linux-kernel - Re: [Y2038] [PATCH v2 2/2] ppdev: add support for compat ioctl

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Message-ID: <20160104131452.GA6276@sudip-pc>
Date:	Mon, 4 Jan 2016 18:44:52 +0530
From:	Sudip Mukherjee <sudipm.mukherjee@...il.com>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	y2038@...ts.linaro.org, gregkh@...uxfoundation.org,
	broonie@...nel.org,
	Bamvor Jian Zhang <bamvor.zhangjian@...aro.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [Y2038] [PATCH v2 2/2] ppdev: add support for compat ioctl

On Sat, Jan 02, 2016 at 11:40:51PM +0100, Arnd Bergmann wrote:
> On Saturday 02 January 2016 11:59:29 Sudip Mukherjee wrote:
> > > 
> > > Just to be sure we are talking about the same thing: you mean running a 64-bit
> > > kernel in a kvm guest with a 32-bit file system, right? Running a 32-bit
> > > kvm guest on a 64-bit host would not be interesting of course.
> > 
> > The kvm (actually qemu, started from virt-manager with -enable-kvm) that
> > I just configured shows the following:
> > 
> > lscpu shows:
> > 
> > Architecture:          i686
> > CPU op-mode(s):        32-bit, 64-bit
> > Byte Order:            Little Endian
> > CPU(s):                1
> > On-line CPU(s) list:   0
> > Thread(s) per core:    1
> > Core(s) per socket:    1
> > Socket(s):             1
> > Vendor ID:             GenuineIntel
> > CPU family:            6
> > Model:                 6
> > Stepping:              3
> > CPU MHz:               2993.200
> > BogoMIPS:              5986.40
> > Virtualization:        VT-x
> > Hypervisor vendor:     KVM
> > Virtualization type:   full
> > L1d cache:             32K
> > L1i cache:             32K
> > L2 cache:              4096K
> > 
> > uname -i shows:
> > i686
> > 
> > 
> > Will it be ok to test in this one?
> 
> 
> If 'uname -i' reports i686, that usually means you have configured the
> kernel for 32-bit. Try rebuilding the kernel with 'CONFIG_64BIT' and
> 'CONFIG_IA32_EMULATION' enabled to test that the 32-bit user space now
> also works under a 64-bit kernel.

done... tested with CONFIG_64BIT and CONFIG_IA32_EMULATION. The original
ppdev code failed with my userspace test code. After applying patch 1/2
of v3 it still failed, but after applying 2/2 of v3 it worked.
will you take v3 through your y2038 tree? or I can keep them for,
ummmmm, 4.6 merge window.

> 
> That reminds me, we should now remove the code from fs/compat_ioctl.c
> that was handling emulating the other ioctl commands, the new .compat_ioctl
> callback in ppdev takes care of that along with the PPGETTIME/PPSETTIME
> calls, see below

Bamvor, care to send a patch for these also...

regards
sudip
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