[PATCH 00/10] Enhance /dev/mem to allow read/write of arbitrary physical addresses

Ingo Molnar mingo at elte.hu
Mon Jun 20 03:31:22 EDT 2011

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

> On 17/06/11 19:30, Ingo Molnar wrote:
> >* Petr Tesarik<ptesarik at 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?




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