linux-kernel - Re: [PATCH update6] drivers: add LCD support

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Message-ID: <653402b90611022245s3115efbev3c003302aa4f2433@mail.gmail.com>
Date:	Fri, 3 Nov 2006 07:45:41 +0100
From:	"Miguel Ojeda" <maxextreme@...il.com>
To:	"David Miller" <davem@...emloft.net>
Cc:	akpm@...l.org, vagabon.xyz@...il.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH update6] drivers: add LCD support

On 11/3/06, David Miller <davem@...emloft.net> wrote:
> From: Andrew Morton <akpm@...l.org>
> Date: Thu, 2 Nov 2006 12:04:12 -0800
>
> > On Thu, 2 Nov 2006 19:33:48 +0000
> > "Miguel Ojeda" <maxextreme@...il.com> wrote:
> >
> > > May 2.6.18-new vmalloc
> > > related functions help correlating userspace & kernel addresses? I
> > > will try them and come with an answer tomorrow.
> > >
> > > Quoting http://lwn.net/Articles/2.6-kernel-api/
> > >
> > > "Some functions have been added to make it easy for kernel code to
> > > allocate a buffer with vmalloc() and map it into user space. They are:
> > >
> > >      void *vmalloc_user(unsigned long size);
> > >      void *vmalloc_32_user(unsigned long size);
> > >      int remap_vmalloc_range(struct vm_area_struct *vma, void *addr,
> > >                              unsigned long pgoff);
> > >
> > > The first two functions are a form of vmalloc() which obtain memory
> > > intended to be mapped into user space; among other things, they zero
> > > the entire range to avoid leaking data. vmalloc_32_user() allocates
> > > low memory only. A call to remap_vmalloc_range() will complete the
> > > job; it will refuse, however, to remap memory which has not been
> > > allocated with one of the two functions above."
> >
> > No, it doesn't look like those helper functions are designed to handle this.
> >
> > I'm really not the person to be asking about this.  I can poke around in
> > arch/sparc64/kernel/sys_sparc.c:arch_get_unmapped_area() as well as the
> > next guy, and it seems to be doing the right thing for MAP_FIXED, but
> > how/whether it handles !MAP_FIXED I do not know.  Ask davem ;)
>
> Unfortunately that code never gets called for MAP_FIXED :-)
>
> I'll comment on these issues and explain what needs to occur,
> we have several things that want to do this kind of user/kernel
> sharing of ring buffers and similar, so best to get the
> infrastructure going to get it right.
>
> As a first approximation, getting remap_vmalloc_range() to do the
> right thing is the best way to start this stuff off.
>

Ok, thanks you! If I can help with anything, please tell me.

In the meantime I will play with vmalloc_user() and friends.
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