Re: Accessing h/w without kernel intervention
- From: Tim Roberts <timr@xxxxxxxxx>
- Date: Sat, 27 Sep 2008 05:59:32 GMT
Mayuresh <b166er.496@xxxxxxxxx> wrote:
Is it at all possible for a user space non privileged process to
access some hardware in the system without making a system call or
otherwise going thru the kernel to gain access?
I have come across fleeting references to memory mapped I/O devices
where you can register some user space memory with the device and
after that I/O is done by just writing to this memory. I want to
understand if this is true or if the kernel is still involved in some
way under the hoods.
Your X server is a normal user-mode process. It access the display
hardware by accessing I/O ports, mapping physical memory, and talking to
the frame buffer and registers through the memory maps.
It is, however, suid root, so I it doesn't really qualify as "non
privileged".
--
Tim Roberts, timr@xxxxxxxxx
Providenza & Boekelheide, Inc.
.
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