linux-kernel - Re: [patch 3/4] timerfd: Implement timerfd_ioctl method to restore timerfd

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Date:	Wed, 02 Jul 2014 21:01:02 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	Cyrill Gorcunov <gorcunov@...il.com>
Cc:	Christopher Covington <cov@...eaurora.org>,
	linux-kernel@...r.kernel.org, linux-api@...r.kernel.org,
	Michael Kerrisk <mtk.manpages@...il.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Andrey Vagin <avagin@...nvz.org>,
	Pavel Emelyanov <xemul@...allels.com>,
	Vladimir Davydov <vdavydov@...allels.com>,
	Linux ARM kernel mailing list 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [patch 3/4] timerfd: Implement timerfd_ioctl method to restore timerfd_ctx::ticks

On Wednesday 02 July 2014 21:04:16 Cyrill Gorcunov wrote:
> On Wed, Jul 02, 2014 at 12:49:51PM -0400, Christopher Covington wrote:
> > >  
> > > +#ifdef CONFIG_CHECKPOINT_RESTORE
> > > +static long timerfd_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
> > > +{
> > > +   struct timerfd_ctx *ctx = file->private_data;
> > > +   int ret = 0;
> > > +
> > > +   switch (cmd) {
> > > +   case TFD_IOC_SET_TICKS: {
> > > +           u64 ticks;
> > > +
> > > +           if (get_user(ticks, (u64 __user *)arg))
> > 
> > 64-bit get_user is currently unsupported on ARM, although it appears work is
> > ongoing [1].
> > 
> > 1. https://lkml.org/lkml/2014/6/17/260
> 
> Thanks for info, Christopher! What arm camp is using then, copy-from-user?
> 

copy_from_user should work on all architectures. I believe a 64-bit get_user
is currently unsupported on most 32-bit architectures, x86-32 being a notable
exception.

	Arnd
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