Re: [PATCH 00/10] Enhance /dev/mem to allow read/write of arbitrary

Ingo Molnar
2011-06-20T07:31:22Z

* Ryan Mallon <rmallon@gmail.com> wrote:

> On 17/06/11 19:30, Ingo Molnar wrote:
> >* Petr Tesarik<ptesarik@suse.cz> wrote:
> >
> >>This patch series enhances /dev/mem, so that read and write is
> >>possible at any address. The patchset includes actual
> >>implementation for x86.
> >This series lacks a description of why this is desired.
> >
> >My strong opinion is that it's not desired at all: /dev/mem never
> >worked beyond 4G addresses so by today it has become largely obsolete
> >and is on the way out really.
> >
> >I'm aware of these current /dev/mem uses:
> >
> > - Xorg maps below 4G non-RAM addresses and the video BIOS
> >
> > - It used to have some debugging role but these days kexec and kgdb
> > has largely taken over that role - partly due to the 4G limit.
> >
> > - there's some really horrible out-of-tree drivers that do mmap()s
> > via /dev/mem, those should be fixed if they want to move beyond
> > 4G: their char device should be mmap()able.
>
> There are drivers where this makes sense. For example an FPGA
> device with a proprietary register layout on the memory bus can be
> done this way. [...]

So you want us to help vendors screw users with insane, proprietary,
user-space drivers with sekrit binary blobs?

Wow.

Thanks,

Ingo