Messages in this thread | | | Date | Fri, 16 Jul 1999 16:38:19 -0600 | From | Christopher Hassell <> | Subject | AGP & non-root mmap calls: "lending" priviledges to a client |
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Here at Xi we're using a client-side rendering model for the new X server, leaving large tasks done entirely in the client space. This in fact gives a much lower latency for some operations. It is simply the wave of the future for the complex graphical output that an SMP system has to support.
A question that has been presented to us is that of direct mmap() access to AGP bridge-viewed RAM. For our AGP/GART device, the client non-root processes that are coordinated by the X server are handed a "magic cookie" that can be used to "bless" a device file descriptor (allowed inside the kernel) ... and thus allow any mmap as needed directly from the AGP/GART device. In general, then, only smart and X-server coordinated processes are then able to do this, enhancing stability, but decreasing unneeded centralization.
Are there any plans to allow "handing over" priviledges to clients, from one process to another? Should a technique of "trusted-cookies" be used to allow non-root clients access to important devices? This technique is easy, sensibly secure (at least, the first priviledges is granted properly) and takes little code.
-- CH
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