linux-kernel - Re: [PATCH v9 2/3] kernel.h: add to_user

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Date:	Fri, 18 Mar 2016 09:23:56 +0100
From:	Daniel Vetter <daniel@...ll.ch>
To:	Joe Perches <joe@...ches.com>
Cc:	Gustavo Padovan <gustavo@...ovan.org>,
	Rob Clark <robdclark@...il.com>,
	Gustavo Padovan <gustavo.padovan@...labora.co.uk>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Paul Mackerras <paulus@...ba.org>,
	Michael Ellerman <mpe@...erman.id.au>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	devel@...verdev.osuosl.org,
	"dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
	Daniel Stone <daniels@...labora.com>,
	Arve Hjønnevåg <arve@...roid.com>,
	Riley Andrews <riandrews@...roid.com>,
	Daniel Vetter <daniel.vetter@...ll.ch>,
	Greg Hackmann <ghackmann@...gle.com>,
	John Harrison <John.C.Harrison@...el.com>,
	Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	David Airlie <airlied@...ux.ie>,
	Daniel Vetter <daniel.vetter@...el.com>,
	linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>
Subject: Re: [PATCH v9 2/3] kernel.h: add to_user_ptr()

On Thu, Mar 17, 2016 at 02:33:50PM -0700, Joe Perches wrote:
> On Thu, 2016-03-17 at 18:19 -0300, Gustavo Padovan wrote:
> > 2016-03-17 Joe Perches <joe@...ches.com>:
> > > On Thu, 2016-03-17 at 16:50 -0400, Rob Clark wrote:
> > > > On Thu, Mar 17, 2016 at 4:40 PM, Joe Perches <joe@...ches.com> wrote:
> > > []
> > > > > 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;
> > > > > }
> > > > ahh, ok.  I guess I was used to using it in the context of ioctl
> > > > structs..  in that context u64 -> (void __user *) made more sense.
> > > > 
> > > > Maybe uapi_to_ptr()?  (ok, not super-creative.. maybe someone has a
> > > > better idea)
> > > Maybe u64_to_user_ptr?
> > That is a good name. If everyone agrees I can resend this patch
> > changing it to u64_to_user_ptr. Then should we still keep it on
> > kernel.h?
> 
> I've no particular opinion about location,
> but maybe compat.h might be appropriate.
> 
> Maybe add all variants:
> 
> 	void __user *u32_to_user_ptr(u32 val)
> 	void __user *u64_to_user_ptr(u64 val)
> 	u32 user_ptr_to_u32(void __user *p)
> 	u64 user_ptr_to_u64(void __user *p)
> 
> Maybe there's something about 32 bit userspace on
> 64 OS that should be done too.

Tbh I really don't think we should add 32bit variants and encourage the
mispractice of having 32bit user ptrs in ioctl structs and stuff. Anyway,
just my bikeshed on top ;-)
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch