Message-ID: <1458247207.9556.28.camel@perches.com>
Subject: Re: [PATCH v9 2/3] kernel.h: add to_user_ptr()
From: Joe Perches <joe@perches.com>
To: Rob Clark <robdclark@gmail.com>
Cc: Gustavo Padovan <gustavo@padovan.org>,
        Gustavo Padovan <gustavo.padovan@collabora.co.uk>,
        Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Paul Mackerras <paulus@samba.org>,
        Michael Ellerman <mpe@ellerman.id.au>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        devel@driverdev.osuosl.org,
        "dri-devel@lists.freedesktop.org" <dri-devel@lists.freedesktop.org>,
        Daniel Stone <daniels@collabora.com>,
        Arve =?ISO-8859-1?Q?Hj=F8nnev=E5g?= <arve@android.com>,
        Riley Andrews <riandrews@android.com>,
        Daniel Vetter <daniel.vetter@ffwll.ch>,
        Greg Hackmann <ghackmann@google.com>,
        John Harrison <John.C.Harrison@intel.com>,
        Maarten Lankhorst <maarten.lankhorst@linux.intel.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        David Airlie <airlied@linux.ie>,
        Daniel Vetter <daniel.vetter@intel.com>,
        linuxppc-dev <linuxppc-dev@lists.ozlabs.org>
Date: Thu, 17 Mar 2016 13:40:07 -0700
In-Reply-To: <CAF6AEGvQa8SOWCtoEfcFAxz6MQ0Nqc-ktqNCdfJU-32-m-mCEQ@mail.gmail.com>
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On Thu, 2016-03-17 at 16:33 -0400, Rob Clark wrote:
> On Thu, Mar 17, 2016 at 4:22 PM, Joe Perches <joe@perches.com> wrote:
> > On Thu, 2016-03-17 at 15:43 -0300, Gustavo Padovan wrote:
> > > 2016-03-17 Gustavo Padovan <gustavo.padovan@collabora.co.uk>:
> > > > 2016-03-17 Joe Perches <joe@perches.com>:
> > > > > On Thu, 2016-03-17 at 14:30 -0300, Gustavo Padovan wrote:
> > > > > > This function had copies in 3 different files. Unify them in
> > > > > > kernel.h.
> > > > > This is only used by gpu/drm.
> > > > > 
> > > > > I think this is a poor name for a generic function
> > > > > that would be in kernel.h.
> > > > > 
> > > > > Isn't there an include file in linux/drm that's
> > > > > appropriate for this.??Maybe drmP.h
> > > > > 
> > > > > Maybe prefix this function name with drm_ too.
> > > > No, the next patch adds a user to drivers/staging (which will be moved
> > > > to drivers/dma-buf) soon. Maybe move to a different header in
> > > > include/linux/? not sure which one.
> > > > 
> > > > > 
> > > > > 
> > > > > Also, there's this that might conflict:
> > > > > 
> > > > > arch/powerpc/kernel/signal_32.c:#define to_user_ptr(p)??????????ptr_to_compat(p)
> > > > > arch/powerpc/kernel/signal_32.c:#define to_user_ptr(p)??????????((unsigned long)(p))
> > > > Right, I'll figure out how to replace these two too.
> > > The powerpc to_user_ptr has a different meaning from the one I'm adding
> > > in this patch. I propose we just rename powerpc's to_user_ptr to
> > > __to_user_ptr and leave the rest as is.
> > I think that's not a good idea, and you should really check
> > this concept with the powerpc folk (added to to:s and cc:ed)
> > 
> > If it were really added, then the function meaning is incorrect.
> > 
> > This is taking a u64, casting that to (unsigned long/uint_ptr_t),
> > then converting that to a user pointer.
> > 
> > Does that naming and use make sense on x86-32 or arm32?
> > 
> fwiw Gustavo's version of to_user_ptr() is in use on arm32 and arm64..
> Not entirely sure what doesn't make sense about it

It's a name that seems like it should be a straightforward
cast of a kernel pointer to a __user pointer like:

static inline void __user *to_user_ptr(void *p)
{
	return (void __user *)p;
}

As a static function in a single file, it's not
great, but OK, fine, it's static.

As a global function in kernel.h, it's misleading.