X11 still uses /dev/mem ?

Adam Jackson ajax at nwnk.net
Mon Feb 22 10:24:38 PST 2010

On Sat, 2010-02-20 at 15:00 +0000, Nix wrote:
> On 17 Feb 2010, Adam Jackson said:
> > On Tue, 2010-02-16 at 10:30 +0200, Nameer Yarkon wrote:
> >> Hi,
> >> 
> >> Does X11 still uses /dev/mem to directly manipulate the physical memory ?
> >
> > strace would tell you.  The answer is "it depends" though.  On Linux,
> > most memory access goes through the PCI BAR resource files in sysfs, but
> > there are some situations where we still have to use /dev/mem.
> Am I right in assuming that pretty much all of these are UMS-related? 
> i.e., in KMS the only thing now stopping us running X as non-root at
> long last is the input-device-revocation problem?

That, and device permissions on /dev/dri/whatever, and that GEM objects
are globally visible so you're still trusting that multiple X servers
don't intentionally snoop on each other.

- ajax
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