Arnd Bergmann wrote:
> On Monday 12 October 2009, Frederic Weisbecker wrote:
> > nvram_ioctl is a bkl locked ioctl, but it can be an unlocked ioctl.
> > 
> > - part is provided by the user
> > - offset is provided by pmac_get_partition() which is safe as it only
> >   touches nvram_partitions, an array inistialized on __init time and
> >   read-only the rest of the time.
> > - nvram_sync() only relies on core99_nvram_sync() which checks
> >   is_core_99, nvram_data, nvram_image. Those are variables initialized
> >   on __init time only and their direct values are not touched further.
> >   The rest modifies the nvram image header, protected by nv_lock
> >   already.
> > 
> > So it's safe to call nvram_ioctl without the big kernel lock held.
> > 
> > Reported-by: Arnd Bergmann <arndbergmann@...glemail.com>
> > Signed-off-by: Frederic Weisbecker <fweisbec@...il.com>
> > Cc: Thomas Gleixner <tglx@...utronix.de>
> > Cc: Ingo Molnar <mingo@...e.hu>
> > Cc: John Kacur <jkacur@...hat.com>
> > Cc: Sven-Thorsten Dietrich <sven@...bigcorporation.com>
> > Cc: Jonathan Corbet <corbet@....net>
> > Cc: Alessio Igor Bogani <abogani@...ware.it>
> > Cc: Arnd Bergmann <arndbergmann@...glemail.com>
> > Cc: Alan Cox <alan@...rguk.ukuu.org.uk>
> 
> Hmm, I wish I had not started using the gmail MTA for sending out
> mail, not that address is public forever.


Sorry, didn't know about that. I'm then taking Arnd Bergmann <arnd@...db.de>
found in the MAINTAINER file for the v2 patch.


 
> >  drivers/char/generic_nvram.c |   10 +++++-----
> >  1 files changed, 5 insertions(+), 5 deletions(-)
> > 
> > diff --git a/drivers/char/generic_nvram.c b/drivers/char/generic_nvram.c
> > index c49200e..fd448aa 100644
> > --- a/drivers/char/generic_nvram.c
> > +++ b/drivers/char/generic_nvram.c
> > @@ -118,11 +118,11 @@ static int nvram_ioctl(struct inode *inode, struct file *file,
> >  }
> >  
> >  const struct file_operations nvram_fops = {
> > -	.owner		= THIS_MODULE,
> > -	.llseek		= nvram_llseek,
> > -	.read		= read_nvram,
> > -	.write		= write_nvram,
> > -	.ioctl		= nvram_ioctl,
> > +	.owner			= THIS_MODULE,
> > +	.llseek			= nvram_llseek,
> > +	.read			= read_nvram,
> > +	.write			= write_nvram,
> > +	.unlocked_ioctl		= nvram_ioctl,
> >  };
> >  
> >  static struct miscdevice nvram_dev = {
> 
> The ioctl and unlocked_ioctl functions have a different signature, so you
> need to adapt that, not just rename it.


Hmm, that's the problem with this file I can't event build test. I really
should grab a cross compiler for powerpc targets.


> 
> Not sure if we should do it in the same patch, but this driver should also 
> have a compat_ioctl method pointing to the same function. The ioctl numbers
> in this driver are all 32/64 bit clean, but are not listed in fs/compat_ioctl.c,
> so adding a .compat_ioctl pointer is the easiest way to fix 32 bit userland
> accessing the device.
> 
> 	Arnd <><


Added in my todolist then, for a saperate patch because it fixes another
issue.

Thanks!

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