linux-kernel - Re: [PATCH] spi: spidev: Add 32 bit compat ioctl()

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Date:	Wed, 2 Feb 2011 10:37:14 +0100
From:	Arnd Bergmann <arnd@...db.de>
To:	Grant Likely <grant.likely@...retlab.ca>
Cc:	Bernhard Walle <walle@...science.de>,
	dbrownell@...rs.sourceforge.net,
	spi-devel-general@...ts.sourceforge.net,
	linux-kernel@...r.kernel.org, akpm@...ux-foundation.org
Subject: Re: [PATCH] spi: spidev: Add 32 bit compat ioctl()

On Wednesday 02 February 2011, Grant Likely wrote:
> On Tue, Feb 01, 2011 at 10:02:46AM +0100, Bernhard Walle wrote:
> > Add the compat_ioctl for operations on /dev/spi* so that 32 bit
> > userspace applications can access SPI. As far as I can see all data
> > structure are already prepared for that, so no additional conversion has
> > to be done.
> > 
> > My use case is MIPS with N32 userspace ABI and toolchain, and that was
> > also the platform where I tested it successfully (Cavium Octeon).
> > 
> > Signed-off-by: Bernhard Walle <walle@...science.de>
> 
> Arnd, can you please give your opinion on this one?  I haven't fully
> got my head around the subtleties of 32/64 bit file_operations.

The patch is correct on everything except s390, which does not have SPI.
The only thing that is missing for s390 is a pointer conversion of the ioctl
argument, like:

static long     
compat_spidev_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
{
	return spidev_ioctl(filp, cmd, (unsigned long)compat_ptr(arg));
}

Some years ago, I proposed adding a common

#ifdef CONFIG_COMPAT
long generic_compat_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
{
	if (!file->unlocked_ioctl)
		return -ENOTTY;
	return filp->f_ops->unlocked_ioctl(filp, cmd, (unsigned long)compat_ptr(arg));
}
#else
#define generic_compat_ioctl NULL
#endif

for this purpose, but it never made it in. Maybe I should try again.

	Arnd
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