RE: Calculating kernel logical address ..

["Imran Badr" <imran.badr@cavium.com>]

-----Original Message-----
From: linux-kernel-owner@vger.kernel.org
[mailto:linux-kernel-owner@vger.kernel.org]On Behalf Of Daniel Phillips
Sent: Monday, September 09, 2002 11:23 AM
To: Andrew Morton; imran.badr@cavium.com
Cc: root@chaos.analogic.com; 'David S. Miller';
linux-kernel@vger.kernel.org
Subject: Re: Calculating kernel logical address ..


On Monday 09 September 2002 20:08, Andrew Morton wrote:
> Imran Badr wrote:
> >
> > The virt_to_bus() macro would work only for kernel logical addresses. I
am
> > trying to find a portable way to figure out the kernel logical address
of a
> > user buffer so that I could use virt_to_bus() for DMA. The user address
is
> > mmap'ed from kmalloc'ed buffer in the mmap() entry of my driver. Now
when
> > the user wants to send this data to the PCI device, it makes an ioctl
call
> > and give the user address to the driver. Now driver has to figure out
the
> > kernel logical address for DMA.
>
> You can obtain this info by walking the user's pagetables with
> get_user_pages().  That give `struct page' pointers, with which
> all things are possible.

>As long as you can be sure they won't spontaneously vanish on you.

>--
>Daniel
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down(&current->mm->mmap_sem) would help.

Imran.