Re: AGP & non-root mmap calls: "lending" priviledges to a client

Matthew Wilcox (Matthew.Wilcox@genedata.com)
Sat, 17 Jul 1999 01:23:07 +0200

On Fri, Jul 16, 1999 at 04:38:19PM -0600, Christopher Hassell wrote:
> 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.

Will the SCM_RIGHTS ancillary message over unix domain sockets do what
you want? See unix(7) for details (and if you don't have an entry for
unix in section 7 of your manual pages, try the latest manpages package,
available from ftp.win.tue.nl:/pub/linux-local/manpages or
ftp.xx.kernel.org /pub/linux/docs/manpages).

With this message, the X server can pass an array of file descriptors to a
client which can then call mmap on it.

-- 
Matthew Wilcox <willy@bofh.ai>
"Windows and MacOS are products, contrived by engineers in the service of
specific companies. Unix, by contrast, is not so much a product as it is a
painstakingly compiled oral history of the hacker subculture." - N Stephenson


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